The role of water in selective heterogeneous catalytic oxidation of hydrocarbons

Molecular Catalysis xxx (xxxx) xxxx

Contents lists available at ScienceDirect

Molecular Catalysis journal homepage: www.elsevier.com/locate/mcat

Review

The role of water in selective heterogeneous catalytic oxidation of hydrocarbons T.V. Andrushkevich, E.V. Ovchinnikova* Boreskov Institute of Catalysis SB RAS, Pr. Akad. Lavrentieva, 5, 630090, Novosibirsk, Russia

A R T I C LE I N FO

A B S T R A C T

Keywords: Water Hydrocarbon Brønsted sites Heterogeneous catalyst Vanadium–content catalyst Selectivity

The review discuss the role of water in the selective oxidation of hydrocarbons of different composition and different chemical nature. The review examines the interaction of water with catalysts, mainly based on vanadium and molybdenum oxides, including volume and surface reconstruction, the mechanism of formation of adsorbed forms of water and their impact on the reaction stages. Positive effect of water is manifested in an increase of the activity and selectivity of the catalysts. The acceleration of the catalytic reaction is associated with the generation of new active centers, namely, Brønsted active sites (BAS), as the part of hydroxyl groups – product of water dissociation on the catalyst. BAS serve as centers for the primary activation of hydrocarbons, facilitating the subsequent limiting stage of dissociation by Lewis active sites (LAS). Possible ways to increase the selectivity are: acceleration of the main reaction associated with the appearance of BAS, without affecting adverse reactions; inhibition reoxidation of the target product by water competing or displacement of a surface oxygenate precursor; facilitation of the desorption of the target product with the catalyst surface oxidized by water; suppressing the formation of strongly bonded intermediates, regulating the acidity of BAS. All these paths simultaneously reduces the coking the catalysts.

1. Introduction Water is of crucial importance in the human life and endeavors. In chemistry, water is a reactant of numerous reaction and an effective solvent [1–5]. In the recent review papers [1–3], these aspects have been covered comprehensively. Much attention has been paid to heterogeneous catalysts including individual and mixed oxides [4]. The products of selective oxidation of hydrocarbons - aldehydes, acids, ketones, anhydrides, alcohols - are of independent value and used in various organic syntheses. Vanadium- and molybdenum-containing oxide systems are most effective catalysts for the production of all these oxygenates [6–10]. Based on literature data and our own researches, we discuss the role of water and ways of its participation in the selective oxidation of hydrocarbons of different composition and different chemical nature. The review examines the interaction of water with metal oxide catalysts, mainly based on bulky and supported vanadium and molybdenum systems. The surface and volume reconstruction of catalysts proceeding under the influence of water are discussed. The review considers the mechanism of formation of adsorbed forms of water and their participation in the conversion of hydrocarbons. The attention has been paid to new active centers, namely, Brønsted active sites (BAS), as the part of ⁎

hydroxyl groups – product of water dissociation on the catalyst. The acceleration of the catalytic reaction is associated with the formation of the BAS. Possible ways and reasons for increasing selectivity are discussed as a result of the effect of water on the state of active centers and the interconnection of the adsorption – desorption processes of water and product 2. Structural changes in catalysts. Mechanism of interaction and adsorbed water species Henderson in his review paper [11] discussed the interaction of water with metals, reported some data on water adsorption on several individual oxides but not vanadia, and mixed vanadium-containing oxides. More attention to these systems was paid by Davydov [12] who considered the formation of complexation of a number of organic compounds and water based on IR spectroscopic studies. In the recent years, the participation of water in various reactions and the interaction of water with vanadium-containing oxide catalysts, both bulky and supported, have been actively discussed in literature. Among the latter, particular attention has been paid to vanadium-titanium and vanadiummolybdenum oxide systems, which are most often used in industrial processes for selective oxidation of hydrocarbons.

Corresponding author. E-mail addresses: [email protected] (T.V. Andrushkevich), [email protected], [email protected] (E.V. Ovchinnikova).

https://doi.org/10.1016/j.mcat.2019.110734 Received 23 October 2019; Received in revised form 2 December 2019; Accepted 3 December 2019 2468-8231/ © 2019 Elsevier B.V. All rights reserved.

Please cite this article as: T.V. Andrushkevich and E.V. Ovchinnikova, Molecular Catalysis, https://doi.org/10.1016/j.mcat.2019.110734

Molecular Catalysis xxx (xxxx) xxxx

T.V. Andrushkevich and E.V. Ovchinnikova

dehydrated reduced active center V4+–O–V4+ equals 84 kJ, while the energy of water desorption from the oxidized center V5+–O–V5+ is far lower (22 kJ). Water, when adsorbed, improves mobility of the lattice oxygen. The author [21] assumed that the role of oxygen in the O2-H2O mixture is to combine monomers O = VO2(OH) to polymer VOn particles and, thus, to arrange active centers for the exchange followed by easy desorption of water. The gas-phase oxygen does not participate in the exchange at below 450 °C [20,21]. Yin et al. [22] studied adsorption of H2O on the V2O5(010) surface using the Periodic Density Functional. A water molecule is adsorbed on vanadium as a V−OH2 group through donating of the lone-pair electrons located on its oxygen to one of the empty d-orbitals of the vanadium site. Two hydrogen bonds are formed via interaction of hydrogen atoms of water with the terminal and nearest-neighbor bridge oxygen atoms, the charge on the vanadium site being decreased by 0.021 electrons. The further electron transfer from oxygen of the catalyst to OH groups results in an increase in negative charges on these two oxygen atoms. The terminal oxygen is most active to molecular and dissociative adsorption and forms the strongest H-bond [22]. The model reaction of hydrolysis catalyzed by MoVOx mixed metal oxide was calculated by W.-Q. Li using density functional modeling. Water splits into OH− and H+ moieties that adsorb subsequently at various sites. According to the calculations, bridging oxygen centers are much more preferable as compared with central Mo = O site. The adsorption of a water molecule is more favorable, by 30 kJ/mol, at the surface Mo6+ center than at the surface V5+ center [23]. Water has oxidizing properties, which can be judged by the data of [24–26]. Hävecker et al. showed an increase in the average oxidation state of vanadium using in situ photoelectron spectroscopy (XPS). In the presence of steam in the feed, the active ensemble in MoVTeNb oxide catalyst for acrylic acid formation consists of V5+ oxo-species [24]. The V2O5/SnO2 catalyst is less reduced upon the addition of H2O [25]. The number of oxygen vacations in vanadia supported on silica-titania (30 %V2O5/SiO-TiO2) decreases in the presence of water [26]. Many of research teams observed the formation of H+ and OH– groups by the method of IR spectroscopy during adsorption of water on the surface of oxide catalysts [11,12,27–31]. Fig. 1 shows the IR spectrum of water acquired at passing an air mixture with 4 % H2O through a cell with a vanadia/titania catalyst at 120 °C [27] Adsorption of water (4 % H2O in air) (Fig. 1) on the V-Ti catalyst leads to appearance of a band at ca. 1620 cm–1 assigned to δ(H2O) vibrations of adsorbed water. This band increases in intensity as the adsorption time increases to 600 s and then remains constant. In the highfrequency region, a gradual decrease in intensity of the band at 3650

The structures, coordination of vanadium species, manners of bonding adsorbed water vary depending on the water concentration and temperature. These processes occur different ways depending on the vanadium content. Thermodesorption and IR spectroscopic techniques were used for studying adsorption of water on 6 %V2O5/TiO2; hydroxylation of the surface and generation of strong BAS was observed. The formation of OH groups is mainly provided by V]O species. A decrease of the V]O overtone band in intensity and its frequency indicates weakening of the V]O bonds during adsorption of water [13]. Processes of hydration-dehydration over V2O5 supported on HfO2, Al2O3, ZrO2, TiO2, SiO2 are accompanied by changes in the surface vanadium oxide species. There are only monovanadate species in dehydrated vanadia. Hydration of the samples causes a decrease in the proportion of monovanadate species and an increase in polyvanadate species [14,15]. Raman spectroscopic studies of the influence of water on the surface vanadium oxide species supported on A12O3, TiO2 and CeO2 were reported by Jehng et al. [16]. Water forms hydrogen bonds with the surface vanadia species V]O, VeOeV and V–O–Support. Polymer VeOeV and V-O-Support species interact less intensively with water than the monomer species. The adsorbed species and influence of water on the catalyst state depends on the surface vanadium content and temperature. At a low surface vanadia coverage and high temperature (450 and 500 °C), effect of water vapor is very little that is indicated by no change in the V]O Raman bands at 1018–1038 cm–1. Considerable influence of water vapor is not observed also at high vanadia coverage at above 350 °C. The hydration process is more intensive at below 230 °C. At the temperature elevation, hydrated vanadate species loose water to decrease the Brønsted sites (BAS) but increase the Lewis acidity (LAS) of the surface. At the same time, isotopic studies demonstrate direct interaction of moisture with the surface vanadia species at elevated temperatures and rapid oxygen exchange with the surface vanadia species [16]. The high Brønsted acidity is characteristic of the vanadia/titania catalyst at a high vanadia content in the presence of water, while the Lewis acidity predominates at a low vanadia content in the absence of water [17].The hydrated vanadium oxides consist of layers of polymerized VO4 units with vanadium in pseudo octahedral coordination. Dehydration leads to depolymerization of the surface oxides accompanied by a change in the vanadium coordination. The formation of adsorbed water bonds on a vanadium – titanium catalyst (2.5–18.7 VOx / nm2 / TiO2) proceeds with the participation of V]O, VeOeV, and V–O–Ti bonds by means of hydrogen bonding. In the monovanadate and polyvanadate species, water is supposed to interact with V]O. In the case of intensive hydration of the low coverage of vanadate surface the V–O–Ti bonds can be hydrolyzed, while water reacts only with vanadium species at the monolayer coverage [19]. Sadovskaya et al. [20] studied oxygen exchange H218O/H216O using a vanadium-titanium catalyst containing 7 wt % of vanadium as a monolayer coverage with VOx particles. The adsorbed water was shown to form OH groups with VeOeV and V]O centers. The isotope exchange of water with terminal and bridge oxygen occurs during formation and decomposition of the [VOH] sites. Water molecules exchange faster with OH groups than with dehydrated VeOeV and V]O centers. At 200 °C, the first order rate constant of exchange is ca. 0.5 s−1 with the activation energy close to zero with OH groups, the rate constant with dehydrated centers is ca. 10−3 s−1 with the activation energy of ca. 70 kJ/mol [20]. A similar trend was revealed by Avdeev et al. [21] using DFT (density functional theory) calculations. Water is adsorbed on VOx/ TiO2 as two OH groups HO–V4+–O–V4+−OH, one of which is bonded as OH from water to terminal V]O, and another is formed through hydrogen transfer to the bridge oxygen. The OH groups are bounded stronger to the reduced vanadium (+3, +4) than to oxidized vanadium (+5). The activation energy of recombination of OH groups of the

Fig. 1. IR spectra of the products of water adsorption at 120 °C upon increase in the adsorption time: 1–20 s, 2–300 s, 3–600 s. Reaction mixture is 4 % H2O in air. 2

Molecular Catalysis xxx (xxxx) xxxx

T.V. Andrushkevich and E.V. Ovchinnikova

cm–1 corresponding to hydroxyl groups of the catalyst is observed as well as appearance and growth of a broad absorption in the region of 3500−2600 cm–1 attributed to νas(H2O) and νs(H2O) vibrations of adsorbed water and ν(OH) vibrations of hydroxyl groups involved in the formation of hydrogen bonds. Besides, as the time of adsorption increases, the ν(OH) band at 3680 cm–1 appears and grows in intensity that indicates dissociative adsorption of water on this catalyst to form hydroxyl groups. The studies of pyridine adsorption reveal latter are strong BAS. The results reported elsewhere [12,27–31] led to conclude about the influence of water on the number and strength of Brønsted acid sites and on the relationship between the selectivity and acidity of the oxide catalysts. In general, water creates new reactive centers; affects the state of oxygen; impacts of catalysts acidity changing relationship between BAS and LAS.

