Structured Catalysts-Based on Open-Cell Metallic Foams for Energy and Environmental Applications

C H A P T E R

15 Structured Catalysts-Based on Open-Cell Metallic Foams for Energy and Environmental Applications Phuoc Hoang Ho*,†, Matteo Ambrosetti‡, Gianpiero Groppi‡, Enrico Tronconi‡, Regina Palkovits†, Giuseppe Fornasari*, Angelo Vaccari*, Patricia Benito* *Department of Industrial Chemistry “Toso Montanari”, Alma Mater Studiorum, University of Bologna, Bologna, Italy †Chair of Heterogeneous Catalysis and Chemical Technology, RWTH Aachen University, Aachen, Germany ‡Laboratory of Catalysis and Catalytic Processes, Department of Energy, Politecnico di Milano, Milano, Italy

O U T L I N E 1 Scenario of the Research 2 State of the Art 2.1 Structured Catalysts 2.2 Preparation of Structured Catalysts 3 Electrodeposited Structured Catalysts for H2 and Syngas Production

Studies in Surface Science and Catalysis, Volume 178 https://doi.org/10.1016/B978-0-444-64127-4.00015-X

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4 Metallic Foams as Structured Catalysts for Environmental Applications References Further Reading

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1 SCENARIO OF THE RESEARCH Improving the sustainability while maintaining the competitiveness of the chemical industry is one of the critical goals highlighted in the roadmap of science and technology on catalysis for Europe to “move ahead for sustainable future” [1]. Forced by the economic competition, environmental problems and the depletion of fossil fuels, it is necessary to move to new refinery and petrochemistry in which the use of CH4, light olefins, and biomass are preferable. To do that, a broad approach has been proposed emphasizing on an innovation in catalysis taking shape through push and pull factors. The former relates to the growing insight into the molecular basis of catalysis, while the latter concerns not only the need to increase energy efficiency and reduce waste chemicals, but address the growing demand to build up novel production routes for chemicals and fuels to improve competitiveness in industry [2]. To reach the pull factors, several aspects have been proposed, which could be classified into finding new approaches/processes or improvements to existing processes. Although new developments are more prioritized (e.g., substitution of fossil fuel derived products, the use of biomass, production of renewable H2, CO2 utilization, integration of solar energy to chemical and fuel production), implementing the improvements is important in several existing processes, for example, hydrogen and syngas technology (steam reforming (SR), catalytic partial oxidation (CPO), water gas shift reaction), production of chemicals (selective oxidation, methanol synthesis, CO2 methanation, and Fischer-Tropsch synthesis). One example of scenario about development and improvement in petrochemistry is presented in Fig. 15.1. In this context, process intensification (PI) has a key role in achieving improvement toward a more economic and sustainable chemistry for the future because it can be applied to all the scales in chemical processes, that is, from

molecular levels to meso and macro scales [3]. PI is a broad term and many definitions have been proposed since it was introduced in the 1970s [4]. In a simplistic view, PI is known as qualitative statements like “cheaper, smaller, cleaner,” or related to two common words “innovative” and “substantial,” which show the characterization and target of the PI [3]. For chemists and chemical engineers, PI concepts based on the major manufactures of PI equipment mainly focus on how to enhance transport rates and give every molecule the same processing experience. PI tends to suggest either a drastic improvement by re-designing conventional unit operations (“hardware” technologies) or a development of new process-control methods (“software” technologies); hence this could help to: (i) improve the control of reactor kinetics giving higher selectivity/reduced waste products, (ii) higher energy efficiency, (iii) reduce capital costs, and (iv) reduce inventory/improve intrinsic safety/fast response times. In heterogeneous catalytic processes, structured catalysts and reactors have been proposed as a great opportunity for implementation of some process solutions into industrial practice, such as enhancement of heat and mass transfer rates as well as to reduce the pressure drop [5,6]. Structured catalysts and reactors are wide research topics involving both chemistry and chemical engineering fields. They are like “a big game” dealing with 3D structured supports with different shapes coated with several types of catalytic materials. Currently both academia and industry are involved in the production of 3D supports, development of coating techniques, applications in catalytic processes, and construction of structured reactors. Although ceramic honeycomb monoliths, a standard representative of structured catalysts, have been extremely successful in commercial application for environmental treatments of exhaust emissions from automobiles and power stations since the 1980s, their extensive usage in other catalytic

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FIG. 15.1 Evolution in the scenario of raw materials from current petrochemistry to the future scenario for a sustainable and low-carbon chemical production. Data from P. Lanzafame, G. Centi, S. Perathoner, Catalysis for biomass and CO2 use through solar energy: opening new scenarios for a sustainable and low-carbon chemical production, Chem. Soc. Rev. 43 (2014) 7562–7580 with permission of The Royal Society of Chemistry.

processes is still limited due to two main issues: (i) a relatively lower load of the catalytic active phase compared to that in a bed of bulk pellets with the same volume and (ii) limitations in the temperature control in several endo-/exothermic processes [7]. On the other hand, innovative metallic honeycomb monoliths exhibit much better performances in nonadiabatic applications [7], but their industrial application is limited by the difficult manufacturing process by extrusion, which makes these supports not yet applicable at the industrial scale. These issues could be overcome by metallic open-cell foams that provide excellent heat and mass transfer properties and

are produced at an industrial scale. Another possible application of metallic foams is as 3D electrodes, a novel electrode concept in electrocatalysis. This opens a wide range of applications of metallic foams, for example, in H2 production by H2O electrolysis, conversion of biomass-based materials, fuel cells, electroorganic synthesis, as proposed in the European roadmap of science and catalysis [5]. Although metallic foams have been recognized as potential supports in structured catalysts, bringing them in real catalysis applications needs simultaneous developments in the coating technique and reactor design [8].

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2 STATE OF THE ART 2.1 Structured Catalysts Structured catalysts are composed of a support, preshaped in a given 3D structure, and a layer of catalytic material [9], Fig. 15.2. The selection of the support (shape and material) depends on the process applications, for example, operation temperature, reaction atmosphere, and transport properties, while the coating properties (adhesion, composition, loading, dispersion of active phase) determine the reactivity of the structured catalyst in a given reaction. Almost all important catalytic material or supports, that is, zeolites, ceria, alumina, and mixed oxides, which can incorporate a large variety of active phases, from transition to noble metals, can be coated, and hence structured catalysts with a wide range of applications prepared (Fig. 15.2).

FIG. 15.2

Overview of structured catalysts.

Structured supports are made by ceramic (Al2O3, cordierite, and SiC), metallic (single elements, i.e., Al, Ni, Cu, Co, or alloy, i.e., stainless steel, Inconel, FeCrAl, NiCrAl, FeNiCrAl), and carbonaceous materials (activated carbon, reticulated vitreous carbon), adopting several 3D configurations; that is, honeycomb, corrugated sheet, gauze, foam, fiber, knitted wire packing, or periodic open cellular structures (POCS) [10] (Table 15.1). These materials fulfill a wide range of competitive requirements in the design of reactors (light weight, mechanical strength) or process applications (corrosion resistance, enhancement of heat transfer). On the other hand, the geometry of the support is responsible for the hydro-dynamics of the fluid that determine the transport properties: gas/solid heat and mass transfer rates, and pressure drops. Finally, the effective thermal conductivity is primarily a function of the geometry and the support material. These cellular materials are also promising as catalyst supports for gas/liquid processes because they couple their excellent heat transfer properties with strong gas/liquid interaction due to their complex geometry, which enhances the mass transfer rates [18]. Honeycombs with square, triangular, or circular parallel channels generate a laminar flow path without radial-mixing of the gas, leading to some limitations in mass and heat transfer and, therefore, in the control of temperature in endo-/exothermic chemical processes [7]. The extrusion is well consolidated technology to obtain ceramic honeycombs but is quite challenging to produce metallic ones. Therefore, the rolling of corrugated sheets has been introduced (Table 15.1). Nevertheless, these corrugated sheets lack cross-sectional continuity of the solid matrix, even if the sheets/layers are welded together [19]. Hence, corrugated or wire-mesh monoliths perform radial thermal conductivities much more poorly than those obtained by the extrusion. It is also noted that the wire-mesh could provide a relatively large

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2 STATE OF THE ART

TABLE 15.1 Commercial Structured Supports Made of Ceramic, Metallic, and Carbonaceous Materials Shape

Material

Reference

Honeycomb monolith

Cordierite, mullite, Al2O3, SiC, SiO2 Cu, Al, Fe FeCrAl, FeNiCrAl, SS 304, Aluminum alloy Activated carbon

[11–14]

Open-cell foam

Al2O3, SiC, Si3N4, B12C3, BN, ZrO2 Co, Cu, Fe, Ni, Al, Zn, Aga, Sna, Aua NiFeCrAl, Inconel, NiCrAl, FeCrAl, Stainless steel AISI 316, Zamak 410 (Zn/Al/Cu/Mg), Monel, Aluminum alloy Reticulated vitreous carbon

[15]

Gauze

90% Pt/Rh Al

[16]

Wire-mesh

Al2O3 Fe, Pd/Ni, Pt/Ir Monel alloy 400, SS AISI 304316, 904; Inconel, Monel, Hastelloy, FeCrAl

[17]

Corrugated sheet

Al2O3 Cu, Al NiCrAl, FeCrAl, NiFeCrAl Inconel, Steel, Stainless Steel, Brass

[15]

Fiber

Al2O3, Al2O3/SiO2, Al2O3/SiO2/B2O3, SiC, FeCrAl

[15]

a

Not commercialized yet.

