γ-Al2O3 guard bed catalysts for gas oil hydrotreating

Journal Pre-proof Influence of alumina precursor on silicon capacity of NiMo/␥-Al2 O3 guard bed catalysts for gas oil hydrotreating K.A. Nadeina, M.O. Kazakov, A.A. Kovalskaya, I.G. Danilova, S.V. Cherepanova, V.V. Danilevich, E.Yu. Gerasimov, I.P. Prosvirin, D.O. Kondrashev, A.V. Kleimenov, O.V. Klimov, A.S. Noskov

PII:

S0920-5861(19)30588-7

DOI:

https://doi.org/10.1016/j.cattod.2019.10.028

Reference:

CATTOD 12533

To appear in:

Catalysis Today

Received Date:

9 April 2019

Revised Date:

2 October 2019

Accepted Date:

18 October 2019

Please cite this article as: Nadeina KA, Kazakov MO, Kovalskaya AA, Danilova IG, Cherepanova SV, Danilevich VV, Gerasimov EYu, Prosvirin IP, Kondrashev DO, Kleimenov AV, Klimov OV, Noskov AS, Influence of alumina precursor on silicon capacity of NiMo/␥-Al2 O3 guard bed catalysts for gas oil hydrotreating, Catalysis Today (2019), doi: https://doi.org/10.1016/j.cattod.2019.10.028

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Influence of alumina precursor on silicon capacity of NiMo/γ-Al2O3 guard bed catalysts for gas oil hydrotreating

K.A. Nadeinaa*, M.O. Kazakova, A.A. Kovalskayaa, I.G. Danilovaa, S.V.

Boreskov Institute of Catalysis SB RAS, Pr. Lavrentieva 5, 630090 Novosibirsk,

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a

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Kondrashevb, A.V. Kleimenovb, O.V. Klimova, A.S. Noskova

Russia

PJSC «Gazprom Neft», str. Pochtamtskaya, 3-5, 190000, St Petersburg, Russia

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Graphcal abstract

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e-mail: [email protected]

Hilights

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b

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Cherepanovaa, V.V. Danilevicha, E.Yu. Gerasimova, I.P. Prosvirina, D.O.

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Si capacity increases with increase of OH groups.

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Increase of OH groups quantity can be predicted.

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Catalysts with higher surface area have lower interaction of Ni and support.

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Length of NiMoS slabs proportional to the length of Al2O3.

Abstract

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The influence of alumina precursors on NiMo/γ-Al2O3 catalysts for silicon removal from gas oil have been studied. Alumina precursors were prepared by hydrothermal treatment of gibbsite,

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precipitation of aluminum nitrate by ammonia and precipitation of aluminum nitrate in autoclave. Alumina precursors, supports and catalysts were studied by XRD, nitrogen adsorption-desorption,

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IR spectroscopy, UV–vis, XPS, SEM, HRTEM. Series of NiMo/γ-Al2O3 catalysts differed in

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preparation method of alumina precursors was tested in hydrotreating of diesel fraction contaminated with decamethylcyclopentasiloxane as a model silicon compound. It was shown that

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prepared alumina precursors were boehmites and dawsonite, which had different particle size. The supports prepared from these alumina precursors were γ-Al2O3 with different particles size. It was

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shown that there was a dependence of the surface area of the support on the size of primary particles measured by XRD. The higher surface area results in the higher content of OH groups and silicon sorption capacity. Morphology of the sulfide active component also depends on the size of primary particles. The higher length of the particles, the higher slab length of NiMoS phase. The catalyst

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with the lowest particle size of alumina and highest length of active component had the highest HDS activity.

1 Introduction

Polydimethylsiloxanes (PDMS) are widely used as antifoaming agents in oil production and refinery. In spite of its obvious positive effect at the stage of oil production, PDMS decomposes during refining and form different siloxanes [1–3]. Interaction of siloxanes with hydroprocessing catalysts results in irreversible deactivation of catalysts and shorten their life-cycle [4,5]. To avoid fast deactivation of hydroprocessing catalysts due to contamination by silicon and to prolong their performance, guard bed catalysts are loaded at the top of industrial unit over the main catalyst.

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Guard bed catalysts for silicon removal compose generally of Ni and Mo compounds

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supported on granulated alumina. Ni and Mo compounds are required for stable performance of catalysts and for mild hydrogenation of sulfur and nitrogen compounds. Alumina support is

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responsible for silicon removal. Recently it was shown for naptha fractions that siloxanes interact

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with Al2O3 via OH groups with formation of Si-O-Al bonds [6,7]. Therefore, amount of free OH groups is very important for such type of catalysts. Similar results for silicon removal from middle

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distillates have been obtained. It was shown that there was a direct dependence of silicon capacity on the amount of OH groups and surface area of the alumina support [8]. Klimov et al. [9] showed

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that textural characteristics of alumina supports are significanly influenced by the morphology of boehmite particles, which are in turn influenced by preparation technique. However, it is not obvious, how preparation method of boehmite would influence hydroxyl cover of aluminas. Alumina precursors can be prepared via different technologies: precipitation [10],

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hydrothermal treatment of gibbsite [11], alcoholate technology [12] etc. Within one preparation method of alumina precursor, it is possible to vary textural characteristics of alumina supports. However, all the methods have restrictions due to the conditions used and can alter certain properties of the supports, for example, the mechanical strength and the pore size distribution. In this case, questions arise: which method of alumina support preparation may be the most suitable for the removal of silicon and is it necessary to provide as large a surface area as possible? In

present work three alumina precursors were prepared by completely different preparation techniques. Alumina precursors, supports and catalysts were characterized by investigation techniques and tested in hydrotreating of diesel fraction with silicon compound.

2 Experimental 2.1 Preparation of alumina precursors, supports and catalysts

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2.1.1 Synthesis of alumina precursors

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The first alumina precursor was prepared by hydration of thermoactivated gibbsite following the protocol described in [8]. Temperature of hydrothermal treatment was 150 ºС and aging time

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was 8 h. This alumina precursor was designated as AP(TGA).

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The second alumina precursor was synthesized by precipitation technique. Aqueous solution of ammonia (9%) was added to the hot water (70 ºC) under stirring until pH7.0. Then aqueous

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solution of aluminum nitrate (2.7M) was added to the mixture under intensive stirring. The resulting white colored suspension was filtered. The precipitate was washed by distilled water, then

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dried at 120 °С for 12 h and grinded up and sieved to obtain the powder less than 0.25 mm in size. This alumina precursor was designated as AP(PR). The third alumina precursor was synthesized following the protocol described in [13]. PEG400 and NH4HCO3 were mixed and grinded up. Then Al(NO3)3∙9H2O was added to the mixture.

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The mixture was again grinded up. The mass ratio of NH4HCO3:Al was 6:1, the amount of PEG400 was 10 wt% of the final mixture. The obtained paste was loaded to the autoclave and heated up to 80 ºС (1 ºC/min) and maintained at this temperature for 7 h. After aging solid product was filtered, washed by distilled water and then by C2H5OH. The solid product was dried at 110 ºC for 12 h, grinded up and sieved to obtain the fraction of 0.5-0.25 mm in size, which was used for the support preparation. This alumina precursor was designated as AP(Autoclave).