Fig. 2. Dependence of the formation rates of acetone (1), acetic acid (2) and complete oxidation products (3) on the water concentration under propylene oxidation over VMo catalyst.

3. Contribution of water to selective transformation of hydrocarbons

the formation two C3 oxygenates [35]. Takita et al. [37] established a linear dependence of the rate of acetone formation over SnO2–MoO3 on the concentration of acidic hydroxyl groups. The involvement of hydroxyl groups in the production of acetone is supported by the rate lowering during titration of the catalyst with n-butylamine. P. Kube et al. [38] showed that propylene produced during propane oxidation over silica-supported vanadium oxide and MoVTeNbOx catalysts is converted to acetone with involvement hydroxyl groups [38]. An increase in the water concentration in the initial mixture for propylene oxidation over V2O5/TiO2 leads to acceleration of the first stage of the reaction. i.e. conversion of propylene to isopropyl alcohol, and suppression of the processes of complete oxidation that, in total, favors an increase in the yield of acetone [39]. Oxidation of propylene over a multicomponent Bi-Mo-based catalyst gives mainly acrolein. Water does not influence the rate of propylene conversion and acrolein formation but increases oxidation of acrolein to acrylic acid and, thus, improves the selectivity to the acid [40]. Over antimony–tin–vanadium oxide (Sb/Sn/V = 2/1/1) a strong effect of water on the oxidation of propylene is observed at water concentrations from 1 to 20 %.The maximal yields of acrolein, acrylic and acetic acids are resulted at the concentration range of 1–5 % of steam. At low levels water maintain the catalyst surface at a high oxidation state and prevents the formation of strongly bonded oxygenates. At high water concentrations, molecules blocked sites for total oxidation. The yield of acetone increases with increasing content water vapor via a parallel reaction route of direct hydration of adsorbed propene or a surface intermediate [41]. Propane is an effective alternative to propylene in the production of acrylic acid and acrylonitrile [42]. A favorable influence of water on oxidative transformations of propane over oxide catalysts is reported in review papers [42–45,7,8]. The most effective catalysts for oxidative transformations of propane are Mo– and V–based mixed metal oxide catalyst [45]. Our results on catalytic oxidation of propane demonstrate the strong influence of water on the activity and selectivity of mixed MoVTeNbO (Fig. 3). Introduction of water to the reaction mixture increased the rates of formation of acrylic and acetic acids. The rate of the formation of carbon oxides decreases as the water concentration increases. The curves reach plateau at the concentration of water vapor higher than 20 mol %. The selectivities to the reaction products change along with the rates: the selectivity to acrylic acid increases from 31 % in the absence of water up to ca. 70 % in the presence of 30–40 % of water vapor, while the selectivity to COx decreases from 48 to 11 %. An increase in the rate of propane conversion is accounted for by the formation of new active sites such as BAS, or by modification of vanadium centers for propane activation. The four-fold increase in the rate of the

The target product of selective oxidation is obtained via a number of intermediate transformations. The sequence of the transformation is established based on experimental dependencies of the selectivity on the conversion of the initial reactant or on the contact time. A huge number of such dependencies are presented in the literature [32]. Based on these dependencies, it is possible to determine the reaction pathways to suggest which stages are affected by water and on which its action the final product yield depends. The transformation of hydrocarbon A to value-added product B and side product C via consecutive and parallel pathways can be shown as a simplified schematic irrespectively of the chemical composition of the reactant and catalyst:

The favorable influence of water on the selective transformation of hydrocarbons has long been known. The main questions are: Does the yield of product B increase due to acceleration of its formation or due to suppression of the formation of side product C? In this paper, we consider the effect of water at different stages of transformation of various hydrocarbons. 3.1. Transformation of C1–C5 hydrocarbons C2–C5 hydrocarbons are transformed to acetic acid, acetaldehyde and propionic acid in the presence of water vapor over the V2O5MoO3 catalyst at below 350 °C. In oxyhydration of olefins, water favors the formation of ketones, which are intermediates for synthesis of acids and aldehydes [33]. In oxidation of propylene, water favors the formation of acetone over complex oxide catalysts such as Mo/W/Sn/Te [34], vanadiummolybdenum (V2O5:MoO3 = 1:9) [35], molybdenum-based catalyst promoted with cobalt and nickel [36], tin-molybdenum SnO2–MoO3 [37], silica-supported vanadium oxide and MoVTeNbOx [38], vanadium-titanium oxide [39]. Dependence of the selectivity on propylene conversion over the vanadium-molybdenum catalyst indicates that the acetic acid is the product of oxidative cleavage of acetone [35]. Water accelerates the formation of acetone and acetic acid but not affects their re-oxidation (Fig. 2). Treatment of the catalyst with water vapor results in increase in intensities of bands at 1425 and 3050 cm–1 assigned to BAS but weakening of bands of the LAS at 1620 cm–1 in the IR spectra; hence the BAS contribute to the selective oxidation. In the authors’ opinion, the promotional effect of water is accounted for by the increase in the concentration of surface hydroxyl groups as active surface species for 3

Molecular Catalysis xxx (xxxx) xxxx

T.V. Andrushkevich and E.V. Ovchinnikova

Fig. 3. Dependence of rates (a) of propane oxidation (1), formation of acrylic acid (2), propylene (3), COx (4), acetic acid (5) and adequate selectivities (b) on the water concentration at the propane conversion of 12–18 %.

acid is increased in the presence of water and the complete oxidation pathway is depressed. VOH and VOх species are active centers for acetic acid formation. The rate of desorption of the oxidation products from the catalyst surface increases in the presence of water [52]. Oxidation of ethane to acetic acid over Mo1V0.25Nb0.12Pd0.0005Ox may follow two pathways: either via formation of ethylene intermediate or directly to the acid along with the formation of ethylene. Acetaldehyde is formed from ethylene and converted to the acid at a high rate. Hydroxyl groups are supposed to participate in the rate determining step. Water contributes to acceleration of all the processes up to certain maxima but then the rates decrease due to blockage of active sites. The authors emphasize that an increase in the acid yield at increasing water content does not result from acceleration of the acid desorption [53]. A significant positive effect of water on the selectivity to acetic acid is observed during oxidation of ethane over VMo catalysts. The effect is accounted for by the involvement of surface OH groups providing an additional parallel route of the formation of CH3COOH [54]. Water is a mild oxidant for the conversion of methane to methanol over copper-containing zeolite. It regenerates the catalyst by donating an oxygen atom for the two-electron reoxidation of the copper active center. The presence of water ensures energetically favorable desorption of methanol [55]. The active participation of water in selective oxidation is not limited by oxide catalysts. Water participates in the activation of oxygen on metal surfaces, creating reactive forms, forms hydroxyl groups with catalyst oxygen and facilitates proton transfer in the oxidation of methane to methanol, in selective propylene epoxidation, in alcohol oxidation [4]. It should finally be noted, that Grabowski in his extended review paper devoted to kinetics of C2-C5 hydrocarbons [56] did not include water as an activating agent in the kinetic equations, even though active participation of water in transformation of these compounds described here and elsewhere [12]. In two equations, the denominators include water as a consequence of the inhibiting effect of the reaction product [56].

acid formation is not proportional to the rate of propane conversion (two-fold) that argues for the favorable effect of water on the rate of acrolein conversion to the acid or on desorption of acrylic acid. The former is more preferably. It was observed during oxidation of propylene [40] and acrolein [46]. The latter is accounted for by weakening of bond between the direct precursor of the acid – surface acrylate – and the active site of the catalyst those results in a decrease in the rate of formation of complete oxidation products (COx). Zheng et al. [47] studied oxidation of propane in the presence of the mixed MoVTeNbO catalyst over a wide range of water concentrations. They observed the maximal selectivity and yield of acrylic acid at 46 % water vapor. The authors refer the increasing yield to the generation of BAS, and the increasing selectivity to an increase in the rate of the acid formation and blockage of the sites of the formation of complete oxidation intermediates. Naraschewski et al. [48], in studying propane oxidation over MoVTeNbO, revealed that the yield of acrylic acid decreases to ca. onethird due to competing formation of acetone. They suggested to improve the yield of acrylic acid by removing the Brønsted sites which are active to oxidation of propane to acetone. Hävecker et al. failed to detect acrylic acid in the dry mixture produced by propane oxidation over MoVTeNbO. On addition of steam to the reaction mixture (C3H8/O2/H2O/N2 = 3/6/x/balance mol%, х = 0–40), the yield of acrylic acid increases, the conversion of propane grows only slightly. During the reaction, V4+ is oxidized to V5+. From XPS data, the proportion of Mo6+ decreases and V5+ increases on the surface. The rate of the acid formation correlates with the proportion of V5+ [24]. Water changes the phase composition and properties of the vanadium-phosphorus catalyst. Introduction of water results in crystallization of phase VOHPO4·0.5H2O and in transition to the pure (VO)2P2O7 phase. The propane conversion decreases slowly at 20 % H2O at the simultaneous increase in the acrylic acid yield [49]. Wannakao et al. [50] reported DFT calculation of the reaction pathway of propane oxidation to propylene over VO2-MCM-22 zeolite. The rate-determining step is the transfer of a methylene hydrogen atom to the oxygen atom of the VO2 group. The formed isopropyl radical is bound to the hydroxyl group or to the oxygen atom on the vanadium atom. At the stage of propene formation, the hydroxyl group is more reactive than the oxy group, the apparent activation energies being 115 kJ/mol and 168 kJ/mol, respectively. Propylene is desorbed easier from the completely oxidized catalyst [50]. When butane oxidation is catalyzed by (VO)2P2O7, dissociative adsorption of water on V-P-oxide leads to cleavage of VeOeV, VeOeP or PeOeP bonds and formation of VeOH and/or PeOH groups. The processes make the catalyst reoxidation easier. Water blocks the active sites for the formation of intermediates of complete oxidation products and favors desorption of maleic anhydride. As a result, the selectivity to maleic anhydride increases in the presence of water [51]. In oxidation of 1-butene over V2O5-TiO2, the selectivity to acetic

3.2. Transformation of functionalized hydrocarbons Hydrocarbons containing different functional group (aldehydes, ketones, alcohols, acids) are strongly influenced by water in relation both to the catalyst activity and to the transformation routes. A series of works by German researchers [57–64] are comprehensive studies of the mechanism of water behavior in oxidation of acrolein to acrylic acid over a MoVW oxide catalyst. Water increase remarkably the rate of acid formation. These sites are surface OH groups as the product of dissociation of adsorbed water on the bridge oxygen. OH groups or the bridge oxygen are involved in the formation of intermediate acetal to be then converted to acrylate. The latter accepts a 4