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geometrical surface area and less pressure drop than other types of monoliths. Knitted gauze is a special case made of 10% Rh/Pt used for NH3 oxidation reactions in nitric acid plants. Considering mass and heat transfer issues, opencell foams are the most relevant structured supports to overcome them. Open-cell foams are 3D cellular materials made of interconnected solid struts, which enclose cavities (the cells), communicating by windows (the pores) (Fig. 15.3). They provide a disruptive and tortuous flow path and hence an exceptional mixing as well as supply or release of the heat to/from the reactor walls especially in cases of metallic foams. In other words, metallic foams can overcome some issues of the honeycomb monoliths, still maintaining and even improving their advantages. This type of material has been commercialized in the past two decades by more than 30 companies all over the world [20], and several types of materials at acceptable quality and cost levels are available [21]. The choice of the open-cell foam metallic materials is governed by the following considerations [9]: (i) tolerance of operation conditions such as high temperature or oxidative and corrosive substances requires a stable alloy, for example, FeCrAlloy, NiCrAlloy [22,23]; (ii) when the

heat transfer is a crucial factor, a highly thermal conductive material like Al, for temperatures below 500°C, or Cu, for temperatures below 720°C and reducing atmospheres [24,25], may be used. Heat transfer rates, related to conductive, convective, and radiative heat transfer mechanisms, depend on both foam properties (materials, porosity, pore size) and operating conditions (gas composition and flow rate) [26,27]. The effective radial and axial conductivity as well as the wall heat transfer coefficient under reaction conditions relevant for chemical processes are very important to predict the thermal behavior of foam structured reactors, in view of both reactor design and process operation. Therefore, many studies on the heat transfer properties of metallic foams have been performed on a wide range of foam pore size (from large to small pore, 10–100 ppi) with different materials (from poor to high thermal conductivity, FeCrAl, Cu/Al) [18,26,28,29]. Thermal conductivity of these supports can be estimated with the model proposed by Lemlich [30]. This simple model states that the thermal conductivity of open cell foams is proportional to the solid conductivity and to the solid volumetric fraction multiplied by a constant value. Lemlich

FIG. 15.3 (A) SEM image of FeCrAlloy open cell foam (1200 μm cell size) supplied by Alantum and (B) tortuous flow path of the fluid passing through its structure. Part figure (B) was reprinted from C.Y. Zhao, Review on thermal transport in high porosity cellular metal foams with open cells, Int. J. Heat Mass Transf. 55 (2012) 3618–3632 with permission of Elsevier.

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2 STATE OF THE ART

proposes a factor equal to one-third. As an example, the solid radial conductivity for an Al foam (40 ppi,
89% porosity) is around 7.7 W m1 K1, which is comparable or higher than typical effective radial thermal conductivities in industrial-packed bed reactors [28]. For either large or small pore foams (high cell densities), the conductive contribution dominates the effective radial thermal conductivity. On the other hand, the wall heat transfer coefficient is mainly related to the heat transport resistance in the gas between the inner surface of the reactor wall and the outer surface of the foam: it is, in fact, proportional to the thermal conductivity of the process gas and inversely proportional to the cell diameter (effect of gap size),

TABLE 15.2

but essentially independent of the flow rate, unlike in packed bed reactors. Therefore, to achieve high heat transfer rates, it is not necessary to reach very high flow velocities (generating more pressure drop and high energy costs), but rather to reduce the gap size; these aspects enable the design of more compact reactors in view of PI [26,27]. In fact, decreasing of the gap size by a packaged foam system has been proposed [8,31]. The combination of different foam materials and coatings has led to structured catalysts for H2 and syngas production, CH3OH and FischerTropsch synthesis, methanation, selective oxidation, total oxidation, and H2O splitting, as summarized in Table 15.2.

Coated Metal Foams and Their Applications Reported Recently in the Literature

Type of Foam

Supplier

Coating Layer

Coating Technique

Reaction

Reference

Ni, 110 ppi

Shenzhen Hanbo

Ru-ZrO2/carbon nano tube

CH4 decomposition + wetness incipient impregnation

Selective CO methanation

[32]

Ni, 110 ppi

Shenzhen Hanbo

Ru-Ni/Al2O3

Evaporation-induced-selfassembly + impregnation

CO selective methanation in H2-rich gas

[33]

Ni (320 g/m2)

Changle

Ni-P

Chemical plating

H2 production from Microbial electrolysis cell

[34]

Ni, 100 ppi

Changsha Lyrun

MgO

Hydrothermal reaction

Catalytic oxy-CH4 reforming

[35]

Ni

–

Pd-Fe

Impregnation-calcinationreduction

Dimetridazole degradation

[36]

Ni

–

CoB

Electroless plating

Hydrolysis of NaBH4

[37]

Ni, 100 ppi

Changsha Lyrun

Ag-CuOx

Sequential galvanicdeposition method

Hydrogenation of DMO

[38]

Ni, 100 ppi

Changsha Lyrun

PdNi (alloy)

Galvanic exchange reaction Combustion of coalbed CH4

[39]

Ni, 100 ppi

Changsha Lyrun

NiO-MOx-Al2O3 (M ¼ Ce or Mg)

Hydrothermal treatment + incipient impregnation

CPO of CH4

[40]

Ni

–

Ni-γ-Al2O3

Washcoating

SR (CO2) of CH4

[41]

Ni

Ailantian

MnO2@NiCo2O4

Hydrothermal treatment

NH3-SCR of NO (de-NOx)

[42] Continued

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15. STRUCTURED CATALYSTS-BASED ON OPEN-CELL METALLIC FOAMS

Coated Metal Foams and Their Applications Reported Recently in the Literature—cont’d

Type of Foam

Supplier

Coating Layer

Coating Technique

Reaction

Reference

Ni

Xin Hua

Al2O3@Ni Al2O3/SiO2@Ni Al2O3/MgO@Ni

Washcoating

Dry reforming of CH4

[43]

Cu

Ailantian

Fe2O3@CuOx

Hydrothermal treatment

NH3-SCR of NO (de-NOx)

[44]

Cu

Asprepared

Ni/Mg3AlOx (γ-Al2O3)

Washcoating

Solar thermal reforming of CH4 with CO2

[24]

Cu

Kunshan Jiayisheng

CuO nanowire

Heat treatment 500°C, 5 h

Plasma oxidation of Toluene

[45]

Cu, 45 ppi

Porvair

Cu-ZnO-Al2O3

Washcoating

CH3OH synthesis

[25]

Ni or Cu 100 ppi or NiCu alloy

–

Ni/Al2O3

Wet chemical etching technique

Methanation of syngas

[46]

Al, 120 ppi

Suzhou Taili CuO-ZnO New Energy

Hydrothermal deposition

CO2 hydrogenation to CH3OH

[47]

Al, SiC, Al2O3 30–40 ppi

–

Ni-Ru/CeriaZirconia

Dipped coating + impregnation

Methanation

[48]

Al, 10, 20, and 40 ppi

ERG

Pt/CeO2-γ-Al2O3

Washcoating and impregnation

Water gas shift

[49]

Nichrome, Steel

–

Pd; Pd + LaCoO3

Thermal or chemical deposition

Benzene or phenol oxidation

[50]

FeCrAlloy, 50 ppi

Porvair, Metpore

Pt 2.9 and 4.3 mg/cm3

Electrodeposition

Combustion of CH3OH

[51]

FeCrAlloy, 50 ppi

Porvair, Metpore

Rh, Rh/AlPO4

Electrodeposition Washcoating

CPO of CH4

[52]

AISI 316

Goodfellow cambridge

Ru/Al2O3 Ni/Al2O3 Ru

Washcoating + impregnation

Dry reforming of CH4

[53]

FeCrAlloy, 20, 30 ppi

Selee

Cu-SSZ-13 Cu-ZSM-5

Hydrothermal synthesis + ion exchange

SCR of NOx with NH3

[54]

FeCrAlloy (0.4–0.5 mm cell)

–

Pd-Rh/CeZrO2Al2O3

Washcoating

SR of model biogas

[23]

Fe-Al-Ni-Cr

–

Pt-Rh/CeO2ZrO2-Al2O3

Washcoating

SR of CH4

[55]

FeCrAlloy, 40 ppi

Porvair

Pd

Spontaneous deposition

Total oxidation of CO or CH4

[56]

NiCrAl, 0.8 mm cell

–

Rh/Ce-Zr-Al

Thermal treatment + evaporation + impregnation

ATR of dodecane

[57]

FeCrAlloy, 60 ppi

Porvair

Ni-Al, Rh-Mg-Al HT derived

Electrodeposition

CPO or SR of CH4

[22,58–64]

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2 STATE OF THE ART

2.2 Preparation of Structured Catalysts The selection of the coating technique is of paramount importance for the development of structured catalysts able to replace conventional pelletized ones. The performances of the structured catalysts are determined not only by the properties of the coated materials (composition, size, and dispersion of active species, loading, textural characteristics), but also the stability of the catalytic layer, thus the coating method must provide a sufficient load of active materials with enhanced adhesion to the support surface. Several methods have been used to coat the structured substrates with approximately 140 patents on catalytic coatings from the years 1990 to 2010, registered mostly from the United States, Europe, Korea, Japan, and China [65]. In addition, some reviews summarize in detail the coating techniques [19,66]. There are two main approaches adopted: (i) direct synthesis of the catalyst on the surface of the support, or (ii) coating of a ready-made catalyst or support, the latter is followed by impregnation of the active phase. In case of metallic supports, the significant dissimilarity between thermal expansion coefficients of coating (usually a ceramic material) and support, and the low interaction between metals and ceramic layers leads to the formation of creeps and peel-off of the coating. To improve the adhesion, metal supports are usually pretreated by thermal oxidation (oxide scale of Al2O3) [67,68] for FeCrAl or manganese and chromium oxides [69]), anodic oxidation [70], chemical treatment (both strong acids or bases, such as HCl, HNO3 or NaOH, although much attention should be paid to avoid severe dissolution of the substrate [71]), or primer deposition [67]. In addition, chemical treatment may be also useful to remove the surface oxide layer before doing the electrodeposition [72].