2.1.2 Synthesis of alumina supports The supports from AP(TGA) and AP(PR) samples were prepared by extrusion of a kneading paste. The preparation of kneading pastes was carried out by plastification of the powder of alumina monohydrate with aqueous ammonia solution (0.09 mol NH3/mol Al2O3) in Z-blade mixer with continuous stirring of the formed paste for 30 min. The obtained paste was extruded using a

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fluoroplastic spinneret with trilobe holes by VINCI extruder at P = 3.5–4.0 MPa and plunger

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moving at 1.2 mm/s. A cross-section diameter of granules was 2.5 ± 0.2 mm. After extrusion, extrudates of the supports were spread out in a thin layer on the sheets of paper and dried at 120 °C

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in air flow for 4 h. Then the supports were crushed to obtain granules with the length of 3-6 mm.

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Granules were placed in the quartz cup in the muffle furnace and calcined at 550 °C in a flow of dried air for 4 h. The supports were designated as Al-1 (precursor AP(TGA)) and Al-2 (precursor

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AP(PR)).

To obtain the support from AP(Autoclave), AP(Autoclave) fraction was also spread in a thin layer,

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dried at 120 °C for 4 h, then placed in the quartz cup in the muffle furnace and calcined at 550 °C in air flow for 4 h. Plastification with aqueous ammonia solution was excluded due to small quantities of the prepared powder.

Due to the presence of sodium in the initial precursors of alumina, supports were analyzed

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for sodium content. The content of sodium was less than 0.05 wt% in all supports.

2.1.3 Synthesis of catalysts Catalysts were prepared by similar preparation technique. The supports were impregnated by

an aqueous solution prepared from nickel carbonate NiCO3·mNi(OH)2·nH2O (Baltic Enterprise, Ltd.), ammonium heptamolybdate (NH4)6Mo7O24·4H2O (Baltic Enterprise, Ltd.) and citric acid

(Reachim Ltd.) with mass ratio of the components 1:2.9:2.5. Then catalysts were dried at 120 °C for 4 h and calcined at 550 °C for 4 h. Drying and calcination procedures were similar to that for the supports. Metals contents in catalysts were 6.0 ± 0.1 wt% of Mo and 2.0 ± 0.1 wt% of Ni. Designation of supports and catalysts is given in Table 1.

2.2 Sulfiding and testing of catalysts

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All the catalysts were sulfided and subsequently tested in hydrotreating of model feedstock

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in a fixed bed reactor. In all cases, catalysts were in the form of fraction with a particle size of 0.250.5 mm. A sample portion equivalent to 2 cm3 of a catalyst was placed in the isothermal zone of

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the reactor. Sulfiding was performed with a dimethyl disulfide solution (20 g/L) in a straight-run

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diesel fraction with 0.25 wt% of sulfur in the following conditions: a pressure of 3.8 MPa, a volumetric hydrogen/sulfiding mixture ratio of 300 and a stepwise elevated temperature (140, 240,

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340 °C). This method of sulfiding is optimized version of the one described in [14]. Diesel fraction (0.25 wt% of S) with addition of decamethylcyclopentasiloxane as a model

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silicon compound was used as a feedstock. The content of Si in the feedstock was 166 ppm. Testing was carried out in the following conditions: LHSV of 10 h−1, a volumetric H2/feed ratio of 550 Nl/l, P = 3.8 MPa, T = 360 °C. After start up, catalysts were tested in HDS of diesel fraction without silicon addition during first 24 h time on stream to measure initial HDS activity. Then the feedstock

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was switched to diesel fraction containing model silicon compound. Testing was carried out until the silicon content at the inlet and outlet of the reactor became the same. Silicon content in the feedstock and in the liquid products was determined by inductively coupled plasma mass spectrometry using Agilent 7700 ICP-MS (Agilent Technologies). Horiba SLFA-2100 was used to measure residual sulfur content in liquid products. Difference in a residual sulfur contents for each HDS point was in precision of 5%. Uncertainty of measurements for sulfur content is ± 5 ppm.

General uncertainty for testing was ± 10 ppm. Silicon sorption capacity of the catalysts was determined by chemical analysis of spent catalysts. Catalysts after testing were transferred to hexane without contacting with air, then washed by hexane prior to analysis to remove the feedstock. Storage after washing was also in hexane until studies by the methods.

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2.3 CHNS elemental analysis

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The CHNS analysis of the catalysts after testing and alumina precursors was performed using

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dried at 70 ºC in air flow for 1 h to remove hexane.

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Euro ЕА3000 analyzer. Before analysis, samples of catalysts were transferred from hexane and

2.4 X-ray diffraction

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Phase composition was analyzed by X-ray diffraction (XRD). The XRD patterns were recorded on a D8 Advance diffractometer (Bruker, Germany) using CuKα radiation. Scanning was

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performed in the 2θ-angle range from 10° to 75° (dried samples) and from 15° to 75° (calcined samples) with step of 0.05° and acquisition time of 3 s at each point. The lattice constants were refined by Rietveld method with the use of TOPAS software (Bruker, Germany). The average

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crystallite (primary particle) sizes were also calculated using TOPAS software.

2.5 HRTEM

HRTEM images were obtained by a JEM-2010 electron microscope (JEOL, Japan) with a

lattice-fringe resolution of 0.14 nm at an accelerating voltage of 200 kV. The high-resolution images of the periodic structures were analysed by the Fourier method. Samples for HRTEM examination were prepared on a perforated carbon film mounted on a copper grid. Stacking number

and the slab length of the sulfide active component were defined using the average data for at least 500 particles or more than 5 microphotographs. It should be noted that HRTEM method allows calculation of the sulfide active component particles which are seen for the beam. Such particles are angled to the electron beam.

2.6 XPS

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Photoelectron spectra were recorded using SPECS spectrometer with PHOIBOS-150-MCD-

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9 hemispherical energy analyzer (AlKα irradiation, hν = 1486.6 eV, 200 W). Binding energy scale was preliminarily calibrated by the position of the peaks of Au4f7/2 (84.0 eV) and Cu2p3/2 (932.7

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eV) core levels. The samples were supported onto double-sided conducting copper scotch tape.

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The binding energy of peaks was corrected to take into account the sample charging by referencing to the C1s peak (Eb=284.8 eV) corresponding to the surface hydrocarbon-like deposits (C-C and

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C-H bonds) [15]. The ratio of surface atomic concentrations of the elements was calculated from the integral intensities of photoelectron peaks corrected by corresponding atomic sensitivity factors

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[16]. Spectral analysis and data processing were performed with XPS Peak 4.1 program. XPS spectra were recorded for the catalysts after testing, which were washed and stored in hexane. To register spectra, samples of catalysts were quickly supported to the sample holder and moved to the chamber of the spectrometer. The contact with air was less than 1 minute, because

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the sample was wetted by hexane, when it was placing into the chamber.