Molecular Catalysis xxx (xxxx) xxxx

T.V. Andrushkevich and E.V. Ovchinnikova

proton from the neighboring OH group and escapes as the acid the surface with water. The surface hydroxyl groups do not influence the formation of complete oxidation products. When water is added to the reaction mixture, the acceleration of the acid formation and the absence of promoting action of water on complete oxidation results in an increase in the selectivity to acrylic acid. The authors claim that water enhances significantly the catalytic performance and is involved in most steps of the catalytic cycle. Recently, Knoche et al. [64] have showed that α-hydrogen-abstraction is the limiting stage of the oxidation of acrolein to acrylic acid and to the complete oxidation products. Surprisingly, the proton is abstracted by a hydroxyl group but not by more nucleophilic lattice oxygen. In our earlier works, we reported an important role of water in oxidation of propylene [40] and acrolein [46,65]. Over a vanadiummolybdenum catalyst, acrolein is oxidized to acrylic acid in a dry mixture without water. Addition of water results in a considerable increase in the rate of acrolein conversion and acid yield, while the rate of the formation complete oxidation products is not changed [46]. These dependencies are described by kinetic equations: oxidation to acrylic acid occurs on centers of two types – oxidized species of cations of the catalyst and BAS generated by water [46,65]. Water generates OH groups on the promoted MoV oxide catalyst to protonate surface oxide species, C3H3O*, by the water-derived surface-bound hydroxyl group to form acid [66]. Water is an important promoter for the conversion of acrolein to acrylic acid over Orth-MoVWO and Tri-MoVWO catalysts [67] Water has a considerable impact on oxidation of methacrolein. The activity of the H3PMo12O40 catalyst and selectivity to methacrylic acid increases in the presence of steam. The increasing rate of the formation of methacrylic acid upon water addition is accounted for by 200-fold increase in the pre-exponential factor [68].The conversion of methacrolein to methacrylic acid catalyzed by chromium oxide modified with H3PW12O40 proceeds through Mars-Van Krevelen mechanism. The key step of the process is the activation of the substrate on strong BAS [69]. V-Ti oxide catalysts are highly active to oxidation of formaldehyde to formic acid [70]. Water accelerates the formation of formic acid and inhibits the formation of CO (Fig. 5) over the 11 % V2O5 / 89 % TiO2 catalyst. The rate of the formation of CO2 does not depend on the concentration of water. Selectivities change in accordance with product formation rates (Fig. 4). The strong influence of water is described by kinetic equations [71]. Kinetic studies of oxidation of formic acid over the same catalyst revealed that water suppresses decomposition of the acid [72, 27]. The rates of the formation of CO and CO2 decrease upon addition of water vapor to the reaction mixture, the abrupt decrease at the water concentration between 2 and 5 mol % and the following monotonic decrease being observed (Fig. 5). The apparent activation energies of the formation CO and CO2 are

Fig. 5. CO (1) and CO2 (2) formation rates under formic acid decomposition on V2O5/TiO2 catalyst as the functions of water concentration under 10 % formic acid conversion at 120 °C (’dot), 130 °C (’’open); 140 °C (”’ solid).

120 kJ/mol and 80 kJ/mol, respectively. The rate of decomposition of formic acid decreases due to the competitive adsorption of H2O and formic acid and to acceleration of the reverse reaction of the formation of formic acid from formates at increasing number of OH groups at water adsorption [27,72]. Contrary, water increases deep oxidation of formaldehyde on Mn0.75Co2.25O4 catalyst [73]. Wang et al. suppose that water generates OH groups on the surface of oxide, which facilitate oxidation of intermediate formate HCOO− species to carbonates HCO3− as intermediate of the complete oxidation of formaldehyde [73]. Oxidation of ethanol over supported vanadium catalysts proceeds via formation of acetaldehyde and ethylene. The selectivities of VOx/ Zr–SBA-15 to the reaction products change in the presence of water. Ganjkhanlo et al. [74] related the decreasing selectivity to acetaldehyde and increasing selectivity to ethylene due to inhibition by stronger acidic OH groups of the oxidative dehydrogenation. With VOX-SiO2, the selectivities change similar way. Selectivity to ethylene increases in the presence of water vapor due to acetaldehyde formation is inhibited more significantly than the formation ethylene. The observed increase in the selectivity to ethylene with an increasing ethanol conversion can be accounted for by the inhibition of the oxidation to acetaldehyde by water vapor formed during the reaction [75]. Again, water inhibits MoO3-catalyzed oxidation of ethanol to acetaldehyde [76]. Glycerol is a new perspective starting raw material for the production of many oxygenates such as aldehydes, acids, alcohols and other derivatives [77]. Water has a favorable impact upon oxidative transformations of glycerol [78–80]. Chai et al. [78] studied gas-phase dehydrogenation of glycerol (molar ratio glycerol/water = 1/9) to acrolein over various oxides and revealed correlation between the selectivity to acrolein and the catalyst

Fig. 4. Formic acid (1), CO (2) and CO2 (3) formation rates (a) and selectivities (b) as the functions of water steady-state concentration under formaldehyde oxidation on V-Ti catalyst at 120 °C (’dot), 130 °C (’’open); 140 °C (”’ solid). 5

Molecular Catalysis xxx (xxxx) xxxx

T.V. Andrushkevich and E.V. Ovchinnikova

acidity. The optimal acidity ranges between –8.2 ≤ HO≤ –3.0. At this range, bulky and supported oxides of niobium, tungsten, PW heteropolyacids produce acrolein at the selectivity of 60–70 mol%. The catalysts selective of glycerol dehydration to acrolein comprised more BAS than LAS [78]. BAS are involved in the direct oxidative transformation of glycerol to acrylic acid over complex W–V–Nb oxides [79]. Molybdenum (tungsten) vanadium based catalysts provided the highest yield (28.4 %) of acrylic acid in the one-step oxydehydration of glycerol in the air-steam reaction mixture [80]. 3.3. The influence of water on transformation of aromatic and heterocyclic compounds Vapour phase oxidation and ammoxidation of substituted methylaromatics and heteroaromatics are important industrial chemical processes [81]. Selective oxidation of toluene over V2O5 in flowing oxygen both in the presence and in the absence of water gives mainly benzaldehyde. The rates of the formation of benzaldehyde and all the products including carbon oxide are doubled in the presence of water compared to those in water-free processes. The main product of the selective oxidation in the presence of water (in the oxygen-free reaction mixture) is benzoic acid. Similar dependence on the composition of the reaction mixture was observed with 2 wt% V/TiO2, the difference being that the addition of water resulted in four-fold increase in the rate of the acid formation and two-fold increase in the rate of the formation of benzaldehyde. The catalyst was inactive in water-free reaction mixtures. Hydrolysis of VeOeV bonds led to an increase in the surface area of vanadium oxide and prevented the catalyst deactivation [82]. D. Bulushev and all assume that strong acid hydroxyl groups associated with bridging oxygen of VeOeV are responsible for coke formation and deactivation of vanadia/titania catalysts in toluene oxidation. [83]. The suppression of the complete oxidation of toluene over mixed oxide catalysts by water is accounted for by the competition between H2O and volatile organic compounds for surface active sites. [84,85]. The effect differs with different aromatic compounds and varies in the series toluene > p-xylene > benzene [86]. A remarkable improvement of catalytic activity and a decrease in the selectivity to CO2 during oxidation of o-xylene over anatase-supported vanadium oxide catalysts is observed in the presence of 3 mol % steam in the inlet feed. A possible reason is changes in the dispersion of bulk vanadium oxide [87]. Water behaves as a particularly active promoter for oxidation of heteroaromatic compounds [25,88–92,94,95]. The oxidation of β–picoline (3-picoline) to nicotinic acid and benzene to phenol proceeds efficiently over V-Ti catalysts in the presence of water, Brønsted and Lewis acid sites promote these reactions [88]. In vapor phase oxidation β-picoline and 3-methyl-5-ethyl pyridine over V2O5/SnO2 = l/1.5, addition of water results in an increase of both conversion and selectivity to aldehyde and nicotinic acid and in lowering of the depth of oxidation. Water decreases the reduction extent of the catalyst and the selectivity to products of deep oxidation. Supposedly, there is correlation between selectivity and reduction extent of the catalyst [25]. Oxidation of β-picoline over CrV oxides also is achieved in excess water vapor [89–91]. The authors assume that β-picoline is effectively oxidized with O2 in the gas-phase to nicotinic acid due to combining BAS and redox properties [91]. A noticeable increase in the activity at almost constant activation energy observed at different water contents illustrates additionally the role of BAS [89]. CrV catalysts provide synthesis of nicotinic acid in the dry reaction mixture, too, but the yield is low. The addition of water in a large amount (up to molar ratio β -picoline/H2O = 1/108) to the reaction mixture enhances the total yield of nicotinic acid and pyridine-3-carbaldehyde to 69 % at 350 °C (Fig. 6) [89].

Fig. 6. Yields of nicotinic acid (1), pyridine-3-carbaldehyde (2), pyridine (3) and COx (4) as functions of water content addition under 3-picoline oxidation on CrVPO catalyst at 350 °C.

Water-free oxidation of β-picoline over CrPVO gives products of deep oxidation (pyridine and CO) in significant quantities but at a very low conversion. The addition of water improves considerably the conversion and selectivity to nicotinic acid and pyridine-3-carbaldehyde [89]. Assumingly, while water positive influences the rate of acid desorption, it may impede reoxidaiton of nicotinic acid to carbon oxides [90]. Analysis of direct oxidation of both benzene to phenol and βpicoline to nicotinic acid shows that Brønsted and Lewis acid sites are necessary to promote the oxidation reaction [88]. The activity of the vanadium-titanium catalyst (20V2O5 / 80TiO2) for oxidation of β-picoline and selectivity to nicotinic acid increases upon introduction of water to the reaction mixture [92]. The influence of water on the oxidation of β-picoline was studied at 30 and 82 % conversions. At the low conversion, water affects mostly the parallel steps. The reactant ratio β-picoline:O2 was 1:18, concentration of water vapor was varied from 5 to 25 mol %, rest nitrogen. Water has a favorable impact upon conversion of β-picoline to form nicotinic acid and pyridine-3-carbaldehyde, as well as upon oxidation of pyridine-3-carbaldehyde to nicotinic acid. A decrease in the selectivity to the aldehyde at the increase in the selectivity to the acid argues for the consecutive oxidation of the aldehyde to acid. The rates of the formation of CO and CO2 increase slightly (Fig. 7) while the selectivity to these products decreases sharply; hence, the increase in the selectivity to the acid and aldehyde is caused by acceleration of their formation but not their reoxidation. Supposedly, the observed acceleration of the formation of pyridine-3-carbaldehyde and nicotinic acid in the presence of water results from an increase in the number of adsorption sites for β-picoline. In the V2O5/TiO2 catalyst, these sites can be Brønsted acid sites. Practically no influence of water is observed at the range of high conversions of β-picoline; the rates and selectivities do not change at the water content varied from 5 to 25 % [92]. Another evidence of the absence of water influence on reoxidation of the acid is the direct oxidation of nicotinic acid in the standard (20 % H2O) and dry mixture over the same catalyst (Table 1). Carbon oxides and pyridine are the reaction products. The rates and selectivities to COx and pyridine remain constant at all the compositions of the reaction mixture [93]. Thus, the role of water on β-picoline oxidation is to increase the rate of the acid formation but not to influence the rate of its reoxidation; as a result, the selectivity to the acid increases [92,94]. In oxidation of 2-picoline over V2O5/SnO2 = l/1.5, the yield of 2pyridinealdehyde increased from 12 to 44 % on addition of steam at the molar ratio H2O/2-picoline = 82 to the reactants, and the selectivity increases from 33 to 64 % [25]. The strong favorable influence of water on the transformation of 6

Molecular Catalysis xxx (xxxx) xxxx

T.V. Andrushkevich and E.V. Ovchinnikova

Fig. 7. The rates of β-picoline conversion (1) and formation of nicotinic acid (2), pyridine-3-carbaldehyde (3) and CO2 (4) (a), adequate selectivities (b) as the functions of water concentration under 28 % β-picoline conversion on V2O5-TiO2 catalyst at 270 °C. Inlet concentration β-picoline and O2 are 1 and 18 mol %.