311

Many techniques have been introduced for deposition of catalytic layers, including washcoating (dipcoating), spin-coating plasma spraying, electrostatic spraying, thermal spraying, sol-gel, and chemical vapor deposition. Washcoating is the most widely used. It usually requires several consecutive steps including: (i) preparation of powder materials, controlling their properties and dispersing them into a solvent, (ii) adjusting the viscosity of the slurry, (iii) coating and removal of excess slurry, (iv) drying and/or calcination, and (v) repeat the process until a desired loading is obtained [19,73]. Additives are mandatory to control rheological properties of the slurry and coating features [66,68]. The properties of the catalytic materials may be modified during the washcoating procedure [25,74,75]. For instance, the use of binders could block the micropores of zeolites [76] or the addition of colloidal ZnO during the washcoating of PdZnO may change in ZnO particle size and Pd dispersion [75], or even the drying and calcination steps can also affect to the coating [77]. Although dip-coating is well established, it is quite challenging to coat a small pore structured support without pore blockage, indeed from literature the technique is usually applied for medium or large pore foams [25,48]. Direct deposition routes, such as hydrothermal treatment [35,39,40,47] and galvanic displacement [38,56], (Table 15.2), allow the catalyst or its precursor growing directly onto the surface of the structured support. Despite the fact they show some advantages, such as absence of any binder as well as stronger coating adhesion, the hydro-thermal treatment faces to some drawbacks such as loss of materials due to the precipitation taking place not only on the support surface, but also in liquid phase or limitation in solid loading by single coating step [78–80]. Electrochemical strategies and electrodeposition offer important advantages and unique possibilities in development of structured catalysts [22,32,51,58,59,61,62,64,81–83].

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3 ELECTRODEPOSITED STRUCTURED CATALYSTS FOR H2 AND SYNGAS PRODUCTION H2 and syngas are essential in chemical, refinery, and energy processes. CH4 mainly derived from natural gas accounted for approximately 80% of the world’s total H2 production [84]. Recently, shale gas [85] and biogas (a mixture of CH4 and CO2) [86] have been recognized as significant sources of CH4, increasing the indispensable role of these sources in the future roadmap of H2 technology despite that renewable energy is pushing to go beyond fossil fuel [5]. In Europe, there are more than 17,000 biogas plants built until 2015 with most contributions from Germany and Italy [85]. The well-established SR is preferred in industrial technology, accounting for a significant portion of current H2 production [87]. However, the high endothermicity makes it intensively energy demanding: CH4 + H2 O Ð 3H2 + CO

ΔH°298K ¼ + 206kJmol1




(15.1)

The CPO becomes an attractive route [88]. The reaction is simply described as: CH4 + ½O2 ! 2H2 + CO

ΔH°298K ¼ 36kJmol1




(15.2)

The process is exothermic, and once preheated could be run autothermally, producing a syngas with a ratio of H2/CO ¼ 2/1, suitable as feedstock for methanol synthesis or a FischerTropsch reaction. The scale up of CPO has been investigated by Eni [89], Shell [90], and ConocoPhillips (called the COPox technology) [91]. However, several challenging issues need to be considered when dealing with this process. Firstly, the CPO is operated at millisecond contact times with Gas Hourly Space Velocity (GHSV) around 500,000 h1, which is relatively higher than other syngas production processes. On one hand, this is more beneficial in terms of reactor volume due to lower reactor and

catalyst costs. But such high GHSV causes a high pressure-drop along the catalytic bed and consequently the catalyst must have a high mechanical strength. Secondly, conversion of a large feedstock generates a huge amount of heat that must be dissipated to avoid the formation of hot spots as well as safety issues during the operation. The formation of hot-spots is related to the great generation of heat in a confined space, so it is linked to the ratio between the activity of the catalyst and the gas/solid heat transfer properties of the support. In other words, the catalyst system for the CPO process should cope with heat and mass transfer limitations at high temperature. Developing a structured reactor based on metallic open-cell foams, merging the architecture of metallic foams and highly active coating materials, will improve both heat and mass transfer as well as decrease the pressure drop. Only a few works deal with metallic foams as a structured support for CPO of CH4 [22,35, 39,52,58,59]. Therefore, it remains a gap to be fulfilled in the use of metallic foams. Adopting this approach provides safety operation conditions, small and compact reactor size working under transient conditions, and reduction of energy demand. All of them lead to a sustainable process, though to be reached many individual goals are required including the development of a well-defined coating technique, a general model for heat transfer prediction, an engineering correlation for the prediction of mass transfer coefficients, and the technical design of the reactor. In this section, we focus on the first point with an attempt to develop a coating procedure that can be an alternative to conventional washcoating method for the preparation of structured catalyst including small pore foams, namely the electrodeposition by the electro-base generation route. The electro-base generation method is a facile electrochemical route allowing to coat in onestep at ambient temperature complex shaped metal structured supports with hydroxides or

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oxides [58,82,92]. This method was originally employed for the preparation of nickel hydroxide electrodes [93], then extended for the synthesis of hydrotalctite-type (HT) compounds, and layered mixed hydroxides, with the general formula M2 + 1x M3 + x ðOHÞ2 ðAn Þx=n mH2 O [94]. Since then it has been investigated and improved for the coating of HT materials on substrates with different shapes (plate, fiber, foam) and compositions (Pt, glassy carbon, Ni), extending to a wide range of applications in electrochemistry as sensors [95], redox supercapacitors [96], and electrocatalysts [97]. The method has been improved by some of us to prepare metallicfoam structured catalysts, adapting the strict requirements of catalysts for SR or CPO of CH4 [61] because HT compounds are widely used as catalyst precursors for processes demanding tailored basic/acidic sites, a relatively high specific surface area, and/or metal dispersion [98,99]. The deposition of HT compounds on the surface of a metallic-structured support may be performed by generating a basic media at the interface of electrode-electrolyte by application of a cathodic potential or current pulse [58,100]. The set-up is quite simple including a threeelectrode electrochemical cell connected to a potentiostat. The structured support is immersed in an aqueous solution containing nitrates of the cations being deposited. During the cathodic pulse, the pH only increases near the foam surface and the selective precipitation of hydroxides occurs on it. In other words, the production of OH by electrochemical reactions and the consumption of OH by chemical precipitation occur simultaneously at the vicinity of the structured support. It is necessary to reach selected pH values to obtain HT materials with wellcontrolled composition [98]. As both of processes proceed concurrently in a short time and are interrelated, the first step for the improvement of the properties of HT compounds electrodeposited on open-cell foams for catalyst preparation is to understand the electrochemical and chemical

processes taking place at the electrolyte-foam electrode interface and if they are modified during the electrodeposition pulse. For nitrate baths in absence of a supporting electrolyte, such as KNO3, (because K can be deposited simultaneously with HT decreasing the catalytic performances [64,83]), after applying a cathodic pulse at a FeCrAl foam (80 ppi), the following four reactions occur at the electrode/electrolyte interface [92]:
E0 ¼ 0:400V O2 g + 2H2 O + 4e ! 4OH (15.3)    NO 3 + H2 O + 2e ! NO2 + 2OH

E0 ¼ 0:010V (15.4)

 +  NO 3 + 7H2 O + 8e ! NH4 + 10OH

E0 ¼ 0:120V (15.5)

2H2 O + 2e ! H2 + 2OH

E0 ¼ 0:828V

(15.6)

OH generation from dissolved O2 has a minor contribution, due to its low concentration in the solution, while H2O and NO 3 reductions are competitive to become a dominant contributor. Although both dominances lead to a pH increase, the former causes H2 bubbles as coproduct giving a negative effect on the stability of the deposited coating. The key role of NO 3 reduction in OH generation during the electrodeposition of Mg-Al HT compound was proven in our recent study [92]. The pH reached in the vicinity of the support was around 2 units lower when nitrates were absent in the bath, that is, under the same reaction conditions, a solution containing chloride precursors reached a pH of around 6.5 while the nitrate solutions went up to 8.5 at the plateau (Fig. 15.4) [92]. Consequently, in a chloride bath, a thin coating with Mg/Al ratio of approximately 0.6/1, much lower than 3/1 of the nominal value was deposited, while in the nitrate bath a thicker electrodeposit of HT materials containing both Mg2+ and Al3+ was obtained. During the cathodic pulse, nitrate was reduced to both NO2  and NH4 +

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FIG. 15.4

Evolution of the pH in the vicinity of the foam surface immersed in 0.06 M Mg/Al-Cl and 0.06 M Mg/Al-NO3 solutions during the electrodeposition at 1.2 V vs SCE for 2000 s. Reprinted from P.H. Ho, M. Monti, E. Scavetta, D. Tonelli, E. Bernardi, L. Nobili, G. Fornasari, A. Vaccari, P. Benito, Reactions involved in the electrodeposition of hydrotalcite-type compounds on FeCrAlloy foams and plates, Electrochim. Acta 222 (2016) 1335–1344 with permission of Elsevier.

(Eqs. 15.4 and 15.5), and their amounts depend on applied potential, time, and presence of cations. Coating the complex structure of metallic foams with HT compounds as catalyst precursors faces many challenges to balance the load of the coating and its properties such as thickness, composition, and adhesion; unlike other known-applications (e.g., electrode, sensor, protection) wherein a thin coating layer is satisfactory. Coating features are determined by several factors, for example, nature of the support (electrical conductivity and roughness [101]), geometrical parameters (size and shape), electrochemical set-up (electrical contact between the working electrode and the potentiostat [59], type of cell, and size of the counter electrode), electrochemical parameters (precursors and concentration of electrolyte [58,92,100], potential applied, and synthesis time [64,83]). They may be classified into two main groups: passive and active. The former is usually related to the nature or geometry of the

support fixed by suppliers or given purposes while the latter are the ones modified to control the coating properties. During the electrodeposition of HT compounds, the deposition of a thicker layer on the tips of the strut than on the flat zones and the preferential coating of the material on the outside of the foam cylinder than the one inside are examples of impacts of passive factors. Composition of the electrolyte bath, synthesis time, and potential applied are common examples of active factors. The metal nitrate concentration governs not only the amount of solid deposited and its distribution on the foam, but also the solid growth mechanism, crystallinity of the phases, and intercalating anions inside the HT lamellar structure [100]. The metal nitrate concentration determined both OH generation by nitrate reduction and OH consumption by precipitations of cations. For example, solid loadings of 3.3, 6.6, and 8.9 wt.% were obtained on FeCrAl foams (80 ppi) immersed in 0.03, 0.06, and 0.10 M

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3 ELECTRODEPOSITED STRUCTURED CATALYSTS FOR H2 AND SYNGAS PRODUCTION

315

SEM images of the foams coated at 1.2 V vs SCE for 2000 s with Mg/Al nitrate solutions at different concentrations: 0.03 M (A, A1, A2), 0.06 M (B, B1, B2, B3), and 0.10 M (C, C1, C2, C3). The table summarizes Mg/Al ratios obtained from EDS spectra in the regions of interest indicated by the numbers. Reprinted from P.H. Ho, E. Scavetta, F. Ospitali, D. Tonelli, G. Fornasari, A. Vaccari, P. Benito, Effect of metal nitrate concentration on the electrodeposition of hydrotalcite-like compounds on open-cell foams, Appl. Clay Sci. 151 (2018) 109–117 with permission of Elsevier.