2.7 Nitrogen adsorption-desorption The textural properties of the catalysts and supports were determined by nitrogen

physisorption using an ASAP 2400 instrument (Micrometrics, USA). Prior to analysis, samples were subjected to a N2 flow at 200 °C for 2 h. The BET surface areas were calculated from the

nitrogen uptakes at relative pressures ranging from 0.05 to 0.30. The total pore volume was derived from the amount of nitrogen adsorbed at a relative pressure close to unity (in practice, P/P0 = 0.995) by assuming that all accessible pores have been filled with condensed nitrogen in the normal liquid state. The pore size distribution was calculated by the BJH method using the desorption branch of the isotherm.

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2.8 UV-vis DRS

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UV-vis diffuse reflectance spectra of calcined at 550 ºC NiMo catalysts were recorded using a UV-2501 PC Shimadzu spectrometer with an IRS-250A diffusion reflection attachment in the

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11000-54000 cm-1 range. The measurements were performed in a 2 mm quartz cell in air at room temperature using the BaSO4 as a reference. The UV-vis spectra were transformed into the

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Kubelka-Munk function (F(R)) calculated as F(R∞) = (1 - R∞)2/2R∞, where R∞ is the

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2.9 IR-spectroscopy

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experimentally measured reflectivity coefficient of the infinitely thick samples.

IR spectra were recorded by Shimadzu FTIR-8300 spectrometer within the spectral range of 700–6000 cm-1 with a resolution of 4 cm–1 and 300 scans for signal accumulation. The powder samples were pressed into thin self-supporting wafers (0.009-0.010 g/cm2) and activated in the

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special IR cell at 500 ºC for 1 h in air and further at 550 ºC for 2 h in dynamic vacuum of 10–3 mbar. The total concentration of the isolated surface OH groups was evaluated from the integral intensity (A) of OH band in the range of 3590 - 3830 cm–1 using molar integral absorption coefficients Ao=1.5 cm/μ-mol for unassociated hydroxyls [17]. In the presented spectra, the absorbance was normalized to sample wafer density.

3 Results 3.1. Characterization of alumina precursors, supports and catalysts Figure 1 shows SEM (left) and HRTEM (right) images of the alumina precursors. AP samples significantly differ in morphology of secondary particles seen in HRTEM and agglomerates of these particles seen in SEM. Secondary particles of AP(TGA) and AP(PR) samples are needle-shaped. The length of AP(TGA) particles varies in the range of 30-100 nm, while AP(PR) sample contains

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particles with the length of 30-60 nm. AP(Autoclave) sample composes of plane-like particles with the

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length of 10-30 nm. Structures of agglomerates are also different. SEM images (Figure 1) of AP(TGA) and AP(PR) samples show large particles with sizes of 4-10 µm, while AP(Autoclave) sample

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seems to be the set of small agglomerates with the size of 0.3-0.5 µm. Absence of agglomerates in

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AP(Autoclave) sample can be due to the fact that this sample was not plastified by ammonia. To obtain information on the nature of alumina precursors, XRD data of the samples have

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been recorded (Figure 2). XRD patterns of AP(TGA) and AP(PR) correspond to pseudoboehmite. There are some insignificant differences in lattice constants and in average crystallite size. The size

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of the crystallites (primary particles) correlates with the size of needles, which was determined from HRTEM data. The XRD pattern of AP(Autoclave) sample significantly differs from AP(TGA) and AP(PR) and corresponds to dawsonite structure. Average crystallite size is higher than the ones of AP(TGA) and AP(PR).

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The supports have also been studied by XRD (Supporting Information, Figure SI1). The

results show that γ-Al2O3 has been obtained in all cases. There is the difference in the average size of primary particles as in the case of AP samples (Table 2). For AP(TGA) and AP(PR) samples, the tendency in changes of particle size remains. Al-1 sample have larger particles. On the contrary, Al-3 support prepared from AP(Autoclave) sample with the largest particles have lower average particle size than Al-1 and Al-2.

The supports prepared from AP(TGA), AP(PR) and AP(Autoclave) differ significantly in textural characteristics (Table 3). Al-1 support has the lowest specific surface area and pore volume. Changing the alumina precursor preparation to precipitation technology results in considerable increase in all textural parameters. The highest surface area and pore volume were obtained for Al3 sample, while pore diameter is slightly lower for this support. Supporting of active metals decreases surface area and pore volume, while pore diameter

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may increase or decrease due to the difference in localization of active metals. Figure 3 shows pore

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size distribution curves. Al-1 support and corresponding NiMo/Al-1 catalyst have bimodal pore size distribution with two main areas at 4-9 nm and 9-30 nm with respective maxima at 6.5 nm and

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15.3 nm. Supporting of active metals leads to smooth decrease of volumes of all pores. Al-2 support

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also contains two similar areas of mesopores with maxima at 6 and 11 nm. However, there is more significant decrease in the area of larger mesopores (9-13 nm) after supporting of active metals.

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Al-3 support have a monomodal pore size distribution with the maximum at 6.3 nm (4-30 nm). Active metals in NiMo/Al-3 catalyst are uniformly distributed in the support pores.

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The effect of alumina precursor on the concentration and ratio of the surface functional groups for Al2O3 supports and NiMo catalysts in the oxide form was studied by IR spectroscopy. The IR spectra recorded after activation in air and in vacuum at 550 °C are shown in Figure 4. The spectra of Al2O3 supports (Al-x) present the main vibration bands at ca. 3786-3795, 3775, 3736-

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3728, 3685-3690 and 3590 cm-1, which are typical surface OH groups of all transition alumina phases [18,19]. The spectra of Al-1 and Al-2 are typical for -Al2O3. In particular, these spectra show well evident band at ca. 3775 cm-1 [20]. The 3775 cm-1 band corresponds to OH groups on well exposed sites such as

[ ]

Al-OH where [ ] indicates an anionic vacancy [21]. The relative

intensity of the band at ca. 3775 cm-1 decreases in the order Al-1  Al-2  Al-3. Low intensity of

this band in the spectrum of Al-3 support can be caused by the presence of surface carbonate species. Difference in relative intensity of the bands at ca. 3685-3690 and 3728-3736 cm-1 for Alx supports can be apparently related to different morphology of alumina nanoparticles (as it was shown by HRTEM), and, therefore, with different ratios of basal and edge crystallographic surfaces. The total concentration of isolated surface hydroxyl groups (absorption bands at 3590 - 3830

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cm-1) decreases in the series Al-1  Al-2  Al-3 (Table 4). Surface OH-density of alumina supports

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decreases in the same manner and corresponds to hydroxyl cover of various aluminas (ca. 2.3÷5.5 OH`s/nm2 [22]) when dehydroxylation temperatures are similar. It should be noted that the

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decrease in surface OH-density is proportional to the decrease in the crystallite size of alumina

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(according to XRD).

Supporting of active metals on alumina followed by calcination at 550 ºC results in

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considerable decrease in concentration of all OH groups of initial supports (Figure 4, Table 4). OHdensity decreases by 1.7 times after supporting of active metals on Al-1 support, by 2.1 for Al-2

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support and by 3.5 for Al-3 support. The total concentration of the residual isolated surface hydroxyl groups of NiMo/Al-x catalysts in oxide state decreases in the same way as for supports (Table 4).