The interdependence between vanadia catalysts and water illustrates such a system as follows:

Table 1 The influence of water on oxidation of nicotinic acid at the initial nicotinic acid concentration of 0.12 ± 0.01 % and conversion of 7 ± 2%. #

1 2 3 4 5 6

Tr, °C

270 270 285 285 300 300

H2O concentration, %

20 0 20 0 20 0

Wi*, 10−9, mol m–2 s–1

Selectivity, %

Nitrile

COx

Nitrile

COx

0.012 0.013 0.037 0.036 0.083 0.085

0.144 0.152 0.256 0.242 0.330 0.305

7.7 7.9 12.6 12.9 20.1 21.8

92.3 92.1 87.4 87.1 79.9 78.2

(i) Variations in the water concentration and temperature on samples results in changes in the structure [14–17], coordination of vanadium species [18,19,103,104], and the catalyst dispersion [16,19,79,82,84,87,103,104]. Hydration of the supported vanadia causes changes in the proportion of the monovanadate species and polyvanadates and leads to an increase in the dispersion of vanadium species. Dehydration results in the appearance of monovanadate species Interconversion between different surface species occurs easily and reversibly depending on the temperature and water content. (ii) Catalysts generate adsorbed water species. Products of dissociation of adsorbed water are hydroxyl groups on all the oxide catalysts. Protons of the OH– group are Brønsted acid sites, cations of the catalysts are Lewis sites. The coverage by BAS and LAS depends on temperature: the temperature elevation causes the catalyst dehydration those results in a decrease of BAS and increase of Las in number. The Lewis acidity predominates on the supported vanadia catalysts at the low vanadia content of in the absence of H2O. Vise versa, Brønsted acidity predominates at the high vanadia content in the presence of H2O [17]. The effect of water in reaction decreases with increasing temperatures [59].

* Wi is rate of products formation.

picolines and the product yields justifies the high ratios of the water to picolines concentrations in the reaction mixture. In oxidative ammonolysis of methylpyrazine over vanadium-titanium catalysts, water creates a new route, i.e. a consecutive stage of hydrolysis of cyanopyrazine to pyrazinamide [95]. Water importance is shown for the oxidation of linear and substituted cyclic alkanes to the corresponding alcohols and ketones by copper-containing and other catalytic systems. The promoting role of water consists in the reaction acceleration and indicates a direct involvement of H2O in the rate-limiting step of the hydroxyl radical generation [96]. Important part of water is developed in the hydrocarboxylation of gaseous alkanes (ethane, propane and n‐butane) to the corresponding Cn+1 carboxylic acids. The role of water is a relevant reagent that provides the main source of the OH group in the carboxylic acid [97,98]. The role of water in homogeneous catalysis involving MOF is comprehensively described in the overview [2]. The above discussion demonstrates that water is an active participant of the reaction system and makes an important contribution to selective transformation of hydrocarbons of different compositions and chemical nature.

The hydrocarbon oxidation mechanism includes a number of surface complexes whose characteristics determine the selective or deep conversion of the initial hydrocarbon and product. The first stage of the reaction is activation of the hydrocarbon. The influence of water on the catalyst activity is based on generation of OH groups as Brønsted sites for adsorption of hydrocarbons to be oxidized. BAS long with LAS take part in the activation of the reactants. Surface complexes of the oxidized reactants formed by hydrogen bonding to the Brønsted sites were detected in the hydrated catalysts. These complexes were identified using IR spectroscopy upon adsorption of acrolein on the VMo catalyst [105,106] and V–Sb–O catalysts [107], adsorption of β-picoline on CrV0.95P0.05O4 [90], adsorption of β-picoline [108,109] and of 2,3,4-picoline isomers [110] and pyridine-3-carbaldehyde [111] on V-Ti catalyst, formaldehyde on V-Ti catalyst [112–114] and on TiO2 [115], formic acid on heteropolyacids [116,117], methanol and ethanol on mixed oxides [118]. FTIR data, together with thermodynamic calculations for H-bonded complexes of formaldehyde, acetaldehyde, acetone, cyclopentanone, cyclohexanone, and 2-cyclohexen-1-one on Aerosil were reported by Allian et al. [119]. The formation of H-bonded complexes brings about changes in spectral features of the OH groups and adsorbate. For example, adsorption of acrolein leads to the shifts of the absorption bands assigned to surface OH groups by 200–250 cm–1 and to a decrease in the

4. The functions of water in selective oxidation of hydrocarbons Referring to Boreskov, the key approach in catalysts is to consider “the catalyst and reactants as an integrated chemical system where not only reactants are transformed under the influence of the catalyst, but also the catalyst does as a result of the chemical interaction with the reactants.” “Solid catalysts are the labile components of the reaction system and, under the influence of the reaction mixture, they change their chemical composition, surface structure, and catalytic properties [99]. These concepts were formulated and substantiated by Boreskov in his papers [100–102]. 7

Molecular Catalysis xxx (xxxx) xxxx

T.V. Andrushkevich and E.V. Ovchinnikova

observed variation in the concentration of surface complexes argues for the competitive mechanism of the water and acid adsorption. Another evidence of this mechanism is that the bidentate formate coverage is lowered to ca. one twentieth in the presence of water at identical gasphase concentrations of the acid. Monodentate formate ions are not formed in the presence of water vapor but identified in IR spectra of the dry mixture. Increasing selectivity to formic acid in formaldehyde oxidation is due to the competitive adsorption of H2O and formic acid on active sites of the V-Ti oxide catalyst and increasing rate of the reverse reaction of conversion of formates to formic acid owing to increasing number of surface protons generated by water adsorption. The mechanism of suppression of the product transformation under the action of water can follow several routes:

frequency of the stretching vibrations of the C]O bond in acroleine by 0.7–2.0 % as compared to the νC = O of the adsorbate in the gas phase. Such complexes were observed upon acrolein adsorption on SiO2 and V–Mo–Si–O [105,106], Bi–Mo–Si–O and other catalysts [12]. Protonation of pyridine rings of isomer picoline molecules by strong Brønsted acid sites activates methyl group [110]. The further fate of the H-linked complexes is determined by the strength of the associated BAS centers. Weakly bonded H-complexes are removed at low temperature and do not take part in the reaction. The strongly bonded complexes form surface oxygenates converting to deep oxidation product or cause coking of the catalysts [83,120]. S.-H. Chai et al. [78] demonstrated as an example the optimal acidity oxidation of glycerol to acrolein. Different dependencies of oxidation rates on the water concentration in the reaction mixtures are characteristic of different reactions. In some cases, the curves reach plateau [46]; alternatively, the rates start decreasing after reaching the maxima [25,47,53]. The latter indicates blockage of the active sites with water and the dependence of the catalyst activity on surface coverage with hydroxyl groups [25]. Water suppresses the formation of CO2 over Sb/Sn/V oxide by blocking the most active sites, which are responsible for CO2 formation. Water prevents the formation of strongly bonded oxygenates [41,83] or facilitate the product desorption [50] by providing a high oxidation state of the catalyst active sites. Many researchers discuss such useful function of water as prevention of the catalyst coking [51,81–83]. Either water blocks concerned active sites or ‘eluates’ strongly bonded surface carbonate-carboxylate complexes. Improving selectivity by water may be caused either by acceleration of the target reaction and no water effect on the transformation of the selective product or by suppression of side reactions. The formed first is implemented in oxidation of acrolein to acrylic acid [46], β-picoline to nicotinic acid [92], and toluene to benzoic acid [82].These works show that hydroxyl groups do not affect the total oxidation. Improvement of the selectivity due to suppression of the side reaction – decomposition of formic acid – with water was exemplified with oxidation of formaldehyde over a V-Ti catalyst [27]. Fig. 8 shows dynamics of the acid adsorption from a mixture of 1 % HCOOH in air (a) and from a mixture of 1 % HCOOH + 4 % H2O in air (b). At joint adsorption of formic acid and water vapor (Fig. 8b) feeding the reaction mixture to the IR cell with the catalyst leads to the simultaneous formation of bidentate formate of a band at ca. 1550 cm–1, molecular of a band at ca. 1620 cm–1 and dissociative adsorbed water of a band at ca. 3680 cm–1. At the early period of the adsorption (no longer than 400 s) concentrations of surface complexes of both the acid and water increase. Then the concentration of the bidentate formate decreases monotonically while the concentration of water adsorption products increases up to the formation of the stationary coverage in ca. 1000s. The

1 Competitive adsorption of the reaction product and water on the same active sites; 2 Displacement of the intermediate (carboxylate in the case of acids) to form stronger bonded products of water dissociation (OH groups); 3 Oxidation of active sites of intermediates (carboxylates) to lessen their bonding energy and to facilitate the product desorption (in the form of acid). Sadovskaya et al. [121] showed that the adsorptive substitution of water for formates is responsible for the suppression in the case of dehydrogenation, and blockage of the active centers by adsorbed water in the case of dehydration. The possibility of the competitive interaction of water and oxygenates results from similar mechanisms of donating of the lone-pair electrons located on oxygen of water [22], acrolein [122], and other oxygenates [123] to one of the empty d-orbitals of the vanadium site. Implementation of routes 1 and 2 are determined by thermodynamic factors, namely heats of adsorption of water and of the corresponding product on the catalyst under the reaction conditions, for example the heats of adsorption of acrylic acid [124], formic acid and water [125]. Heats of adsorption of these reactants depend on the coverage. The differential heat of water adsorption is 75 kJ/mol at the water coverage of 0 to 0.85 and decreases from 75 to 50 kJ/mol at the coverage of 0.8 to 0.98, i.e. it tends to the level close to the evaporation heat of liquid water (41 kJ at 100 °C) as the coverage increases. The heat of adsorption of formic acid is 100 kJ/mol at the water coverage of 0 to 0.85 and decreases to 50 kJ/mol at the coverage of 0.8 to 0.98 [125]. Hence, it is reasonable to suppose that the mechanism of the acid decomposition changes on varying the concentration ratio of water and acid in the reaction mixture. The difference in the effect of water at different concentrations of water and the reactant to be oxidized is reported in literature. Miller et al. [126] used DFT of adsorption of water and formic acid on TiO2 to show that the stability (strength, energy) of formic acid, type of species

Fig. 8. IR spectra of adsorption of formic acid at 120 °C for 40 s (1), 400 s (2) and 600 s (3) from a mixture of 1 % HCOOH in air (a) and from a mixture of 1 % HCOOH + 4 % H2O in air (b). 8