FIG. 15.5

of Mg-Al/NO3 solution, respectively, after the application of a cathodic potential 1.2 V vs saturated calomel electrode (SCE) for 2000 s, Fig. 15.5. A low concentration provided thin coatings, while a more concentrated one may cause the pore blockage. In addition, an increase in the concentration from 0.03 to 0.10 M favored the formation of larger and more crystalline Mg(OH)2 particles near the foam surface, poor crystalline nitrate intercalated HT phases with a higher interlayer region and fostered the sequential precipitation of layers with different composition. In the top of thick coatings, an Al-rich layer

deposited probably related to the ineffective replenishment of the solution near the foam surface and the formation of an insulating layer during the deposition. HT materials containing Ni and/or Rh are well-known catalyst precursors for syngas production from CH4 via SR, CPO, or dry reforming [102]. Ni/Al HT precursors electrodeposited on FeCrAl foam (80 ppi) were prepared and after calcination and reduction proposed as structured catalysts for SR of CH4 [62,103]. A quite good control of composition with Ni/Al around 2.8/1 compared to 3/1 of the nominal value was obtained. Despite the thin coating, they exhibited

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15. STRUCTURED CATALYSTS-BASED ON OPEN-CELL METALLIC FOAMS

Commercial

exHT-1.2-1000

100.0 90.0 80.0

%

70.0 60.0 50.0 40.0 30.0

Conv. CH4

SeI. CO

Yield H2

FIG. 15.6 Catalytic activity of Ni-based commercial and electrosynthesized (0.03 M nitrate electrolyte, Ni/Al ¼ 3/1, 1.2 V vs SCE, 1000 s) catalysts. Reprinted from F. Basile, P. Benito, P. Del Gallo, G. Fornasari, D. Gary, V. Rosetti, E. Scavetta, D. Tonelli, A. Vaccari, Highly conductive Ni steam reforming catalysts prepared by electrodeposition, Chem. Commun. (2008), 2917–2919 with permission of the Royal Society of Chemistry.

comparable catalytic performances with Ni commercial catalyst under industrial-type conditions (S/C ¼ 1.7, P ¼ 20 bar, contact time 4 s, and Toven ¼ 900°C) as shown in Fig. 15.6 [103]. Although the best electrosynthesized Ni catalyst worked well for SR, it was not active for the CPO due to the oxidation of Ni0 active phase [60]. Therefore, Rh-based catalysts were a better option for the CPO. However, noble metals are easily reducible and the deposition of Rh metallic particles, rather the inclusion of Rh3+ in the HT structure might take place during the electrosynthesis, decreasing the catalytic performances [59,83]. To avoid this problem, the initial pH of the electrolyte could be increased to suppress the reduction of Rh3+ (by modification of reduction potential according to Pourbaix’s diagram) but the precipitation of bulk Al(OH)3 should be avoided so a pH value of 3.8 was used [64,83]. In this way, the presence of Rh did not modify the electrodeposition process at 1.2 V vs SCE for 2000 s,

indeed, the evolution of the current density and properties of the coating were quite similar in the absence and presence of Rh in Mg/Al electrolyte solution with Mg/Al ¼ 75/25 and Rh/Mg/Al ¼ 5/70/25 atomic ratio (a.r.), respectively [55,92,100]. A change of Rh amount in an electrolytic solution (Rh/Mg/Al ¼ 11/70/19, 5/70/25, and 2/70/28 a.r.) did not alter the typical features of both the electrodeposited precursors and the catalyst but did determine the size of Rh particles [58]. Differences in current distribution, due to inhomogeneous composition of the foams and different geometry of strut, node, and flat zone, accessibility of the eletrolyte inside the foam (pore size effect), mass transfer limitation of electroactive species, and a decrease of pH with the formation of a thick layer, led to the following coating features: (i) preferential electrodeposition on the tips of the strut resulting in a 5–15 μm thickness, while a thinner layer (2–6 μm) was deposited in the flat zone; (ii) a

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3 ELECTRODEPOSITED STRUCTURED CATALYSTS FOR H2 AND SYNGAS PRODUCTION

sequential precipitation of hydroxides of different composition, that is, growing of an outer layer rich in Rh and Al precipitates on the top of the existing deposits consisting of first a Mg(OH)2 and second HT layer. The thickness and chemical composition of the electrodeposited precursors strongly determined the properties of the catalytic layer obtained after calcination at 900°C for 12 h. The outer layers in thick coating zones developed a high number of cracks and the solid easily detaches, whereas Mg-rich coatings, or those with well-defined composition, were more stable after the calcination step. During calcination, both the decomposition of the HT precursor and the oxidation of the foam took place simultaneously. In this process, the chemical reaction between Al coming from the foam and Mg in the coating led to the formation of spinel phases, inhibiting the formation of the MgO phase in the coating and the protective Al2O3 scale on the foam. This interfacial spinel phase increased

317

the coating adhesion to the support, but it also modified the Rh distribution in the catalyst (mainly presence in spinel phase, some Rh0 and Rh2O3) and therefore its reducibility [22]. The catalytic activities of Rh/Mg/Al structured catalysts depended on both the number of active sites and Rh particle size. Feeding a diluted feedstock (CH4/O2/He ¼ 2/1/20 v/v, 63,300 h1) after the reduction pretreatment, the catalyst with large number of Rh (e.g., Rh11 Mg70Al19) quickly reached stable conversion values, while the catalysts containing lower amounts of Rh (Rh5Mg70Al25 and Rh2Mg70Al28) activated with time-on-stream (TOS) due to the presence of the hardly reducible Rh3+ species stabilized inside the spinel phase [58] (Fig. 15.7). Remarkably, at 15,250 h1, the best catalyst tested could reach 90% of CH4 conversion with high selectivity to syngas (>90%). Multiple processes are involved in CH4 conversion, including the exothermic total or partial oxidation reactions, followed by the endothermic SR.

FIG. 15.7 Evolution of CH4 conversion with time-on-stream obtained with catalyst synthesized using different electrolytic solutions (Rh/Mg/Al ¼ 11/70/19, 5/70/25, and 2/70/28 a.r., 0.03 M) at 1.2 V vs SCE for 2000 s, calcination at 900°C for 12 h. Test conditions: Toven ¼ 750°C, CH4/O2/He ¼ 2/1/20 and 2/1/4 v/v, GHSV ¼ 63,300, 38,700, 15,250, and 11,500 h1). Reprinted from P. Benito, G. Nuyts, M. Monti, W. De Nolf, G. Fornasari, K. Janssens, E. Scavetta, A. Vaccari, Stable Rh particles in hydrotalcitederived catalysts coated on FeCrAlloy foams by electrosynthesis, Appl. Catal. Environ. 179 (2015) 321–332 with permission of Elsevier.

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As the oxidations are fast and controlled by O2 mass transfer, the contribution of the catalyst for the consecutive SR mainly respond for the differences in CH4 conversion and syngas selectivity. A small amount of available Rh0, formation of big particles, or existence of unreduced Rh3+ species, could slow down the CH4 conversion by SR and hence decrease overall catalytic performance of the catalysts. When feeding concentrated gas mixtures, the heat generated by exothermic reactions promoted the catalytic activity but also favored the sintering of Rh metallic particles leading to the slight deactivation of the catalyst, and it was more visible in the case of the high Rh loading sample (e.g., Rh11Mg70Al19) (Fig. 15.7). In fact, characterization of spent catalysts by FEG-SEM evidenced that the higher amount of Rh loading, the larger the Rh particles were. The effect of electrolyte concentration on the electrodeposition of HT compounds on the foam was identical in the absence or presence of Rh in Mg/Al nitrate baths. The use of a 0.06 M nitrate solution (instead of 0.03 and 0.10 M solutions) produced a more compact layer with thickness up to 15–20 μm on struts and around 5 μm on flat zones (nodes). The composition was close to the expected one (Rh/Mg/Al ¼ 4/68/28 a.r.) in TABLE 15.3

some parts of the foam, but the sequential precipitation phenomena still took place where thicker layers are coated. The best coverage of the HT precursor in terms of thickness and homogeneity obtained with 0.06 M instead of 0.03 or 0.10 M solutions improved the coating properties of the calcined catalyst, that is, less cracks and detachments, 5–15 wt.% Rh, and hence it exhibited better performances. Compared with the catalyst prepared by 0.03 M, the one from 0.06 M achieved higher CH4 conversion in all reaction conditions, about 10% and 4% higher in diluted and concentrated feedstock, respectively. To evaluate the feasibility of the electrodeposition coating technique, a rough comparison between previous results and those obtained with electrodeposited catalysts is made in Table 15.3. Although it is quite challenging because the CPO tests were performed under different conditions, some appropriate points could be summarized: (i) Rh/Mg/Al structured catalyst could reach satisfactory catalytic performances, (ii) Rh is stabilized in HT-derived materials, decreasing sintering of Rh particles under the CPO test. In summary, the electro-base generation method is a promising technique allowing

Comparison of Rh-Based Catalyst on FeCrAl Foams in the CPO of CH4

Catalyst/Support

Coating Properties

Rh/Mg/Al ¼ (5/70/25 a.r.), FeCrAl 60 ppi, electrodeposition

5–15 wt.% Rh by EDS, 10–80 nm Rh particles (used catalyst)

Rh, FeCrAl 50 ppi, electrodeposition Rh/AlPO4, FeCrAl 50 ppi, washcoat

0.86 wt.% Rh/AlPO4, FeCrAl, 50 ppi

CH4 Conversion and Condition of CPO Tests Syngas Selectivity Vfoam ¼ 1.87 cm3 15,520–63,300 h1 CH4/O2/He ¼ 2/1/4, 2/1/20

Reference

XCH4 ¼ 80%, Ysyngas around 90% (diluted feed) XCH4 ¼ 85%, Ysyngas between 85% and 90% (concentrated feed)

[58]

Vfoam ¼ 2.44 cm3 4.7%–9.0% Rh a.r., <150 nm particle (after electrodeposition), 55,300 h1 CH4/O2 ¼ 2/1 270 nm (used catalyst)

XCH4 ¼ 64.5% YCO ¼ 54.3% YH2 ¼ 54.0%

[52]

55,300 h1 Vfoam ¼ 2.44 cm3 CH4/O2 ¼ 2/1

XCH4 ¼ 63.3% YCO ¼ 56.7% YH2 ¼ 50.0%

[52]

3. ADVANCED SUSTAINABLE CHEMICAL PROCESSES AND CATALYSTS FOR ENVIRONMENT PROTECTION

4 METALLIC FOAMS AS STRUCTURED CATALYSTS FOR ENVIRONMENTAL APPLICATIONS

the coating of metallic foams of small pores (60–80 ppi) with HT materials as precursors of catalysts. The catalysts obtained through calcination at high temperatures possess a strong interfacial interaction between the coating and the foam due to a solid-state chemical reaction, forming a MgAl2O4 layer, despite of some cracks and detachments. The catalysts reach a satisfactory CH4 conversion and syngas selectivity in both diluted and concentrated feedstocks. However, the electrodeposition of HT compounds, for example, Rh, Mg, Al, still face the following issues: (i) replenishment of the electrolyte at the electrode-electrolyte interface, mainly in the inner part of the foam vicinity; (ii) control of coating composition; (iii) decrease the crack formation during drying and calcination; and (iv) effect of the foam size when scaling up.