Diffuse reflectance UV–vis spectroscopy (UV–vis DRS) was used to study the symmetry

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and coordination of the surface species of the NiMo/Al2O3 catalysts in the oxide form. The spectra are shown in Figure 5. The intense absorption band at about 225–320 nm could be assigned to the ligand-metal charge transfer (LMCT) transitions O2−→ Mo6+. The CT band centered at ca. 225 nm and 250-300 nm for all samples can indicate the presence of isolated tetrahedral coordinated Mo sites and polymolybdate-like structure containing ions with Mo in octahedral surrounding,

respectively [23]. The red shifts of the absorption edge of molybdenum polyhedra in the spectrum of NiMo/Al-1 catalyst can be explained by an increase in the average particle size (domain) of molybdenum oxide species in this catalyst [24]. Ni2+ ions (O2−→ Ni2+ LMCT transitions) can also contribute to the absorption in the UV region [25]. In addition to the CT bands due to overlapping of Mo and Ni species, appearing in the UV region, the visible spectra of these catalysts exhibit bands in the 400–900 nm region, which are

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associated only with d-d transitions of Ni2+ species.

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The spectra of NiMo/Al-1 and NiMo/Al-2 catalysts are characterized by the presence of intense doublet at 600 and 635 nm with shoulder at 550 nm and absorbance band at 775 nm. These

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bands can be assigned to 3T1(F) → 3T1g(P) transitions of tetrahedrally coordinated Ni (II) ions.

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The absorption band at 710 nm can be ascribed to the 3A2g → 3T1g(P) transitions of octahedrally coordinated Ni (II) ions. These features are characteristic of a partial inverse NiAl2O4 spinel phase

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where Ni (II) ions occupy both octahedral and tetrahedral sites [26–28]. The intensity of the bands at 600 and 635 nm, which are assigned to the interaction between Ni ions and a support, decreases

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in the series NiMo/Al-1 > NiMo/Al-2 >> NiMo/Al-3. Low intensity of these bands in the spectrum of NiMo/Al-3 catalyst can indicate weaker interaction of Ni species with Al-3 support. The spectrum of NiMo/Al-3 catalyst is characterized by the presence of the intense bands at 430 and 800 nm. The last feature is associated with octahedrally coordinated Ni (II) species in

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NiMoO4 [29]. Such species are considered as precursors of the sulfide active phase of these catalysts [30,31]. Less intense band at ca. 800 nm is also observed in the spectrum of NiMo/Al-2 catalyst. The spectrum of NiMo/Al-1 catalyst shows the increase of background line in the region of 760-900 nm that also can be evident for the presence of small quantities of nickel molybdate. The band at 430 nm is traditionally considered with the band at 710-720 nm and ascribed to the

octahedrally coordinated Ni (II) ions in NiO [28,32]. However, relation of the band at 430 nm to Ni ions in dispersed NiO is questionable for our catalysts. Therefore, UV–vis data suggest the existence of two types of Ni species in our catalysts: highly dispersed and isolated Ni2+ interacting with alumina (NiAl2O4 spinel-like phases), and NiMoO4 nanoparticles. The concentration of NiMoO4 phases is the highest in NiMo/Al-3 catalyst,

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3.2. Catalytic activity and characterization of sulfide catalysts

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the concentration of NiAl2O4 spinel-like phases is the highest in NiMo/Al-1 catalyst.

Testing of the catalysts in hydrotreating of diesel fraction with siloxane showed that the

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higher surface area, the higher Si sorption capacity (Figure 6a). Due to the presence of Ni and Mo

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compounds, hydrodesulfurization (HDS) activity of the catalysts was determined. Figure 6b shows that catalytic activity depends on the specific surface area and, therefore, on silicon capacity. The

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highest HDS activity was obtained for NiMo/Al-1 catalyst, while the lowest one was shown by NiMo/Al-3 catalyst. Silicon uptake resulted in the decrease of hydrodesulfurization activity in all

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cases approximately by 30 %.

After testing catalysts have been studied by HRTEM, XPS, CHNS and nitrogen adsorptiondesorption. HRTEM images of the catalysts (Supporting Information, Figure SI2) show particles of the support, which are similar in the shape and size to the ones of initial alumina precursors, and

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black lines corresponding to the sulfide active component [33]. Morphology of the active component particles varies depending on the alumina precursor. Stacking number and slab length are inversely proportional to the size of alumina precursor particles and to HDS activity (Table 5). Visualization of active component particles is very similar and have no evident dependence.

The state of active metals in sulfide catalysts after reaction was determined by XPS. XPS data obtained from decomposition of the spectra are given in Table 6. Decompositions of XPS spectra of Ni2p and Mo3d are given in Supporting Information, Figure SI3. Ni2p spectra for all catalysts contain the peak at Eb = 853.9 eV. Such binding energy value and the presence of satellites indicate Ni2+ state [34,35]. Decomposition of the spectra to Ni2+, NiMoS and NiS shows that content of Ni in the composition of NiMoS phase is similar, however,

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there is slight tendency in the increase of Ni in NiMoS phase with increasing surface area.

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Mo3d+S2s spectra (Supporting Information, Figure SI3) of all the catalysts contain the line with binding energy 228.9±0.1 eV from Mo3d5/2 and its satellite (232.7±0.1 eV) corresponding to

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Mo4+ state. These binding energies characterize molybdenum in sulfur surrounding in sulfide

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catalysts [36,37]. The spectra were decomposed into three states – Mo4+, Mo5+ and Mo6+. Catalysts were shown to contain Mo4+ – 76.5 ± 6.0 %, Mo5+ – 13.0 ± 4.0% and Mo6+ – 10.0 ± 2.0%. Thus,

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Mo in sulfide catalysts after reaction is preferentially in the composition of NiMoS phase. CHNS analysis data of the sulfide catalysts after testing are given in Table 7. Carbon content

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varies from 4.4 to 8.8 wt% and have irreversible dependence on surface area of the catalysts. Hydrogen content in catalysts have similar dependence on the surface area of catalysts. It is possible that supports with lower pore volume and surface area have more tendency to coke deposition. Sulfur content in catalysts is slightly lower than calculated according to metals content

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(~4 wt%). It can be accounted for by washing conditions of the catalysts before analysis. Textural characteristics of the calcined catalysts after reaction become lower. There is a

significant decrease of the surface area for NiMo/Al-2 and NiMo/Al-3 catalysts after reaction in comparison with the calcined catalysts before reaction . While for NiMo/Al-1 catalyst, the change of surface area after reaction is much lower. Pore volume of the catalysts after reaction is also considerably lower than that of fresh catalysts. Pore size distribution curves (Figure 7) show

uniform decrease of pore volumes in the whole range of pore presence. It is noted that there is a strong decrease of large mesopores and shift of the peaks to the area of smaller mesopores. However, it is not possible to determine directly the amount of small mesopores and large mesopores which were filled by silicon. It is caused by the decrease of pore diameter of larger mesopores after localization of silicon compounds in these pores. Therefore, their diameter decreases and nitrogen adsorption-desorption method identifies them as smaller mesopores. While

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small mesopores are also filled by Si compounds and become smaller or blocked after deposition

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of Si species.

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4 Discussion

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Guard bed catalysts for silicon removal provide two main functions during their performance in hydrotreating unit: 1) conversion of siloxanes to remove silica compounds from distillates; 2)

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conversion of sulfur compounds to decrease burden of the hydrotreating catalyst. The first function is provided by alumina support, while the second one is carried out by active metals (Ni and Mo).