Molecular Catalysis xxx (xxxx) xxxx

T.V. Andrushkevich and E.V. Ovchinnikova

5. Conclusions

(molecular, mono, bi, dimer) and type of bond (through C or O of the acid) depend on the proportions of water and formic acid coverage. The fact that water does not influence reoxidation of acrylic, nicotinic and benzoic acids but has a strong influence on oxidation of formic acid can be accounted for by different acidities of these reactants. The former are weak organic acids and form weakly bonded carboxylic intermediates. Formic acid is strongest among organic acids; desorption of this acid as it is needs some energy compensation [99] for weakening bonds of formates with the active site, and water does it. Isotopic transient experiments with labeled oxygen in the water indicate a strong interaction between water and the catalyst surface [21,41] As follows from the work [21,24–26], water exhibits oxidizing behavior. As an oxidant, water can contribute to suppression of reoxidation of formic acid (route 3). Water adsorption results in a decrease in the charge on the vanadium sites by 0.021 electrons [22]. The completely oxidized catalyst favors the product desorption and prevents the formation of strongly bonded oxygenates [41]. Oxidation of the active site with water causes weakening of corboxylate (formate in the present case) bonding and favors their desorption in the form of acid (formic acid) [127]. It is common knowledge that oxidation of hydrocarbons over heterogeneous catalysts proceeds according to the Mars-van Krevelen redox cycle [7,127–132] where a MeO pair (a cation of the catalyst and lattice oxygen) is the active site. The comprehensive functions of water described here raise the question about place of the active centers produced by water in the Mars-van Krevelen mechanism. We believe that the role of the Brønsted sites (comprised in OH groups) is the primary activation of oxidized reactants to form hydrogen-bonded species with slightly deformed bonds in oxidizable components. This step does not limit the reaction. At the next, reaction-limiting, step, the reactant is dissociated on the Lewis acid site, which bounds the deprotonated carbon fragment and contributes to electron transfer at the further intermediate transformations. The LAS are principal for the activation and further transformations of reactants. Vanadium is such an unconditional Lewis site for selective oxidation of simple and functionalized hydrocarbons [7,127–132]. Another product of dissociation – proton – interacts directly with the lattice oxygen to form a hydroxyl group and, eventually, water. These pathways are described for transformation of 3-picoline over VCr [88] and V-Ti [133] catalysts. German researchers [57–64,134] consider water as the main reactant of the selective oxidation. R.Schlögl [134] insists that namely OH groups govern the catalytic process. They participate in oxidation-reduction of the active site (V). It is interesting that the reactant under oxidation takes part neither in electron transfer nor in reduction of the active site. According R.Schlögl that the function is performed by water correspondingly to the scheme [134]:

Water is an affordable and cheap chemical reagent of chemical reactions. In selective oxidation of hydrocarbons, its positive effect is manifested in an increase of the activity and selectivity of the catalysts. The acceleration of the catalytic reaction is associated with the generation of new active centers, namely, Brønsted active sites as the part of hydroxyl groups - water dissociation products. Brønsted active sites can serve by centers for the primary activation of hydrocarbons, facilitating the subsequent limiting stage of dissociation by Lewis active sites, or, on suitable acidity, represent self-acting active centers. The increase in selectivity in the presence of water can be carried out in several ways: - acceleration of the main reaction associated with the appearance of Brønsted active sites and no influence on the side reactions; - inhibition reoxidation by competing adsorption of water and a product or water displacement of a surface oxygenate precursor; - facilitation of the desorption of the target product from oxidized water on the surface of the catalyst; - suppression of the formation of strongly bonded intermediates by adjusting the Brønsted active sites acidity. All of the above, increasing selectivity, at the same time reduces the coking the catalysts, which is the result of the strong binding of carboncontaining components of the reaction mixture. Water influences the reaction in multiple ways and the reaction itself proceeds via multiple stages. This determines the need for kinetic studies. Kinetics will provide evidence for the mechanism of water interaction with the catalyst including formation of surface intermediates. Also, kinetics will enable to quantify the participation of water at different stages, to optimize the water content in reaction gas, and to assess the contribution of reaction water. Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgements This work was conducted within the framework of the budget projects АААА-А17-117041710083-5 and AAAA-A17-117041710076-7 for Boreskov Institute of Catalysis and was supported by Russian Foundation for Basic Research (project no. 18-03-01160).

C3H8 + 2OH− → C3H6 + 2H2O + 2e− → C3H6 + 2H2O + 2e−

References

V+5 = (O) + e− + H2O → V+4 (OH) + OH− [1] T. Kitanosono, K. Masuda, P. Xu, S. Kobayashi, Catalytic organic reactions in water toward sustainable society, Chem. Rev. 118 (2018) 679–746, https://doi.org/10. 1021/acs.chemrev.7b00417. [2] A. Dhakshinamoorthy, A.M. Asiric, H. Garcia, Catalysis by metal–organic frameworks in water, Chem. Commun. 50 (2014) 12800–12814, https://doi.org/10. 1039/c4cc04387a. [3] C.-R. Chang, Z.-Q. Huang, J. Li, The promotional role of water in heterogeneous catalysis: mechanism insights from computational modeling, WIREs Comput. Mol. Sci. 6 (2016) 679–693, https://doi.org/10.1002/wcms.1272. [4] R. Davies, On the role of water in heterogeneous catalysis: a Tribute to Professor M. Wyn Roberts, Top. Catal. 59 (8–9) (2016) 671–677, https://doi.org/10.1007/ s11244-016-0539-5. [5] L. Filiciotto, A.M. Balu, A.A. Romero, C. Angelici, J.C. van der Waal, R. Luque, Reconstruction of humins formation mechanism from decomposition products: a GC-MS study based on catalytic continuous flow depolymerizations, Mol. Catal. 479 (2019) 110564, https://doi.org/10.1016/j.mcat.2019.110564. [6] B. Grzybowska-Świerkosz, Vanadia-titania catalysts for oxidation of o-xylene and other hydrocarbons, Appl. Catal. A 157 (1997) 263–310, https://doi.org/10. 1016/S0926-860X(97)00015-X. [7] J.C. Védrine, I. Fechete, Heterogeneous partial oxidation catalysis on metal oxides, C. R. Chim. 19 (2016) 1203–1225, https://doi.org/10.1016/j.crci.2015.09.021. [8] C.A. Carrero, R. Schloegl, I.E. Wachs, R. Schomaecker, Critical literature review of

In oxidation of acrolein to acrylic acid over VMoW oxide, hydroxyl groups bound protons at the limiting stage of acrolein dissociation [64], then contribute to the formation of intermediates, and water [61]. Water is an important product and reactant simultaneously. “The combination of the heterogeneous system (mixed oxide) and the homogenous catalyst (water) forms the real catalyst” [61]. Dwivedi et al. [135] studied oxidative ammoxidation of 2,6-dichlorotoluene over the V2O5/γ-Al2O3 catalyst and came to an exciting conclusion: The reaction follows, in general, the Mars-van Krevelen mechanism but “water desorption seems to be the driving force for H abstraction from reactant and reoxidation of the catalyst”. Finally, paying tribute to the role of water, we affirm that the chemical composition of the catalysts determines indeed the catalytic performance for oxidation of hydrocarbons and the Brønsted sites are useful complement to the chemical composition.

9

Molecular Catalysis xxx (xxxx) xxxx

T.V. Andrushkevich and E.V. Ovchinnikova

[9]

[10]

[11]

[12]

[13]

[14]

[15]

[16]

[17]

[18]

[19]

[20]

[21]

[22]

[23]

[24]

[25]

[26]

[27]

[28]

[29]

[30]

[31]

[32]

C8RE00285A. [33] T. Seiyama, K. Nita, T. Maehara, N. Yamazoe, Y. Takita, Oxyhydrative scission of olefins 1. Oxidation of lower olefins, J. Catal. 49 (1977) 164–173, https://doi.org/ 10.1016/0021-9517(77)90252-4. [34] J. Nováková, Z. Dolejšek, K. Habersberger, A note on the influence of water vapour in the oxidation of propene to acrylic acid on a mixed oxide catalyst, React. Kinet. Catal. Lett. 4 (1976) 389–395, https://doi.org/10.1007/BF02342580. [35] E.M. Erenburg, T.V. Andrushkevich, G.Ya. Popova, A.A. Davydov, V.M. Bondareva, Influence of water on propylene oxidation on VMo catalyst, React. Kinet. Catal. Lett. 12 (1) (1979) 5–11, https://doi.org/10.1007/ BF02071417. [36] L. Bui, A. Bhan, Mechanisms for CeC bond cleavage and formation during acrolein production on a mixed metal oxide catalyst, Appl. Catal. A 546 (2017) 87–95, https://doi.org/10.1016/j.apcata.2017.08.011. [37] Y. Takita, A. Ozaki, Y. Moro-oka, Catalytic oxidation of olefins over oxide catalysts containing molybdenum: V. Relation between the surface concentration of acidic sites and the catalytic activity to form acetone, J. Catal. 27 (1972) 185–192, https://doi.org/10.1016/0021-9517(72)90259-X. [38] P. Kube, B. Frank, R. Schlögl, A. Trunschke, Isotope studies in oxidation of propane over vanadium oxide, ChemCatChem 9 (2017) 3446–3455, https://doi.org/10. 1002/cctc.201700847. [39] A.N. Chernov, V.I. Sobolev, K.Yu. Koltunov, Gas-phase oxidation of propylene into acetone on a V2O5/TiO2 catalyst: effect of pressure and role of water, Russ. J. Appl. Chem. 90 (2017) 1439–1442, https://doi.org/10.1134/S1070427217090105. [40] G.K. Boreskov, E.M. Erenburg, T.V. Andrushkevich, T.V. Zelenkova, V.N. Bibin, V.D. Meshcheryakov, N.P. Boronina, Yu.N. Tyurin, Kinetics of propylene oxidation on multicomponent oxide catalyst, Kinet. Catal. 23 (1982) 755–762. [41] Y.A. Saleh-Alhamed, R.R. Hudgins, P.L. Silveston, Role of water vapor in the partial oxidation of propene, J. Catal. 161 (1996) 430–440, https://doi.org/10. 1006/jcat.1996.0201. [42] F. Cavani, N. Ballarini, A. Cericola, Oxidative dehydrogenation of ethane and propane: how far from commercial implementation? Catal. Today 127 (2007) 113–131, https://doi.org/10.1016/j.cattod.2007.05.009. [43] M.M. Bettahar, G. Costentin, L. Savary, J.C. Lavalley, On the partial oxidation of propane and propylene on mixed metal oxide catalysts, Appl. Catal. A 145 (1996) 1–48, https://doi.org/10.1016/0926-860X(96)00138-X. [44] J.C. Vedrine, J.M.M. Millet, J.-C. Volta, Molecular description of active sites in oxidation reactions: acid-base and redox properties, and role of water, Catal. Today 32 (1996) 115–123, https://doi.org/10.1016/S0920-5861(96)00185-X. [45] M.M. Lin, Selective oxidation of propane to acrylic acid with molecular oxygen, Appl. Catal. A 207 (2001) 1–16, https://doi.org/10.1016/S0926-860X(00) 00609-8. [46] E.M. Erenburg, T.V. Andrushkevich, V.N. Bibin, Kinetics of the oxidation of acrolein on a vanadium-molybdenum catalyst, Kinet. Catal. 20 (1979) 561–566. [47] W. Zheng, Z. Yu, P. Zhang, Y. Zhang, H. Fu, X. Zhang, Q. Sun, X. Hu, Selective oxidation of propane to acrylic acid over mixed metal oxide catalysts, J. Nat. Gas Chem. 17 (2008) 191–194, https://doi.org/10.1016/S1003-9953(08)60050-X. [48] F.N. Naraschewski, A. Jentys, J.A. Lercher, On the role of the vanadium distribution in MoVTeNbOx mixed oxides for the selective catalytic oxidation of propane, Top. Catal. 54 (2011) 639–649, https://doi.org/10.1007/s11244-0119686-x. [49] G. Landi, L. Lisi, J.C. Volta, Effect of water on the catalytic behaviour of VPO in the selective oxidation of propane to acrylic acid, Chem. Commun. 4 (2003) 492–493, https://doi.org/10.1039/B211619G. [50] S. Wannakao, B. Boekfa, P. Khongpracha, M. Probst, J. Limtrakul, Oxidative dehydrogenation of propane over a VO2‐exchanged MCM‐22 zeolite: a DFT study, Chem. Phys. Chem. 11 (2010) 3432–3438, https://doi.org/10.1002/cphc. 201000586. [51] H.W. Zanthoff, M. Sananes-Schultz, S.A. Buchholz, U. Rodemerck, B. Kubias, M. Baerns, On the active role of water during partial oxidation of n-butane to maleic anhydride over (VO)2P2O7 catalysts, Appl. Catal. A 172 (1998) 49–58, https://doi.org/10.1016/S0926-860X(98)00092-1. [52] W. Suprun, E.M. Sadovskaya, C. Rüdinger, H.-J. Eberle, M. Lutecki, H. Papp, Effect of water on oxidative scission of 1-butene to acetic acid over V2O5-TiO2 catalyst. Transient isotopic and kinetic study, Appl. Catal. A 391 (2011) 125–136, https:// doi.org/10.1016/j.apcata.2010.03.043. [53] D. Linke, D. Wolf, M. Baerns, O. Timpe, R. Schlögl, S. Zeyβ, U. Dingerdissen, Catalytic partial oxidation of ethane to acetic acid over Mo1V0.25Nb0.12Pd0.0005Ox: I. Catalyst performance and reaction mechanism, J. Catal. 205 (2002) 16–31, https://doi.org/10.1006/jcat.2001.3367. [54] F. Rahman, K.F. Loughlin, M.A. Al-Saleh, M.R. Saeed, N.M. Tukur, M.M. Hossain, K. Karim, A. Mamedov, Kinetics and mechanism of partial oxidation of ethane to ethylene and acetic acid over MoV type catalysts, Appl. Catal. A 375 (2010) 17–25, https://doi.org/10.1016/j.apcata.2009.11.026. [55] V.L. Sushkevich, D. Palagin, M. Ranocchiari, J.A. van Bokhoven, Selective anaerobic oxidation of methane enables direct synthesis of methanol, Science 356 (2017) 523–527, https://doi.org/10.1126/science.aam9035. [56] R. Grabowski, Kinetics of oxidative dehydrogenation of C2‐C3 alkanes on oxide catalysts, Catal. Rev. 48 (2006) 199–268, https://doi.org/10.1080/ 01614940600631413. [57] P. Kube, B. Frank, S. Wrabetz, J. Kröhnert, M. Hävecker, J. Velasco-Vélez, J. Noack, R. Schlögl, A. Trunschke, Functional analysis of catalysts for lower alkane oxidation, ChemCatChem 9 (2017) 573–585, https://doi.org/10.1002/cctc. 201601194. [58] P. Kampe, L. Giebeler, D. Samuelis, J. Kunert, A. Drochner, F. Haaβ, A.H. Adams, J. Ott, S. Endres, G. Schimanke, T. Buhrmester, M. Martin, H. Fuess, H. Vogel,