4 METALLIC FOAMS AS STRUCTURED CATALYSTS FOR ENVIRONMENTAL APPLICATIONS Despite the fact that ceramic monolith reactors are well-established for exhaust gas treatment in environmental applications, the use of metallic foams as support is an attractive approach [104]. Metallic foams not only inherit the advantages of ceramic foams, based on unique foam configurations, like large geometrical surface area, radial mixing of the fluid, and low pressure drop, but they also possess more distinctive features based on properties of metallic materials, such as high mechanical strength and thermal conductivity [7]. However, moving to metallic foams still requires more studies on both heat and mass transfer properties, which are closely associated with properties of the coated layers defined by the coating techniques. In typical environmental catalytic applications, the tradeoff between mass transfer properties and pressure drops is central. Therefore, many studies were devoted to these properties

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in order to enable the potential of open-cell foams for exhaust in after-treatment applications. Edouard et al. [105] presented a review of literature data of pressure drops collected on foams with a wide range of pores per inch and porosity. Dietrich [106] proposed a generalized correlation for the estimation of pressure drops in metallic and ceramic foams based on dimensionless number; the proposed correlation exhibits the same functional dependencies of the Ergun correlation for packed beds. Pressure drops of open cell foams with different porosities and strut shapes can be estimated by the correlation proposed by Inayat et al., which has been validated in several flow regimes [107]. Mass transfer is another transport property of fundamental interest for any catalytic application based on this technology. The first documented work devoted to the study of mass transfer properties of ceramic foams was presented by Richardson et al. [108]. In this work, mass transfer properties were derived by running CO oxidation onto ceramic foams washcoated with Pt/γ-Al2O3. Giani et al. [109] performed an investigation of mass transfer properties of Pd/γ-Al2O3 washcoated metallic foams. The authors derived a correlation for the dimensionless mass transfer performances (Sherwood number) in function of the Reynolds number based on the strut diameter. Groppi et al. [110] extended the previous correlation performing additional tests on ceramic foams. Incera Garrido et al. [111] published an experimental investigation of mass transfer in ceramic foams in a wide range of cell size and porosities activated with Pt/SnO2 for CO catalytic oxidation. The authors propose a correlation for the mass transfer where the sum of pore and strut diameter has been chosen as characteristic length; in the correlation additional geometrical dependencies should be accounted. Giani et al. [109] introduced a dimensionless merit index to compare the performances of several structures in typical conditions of environmental catalytic processes. This index is the ratio between the conversion of the limiting reactant in the

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−ln(1 − h)

FIG. 15.8 Conversion-pressure drop tradeoff index for different catalyst support. Reprinted with permission from L. Giani, G. Groppi, E. Tronconi, Mass-transfer characterization of metallic foams as supports for structured catalysts, Ind. Eng. Chem. Res. Metallic honeycomb (e = 0.85) 44 (2005) 4993–5002. Copyright (2005) American Chemical Society. Ceram. honeycomb (e = 0.7)

ΔP r × u2

1

0.1

Foam (e = 0.95)

0.01 Spheres (e = 0.4)

1E-3 10

100

1000

Re

mass transfer regime and the dimensionless pressure drops. The tested foams exhibited outstanding advantages over packed beds in the CO oxidation in a trade-off consideration between pressure drop and mass transfer performance, but they performed slightly worse than honeycomb monoliths (Fig. 15.8). However, foams characterized by higher void fraction can overcome the typical values of square-channel honeycombs. In fast diffusion-limited processes, such as CO oxidation, in which pressure drop is a minor concern, metallic foams could obtain comparable conversions to honeycombs with a remarkable decrease of the reactor size by a factor of 2.5–3 as shown in Fig. 15.9. This is due to the fact that in open cell foam’s mass transfer rates increase with the flow rate, while in laminar honeycombs this property is flow insensitive. This aspect can be further magnified by the adoption of high cell density foams. The mass transfer coefficients and the activity of the catalysts in diffusion-controlled regime are strongly dependent on the coating procedure because an ineffective coating technique may lead to uncoated or nonactive portions of the surface. The differences in Pd and total

washcoat loading and homogeneity obtained by a sol-gel (sequential deposit of γ-Al2O3 and wet impregnation of Pd(NO3)2) and a slurry route (powder Pd/γ-Al2O3 was dispersed into slurry) significantly influence the activity in a diffusion-controlled regime in which the former catalyst performed a mass transfer coefficient 15%–20% higher than that of the latter. When using small pore foams, the pore blockage may be avoided by direct deposition of metallic particles using the galvanic displacement method. The galvanic deposition of Pd onto Ni foam (100 ppi, 95% porosity) [38] and FeCrAl foam (medium pore 40 ppi) [56] takes place spontaneously as soon as the support is immersed into an aqueous solution containing any Pd salt due to a large disparity of reduction potentials between Pd2+/Pd0 (or Pd4+/Pd0) and Ni2+/Ni0 or Fe2+/Fe0 (Fe3+/Fe0) pairs, respectively. The concentration of the precursor [112] and the pH strongly influenced the properties of the Pd coating in terms of loading and particle size (Fig. 15.10). Following this method, Pd loadings around 1.0 wt.% and 1.7 wt.% were obtained, on Ni and FeCrAl foams, respectively, suitable for catalyzing the abatement of CH4 existing in coalbed by

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4 METALLIC FOAMS AS STRUCTURED CATALYSTS FOR ENVIRONMENTAL APPLICATIONS

A

B 100

100 20 ppi

10 ppi

600 cpsi 80

400 cpsi

% conversion

% conversion

80 60

10 ppi Foams Honeycombs

40 20 0 0.000

20 ppi 600 cpsi 400 cpsi

60

Foams Honeycombs

40 20

0.002

0.004

0.006

0.008

0.010

L/v (s)

0 0.000

0.002

0.004

0.006

0.008

0.010

L/v (s)

FIG. 15.9 Calculated conversions in foams (open volume fraction ε ¼ 0.95) and honeycombs (ε ¼ 0.7) versus reactor length (L) for two different feed flow velocities (v): (A) 5 m/s and (B) 20 m/s. Reprinted with permission from L. Giani, G. Groppi, E. Tronconi, Mass-transfer characterization of metallic foams as supports for structured catalysts, Ind. Eng. Chem. Res. 44 (2005) 4993–5002. Copyright (2005) American Chemical Society.

FIG. 15.10 SEM images of Pd-modified FeCrAlloy foams obtained by spontaneous deposition from 0.005 M PdCl2 solution of different pH for 30 min. Reprinted from S. Cimino, R. Gerbasi, L. Lisi, G. Mancino, M. Musiani, L. Va´zquez-Go´mez, E. Verlato, Oxidation of CO and CH4 on Pd–Fecralloy foam catalysts prepared by spontaneous deposition, Chem. Eng. J. 230 (2013) 422–431 with permission of Elsevier.

O2-lean catalytic combustion and CO oxidation. The Pd nanoparticles (<5 nm) deposited on Ni foams suffer from activation-promotion processes during in situ reaction activation

(CH4/O2/N2 ¼ 40/3/57 v/v, 480°C, 1 h) due to the simultaneous autoreduction of both NiO and PdO and formation of PdNi alloy, by diffusion of Ni into Pd nanoparticles. The surface

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reconfiguration results in a four-fold increase in the available Pd atomic surface. In a simulated gas reaction mixture, CH4/O2/N2 ¼ 40/3/57 v/v 1 a comat 350°C and GHSV ¼ 12,000 mL g1 cat h plete conversion of O2 was reached with turnover frequency (TOF) 292 h1 and the catalyst was stable under 500 h of TOS without reaction oscillation and performance deterioration. More importantly, as the catalytic combustion of coalbed CH4 is fast and strongly exothermic, the excellent permeability and heat conductivity of the foams are of paramount importance. The foam structured bed generated much lower pressure drop than particulate Pd/SiO2 (0.2 mm particle size). Although the formation of hot spots was not avoided within the foam, the temperature rising calculated by computational fluid dynamics (CFD) was intensively lowered (70°C vs 290°C for the foam and pellet, respectively). The galvanic displacement method is, however, limited to the direct deposition of noble metals (e.g., Pd, Ag) onto the surface of metallic supports in which the galvanic potentials of reductant/oxidant between two pairs are largely different. Such direct coating of active species onto the substrate may lead to a low surface area and metallic particles prone to the sintering, especially for high temperature applications. As an alternative, the in situ hydrothermal synthesis (one or two steps) was proposed. This route is typically used for the in-situ synthesis of zeolites or urea assisted co-precipitation of mixed hydroxides onto the foam surface. Either ZSM-5 or SSZ-13 zeolite were hydrothermally synthesized and coated on FeCrAl foam, the incorporation of Cu took place in a following step by Cu-ion-exchange. The resulting structured catalysts were evaluated in the SCR of NOx in the presence of NH3 [54]; however, this survey study just confirmed the potentiality of the coating method and provided brief conclusions about enhanced performances as well as better hydrothermal stability of Cu-SSZ 13 than that of Cu-ZSM 5. Further studies on optimization of the synthesis conditions and stability tests are lacking.