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Silicon compounds present in real feedstock in the form of different siloxanes [1,38,39]. Structure of siloxane species in the feed depends significantly on pretreatment conditions of the fraction

that

will

be

processed

in

hydrotreating

unit.

In

present

work,

decamethylcyclopentasiloxane was chosen as the model compound that can be present in diesel

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fractions. Obviously, such system is much simpler than real contaminated diesel fraction, but provides information on the performance of the catalysts. It is known from the literature data that silicon compounds react irreversibly with OH groups

of alumina [6]. Therefore, it is generally considered that the higher amount of OH groups, the higher silicon capacity can be obtained. Recently, it was shown that within one preparation technique this dependence was right [8]. However, properties of alumina can be significantly

influenced by alumina precursors [9]. In this case, could silicon sorption capacity be predicted if alumina supports have been prepared from different precursors? In present work, three alumina supports have been synthesized from different precursors. Two of them are widely used at laboratory and industrial scale, the third was prepared using the method proposed in [13] to obtain alumina with high surface area (experimental methodology). Unfortunately, the third method is very hard to reproduce in large scale, because product yield is

of

very small. XRD studies of the precursors showed that hydrothermal treatment of thermoactivated

ro

alumina and precipitation method provided preparation of pseudoboehmites, while the third method of precipitation in autoclave resulted in preparation of dawsonite structure. The alumina

-p

precursors had different particle shape, the size of primary particles, the size and shape of secondary

re

particles and agglomerates. Needle-shaped particles have been prepared by conventional preparation techniques, while plane-like particles have been formed via experimental

lP

methodology.

Regardless of the alumina precursors, the prepared supports were γ-Al2O3. Similarly to the

ur na

initial alumina precursors, the tendency in changing of sizes of alumina primary particles was observed. For the supports prepared from boehmites (Al-1 and Al-2 samples), average crystallite sizes (according to XRD) of the supports change proportionally to the size of secondary particles and agglomerates of the particles of corresponding boehmites. As for experimental support (Al-3

Jo

sample), average particle size became much smaller. This can be caused by the shape of the particles and conversion of alumina precursor during calcination step. It should be noted that conditions of calcination were similar and changes in transformation of alumina precursors should be due to the difference of the alumina source. Various particle shape and size resulted in significantly different textural properties. The surface area varied from 200 to 400 m2/g, pore volume - from 0.6 to 1.0 cm3/g and there was different pore size distribution. It is interesting that

the sizes of primary (according to XRD) and secondary particles of needle shaped boehmites are inverse to the surface area of the support. Therefore, it can be proposed that if we vary particle size at the stage of alumina precursor preparation, we may predict OH cover of the support. These data are in agreement with [8]. However, this question on the correlation between alumina surface and content of OH groups is very controversial for alumina supports prepared from different precursors. It is known that depending on the faces in alumina surface there could be different quantities of

of

OH groups [22]. Therefore, if it is possible to vary ratio of alumina faces, it will be possible to

ro

adjust surface properties for the reaction with silicon compounds. In addition, we cannot include the Al-3 sample prepared from dawsonite to this correlation due to the fact that it contains trace

-p

amounts of carbonate species. However, the sample also fits to the correlation between particle size

re

of alumina and surface area. We could imagine that plane needle-shaped particles of Al-1 and Al2 supports are agglomerates of small plane-like particles. Therefore, we can compare all the

lP

supports in terms of sizes of secondary particles. In this case, the tendency of the increase of surface area with a decrease of secondary particles becomes predictable.

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As for the hydroxyl cover of the samples, the increase in the surface area results in the decrease of concentration of OH groups per 1 g of a catalyst and density of OH groups per 1 m2. The silicon capacity increases with the increase of surface area, therefore, it is inverse to the concentration of OH groups and their density on the support surface. It should be noted that some

Jo

of the OH groups in catalysts are covered by NiMoS phase after active phase formation. It was shown in [8] that Si localizes in catalysts after reaction near sulfide active component particles, even if content of Si is high. Therefore, part of OH groups of the supports is covered by active metals, while another part reacts with Si compounds. Probably, high density of OH groups can negatively influence silicon capacity, because large siloxane molecule can block not only OH groups via direct reaction, but also obstruct access to neighbor OH groups. The literature data of

Si interaction with alumina surface show that silicon compounds form Si-O-Si bonds due to the formation of a silica-like or silico–aluminate phase [40]. In [41], it was shown that incorporation of small amounts of silica to alumina results in formation of isolated hydrogen-orthosilicate species. These silicon species block specifically alumina acid-base sites. The authors proposed the idea that orthosilicate species anchor specific sites of alumina, which are very likely located on the edges and corners and surface defects of alumina particles. However, the catalytic system studied

of

in [41] contained only 5% of SiO2 that is much lower than Si capacity of the samples in present

ro

work. Also, it was shown in [32, 41] that Ni and Mo compete with Si for OH groups of alumina. Thus, silica species likely interact with OH groups, which are free of NiMoS phase and form silica-

-p

aluminate phase. Unfortunately, it is not possible to calculate OH groups, which are free of NiMoS

re

phase, even if we measure OH groups after anchoring of active metals precursor. It results from release of OH groups after transformation of the precursors to NiMoS phase. However, the

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following approximation can be made. Sulfide active component particles may interact with more OH groups of alumina with higher OH groups density. However, the samples with similar

ur na

morphology of active component have significantly different Si sorption capacity. Therefore, the morphology of active component particles do not have significant influence. In this case, it is almost correct to compare Si sorption capacity with initial content of OH groups in the support. The increase of OH density from 1.5 to 3.4 OH’s/cm2 results in the decrease of silicon capacity on

Jo

2 wt%. Therefore, the supports with lower OH density are preferable. Also, it was observed that the decrease of the supports OH-density after NiMo impregnation became more pronounced with decreasing average size of primary particles of Al-x supports. Apparently, localization of the active component particles depends on the morphology of alumina support nanoparticles in this case. In terms of silicon capacity, the choice of the support is obvious. The most preferable is experimental methodology of precipitation in autoclave, but precipitation of alumina nitrate by

ammonia is most suitable for industry. Indeed, there is the necessity to provide also mild HDS activity. Varying the preparation conditions of alumina support influences interaction of the active component with alumina surface. Studies of the catalysts after reaction showed that active metals are mostly in the form of NiMoS phase. Content of NiMoS phase in prepared catalysts is similar to highly active hydrotreating catalysts [34,42]. Resulting active component particles differed in the morphology. It was noted that the larger length of alumina support particles, the larger length

of

of NiMoS slabs. Interestingly, the length of NiMoS particles also correlates with NiMoO4 particles

ro

in oxide samples (according to UV-vis). Characterization of the oxide precursors also shows that the catalysts with lower surface area contain higher amount of Ni in the form of aluminate, while