the kinetics for the oxidative dehydrogenation of propane over well-defined supported vanadium oxide catalysts, ACS Catal. 4 (2014) 3357–3380, https://doi.org/ 10.1021/cs5003417. P. Botella, B. Solsona, J.M. López Nieto, Selective oxidation of C3–C4 olefins over Mo-containing catalysts with tetragonal tungsten bronze structure, Catal. Today 141 (2009) 311–316, https://doi.org/10.1016/j.cattod.2008.04.024. J.M. López Nieto, The selective oxidative activation of light alkanes. From supported vanadia to multicomponent bulk V-containing catalysts, Top. Catal. 41 (2006) 3–15, https://doi.org/10.1007/s11244-006-0088-4. M.A. Henderson, The interaction of water with solid surfaces: fundamental aspects revisited, Surf. Sci. Rep. 46 (2002) 1–308, https://doi.org/10.1016/S01675729(01)00020-6. A. Davydov, N.T. Sheppard (Ed.), Molecular Spectroscopy of Oxide Catalyst Surfaces, John Wiley & Sons Ltd, The Atrium, Southern Gate, Chichester, West Sussex PO19 8SQ, England, 2003, , https://doi.org/10.1002/0470867981. N.-Y. ToPsøE, T. Slabiak, B.S. Clausen, T.Z. Srnak, J.A. Dumesic, Influence of water on the reactivity of vanadia/titania for catalytic reduction of NOx, J. Catal. 134 (1992) 742–746, https://doi.org/10.1016/0021-9517(92)90358-O. B. Olthof, A. Khodakov, A.T. Bell, E. Iglesia, Effects of support composition and pretreatment conditions on the structure of vanadia dispersed on SiO2, Al2O3, TiO2, ZrO2, and HfO2, J. Phys. Chem. B 104 (2000) 1516–1528, https://doi.org/ 10.1021/jp9921248. S. Xie, E. Iglesia, A.T. Bell, Effects of hydration and dehydration on the structure of silica-supported vanadia species, Langmuir 16 (2000) 7162–7167, https://doi. org/10.1021/la0003342. J.-M. Jehng, G. Deo, B.M. Weckhuysen, I.E. Wachs, Effect of water vapor on the molecular structures of supported vanadium oxide catalysts at elevated temperatures, J. Mol. Catal. A 110 (1996) 41–54, https://doi.org/10.1016/1381-1169(96) 00061-1. C.-H. Lin, H. Bai, Adsorption behavior of moisture over a vanadia/titania catalyst: a study for the selective catalytic reduction process, Ind. Eng. Chem. Res. 43 (2004) 5983–5988, https://doi.org/10.1021/ie0308487. C. Hess, Nanostructured vanadium oxide model catalysts for selective oxidation reactions, Chem. Phys. Chem. 10 (2009) 319–326, https://doi.org/10.1002/cphc. 200800585. I. Giakoumelou, C. Fountzoula, C. Kordulis, S. Boghosian, Molecular structure and catalytic activity of V2O5/TiO2 catalysts for the SCR of NO by NH3: in situ Raman spectra in the presence of O2, NH3, NO, H2, H2O, and SO2, J. Catal. 239 (2006) 1–12, https://doi.org/10.1016/j.jcat.2006.01.019. E.M. Sadovskaya, V.B. Goncharov, Yu.K. Gulyaeva, G.Ya. Popova, T.V. Andrushkevich, Kinetics of the H218O/H216O isotope exchange over vanadia–titania catalyst, J. Mol. Catal. A 316 (2010) 118–125, https://doi.org/10. 1016/j.molcata.2009.10.009. V.I. Avdeev, V.M. Tapilin, Water effect on the electronic structure of active sites of supported vanadium oxide catalyst VOx/TiO2 (001), J. Phys. Chem. C 114 (2010) 3609–3613, https://doi.org/10.1021/jp911145c. X. Yin, A. Fahmi, H. Han, A. Endou, S.S.C. Ammal, M. Kubo, K. Teraishi, A. Miyamoto, Adsorption of H2O on the V2O5(010) surface studied by periodic density functional calculations, J. Phys. Chem. B 103 (1999) 3218–3224, https:// doi.org/10.1021/jp9833395. W.-Q. Li, T. Fjermestad, A. Genest, N. Rösch, Reactivity trends of the MoVOx mixed metal oxide catalyst from density functional modeling, Catal. Sci. Technol. 9 (2019) 1559–1569, https://doi.org/10.1039/C8CY02545B. M. Hävecker, S. Wrabetz, J. Kröhnert, L.-I. Csepei, R.N. d’Alnoncourt, Y.V. Kolen’ko, F. Girgsdies, R. Schlögl, A. Trunschke, Surface chemistry of phasepure M1 MoVTeNb oxide during operation in selective oxidation of propane to acrylic acid, J. Catal. 285 (2012) 48–60, https://doi.org/10.1016/j.jcat.2011.09. 012. S. Lars, T. Andersson, S. Järås, Activity Measurements and ESCA investigations of a V2O5/SnO2 catalyst for the vapor-phase oxidation of alkylpyridines, J. Catal. 64 (1980) 51–67, https://doi.org/10.1016/0021-9517(80)90478-9. C.U.I. Odenbrand, P.L.T. Gabrielsson, J.G.M. Brandin, L.A.H. Andersson, Effect of water vapor on the selectivity in the reduction of nitric oxide with ammonia over vanadia supported on silica-titania, Appl. Catal. 78 (1991) 109–122, https://doi. org/10.1016/0166-9834(91)80092-B. G.Ya. Popova, Y.A. Chesalov, E.M. Sadovskaya, T.V. Andrushkevich, Effect of water on decomposition of formic acid over V–Ti oxide catalyst: kinetic and in situ FTIR study, J. Mol. Catal. A 357 (2012) 148–153, https://doi.org/10.1016/j. molcata.2012.02.005. C. Tao, W. Guopeng, H. Gengshen, S. Weiguang, Y. Pinliang, L. Can, In situ FT-IR study of photocatalytic decomposition of formic acid to hydrogen on Pt/TiO2 catalyst, Chin. J. Catal. 29 (2008) 105–107, https://doi.org/10.1016/S18722067(08)60019-4. L. Savary, J. Saussey, G. Costentin, M.M. Bettahar, M. Gubelmann-Bonneau, J.C. Lavalley, Propane oxydehydrogenation reaction on a VPO/TiO2 catalyst. Role of the nature of acid sites determined by dynamic in-situ IR studies, Catal. Today 32 (1996) 57–61, https://doi.org/10.1016/S0920-5861(96)00090-9. H. Miyata, J.B. Moffat, Infrared studies of pyridine, 2,6-dimethylpyridine, and 2,6di-tert-butylpyridine on stoichiometric and nonstoichiometric boron phosphate, J. Catal. 62 (1980) 357–366, https://doi.org/10.1016/0021-9517(80)90464-9. H. Miyata, J.B. Moffat, Infrared studies of the adsorption of alkenes on non-stoichiometric boron phosphate, J. Chem. Soc. Faraday Trans. 1 77 (1981) 2493–2501, https://doi.org/10.1039/F19817702493. J.H. Miller, L. Bui, A. Bhan, Pathways, mechanisms, and kinetics: a strategy to examine byproduct selectivity in partial oxidation catalytic transformations on reducible oxides, React. Chem. Eng. 4 (2019) 784–805, https://doi.org/10.1039/

10

Molecular Catalysis xxx (xxxx) xxxx

T.V. Andrushkevich and E.V. Ovchinnikova

[59]

[60]

[61]

[62]

[63]

[64]

[65] [66]

[67]

[68]

[69]

[70]

[71]

[72]

[73]

[74]

[75]

[76]

[77]

[78]

[79]

[80]

[81]

[82]