In the two-step hydrothermal treatment, coatings made by layers of different compositions could be prepared. Ni-Co-mixed hydroxides are synthesized by the urea-assisted co-precipitation in a first step and then the KMnO4 hydrothermal pyrolysis creates a MnO2 phase. As a result, MnO2@NiCo2O4@Ni foam structured catalysts for NH3-SCR of NO were obtained [42]. These catalysts exhibited a superior catalytic performance for the NH3SCR of NO at low temperature and high H2O resistance. The advantages of the hydrothermal procedure are related to the applicability to the deposition of a different oxides (or their precursors) onto several metallic foams, modifying the source of basic media. For instance, Fe2O3 precursors are coated using NaOH as a basic source on a preoxidized Cu foam containing a CuOx layer [44]. The obtained Fe2O3@CuOx/Cu foam catalyst showed a high activity both in a wide operating temperature range and in a stability test in the presence of inhibitors, such as SO2 and H2O. A co-existence of both H2O (8 vol.%) and SO2 (250 ppm) caused a decrease of only ca. 4% in NO conversion but the activity was recovered when stopping the supply of the inhibitors. However, the main drawback of the hydrothermal method is that the solid is selectively deposited not only on the support surface but also in bulk solution. Therefore, it has limitations for the preparation of noble metal-based catalysts which are common in environmental catalysis process. In summary, the structured catalysts based on metallic foams exhibit satisfactory performances for environmental applications. Future research may focus on: (i) improving or finding more powerful coating techniques, allowing for good coatings on different types of metallic foams (pore size, materials), (ii) applications of metallic foam structured catalysts for other environmental related processes, and (iii) investigation on models for heat/mass transfer of real coated foams.

3. ADVANCED SUSTAINABLE CHEMICAL PROCESSES AND CATALYSTS FOR ENVIRONMENT PROTECTION

REFERENCES

References [1] P. Lanzafame, S. Perathoner, G. Centi, S. Gross, E.J. M. Hensen, Grand challenges for catalysis in the science and technology roadmap on catalysis for Europe: moving ahead for a sustainable future, Cat. Sci. Technol. 7 (2017) 5182–5194. [2] S. Perathoner, S. Gross, E.J.M. Hensen, H. Wessel, H. Chraye, G. Centi, Looking at the future of chemical production through the European roadmap on science and technology of catalysis the EU effort for a long-term vision, ChemCatChem 9 (2017) 904–909. [3] V. Piemonte, M. De Falco, A. Basile, Sustainable Development in Chemical Engineering Innovative Technologies, John Wiley & Sons, West Sussex, 2013. [4] F.M. Dautzenberg, M. Mukherjee, Process intensification using multifunctional reactors, Chem. Eng. Sci. 56 (2001) 251–267. [5] S. Perathoner, G. Centi, Science and Technology Roadmap on Catalysis for Europe, http://www.catalysiscluster.eu/, 2017. Accessed 25 November 2017. [6] D. Reay, C. Ramshaw, A. Harvey, Process Intensification Engineering for Efficiency, Sustainability and Flexibility, second ed., Elsevier, Oxford, 2013. [7] E. Tronconi, G. Groppi, C.G. Visconti, Structured catalysts for non-adiabatic applications, Curr. Opin. Chem. Eng. 5 (2014) 55–67. [8] C.G. Visconti, G. Groppi, E. Tronconi, Highly conductive “packed foams”: a new concept for the intensification of strongly endo- and exo-thermic catalytic processes in compact tubular reactors, Catal. Today 273 (2016) 178–186. [9] P. Avila, M. Montes, E.E. Miro´, Monolithic reactors for environmental applications, Chem. Eng. J. 109 (2005) 11–36. [10] K. Pangarkar, T.J. Schildhauer, J.R. van Ommen, J. Nijenhuis, F. Kapteijn, J.A. Moulijn, Structured packings for multiphase catalytic reactors, Ind. Eng. Chem. Res. 47 (2008) 3720–3751. [11] H. Takashi, O. Tsuneaki, Method of sintering a sinterable metal powder honeycomb monolith structure, Patent US 5064609 A, 1991. [12] H. Takashi, M. Hiroshige, A. Fumio, O. Tsuneaki, Heatresistant metal monolith, Patent US 5292485 A, Ngk Insulators Ltd, 1994. [13] C. Willard, H. Lin, O. Anthony, S. Charles, Thermally conductive honeycombs for chemical reactors, Patent US 20030100448 A1, 2003. [14] E. Tronconi, G. Groppi, T. Boger, A. Heibel, Monolithic catalysts with ‘high conductivity’ honeycomb supports for gas/solid exothermic reactions: characterization of the heat-transfer properties, Chem. Eng. Sci. 59 (2004) 4941–4949. [15] http://www.metalfoam.net/companies.html. Accessed 23 October 2017.

323

[16] B.T. Horner, Knitted gauze for ammonia oxidation— new industrial rhodium-platinum fabric catalyst, Platin. Met. Rev. 35 (1991) 58–64. [17] H. Sun, Y. Zhang, X. Quan, S. Chen, Z. Qu, Y. Zhou, Wire-mesh honeycomb catalyst for selective catalytic reduction of NOx under lean-burn conditions, Catal. Today 139 (2008) 130–134. [18] L. Giani, G. Groppi, E. Tronconi, Heat transfer characterization of metallic foams, Ind. Eng. Chem. Res. 44 (2005) 9078–9085. [19] A. Montebelli, C.G. Visconti, G. Groppi, E. Tronconi, C. Cristiani, C. Ferreira, S. Kohler, Methods for the catalytic activation of metallic structured substrates, Cat. Sci. Technol. 4 (2014) 2846–2870. [20] F. Garcia-Moreno, Commercial applications of metal foams: their properties and production. Materials 9 (2016) 85, https://doi.org/10.3390/ma9020085. [21] L.P. Lefebvre, J. Banhart, D.C. Dunand, Porous metals and metallic foams: current status and recent developments, Adv. Eng. Mater. 10 (2008) 775–787. [22] P. Benito, W. de Nolf, G. Nuyts, M. Monti, G. Fornasari, F. Basile, K. Janssens, F. Ospitali, E. Scavetta, D. Tonelli, A. Vaccari, Role of coating-metallic support interaction in the properties of electrosynthesized Rh-based structured catalysts, ACS Catal. 4 (2014) 3779–3790. [23] P.S. Roy, A.S.K. Raju, K. Kim, Influence of S/C ratio and temperature on steam reforming of model biogas over a metal-foam-coated Pd–Rh/(CeZrO2–Al2O3) catalyst, Fuel 139 (2015) 314–320. [24] J. Qi, Y. Sun, Z. Xie, M. Collins, H. Du, T. Xiong, Development of Cu foam-based Ni catalyst for solar thermal reforming of methane with carbon dioxide, J. Energy Chem. 24 (2015) 786–793. [25] A. Montebelli, C.G. Visconti, G. Groppi, E. Tronconi, S. Kohler, H.J. Venvik, R. Myrstad, Washcoating and chemical testing of a commercial Cu/ZnO/Al2O3 catalyst for the methanol synthesis over copper open-cell foams, Appl. Catal. Gen. 481 (2014) 96–103. [26] P. Aghaei, C.G. Visconti, G. Groppi, E. Tronconi, Development of a heat transport model for open-cell metal foams with high cell densities, Chem. Eng. J. 321 (2017) 432–446. [27] E. Bianchi, T. Heidig, C.G. Visconti, G. Groppi, H. Freund, E. Tronconi, Heat transfer properties of metal foam supports for structured catalysts: wall heat transfer coefficient, Catal. Today 216 (2013) 121–134. [28] E. Bianchi, T. Heidig, C.G. Visconti, G. Groppi, H. Freund, E. Tronconi, An appraisal of the heat transfer properties of metallic open-cell foams for strongly exo-/ endo-thermic catalytic processes in tubular reactors, Chem. Eng. J. 198-199 (2012) 512–528. [29] C.Y. Zhao, Review on thermal transport in high porosity cellular metal foams with open cells, Int. J. Heat Mass Transf. 55 (2012) 3618–3632.