-p

increase of the surface area results in the increase of NiMoO4 portion and then in the increase of

re

NiMoS phase. Introduction of Ni into the support does not influence significantly hydrodesulfurization activity. On the contrary, the catalyst with higher Ni aluminate content have

lP

higher activity. It can be accounted for by the following. First of all, there are significant changes in morphologies of active component particles (decrease in the slab length and increase in the

ur na

stacking number with increasing surface area) and some difference can be caused by ratios of edge/corner sites. But due to the very small concentrations of active component particles, such significant difference in the conversion of sulfur compounds (more than 10%) between NiMo/Al1 and NiMo/Al-2 should be influenced by some more significant factor than just morphology of

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active component. In this case, it can be suggested that sulfide active component takes part in conversion of Si species too. When Si compound reacts with OH groups, it is necessary to crack the ring. However, OH groups itself cannot provide this reaction, while NiMo sulfide particles have high hydrogenation activity and can seize siloxane molecule. Thus, if NiMoS particles are localized on a longer distance to each other, it will be easier for siloxane and sulfur molecules to react with them, but they will compete for the active sites. Meanwhile, localization of active component

particles closer to each other makes it harder for siloxanes to achieve NiMoS sites and thereby decreases Si sorption capacity, while HDS activity increases. In addition, it was noted that there was the direct dependence of silicon capacity on carbon content and inverse dependence of carbon content to the surface area. The catalyst with lower surface area and lower silicon capacity accumulated twice-higher coke amount. It was also noted that coke amount correlated with HDS activity and indirectly confirmed competitive reactions of

of

Si and sulfur molecules with NiMoS particles. In terms of catalysts deactivation, catalysts with

ro

lower surface area are not preferred to be used as guard bed catalyst due to lower silicon capacity and faster coke deposition.

-p

After investigation of the series of the catalysts, which were prepared from different

re

precursors of the alumina supports, the following conclusions can be made: 1. Silicon capacity depends on the content of OH groups independently to the nature of the

lP

alumina precursor of NiMo/γ-Al2O3.

2. The amount of OH groups can be predicted from the sizes of alumina precursor particles.

ur na

3. The lower content of “reactive” OH groups in the support, the lower content of Ni in the form of Ni aluminate.

4. The length of NiMoS particles is proportional to the length of alumina support particles. 5. The catalysts with lower surface area have lower silicon capacity and accumulate higher

Jo

amount of coke.

5 Conclusion Three NiMo/γ-Al2O3 catalysts obtained using different alumina precursors have been

studied. Alumina precursors were prepared by hydrothermal treatment of gibbsite, precipitation of alumina nitrate with ammonia and precipitation in autoclave. The first and second methods resulted

in preparation of boehmites with needle-shaped particles, while the third one resulted in preparation of dawsonite with plane-like particles. Alumina precursors differed in particle sizes. The prepared supports were γ-Al2O3 with different particle size, significantly different texture and concentration of OH groups. It was established that the higher surface area, the lower concentration and density of OH groups. However, higher surface area resulted in the higher Si capacity. In addition, it was noted that surface area increased with decreasing particle size of the support. There was the

of

dependence of the length of NiMoS slabs on the particle size of alumina supports and their

ro

crystallites. Funding

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Funding was received for this work.

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Research Ethics

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We further confirm that any aspect of the work covered in this manuscript that has involved human patients has been conducted with the ethical approval of all relevant bodies and that such approvals are acknowledged within the manuscript.

Conflict of Interest

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No conflict of interest exists.

Acknowledgement This work was conducted within the framework of the budget project #АААА-А17-

117041710077-4 for Boreskov Institute of Catalysis.

References [1]

F. Chainet, L. Le Meur, C.-P. Lienemann, J. Ponthus, M. Courtiade, O.F.X. Donard, Characterization of silicon species issued from PDMS degradation under thermal cracking of hydrocarbons: Part 1 – Gas samples analysis by gas chromatography-time of flight mass spectrometry, Fuel. 111 (2013) 519–527. doi:https://doi.org/10.1016/j.fuel.2013.03.046. L.N. Kremer, Foam control methods in delayed cokers, Pet. Technol. Quarterly. 7 (2002)

of

[2]

ro

65–69.

C. Rome, Silicone in the Oil and Gas Industry, Dowcorning.Com. (2002).

[4]

L. Kellberg, P. Zeuthen, H.J. Jakobsen, Deactivation of HDT Catalysts by Formation of

-p

[3]

Naphtha Using

29

Si and

13

re

Silica Gels from Silicone Oil. Characterization of Spent Catalysts from HDT of Coker C CP/MAS NMR, J. Catal. 143 (1993) 45–51.

[5]

lP

doi:https://doi.org/10.1006/jcat.1993.1252.

M. Marafi, A. Stanislaus, E. Furimsky, Chapter 4 - Catalyst Deactivation, in: M. Marafi, A.

ur na

Stanislaus, E. Furimsky (Eds.), Handb. Spent Hydroprocessing Catal. (Second Ed., Second Edition, Elsevier, 2017: pp. 67–140. doi:https://doi.org/10.1016/B978-0-444-638816.00004-4. [6]

P. Pérez-Romo, J. Navarrete-Bolaños, C. Aguilar-Barrera, C. Angeles-Chavez, G.C. Laredo,

Jo

Morphological and structural study of the Si deposition on the sulfided NiMo/γ-Al2O3 catalyst:

Effect

on

the

support,

Appl.

Catal.

A

Gen.

485

(2014)

84–90.

doi:10.1016/j.apcata.2014.07.038.

[7]

J. Siegel, C. Olsen, Feed Contaminants in Hydroprocessing Units, ART Catalagram104 Spec. Ed. Fall (2008) 1–6.

[8]

K.A. Nadeina, M.O. Kazakov, A.A. Kovalskaya, V. V Danilevich, O. V Klimov, I.G.

Danilova, D.F. Khabibulin, E.Y. Gerasimov, I.P. Prosvirin, V.A. Ushakov, K. V Fedotov, D.O. Kondrashev, A. V Kleimenov, A.S. Noskov, Guard bed catalysts for silicon removal during hydrotreating of middle distillates, Catal. Today. 329 (2019) 53–62. doi:https://doi.org/10.1016/j.cattod.2018.11.075. [9]

O.V. Klimov, K.A. Leonova, G.I. Koryakina, E.Y. Gerasimov, I.P. Prosvirin, S.V. Cherepanova, S.V. Budukva, V.Y. Pereyma, P.P. Dik, O.A. Parakhin, A.S. Noskov,

of

Supported on alumina Co-Mo hydrotreating catalysts: Dependence of catalytic and strength

ro

characteristics on the initial AlOOH particle morphology, Catal. Today. 220–222 (2014) 66–77. doi:10.1016/j.cattod.2013.09.001.

-p

[10] S. Kirchner, S. Teychené, M. Boualleg, A. Dandeu, C. Frances, B. Biscans, Effect of

re

precipitation process parameters on boehmite properties: In situ optical monitoring, Chem. Eng. J. 280 (2015) 658–669. doi:https://doi.org/10.1016/j.cej.2015.06.002.

lP

[11] V. V Danilevich, O. V Klimov, K.A. Nadeina, E.Y. Gerasimov, S. V Cherepanova, Y. V Vatutina, A.S. Noskov, Novel eco-friendly method for preparation of mesoporous alumina

ur na

from the product of rapid thermal treatment of gibbsite, Superlattices Microstruct. 120 (2018) 148–160. doi:https://doi.org/10.1016/j.spmi.2018.05.025. [12] Sasoltechdata,

PURAL/CATAPAL

High

purity

aluminas,

n.d.

http://www.sasoltechdata.com/tds/PURAL_CATAPAL.pdf.