Heterogeneously catalysed partial oxidation of acrolein to acrylic acid —structure, function and dynamics of the V–Mo–W mixed oxides, Phys. Chem. Chem. Phys. 9 (2007) 3577–3589, https://doi.org/10.1039/B700098G. T. Jekewitz, N. Blickhan, S. Endres, A. Drochner, H. Vogel, The influence of water on the selective oxidation of acrolein to acrylic acid on Mo/V/W-mixed oxides, Catal. Commun. 20 (2012) 25–28, https://doi.org/10.1016/j.catcom.2011.12. 022. T. Petzold, N. Blickhan, A. Drochner, H. Vogel, The effect of water on the heterogeneously catalyzed selective oxidation of acrolein: an isotope study, ChemCatChem 6 (2014) 2053–2058, https://doi.org/10.1002/cctc.201400099. A. Drochner, D. Ohlig, S. Knoche, N. Gora, M. Heid, N. Menning, T. Petzold, H. Vogel, Mechanistic studies on the transition metal oxide catalysed partial oxidation of (meth)acrolein to the corresponding carboxylic acids, Top. Catal. 59 (2016) 1518–1532, https://doi.org/10.1007/s11244-016-0670-3. S. Knoche, M. Heid, N. Gora, D. Ohlig, A. Drochner, H. Vogel, B.J.M. Etzold, Activity hysteresis during cyclic temperature-programmed reactions in the partial oxidation of acrolein to acrylic acid, Chem. Eng. Technol. 40 (2017) 2084–2095, https://doi.org/10.1002/ceat.201700111. A. Drochner, P. Kampe, N. Menning, N. Blickhan, T. Jekewitz, H. Vogel, Acrolein oxidation to acrylic acid on Mo/V/W-mixed oxide catalysts, Chem. Eng. Technol. 37 (2014) 398–408, https://doi.org/10.1002/ceat.201300797. S. Knoche, M. Heid, N. Gora, D. Ohlig, A. Drochner, C. Hess, B. Etzoland, H. Vogel, Mechanistic study on the selective oxidation of acrolein to acrylic acid: identification of the rate‐limiting step via perdeuterated acrolein, ChemCatChem 11 (2019) 3242–3252, https://doi.org/10.1002/cctc.201900549. T.V. Andrushkevich, The heterogeneous oxidation of acrolein to acrylic acid: from mechanism to process, Rus. Chem. Ind. 26 (1994) 9–21. J.H. Miller, A. Bhan, Kinetic modeling of acrolein oxidation over a promoted MoV oxide catalyst, ChemCatChem 10 (2018) 5511–5522, https://doi.org/10.1002/ cctc.201801029. C. Qiu, C. Chen, S. Ishikawa, T. Murayama, W. Ueda, Crystalline Mo-V–W-mixed oxide with orthorhombic and trigonal structures as highly efficient oxidation catalysts of acrolein to acrylic acid, Top. Catal. 57 (2014) 1163–1170, https://doi. org/10.1007/s11244-014-0283-7. S. Yasuda, J. Hirata, M. Kanno, W. Ninomiya, R. Otomo, Y. Kamiya, The role of steam in selective oxidation of methacrolein over H3PMo12O40, Appl. Catal. A 570 (2019) 164–172, https://doi.org/10.1016/j.apcata.2018.11.007. S. Yasuda, A. Iwakura, J. Hirata, M. Kanno, W. Ninomiya, R. Otomo, Y. Kamiya, Strong Brønsted acid-modified chromium oxide as an efficient catalyst for the selective oxidation of methacrolein to methacrylic acid, Catal. Commun. 125 (2019) 43–47, https://doi.org/10.1016/j.catcom.2019.03.020. G.Ya. Popova, T.V. Andrushkevich, V. Danilevich, E.Yu.A. Chesalov, L.S. Dovlitova, V.A. Rogov, V.N. Parmon, Heterogeneous selective oxidation of formaldehyde to formic acid on V/Ti oxide catalysts: the role of vanadia species, J. Mol. Catal. A 283 (2008) 146–152, https://doi.org/10.1016/j.molcata.2007.12. 019. E.V. Danilevich, G.Ya. Popova, I.A. Zolotarskii, A. Ermakova, T.V. Andrushkevich, Kinetics of formaldehyde oxidation on a vanadia-titania catalyst, Catal. Ind. 2 (2010) 320–328, https://doi.org/10.1134/S2070050410040057. E.V. Danilevich, G.Ya. Popova, T.V. Andrushkevich, Yu.A. Chesalov, E.A. Ivanov, Mechanism and kinetics of formic acid decomposition on V-Ti oxide catalyst. The effect of water, Abstract. VIII International Conference Mechanisms of Catalytic Reactions, Novosibirsk (Russia), June 28 - July 2 (2009) 185. Y. Wang, X. Zhu, M. Crocker, B. Chen, C. Shi, A comparative study of the catalytic oxidation of HCHO and CO over Mn0.75Co2.25O4 catalyst: the effect of moisture, Appl. Catal. B 160–161 (2014) 542–551, https://doi.org/10.1016/j.apcatb.2014. 06.011. Y. Ganjkhanlo, Z. Tišler, J.M. Hidalgo, K. Frolich, J. Kotera, P. Čičmanec, R. Bulánek, VOx/Zr–SBA‑15 catalysts for selective oxidation of ethanol to acetaldehyde, Chem. Pap. 72 (2018) 937–946, https://doi.org/10.1007/s11696-0170336-z. P. Čičmanec, K. Raabová, J.M. Hidalgo, D. Kubička, R. Bulánek, Conversion of ethanol to acetaldehyde over VOX-SiO2 catalysts: the effects of support texture and vanadium speciation, React. Kinet Mech. Cat. 121 (2017) 353–369, https://doi. org/10.1007/s11144-017-1169-z. W. Zhang, S.T. Oyama, Non-uniform surface kinetics with two types of sites: the case of ethanol oxidation on molybdenum oxide, Catal. Lett. 39 (1996) 67–71, https://doi.org/10.1007/BF00813732. D. Sun, Y. Yamada, S. Sato, W. Ueda, Glycerol as a potential renewable raw material for acrylic acid production, Green Chem. 19 (2017) 3186–3213, https://doi. org/10.1039/c7gc00358g. S.-H. Chai, H.-P. Wang, Y. Liang, B.-Q. Xu, Sustainable production of acrolein: investigation of solid acid–base catalysts for gas-phase dehydration of glycerol, Green C hem. 9 (2007) 1130–1136, https://doi.org/10.1039/B702200J. K. Omata, K. Matsumoto, T. Murayama, W. Ueda, Direct oxidative transformation of glycerol to acrylic acid over Nb-based complex metal oxide catalysts, Catal. Today 259 (2015) 205–212, https://doi.org/10.1016/j.cattod.2015.07.016. J. Deleplanque, J.-L. Dubois, J.-F. Devaux, W. Ueda, Production of acrolein and acrylic acid through dehydration and oxydehydration of glycerol with mixed oxide catalysts, Catal. Today 157 (2010) 351–358, https://doi.org/10.1016/j.cattod. 2010.04.012. A. Martin, B. Lücke, Ammoxidation and oxidation of substituted methyl aromatics on vanadium-containing catalysts, Catal. Today 57 (2000) 61–70, https://doi.org/ 10.1016/S0920-5861(99)00309-0. J. Zhu, S.L.T. Andersson, Effect of water on the catalytic oxidation of toluene over vanadium oxide catalysts, Appl. Catal. 53 (1989) 251–262, https://doi.org/10.

1016/S0166-9834(00)80024-X. [83] D.A. Bulushev, F. Rainone, L. Kiwi-Minsker, Partial oxidation of toluene to benzaldehyde and benzoic acid over model vanadia/titania catalysts: role of vanadia species, Catal. Today 96 (2004) 195–203, https://doi.org/10.1016/j.cattod.2004. 06.143. [84] S.M. Saqer, D.I. Kondarides, X.E. Verykios, Catalytic oxidation of toluene over binary mixtures of copper, manganese and cerium oxides supported on γ-Al2O3, Appl. Catal. B 103 (2011) 275–286, https://doi.org/10.1016/j.apcatb.2011.01. 001. [85] X. Li, L. Wang, Q. Xia, Z. Liu, Z. Li, Catalytic oxidation of toluene over copper and manganese based catalysts: effect of water vapor, Catal. Commun. 14 (2011) 15–19, https://doi.org/10.1016/j.catcom.2011.07.003. [86] C.-H. Wang, S.-S. Lin, C.-L. Chen, H.-S. Weng, Performance of the supported copper oxide catalysts for the catalytic incineration of aromatic hydrocarbons, Chemosphere 64 (2006) 503–509, https://doi.org/10.1016/j.chemosphere.2005. 11.023. [87] S. Luciani, N. Ballarini, F. Cavani, C. Cortelli, F. Cruzzolin, A. Frattini, R. Leanza, B. Panzacchi, Anatase-supported vanadium oxide catalysts for o-xylene oxidation: from consolidated certainties to unexpected effects, Catal. Today 142 (2009) 132–137, https://doi.org/10.1016/j.cattod.2008.08.044. [88] W.F. Hoelderich, ‘One-pot’ reactions: a contribution to environmental protection, Appl. Catal. A 194/195 (2000) 487–496, https://doi.org/10.1016/S0926-860X (99)00395-6. [89] Z. Song, T. Matsushita, T. Shishido, K. Takehira, Crystalline CrV1−xPxO4 catalysts for the vapor-phase oxidation of 3-picoline, J. Catal. 218 (2003) 32–41, https:// doi.org/10.1016/S0021-9517(03)00076-9. [90] T. Shishido, Z. Song, T. Matsushita, K. Takaki, K. Takehira, In situ DRIFTS study of picoline oxidation over CrV0.95P0.05O4 catalyst, Phys. Chem. Chem. Phys. 5 (2003) 2710–2718, https://doi.org/10.1039/B302571C. [91] T. Shishido, Z. Song, E. Kadowaki, Y. Wang, K. Takehira, Vapor-phase oxidation of 3-picoline to nicotinic acid over Cr1−xAlxVO4 catalysts, Appl. Catal. A 239 (2003) 287–296, https://doi.org/10.1016/S0926-860X(02)00394-0. [92] Е.V. Ovchinnikova, T.V. Andrushkevich, L.A. Shadrina, Kinetics of the oxidation of β-picoline to nicotinic acid over vanadia-titania catalyst. 1. the network of the reaction and the effect of water, React. Kinet. Catal. Lett. 82 (2004) 191–197, https://doi.org/10.1023/B:REAC.0000028821.70527.37. [93] V.M. Bondareva, E.V. Ovchinnikova, T.V. Andrushkevich, Kinetics of β-picoline oxidation to nicotinic acid overvanadia-titania catalyst. 3. The oxidation of nicotinic acid, React. Kinet. Catal. Lett. 94 (2008) 327–335, https://doi.org/10.1007/ s11144-008-5356-9. [94] E.V. Ovchinnikova, T.V. Andrushkevich, G.Ya. Popova, V.D. Meshcheryakov, V.A. Chumachenko, Oxidation of β-picoline to nicotinic acid over V2O5-TiO2 catalyst: kinetic studies and reaction mechanism, Chem. Eng. J. 154 (2009) 60–68, https://doi.org/10.1016/j.cej.2009.04.034. [95] V.M. Bondareva, T.V. Andrushkevich, O.B. Lapina, V.V. Malakhov, L.S. Dovlitova, A.A. Vlasov, Ammoxidation of methylpyrazine over binary oxide systems: IV. A vanadia-titania system, Kinet. Catal. 41 (2000) 670–678. [96] T.A. Fernandes, C.I.M. Santos, V. André, S.S.P. Dias, M.V. Kirillova, A.M. Kirillov, New aqua-soluble dicopper(ii) aminoalcoholate cores for mild and water-assisted catalytic oxidation of alkanes, Catal. Sci. Technol. 6 (2016) 4584–4593, https:// doi.org/10.1039/C5CY02084K. [97] M.V. Kirillova, A.M. Kirillov, A.J.L. Pombeiro, Mild, single‐pot hydrocarboxylation of gaseous alkanes to carboxylic acids in metal‐free and copper‐promoted aqueous systems, Chem. Eur. J. 16 (2010) 9485–9493, https://doi.org/10.1002/chem. 201000352. [98] M.V. Kirillova, Y.N. Kozlov, L.S. Shul’pina, O.Y. Lyakin, A.M. Kirillov, E.P. Talsi, A.J.L. Pombeiro, G.B. Shul’pin, Remarkably fast oxidation of alkanes by hydrogen peroxide catalyzed by a tetracopper(II) triethanolaminate complex: promoting effects of acid co-catalysts and water, kinetic and mechanistic features, J. Catal. 268 (2009) 26–38, https://doi.org/10.1016/j.jcat.2009.08.016. [99] T.V. Andrushkevich, V.I. Bukhtiyarov, Scientific heritage of Georgii Konstantinovich Boreskov, Kinet. Catal. 60 (2019) 123–136, https://doi.org/10. 1134/S0023158419020010. [100] G.K. Boreskov, The effect of the reaction system and catalyst interaction on the kinetics of catalytic reactions, Rus. J. Phys. Chem. A. 33 (1959) 1969–1975. [101] G.K. Boreskov, Interaction between a catalyst and a reaction system, Rus. J. Phys. Chem. A. 32 (1958) 2739–2747. [102] G.K. Boreskov, Influence of the reaction medium on the properties of solid catalysts, Kinet. Catal. 21 (1980) 1–10. [103] A.E. Lewandowska, M. Calatayud, F. Tielens, M.A. Bañares, Hydration dynamics for vanadia/titania catalysts at high loading: a combined theoretical and experimental study, J. Phys. Chem. C. 117 (2013) 25535–25544, https://doi.org/10. 1021/jp408836d. [104] A.E. Lewandowska, M. Calatayud, F. Tielens, M.A. Bañares, Dynamics of hydration in vanadia–titania catalysts at low loading: a theoretical and experimental study, J. Phys. Chem. C. 115 (2011) 24133–24142, https://doi.org/10.1021/jp204726b. [105] G.Ya. Popova, A.A. Davydov, T.V. Andrushkevich, I.I. Zakharov, Surface complexes of acrolein on oxide catalysts, Kinet. Catal. 36 (1995) 125–136. [106] G.Ya. Popova, A.A. Davydov, I.I. Zakharov, T.V. Andrushkevich, Investigation of interaction of acrolein with surface of V-Mo-Si oxide catalyst by means of IR spectroscopy and thermal desorption, Kinet. Catal. 23 (1982) 582–589. [107] G.Ya. Popova, A.A. Davydov, T.V. Andrushkevich, Infrared spectroscopic studies of the adsorbed forms of acrolein and acrylic acid on Sb6O13 and V-Sb-O catalysts, React. Kinet. Catal. Lett. 41 (1990) 33–38, https://doi.org/10.1007/BF02075478. [108] G.Ya. Popova, T.V. Andrushkevich, Yu.A. Chesalov, E.V. Ovchinnikova, Mechanism of β-Picoline oxidation to nicotinic acid on V-Ti-O catalyst as studied