3. ADVANCED SUSTAINABLE CHEMICAL PROCESSES AND CATALYSTS FOR ENVIRONMENT PROTECTION

324

15. STRUCTURED CATALYSTS-BASED ON OPEN-CELL METALLIC FOAMS

[30] R. Lemlich, A theory for the limiting conductivity of polyhedral foam at low density, J. Colloid Interface Sci. 64 (1978) 107–110. [31] G. Groppi, E. Tronconi, C.G. Visconti, A. Tasso, R. Zennaro, Packed-bed tubular reactor for heterogeneous exothermic or endothermic catalytic reactions, Patent WO/2015/033266, Eni S.P.A, 2015. [32] S. Yoon, J.Y. Yun, J.H. Lim, B. Yoo, Enhanced electrocatalytic properties of electrodeposited amorphous cobalt-nickel hydroxide nanosheets on nickel foam by the formation of nickel nanocones for the oxygen evolution reaction, J. Alloys Compd. 693 (2017) 964–969. [33] J. Xiong, X. Dong, Y. Song, Y. Dong, A high performance Ru–ZrO2/carbon nanotubes–Ni foam composite catalyst for selective CO methanation, J. Power Sources 242 (2013) 132–136. [34] C. Wang, D. Ping, X. Dong, Y. Dong, Y. Zang, Construction of Ru/Ni-Al-oxide/Ni-foam monolithic catalyst for deep-removing CO in hydrogen-rich gas via selective methanation, Fuel Process. Technol. 148 (2016) 367–371. [35] R. Chai, Y. Li, Q. Zhang, G. Zhao, Y. Liu, Y. Lu, Freestanding NiO–MgO nanosheets in-situ controllably composited on Ni-foam as monolithic catalyst for catalytic oxy-methane reforming, Mater. Lett. 171 (2016) 248–251. [36] C. Mu, K. Huang, T. Cheng, H. Wang, H. Yu, F. Peng, Ni foams decorated with carbon nanotubes as catalytic stirrers for aerobic oxidation of cumene, Chem. Eng. J. 306 (2016) 806–815. [37] A. Sivanantham, S. Shanmugam, Nickel selenide supported on nickel foam as an efficient and durable non-precious electrocatalyst for the alkaline water electrolysis, Appl. Catal. Environ. 203 (2017) 485–493. [38] Q. Zhang, Y. Li, R. Chai, G. Zhao, Y. Liu, Y. Lu, Lowtemperature active, oscillation-free PdNi(alloy)/Nifoam catalyst with enhanced heat transfer for coalbed methane deoxygenation via catalytic combustion, Appl. Catal. Environ. 187 (2016) 238–248. [39] R. Chai, Z. Zhang, P. Chen, G. Zhao, Y. Liu, Y. Lu, Nifoam-structured NiO-MOx-Al2O3 (M ¼ Ce or Mg) nanocomposite catalyst for high throughput catalytic partial oxidation of methane to syngas, Microporous Mesoporous Mater. 253 (2017) 123–128. [40] C. Xiao, B. Zhang, D. Li, Partial-sacrificial-template synthesis of Fe/Ni phosphides on Ni foam: a strongly stabilized and efficient catalyst for electrochemical water splitting, Electrochim. Acta 242 (2017) 260–267. [41] D. Park, D.J. Moon, T. Kim, Preparation and evaluation of a metallic foam catalyst for steam-CO2 reforming of methane in GTL-FPSO process, Fuel Process. Technol. 124 (2014) 97–103. [42] Y. Liu, J. Xu, H. Li, S. Cai, H. Hu, C. Fang, L. Shi, D. Zhang, Rational design and in situ fabrication of MnO2@NiCo2O4 nanowire arrays on Ni foam as high-

[43]

[44]

[45]

[46]

[47]

[48]

[49]

[50]

[51]

[52]

[53]

[54]

[55]

performance monolith de-NOx catalysts, J. Mater. Chem. A 3 (2015) 11543–11553. N. Pegios, G. Schroer, K. Rahimi, R. Palkovits, K. Simeonov, Design of modular Ni-foam based catalysts for dry reforming of methane, Cat. Sci. Technol. 6 (2016) 6372–6380. C. Fang, L. Shi, H. Hu, J. Zhang, D. Zhang, Rational design of 3D hierarchical foam-like Fe2O3@CuOx monolith catalysts for selective catalytic reduction of NO with NH3, RSC Adv. 5 (2015) 11013–11022. M. Zheng, D. Yu, L. Duan, W. Yu, L. Huang, In-situ fabricated CuO nanowires/Cu foam as a monolithic catalyst for plasma-catalytic oxidation of toluene, Catal. Commun. 100 (2017) 187–190. Y. Li, Q. Zhang, R. Chai, G. Zhao, F. Cao, Y. Liu, Y. Lu, Metal-foam-structured Ni–Al2O3 catalysts: wet chemical etching preparation and syngas methanation performance, Appl. Catal. Gen. 510 (2016) 216–226. Z. Liang, P. Gao, Z. Tang, M. Lv, Y. Sun, Three dimensional porous Cu-Zn/Al foam monolithic catalyst for CO2 hydrogenation to methanol in microreactor, J. CO2 Util. 21 (2017) 191–199. M. Frey, T. Romero, A.C. Roger, D. Edouard, Open cell foam catalysts for CO2 methanation: presentation of coating procedures and in situ exothermicity reaction study by infrared thermography, Catal. Today 273 (2016) 83–90. V. Palma, D. Pisano, M. Martino, The influence of the textural properties of aluminum foams as catalyst carriers for water gas shift process, Int. J. Hydrogen Energy 42 (2017) 23517–23525. A.N. Pestryakov, V.V. Lunin, V.P. Petranovskii, Catalysts based on foam materials for neutralization of waste gases, Catal. Commun. 8 (2007) 2253–2256. S. Cimino, A. Gambirasi, L. Lisi, G. Mancino, M. Musiani, L. Va´zquez-Go´mez, E. Verlato, Catalytic combustion of methanol on Pt–Fecralloy foams prepared by electrodeposition, Chem. Eng. J. 285 (2016) 276–285. E. Verlato, S. Barison, S. Cimino, F. Dergal, L. Lisi, G. Mancino, M. Musiani, L. Va´zquez-Go´mez, Catalytic partial oxidation of methane over nanosized Rh supported on Fecralloy foams, Int. J. Hydrogen Energy 39 (2014) 11473–11485. L. Sang, B. Sun, H. Tan, C. Du, Y. Wu, C. Ma, Catalytic reforming of methane with CO2 over metal foam based monolithic catalysts, Int. J. Hydrog. Energy 37 (2012) 13037–13043. J. Kryca, P.J. Jodłowski, M. Iwaniszyn, B. Gil, M. Sitarz, A. Kołodziej, T. Łojewska, J. Łojewska, Cu SSZ-13 zeolite catalyst on metallic foam support for SCR of NOx with ammonia: catalyst layering and characterisation of active sites, Catal. Today 268 (2016) 142–149. P.S. Roy, N.K. Park, K. Kim, Metal foam-supported Pd–Rh catalyst for steam methane reforming and its

3. ADVANCED SUSTAINABLE CHEMICAL PROCESSES AND CATALYSTS FOR ENVIRONMENT PROTECTION

REFERENCES

[56]

[57]

[58]

[59]

[60]

[61]

[62]

[63]

[64]

[65]

[66]

application to SOFC fuel processing, Int. J. Hydrogen Energy 39 (2014) 4299–4310. S. Cimino, R. Gerbasi, L. Lisi, G. Mancino, M. Musiani, L. Va´zquez-Go´mez, E. Verlato, Oxidation of CO and CH4 on Pd–Fecralloy foam catalysts prepared by spontaneous deposition, Chem. Eng. J. 230 (2013) 422–431. W.Y. Choi, J.W. Lee, M.J. Kim, C.J. Park, Y.H. Jeong, H. Y. Choi, N.K. Park, T.J. Lee, Durability tests of Rh/AlCe-Zr catalysts coated on NiCrAl metal foam for ATR of dodecane at high temperature, Int. J. Precis. Eng. Manuf. Green Technol. 4 (2017) 183–189. P. Benito, G. Nuyts, M. Monti, W. De Nolf, G. Fornasari, K. Janssens, E. Scavetta, A. Vaccari, Stable Rh particles in hydrotalcite-derived catalysts coated on FeCrAlloy foams by electrosynthesis, Appl. Catal. Environ. 179 (2015) 321–332. P. Benito, M. Monti, W. De Nolf, G. Nuyts, G. Janssen, G. Fornasari, E. Scavetta, F. Basile, K. Janssens, F. Ospitali, D. Tonelli, A. Vaccari, Improvement in the coating homogeneity in electrosynthesized Rh structured catalysts for the partial oxidation of methane, Catal. Today 246 (2015) 154–164. F. Basile, P. Benito, G. Fornasari, M. Monti, E. Scavetta, D. Tonelli, A. Vaccari, A novel electrochemical route for the catalytic coating of metallic supports, in: E.M. Gaigneaux, M. Devillers, S. Hermans, P. A. Jacobs, J.A. Martens, P. Ruiz (Eds.), Studies in Surface Science and Catalysis, vol. 175, Elsevier, Amsterdam, NL, 2010, pp. 51–58. P. Benito, F. Basile, G. Fornasari, M. Monti, E. Scavetta, D. Tonelli, A. Vaccari, Electrosynthesized Structured Catalysts for H2 Production, New Strategies in Chemical Synthesis and Catalysis, Wiley-VCH, Weinheim, 2012, pp. 201–217. F. Basile, P. Benito, G. Fornasari, V. Rosetti, E. Scavetta, D. Tonelli, A. Vaccari, Electrochemical synthesis of novel structured catalysts for H2 production, Appl. Catal. Environ. 91 (2009) 563–572. F. Basile, P. Benito, S. Bugani, W. De Nolf, G. Fornasari, K. Janssens, L. Morselli, E. Scavetta, D. Tonelli, A. Vaccari, Combined use of synchrotron-radiation-based imaging techniques for the characterization of structured catalysts, Adv. Funct. Mater. 20 (2010) 4117–4126. P. Benito, M. Monti, I. Bersani, F. Basile, G. Fornasari, E. Scavetta, D. Tonelli, A. Vaccari, Coating of FeCrAlloy foam with Rh catalysts: optimization of electrosynthesis parameters and catalyst composition, Catal. Today 197 (2012) 162–169. L.N. Protasova, M.H.J.M. d. Croon, V. Hessel, Review of patent publications from 1990 to 2010 on catalytic coatings on different substrates, including microstructured channels: preparation, deposition techniques, applications, Recent Pat. Chem. Eng. 5 (2012) 28–44. V. Meille, Review on methods to deposit catalysts on structured surfaces, Appl. Catal. Gen. 315 (2006) 1–17.