Jo

[13] X. Hu, Y. Liu, Z. Tang, G. Li, R. Zhao, C. Liu, Fabrication of high-surface-area γ-alumina by thermal decomposition of AACH precursor using low-temperature solid-state reaction, Mater.

Res.

Bull.

47

(2012)

4271–4277.

doi:https://doi.org/10.1016/j.materresbull.2012.09.019. [14] O.V. Klimov, A.V. Pashigreva, K.A. Leonova, G.A. Bukhtiyarova, S.V. Budukva, A.S. Noskov, Bimetallic Co-Mo-complexes with optimal localization on the support surface: A

way for highly active hydrodesulfurization catalysts preparation for different petroleum distillates, 2010. doi:10.1016/S0167-2991(10)75096-5. [15] John F. Moulder, Handbook of X-ray Photoelectron Spectroscopy, Physical Electronics Division, Perkin-Elmer Corporation, 1992. [16] J.H. Scofield, Hartree-Slater subshell photoionization cross-sections at 1254 and 1487 eV, J.

Electron

Spectros.

Relat.

Phenomena.

8

129–137.

of

doi:https://doi.org/10.1016/0368-2048(76)80015-1.

(1976)

ro

[17] E. Baumgarten, R. Wagner, C. Lentes-Wagner, Quantitative determination of hydroxyl groups on alumina by IR spectroscopy, Anal. Bioanal. Chem. 334 (1989) 246–251.

-p

doi:10.1007/BF00497251.

re

[18] G. Busca, V. Lorenzelli, G. Ramis, R.J. Willey, Surface sites on spinel-type and corundumtype metal oxide powders, Langmuir. 9 (1993) 1492–1499. doi:10.1021/la00030a012.

lP

[19] C. Morterra, G. Magnacca, A case study: surface chemistry and surface structure of catalytic aluminas, as studied by vibrational spectroscopy of adsorbed species, Catal. Today. 27

ur na

(1996) 497–532. doi:https://doi.org/10.1016/0920-5861(95)00163-8. [20] A.B.M. Saad, V.A. Ivanov, J.C. Lavalley, P. Nortier, F. Luck, Comparative study of the effects of sodium impurity and amorphisation on the Lewis acidity of γ- alumina, Appl. Catal. A Gen. 94 (1993) 71–83. doi:https://doi.org/10.1016/0926-860X(93)80046-S.

Jo

[21] P. Nortier, P. Fourre, A.B.M. Saad, O. Saur, J.C. Lavalley, Effects of crystallinity and morphology on the surface properties ofalumina, Appl. Catal. 61 (1990) 141–160. doi:https://doi.org/10.1016/S0166-9834(00)82140-5.

[22] H. Knözinger, P. Ratnasamy, Catalytic Aluminas: Surface Models and Characterization of Surface Sites, Catal. Rev. 17 (1978) 31–70. doi:10.1080/03602457808080878. [23] H. Jeziorowski, H. Knoezinger, Raman and ultraviolet spectroscopic characterization of

molybdena

on

alumina

catalysts,

J.

Phys.

Chem.

83

(1979)

1166–1173.

doi:10.1021/j100472a012. [24] M. Fournier, C. Louis, M. Che, P. Chaquin, D. Masure, Polyoxometallates as models for oxide catalysts: Part I. An UV-visible reflectance study of polyoxomolybdates: Influence of polyhedra arrangement on the electronic transitions and comparison with supported molybdenum catalysts, J. Catal. 119 (1989) 400–414. doi:https://doi.org/10.1016/0021-

of

9517(89)90170-X.

ro

[25] Z. Boukha, C. Jiménez-González, B. de Rivas, J.R. González-Velasco, J.I. Gutiérrez-Ortiz, R. López-Fonseca, Synthesis, characterisation and performance evaluation of spinel-derived

-p

Ni/Al2O3 catalysts for various methane reforming reactions, Appl. Catal. B Environ. 158–

re

159 (2014) 190–201. doi:https://doi.org/10.1016/j.apcatb.2014.04.014. [26] E. Heracleous, A.F. Lee, K. Wilson, A.A. Lemonidou, Investigation of Ni-based alumina-

characterization

and

lP

supported catalysts for the oxidative dehydrogenation of ethane to ethylene: structural reactivity

studies,

J.

Catal.

231

(2005)

159–171.

ur na

doi:https://doi.org/10.1016/j.jcat.2005.01.015. [27] M. Jitianu, A. Jitianu, M. Zaharescu, D. Crisan, R. Marchidan, IR structural evidence of hydrotalcites

derived

oxidic

forms,

Vib.

Spectrosc.

22

(2000)

75–86.

doi:https://doi.org/10.1016/S0924-2031(99)00067-3.

Jo

[28] A. Cimino, M. Lo Jacono, M. Schiavello, Structural, magnetic, and optical properties of nickel oxide supported on .eta.- and .gamma.-aluminas, J. Phys. Chem. 75 (1971) 1044– 1050. doi:10.1021/j100678a005.

[29] V.L.S. Teixeira da Silva, R. Frety, M. Schmal, Activation and Regeneration of a NiMo/A12O3 Hydrotreatment Catalyst, Ind. Eng. Chem. Res. 33 (1994) 1692–1699. [30] S. Chaturvedi, J.A. Rodriguez, J.L. Brito, Characterization of pure and sulfided NiMoO4

catalysts using synchrotron-based X-ray absorption spectroscopy (XAS) and temperatureprogrammed

reduction

(TPR),

Catal.

Letters.

51

(1998)

85–93.

doi:10.1023/A:1019089002041. [31] J.M. Britto, M. V. Reboucas, I. Bessa, S.A. Braskem, Troubleshoot silicon contamination on catalysts, Hydrocarb. Process. (2010) 65–69. [32] G. Garbarino, P. Riani, A. Infantes-Molina, E. Rodríguez-Castellón, G. Busca, On the

of

detectability limits of nickel species on NiO/γ-Al2O3 catalytic materials, Appl. Catal. A Gen.

ro

525 (2016) 180–189. doi:https://doi.org/10.1016/j.apcata.2016.07.017.

[33] S. Eijsbouts, Chapter 14. Hydrotreating Catalysts, in: Synth. Solid Catal., 2009: pp. 301–

-p

328.

re

[34] B. Guichard, M. Roy-Auberger, E. Devers, C. Pichon, C. Legens, P. Lecour, Influence of the promoter’s nature (nickel or cobalt) on the active phases ‘Ni(Co)MoS’ modifications

lP

during deactivation in HDS of diesel fuel, Catal. Today. 149 (2010) 2–10. doi:https://doi.org/10.1016/j.cattod.2009.03.016.

ur na

[35] J. Mérida-Robles, E. Rodrı́guez-Castellón, A. Jiménez-López, Characterization of Ni, Mo and Ni–Mo catalysts supported on alumina-pillared α-zirconium phosphate and reactivity for the thiophene HDS reaction, J. Mol. Catal. A Chem. 145 (1999) 169–181. doi:10.1016/S1381-1169(99)00048-5. Q. Gao, T.N.K. Ofosu, S.-G. Ma, V.G. Komvokis, C.T. Williams, K. Segawa, Catalyst

Jo

[36]

development for ultra-deep hydrodesulfurization (HDS) of dibenzothiophenes. I: Effects of Ni promotion in molybdenum-based catalysts, Catal. Today. 164 (2011) 538–543. doi:10.1016/j.cattod.2010.10.016.