11

Molecular Catalysis xxx (xxxx) xxxx

T.V. Andrushkevich and E.V. Ovchinnikova

[109]

[110]

[111]

[112]

[113]

[114]

[115]

[116]

[117]

[118] [119]

[120]

[121] E.M. Sadovskaya, Yu.A. Chesalov, V.B. Goncharov, V.I. Sobolev, T.V. Andrushkevich, Formic acid decomposition over V-Ti oxide catalyst: mechanism and kinetics, J. Mol. Catal. A 430 (2017) 54–62, https://doi.org/10. 1016/j.molcata.2016.12.010. [122] T.V. Andrushkevich, Mechanism of catalytic action of oxide systems in reactions of aldehydes oxidation to carboxylic acids, Kinet. Catal. 38 (2) (1997) 266–276. [123] P.C. Stair, The concept of Lewis acids and bases applied to surfaces, J. Am. Chem. Soc. 104 (1982) 4044–4052, https://doi.org/10.1021/ja00379a002. [124] V.M. Bondareva, T.V. Andrushkevich, Y.D. Pankratiev, V.M. Turkov, Adsorption heats of acrolein and acrylic acid on promoted V-Mo-O catalysts, React. Kinet. Catal. Lett. 32 (1986) 371–376, https://doi.org/10.1007/BF02068338. [125] V.A. Rogov, Y.A. Chesalov, E.V. Danilevich, T.V. Andrushkevich, V.N. Parmon, IR spectroscopic and calorimetric study of water and formic acid adsorption on a vanadium-titanium catalyst, Kinet. Catal. 56 (2015) 237–243, https://doi.org/10. 1134/S0023158415020093. [126] K.L. Miller, J.L. Falconer, J.W. Medlin, Effect of water on the adsorbed structure of formic acid on TiO2 anatase (1 0 1), J. Catal. 278 (2011) 321–328, https://doi. org/10.1016/j.jcat.2010.12.019. [127] T.V. Andrushkevich, Yu.A. Chesalov, Mechanism of heterogeneous catalytic oxidation of organic compounds to carboxylic acids, Russ. Chem. Rev. 87 (2018) 586–603, https://doi.org/10.1070/RCR4779. [128] S. Valange, J.C. Védrine, General and prospective views on oxidation reactions in heterogeneous catalysis, Catalysts 8 (2018) 483, https://doi.org/10.3390/ catal8100483. [129] J.M.L. Nieto, The selective oxidative activation of light alkanes. From supported vanadia to multicomponent bulk V-containing catalysts, Top. Catal. 41 (2006) 3–15, https://doi.org/10.1007/s11244-006-0088-4. [130] A. Chieregato, J.M.L. Nieto, F. Cavani, Mixed-oxide catalysts with vanadium as the key element for gas-phase reactions, Coord. Chem. Rev. 301–302 (2015) 3–23, https://doi.org/10.1016/j.ccr.2014.12.003. [131] D. Shee, B. Mitra, K.V.R. Chary, G. Deo, Characterization and reactivity of vanadium oxide supported on TiO2-SiO2 mixed oxide support, Mol. Catal. 451 (2018) 228–237, https://doi.org/10.1016/j.mcat.2018.01.020. [132] N.E. Damoyi, H.B. Friedrich, G.H. Kruger, D. Willock, A DFT mechanistic study of the ODH of n-hexane over isolated H3VO4, Mol. Catal. 452 (2018) 83–92, https:// doi.org/10.1016/j.mcat.2018.03.019. [133] T.V. Andrushkevich, E.V. Ovchinnikova, Gas phase catalytic oxidation of β-picoline to nicotinic acid: catalysts, mechanism and reaction kinetics, Catal. Rev. 54 (2012) 399–436, https://doi.org/10.1080/01614940.2012.665670. [134] R. Schlögl, Active sites for propane oxidation: some generic considerations, Top. Catal. 54 (2011) 627–638, https://doi.org/10.1007/s11244-011-9683-0. [135] R. Dwivedi, A. Kumar, S. Khare, R. Prasad, Process development and DFT‐assisted mechanism of the vapour phase ammoxidation of 2,6‐Dichlorotoluene to 2,6‐Dichlorobenzonitrile over the V2O5/γ‐Al2O3 catalyst, Chemistry Select 4 (2019) 6277–6289, https://doi.org/10.1002/slct.201900028.

by in situ FTIR, React. Kin. Catal. Lett. 87 (2006) 387–394, https://doi.org/10. 1007/s11144-006-0047-x. G.B. Chernobay, Yu.A. Chesalov, V.P. Baltakhinov, G.Ya. Popova, T.V. Andrushkevich, In situ FTIR study of β-picoline transformations on V–Ti–O catalysts, Catal. Today 164 (2011) 58–61, https://doi.org/10.1016/j.cattod.2010. 10.041. Yu.A. Chesalov, T.V. Andrushkevich, V.P. Baltakhinova, FTIR study of the role of surface complexes in a transformation of picoline isomers on vanadium-titanium oxide catalysts, Vib. Spectrosc. 83 (2016) 138–150, https://doi.org/10.1016/j. vibspec.2016.02.004. G.Ya. Popova, Yu.A. Chesalov, T.V. Andrushkevich, In situ FTIR study of pyridine3-carbaldehyde adsorption on TiO2 (Anatase) and V-Ti-O catalyst, React. Kinet. Catal. Lett. 83 (2004) 353–360, https://doi.org/10.1023/B:REAC.0000046097. 85909.b2. G.Ya. Popova, Yu.A. Chesalo, T.V. Andrushkevich, I.I. Zakharov, E.S. Stoyanov, Determination of surface intermediates during the selective oxidation of formaldehyde over V–Ti–O catalyst by in situ FTIR spectroscopy, J. Mol. Catal. A. 158 (2000) 345–348, https://doi.org/10.1016/S1381-1169(00)00102-3. G.Ya. Popova, T.V. Andrushkevich, I.I. Zakharov, Yu.A. Chesalov, Mechanism of carboxylic acid formation on vanadium-containing oxide catalysts, Kinet. Catal. 46 (2005) 217–226, https://doi.org/10.1007/s10975-005-0069-9. G.Ya. Popova, T.V. Andrushkevich, I.I. Zakharov, A.A. Budneva, E.S. Stoyanov, Yu.A. Chesalov, In situ FTIR study of the oxidation of formaldehyde to formic acid onV2O5/ TiO2 catalyst, in: R.K. Grasselli, S.T. Oyama, A.M. Gaffney, J.E. Lyons (Eds.), Proc. 3rd World Congr. on Oxidation Catalysis. San Diego. CA, U.S.A., 2126 September 1997, Amsterdam, New York: Elsevier, 1997 L-G-2. G.Ya. Popova, T.V. Andrushkevich, Yu.A. Chesalov, E.S. Stoyanov, In situ FTIR study of the adsorption of formaldehyde, formic acid, and methyl formiate at the surface of TiO2(anatase), Kinet. Catal. 41 (2000) 805–811, https://doi.org/10. 1023/A:1026681321584. G.Ya. Popova, A.A. Budneva, T.V. Andrushkevich, Influence of H3PMo12O40/SiO2 thermal treatment on adsorbed forms of formaldehyde and formic acid, React. Kinet. Catal. Lett. 62 (1997) 97–103, https://doi.org/10.1007/BF02475719. G.Ya. Popova, I.I. Zakharov, T.V. Andrushkevich, Mechanism of formic acid decomposition on P-Mo heteropolyacid, React. Kinet. Ctal. Lett. 66 (1999) 251–256, https://doi.org/10.1007/BF02475798. J.B. Moffat, Chemical intermediates in heterogeneous catalysis, Rev. Chemic. Intermediates 8 (1987) 1–20, https://doi.org/10.1007/BF03155658. M. Allian, E. Borello, P. Ugliengo, G. Spano, E. Garrone, Infrared spectroscopic study of the adsorption of carbonyl compounds on severely outgassed silica: spectroscopic and thermodynamic results, Langmuir 11 (1995) 4811–4817, https://doi.org/10.1021/la00012a037. Yu.A. Chesalov, T.V. Andrushkevich, V.I. Sobolev, G.B. Chernobay, FTIR study of β-picoline and pyridine-3-carbaldehyde transformation on V–Ti–O catalysts. The effect of sulfate content on β-picoline oxidation into nicotinic acid, J. Mol. Catal. A 380 (2013) 118–130, https://doi.org/10.1016/j.molcata.2013.09.028.

12