325

[67] X. Wu, D. Weng, S. Zhao, W. Chen, Influence of an aluminized intermediate layer on the adhesion of a γ-Al2O3 washcoat on FeCrAl, Surf. Coat. Technol. 190 (2005) 434–439. [68] L. Giani, C. Cristiani, G. Groppi, E. Tronconi, Washcoating method for Pd/γ-Al2O3 deposition on metallic foams, Appl. Catal. Environ. 62 (2006) 121–131. [69] L.M. Martı´nez T, O. Sanz, M.I. Domı´nguez, M. A. Centeno, J.A. Odriozola, AISI 304 austenitic stainless steels monoliths for catalytic applications, Chem. Eng. J. 148 (2009) 191–200. [70] N. Burgos, M. Paulis, M. Montes, Preparation of Al2O3/Al monoliths by anodisation of aluminium as structured catalytic supports, J. Mater. Chem. 13 (2003) 1458–1467. [71] Brewer Gerald L., Nickel-free, all metal, catalyst element, Patent US3867313 A, Universal Oil Production, 1975. [72] L. Wang, Y. Xie, C. Wei, X. Lu, X. Li, Y. Song, Hierarchical NiO superstructures/foam Ni electrode derived from Ni metal-organic framework flakes on foam Ni for glucose sensing, Electrochim. Acta 174 (2015) 846–852. [73] P. Caze, D. Letourneur, P. Marques, C. Remy, P. Woehl, Structured catalysts incorporating thick washcoats and method, Patent WO2003074174 A1, Corning Incorporated, 2003. [74] J. Lefevere, S. Mullens, V. Meynen, J. Noyen, Structured catalysts for methanol-to-olefins conversion: a review, Chem. Pap. 68 (2014). [75] F.J. Echave, O. Sanz, M. Montes, Washcoating of microchannel reactors with PdZnO catalyst for methanol steam reforming, Appl. Catal. Gen. 474 (2014) 159–167. [76] F.C. Buciuman, B. Kraushaar-Czarnetzki, Preparation and characterization of ceramic foam supported nanocrystalline zeolite catalysts, Catal. Today 69 (2001) 337–342. [77] V.G. Milt, S. Ivanova, O. Sanz, M.I. Domı´nguez, A. Corrales, J.A. Odriozola, M.A. Centeno, Au/TiO2 supported on ferritic stainless steel monoliths as CO oxidation catalysts, Appl. Surf. Sci. 270 (2013) 169–177. [78] M.J.M. Mies, J.L.P. van den Bosch, E.V. Rebrov, J. C. Jansen, M.H.J.M. de Croon, J.C. Schouten, Hydrothermal synthesis and characterization of ZSM-5 coatings on a molybdenum support and scale-up for application in micro reactors, Catal. Today 110 (2005) 38–46. [79] A. Eleta, P. Navarro, L. Costa, M. Montes, Deposition of zeolitic coatings onto Fecralloy microchannels: washcoating vs. in situ growing, Microporous Mesoporous Mater. 123 (2009) 113–122. [80] S. Catillon, C. Louis, R. Rouget, Development of new Cu0–ZnII/Al2O3 catalyst supported on copper metallic foam for the production of hydrogen by methanol steam reforming, Top. Catal. 30 (2004) 463–467.

3. ADVANCED SUSTAINABLE CHEMICAL PROCESSES AND CATALYSTS FOR ENVIRONMENT PROTECTION

326

15. STRUCTURED CATALYSTS-BASED ON OPEN-CELL METALLIC FOAMS

[81] P. Guo, Y.-X. Wu, W.-M. Lau, H. Liu, L.-M. Liu, CoS nanosheet arrays grown on nickel foam as an excellent OER catalyst, J. Alloys Compd. 723 (2017) 772–778. [82] Y. Li, S. Yang, H. Li, G. Li, M. Li, L. Shen, Z. Yang, A. Zhou, Electrodeposited ternary iron-cobalt-nickel catalyst on nickel foam for efficient water electrolysis at high current density, Colloids Surf. A Physicochem. Eng. Asp. 506 (2016) 694–702. [83] F. Basile, P. Benito, G. Fornasari, M. Monti, E. Scavetta, D. Tonelli, A. Vaccari, Novel Rh-based structured catalysts for the catalytic partial oxidation of methane, Catal. Today 157 (2010) 183–190. [84] A. Simpson, A. Lutz, Exergy analysis of hydrogen production via steam methane reforming, Int. J. Hydrogen Energy 32 (2007) 4811–4820. [85] Statistical report of European Biomass Association, http://www.aebiom.org/statistical-report-2016/, 2016. Accessed 25 November 2017. [86] G. Nahar, D. Mote, V. Dupont, Hydrogen production from reforming of biogas: review of technological advances and an Indian perspective, Renew. Sust. Energ. Rev. 76 (2017) 1032–1052. [87] T.L. LeValley, A.R. Richard, M. Fan, The progress in water gas shift and steam reforming hydrogen production technologies—a review, Int. J. Hydrogen Energy 39 (2014) 16983–17000. [88] J.N. Armor, Catalysis and the hydrogen economy, Catal. Lett. 101 (2005) 131–135. [89] L.E. Basini, A. Guarinoni, Short contact time catalytic partial oxidation (SCT-CPO) for synthesis gas processes and olefins production, Ind. Eng. Chem. Res. 52 (2013) 17023–17037. [90] L.L.G. Jacobs, P.W. Lednor, P.J.M. Van Loon, M. Oosterveld, K.A. Vonkeman, Process for the catalytic partial oxidation of hydrocarbons, Patent US5639401 A, Shell Oil, 1997. [91] H.A. Wright, J.D. Allison, D.S. Jack, G.H. Lewis, S. R. Landis, ConocoPhillips GTL technology: the COPox™ process as syngas generator, Prepr. Pap. - Am. Chem. Soc., Div. Fuel Chem. 48 (2003) 2. [92] P.H. Ho, M. Monti, E. Scavetta, D. Tonelli, E. Bernardi, L. Nobili, G. Fornasari, A. Vaccari, P. Benito, Reactions involved in the electrodeposition of hydrotalcite-type compounds on FeCrAlloy foams and plates, Electrochim. Acta 222 (2016) 1335–1344. [93] P.K. Ng, E.W. Schneider, Distribution of nickel hydroxide in sintered nickel plaques measured by radiotracer method during electroimpregnation, J. Electrochem. Soc. 133 (1986) 17–21. [94] L. Indira, P.V. Kamath, Electrogeneration of base by cathodic reduction of anions: novel one-step route to unary and layered double hydroxides (LDHs), J. Mater. Chem. 4 (1994) 1487–1490.

[95] I. Gualandi, Y. Vlamidis, A. Casagrande, E. Scavetta, D. Tonelli, Co/Al layered double hydroxide coated electrode for in flow amperometric detection of sugars, Electrochim. Acta 173 (2015) 67–75. [96] Y. Vlamidis, E. Scavetta, M. Giorgetti, N. Sangiorgi, D. Tonelli, Electrochemically synthesized cobalt redox active layered double hydroxides for supercapacitors development, Appl. Clay Sci. 143 (2017) 151–158. [97] Y. Vlamidis, E. Scavetta, M. Gazzano, D. Tonelli, Iron vs aluminum based layered double hydroxides as water splitting catalysts, Electrochim. Acta 188 (2016) 653–660. [98] F. Cavani, F. Trifiro`, A. Vaccari, Hydrotalcite-type anionic clays: preparation, properties and applications, Catal. Today 11 (1991) 173–301. [99] P. Benito, F.M. Labajos, J. Rocha, V. Rives, Influence of microwave radiation on the textural properties of layered double hydroxides, Microporous Mesoporous Mater. 94 (2006) 148–158. [100] P.H. Ho, E. Scavetta, F. Ospitali, D. Tonelli, G. Fornasari, A. Vaccari, P. Benito, Effect of metal nitrate concentration on the electrodeposition of hydrotalcite-like compounds on open-cell foams, Appl. Clay Sci. 151 (2018) 109–117. [101] M. Monti, P. Benito, F. Basile, G. Fornasari, M. Gazzano, E. Scavetta, D. Tonelli, A. Vaccari, Electrosynthesis of Ni/Al and Mg/Al layered double hydroxides on Pt and FeCrAlloy supports: study and control of the pH near the electrode surface, Electrochim. Acta 108 (2013) 596–604. [102] F. Basile, P. Benito, G. Fornasari, A. Vaccari, Hydrotalcite-type precursors of active catalysts for hydrogen production, Appl. Clay Sci. 48 (2010) 250–259. [103] F. Basile, P. Benito, P. Del Gallo, G. Fornasari, D. Gary, V. Rosetti, E. Scavetta, D. Tonelli, A. Vaccari, Highly conductive Ni steam reforming catalysts prepared by electrodeposition, Chem. Commun. (2008) 2917–2919. [104] J.W. Kim, B.K. Choi, M.J. Jang, Metal foam stack and manufacturing method therefor, Patent US 20170210090 A1, Alantum, 2017. [105] D. Edouard, M. Lacroix, C.P. Huu, F. Luck, Pressure drop modeling on SOLID foam: state-of-the art correlation, Chem. Eng. J. 144 (2008) 299–311. [106] B. Dietrich, Pressure drop correlation for ceramic and metal sponges, Chem. Eng. Sci. 74 (2012) 192–199. [107] A. Inayat, M. Klumpp, M. L€ammermann, H. Freund, W. Schwieger, Development of a new pressure drop correlation for open-cell foams based completely on theoretical grounds: taking into account strut shape and geometric tortuosity, Chem. Eng. J. 287 (2016) 704–719. [108] J.T. Richardson, D. Remue, J.K. Hung, Properties of ceramic foam catalyst supports: mass and heat transfer, Appl. Catal. Gen. 250 (2003) 319–329.

3. ADVANCED SUSTAINABLE CHEMICAL PROCESSES AND CATALYSTS FOR ENVIRONMENT PROTECTION

FURTHER READING

[109] L. Giani, G. Groppi, E. Tronconi, Mass-transfer characterization of metallic foams as supports for structured catalysts, Ind. Eng. Chem. Res. 44 (2005) 4993–5002. [110] G. Groppi, L. Giani, E. Tronconi, Generalized correlation for gas/solid mass-transfer coefficients in metallic and ceramic foams, Ind. Eng. Chem. Res. 46 (2007) 3955–3958. [111] G. Incera Garrido, F.C. Patcas, S. Lang, B. KraushaarCzarnetzki, Mass transfer and pressure drop in ceramic foams: a description for different pore sizes and porosities, Chem. Eng. Sci. 63 (2008) 5202–5217. [112] E. Verlato, S. Cattarin, N. Comisso, A. Gambirasi, M. Musiani, L. Va´zquez-Go´mez, Preparation of

327

Pd-modified Ni foam electrodes and their use as anodes for the oxidation of alcohols in basic media, Electrocatalysis 3 (2011) 48–58.

Further Reading [113] P. Lanzafame, G. Centi, S. Perathoner, Catalysis for biomass and CO2 use through solar energy: opening new scenarios for a sustainable and low-carbon chemical production, Chem. Soc. Rev. 43 (2014) 7562–7580. [114] S.H. Tan, P.I. Barton, Optimal shale oil and gas investments in the United States, Energy 141 (2017) 398–422.

3. ADVANCED SUSTAINABLE CHEMICAL PROCESSES AND CATALYSTS FOR ENVIRONMENT PROTECTION