[37] J. Mazurelle, C. Lamonier, C. Lancelot, E. Payen, C. Pichon, D. Guillaume, Use of the cobalt salt of the heteropolyanion [Co2Mo10O38H4]6− for the preparation of CoMo HDS catalysts

supported

on

Al2O3,

TiO2

and

ZrO2,

Catal.

Today.

130

(2008)

41–49.

doi:10.1016/j.cattod.2007.07.008. [38] G. Camino, S.M. Lomakin, M. Lageard, Thermal polydimethylsiloxane degradation. Part 2. The

degradation

mechanisms,

Polymer

(Guildf).

43

(2002)

2011–2015.

doi:https://doi.org/10.1016/S0032-3861(01)00785-6. [39] G. Camino, S.. Lomakin, M. Lazzari, Polydimethylsiloxane thermal degradation Part 1. aspects,

Polymer

(Guildf).

42

(2001)

2395–2402.

doi:10.1016/S0032-

of

Kinetic

ro

3861(00)00652-2.

[40] E. Finocchio, G. Garuti, M. Baldi, G. Busca, Decomposition of hexamethylcyclotrisiloxane solid

oxides,

Chemosphere.

72

-p

over

(2008)

1659–1663.

re

doi:https://doi.org/10.1016/j.chemosphere.2008.05.032.

[41] A. Villarreala, G. Garbarino, P. Riani, A. Gutiérrez-Alejandre, J. Ramírez, G. Busca,

lP

Influence of incorporating a small amount of silica on the catalytic performance of a MoO3/Al2O3 catalyst in ethanol oxidative dehydrogenation, J. Appl. Res. Technol. 16 (2018)

ur na

484–497.

[42] O.V. Klimov, K.A. Nadeina, P.P. Dik, G.I. Koryakina, V.Y. Pereyma, M.O. Kazakov, S.V. Budukva, E.Y. Gerasimov, I.P. Prosvirin, D.I. Kochubey, A.S. Noskov, CoNiMo/Al2O3 catalysts for deep hydrotreatment of vacuum gasoil, Catal. Today. 271 (2016) 56–63.

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doi:10.1016/j.cattod.2015.11.004.

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Figure 1 – SEM (left) and HRTEM (right) images of alumina precursors

Figure 2 – XRD patterns of alumina precursors

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Figure 3 – Pore size distributions of supports and catalysts in the oxide form

Figure 4 – IR spectra in the OH region of alumina supports (Al-x) and corresponding NiMo-

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catalysts in oxide states (NiMo/Al-x) after activation in vacuum at 550°C.

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Figure 5 - UV–vis DR spectra of NiMo/Al2O3 catalysts with different supports: (1) NiMo/Al-1, (2) NiMo/Al-2, (3) NiMo/Al-3.

Figure 6 – Catalytic properties in hydrotreating of diesel fraction containing 166 ppm of silicon: a) Silicon sorption capacity vs concentration of OH groups and surface area of supports, b) Dependence of sulfur conversion at the start(end)-of-run on surface area of catalysts

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Figure7 – Pore size distributions of fresh catalysts (NiMo/Al-x) and catalysts after reaction

ro

in the oxide form (NiMo/Al-xD)

Table 1 – Designation of alumina precursors, supports and catalysts Supports

Catalysts

AP(TGA)

Al-1

NiMo/Al-1

AP(PR)

Al-2

NiMo/Al-2

AP(Autoclave)

Al-3

re

-p

Alumina precursor

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NiMo/Al-3

Table 2 – XRD data for alumina precursors and supports Alumina precursors

AP(TGA) AP(PR)

Phase

a, Å

b, Å

c, Å

, nm

Pseudoboehmite*

3.698(2)

12.28(1)

2.863(1)

5.0

Pseudoboehmite*

3.684(3)

12.30(2)

2.824(3)

2.5

Dawsonite**

6.650(4)

11.92(7)

5.716(3)

6.0

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Sample

AP(Autoclave)

Supports

Phase

a, Ǻ

, nm

Al-1

γ-Al2O3

7.91(1)

3.5

Al-2

γ-Al2O3

7.92(1)

2.0

Al-3

γ-Al2O3

7.93(1)

1.6

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Sample

* Boehmite AlO(OH), PDF#00-021-1307 (Space group: Amam, a=3.700Å, b=12.22Å, c=2.868Å)

** Dawsonite NH4Al(OH)2CO3, PDF#01-076-1923 (Space group: Cmcm, a=6.618Å, b=11.944Å, c=5.724Å) Table 3 – Textural properties of calcined supports and catalysts before reaction Supports

Catalysts Sample

3

2 S, m /g Vpore, cm /g Dpore, nm

241

0.6

10.2

NiMo/Al-1

209

Al-2

295

0.8

11.0

NiMo/Al-2

262

Al-3

414

1.0

9.8

NiMo/Al-3

397

0.6

10.5

0.7

11.1

0.9

9.0

ro

Al-1

of

3

2 Sample S, m /g Vpore, cm /g Dpore, nm

Table 4 – Concentration of OH groups of supports and catalysts in oxide state OH`s/cm2

Al-1

1366

3.4

Al-2

1320

Al-3

1038

OH groups concentration -mol/g

OH`s/cm2

NiMo/Al-1

685

2

2.7

NiMo/Al-2

560

1.3

1.5

NiMo/Al-3

283

0.4

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-mol/g

Catalyst

-p

OH groups concentration

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Support

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Table 5 – Morphology of active component particles Sample

Stacking number

Slab length, nm

Number of slabs per 1000 nm2 of a catalyst

NiMo/Al-1

2.2

5.3

46

NiMo/Al-2

2.6

3.9

54

Jo

2.8 4.0 52 NiMo/Al-3 Table 6 - Binding energies and content of Mo and Ni states based on decomposition of the respective XP spectra Sample

Mo3d

Ni2p

Mo4+

Mo5+

Mo6+

NiS

NiMoS

Ni2+

NiMo/Al-1

228.9

853.9

71

17

12

11

42

47

NiMo/Al-2

229.0

853.9

82

10

8

18

45

37

NiMo/Al-3

229.0

853.9

78

13

9

13

47

40

Table 7 – CHNS analysis and textural properties of the catalysts (calcined) after reaction Sample

Textural properties

CHNS analysis 2

3

Н, wt%

N, wt%

S, wt%

S, m /g

V, cm /g

D, nm

NiMo/Al-1

8.8

4.0

0.1

3.0

170

0.3

8.1

NiMo/Al-2

5.9

2.5

0.2

3.3

201

0.5

8.9

NiMo/Al-3

4.4

1.6

0.2

3.9

201

0.5

9.2

Jo

ur na

lP

re

-p

ro

of

С, wt%