Search

The structure of γ-Al 2 O 3 , the most important catalyst support, is still under discussion; especially the positions of the Al3+cations and vacancies are debated. One model proposes that γ-Al 2 O 3 consists of irregularly stacked nanocrystals with all Al3+ cations occupying spinel positions, another that some Al3+ cations occupy non-spinel positions, while a third model proposes that γ-Al 2 O 3 does not have a spinel structure. 17O and 27Al NMR measurements showed that 62.5–65% of the cations are at octahedral positions, in agreement with a spinel structure model, with DFT calculations, and with isostructural γ - Fe 2 O 3 , but in disagreement with the non-spinel model. A reconsideration of the non-spinel model is, therefore, strongly recommended. In agreement with DFT calculations, TEM measurements showed that strong reconstruction of the surface of γ-Al 2 O 3 occurs. The (1 1 0) surface of γ-Al 2 O 3 is not atomically flat but forms nanoscale (1 1 1) facets, indicating that (1 0 0) and (1 1 1) facets have the lowest energy. [ABSTRACT FROM AUTHOR]

Ein Nicht‐Spinellmodell für die Struktur von γ‐Al2O3, bei dem sich 25 % der Al3+‐Kationen an tetraedrischen Positionen befinden, hat viel Interesse erregt. 17O‐NMR‐Messungen und – erst kürzlich – 27Al‐NMR‐Messungen haben aber gezeigt, dass sich erheblich mehr Al3+‐Kationen an tetraedrischen Positionen befinden. Dies bedeutet, dass sich die Al3+‐Fehlstellen in γ‐Al2O3 nicht an tetraedrischen, sondern an oktaedrischen Positionen befinden, wie beim isostrukturellen γ‐Fe2O3 und in Übereinstimmung mit dichtefunktionaltheoretischen Voraussagen. Dies hat Folgen für die Struktur der γ‐Al2O3‐Oberfläche und für die Katalyse. [ABSTRACT FROM AUTHOR]

A non‐spinel model for the structure of γ‐Al2O3, with 25 % of the Al3+ cations at tetrahedral positions, has been the subject of wide interest. However, 17O NMR measurements and, more recently, 27Al NMR measurements have shown that there are considerably more Al3+ cations at tetrahedral positions. This means that the Al3+ vacancies in γ‐Al2O3 are not at tetrahedral but at octahedral positions, as in isostructural γ‐Fe2O3 and in accordance with density functional theory predictions. This has consequences with regard to the surface structure of γ‐Al2O3, and thus, for catalysis. [ABSTRACT FROM AUTHOR]

[Display omitted] • Mixtures of Ni(NO 3) 2 and H 3 PO 3 on SiO 2 and B 2 O 3 -Al 2 O 3 were used as precursors. • Reduction of the precursors yielded ultrasmall Ni 2 P particles (ca. 3 ∼ 5 nm). • Ni 2 P was formed on SiO 2 and B 2 O 3 -Al 2 O 3 at P/Ni ratios of 0.8 and 0.7, respectively. • Ultrasmall Ni 2 P particles on SiO 2 were as active as large Ni 2 P particles. • The strong Ni 2 P-support interaction inhibited the activity of Ni 2 P/B 2 O 3 -Al 2 O 3. Ultrasmall Ni 2 P nanoparticles with dimensions around 3 ∼ 5 nm supported on SiO 2 (Ni-P/SiO 2) and an Al 2 O 3 -B 2 O 3 mixed oxide (Ni-P/AB) were prepared by a temperature-programmed reduction method using mixtures of Ni(NO 3) 2 and H 3 PO 3 as precursors. The minimum P/Ni ratios of the precursors needed for the formation of phase-pure Ni 2 P on SiO 2 and Al 2 O 3 -B 2 O 3 were as low as 0.8 and 0.7, respectively. The introduction of B 2 O 3 to γ-Al 2 O 3 inhibited the formation of AlPO 4 during the reduction process. For such small particles, the effect of Ni 2 P-support interaction became significant, resulting in different properties of the Ni-P/SiO 2 and Ni-P/AB catalysts as well as different performances in the hydrodesulfurization of dibenzothiophene. The ultrasmall Ni 2 P nanoparticles in the Ni-P/SiO 2 catalysts that possess weak Ni 2 P-support interaction were as active as large Ni 2 P particles on SiO 2 and a macro-mesoporous Al 2 O 3. These catalysts were one order of magnitude more active than the Ni-P/AB catalysts with strong Ni 2 P-support interaction. [ABSTRACT FROM AUTHOR]

The preparation, characterization, and catalytic activity of supported metal phosphides are reviewed. Reduction of metal compounds together with phosphate is a convenient method to prepare metal phosphides, but requires high temperature. Reduction with phosphite, hypophosphite, or phosphine and the plasma reduction of phosphate can be carried out at lower temperatures, which leads to smaller metal phosphide particles and more active catalysts. Organometallic routes allow the separate synthesis of metal phosphide nanoparticles, which have to be added to the support in a second step. LEED, STM, XPS, and DFT studies have shown that the surfaces of NiP reconstruct to P-rich surfaces. The investigation of metal phosphides as catalysts for hydrotreating reactions continues to be a topic of considerable research with recent advances realized in using bimetallic and noble metal phosphides to achieve high activities and tailored selectivities. Finally, hydrodeoxygenation catalysis over metal phosphides is a growing area of research given the need to develop catalysts for upgrading biomass to transportation fuels. Graphical Abstract: [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Abstract: The mechanism and kinetics of the hydrodesulfurization (HDS) of dibenzothiophene (DBT) and its hydrogenated intermediates tetrahydro- and hexahydro-dibenzothiophene (THDBT and HHDBT) over Co–MoS2/γ–Al2O3 were studied. The desulfurization of DBT was faster than that of THDBT and HHDBT. Cyclohexenylbenzene and cyclohexylbenzene were observed as primary products in the HDS of THDBT, indicating that THDBT was desulfurized by hydrogenolysis of the C–S bonds. Desulfurization of HHDBT occurred mainly by dehydrogenation to THDBT and subsequent desulfurization of THDBT. The addition of H2S during HDS strongly inhibited the desulfurization of DBT and THDBT, while the addition of 2-methylpiperidine inhibited their hydrogenation. Direct desulfurization probably takes place on the metal edges of the Co–MoS2 crystallites, while hydrogenation takes place at brim sites near the edges of the MoS2 plane and on those Co sites that are located at the metal edge. [Copyright &y& Elsevier]

The rate constants of all reaction steps in the hydrodesulfurization (HDS) of dibenzothiophene (DBT), 4,6-dimethyldibenzothiophene (DMDBT), and their tetra- and hexahydro intermediates TH(DM)DBT and HH(DM)DBT over Ni–MoS2/γ-Al2O3 were determined. DBT, THDBT, DMDBT, and THDMDBT underwent desulfurization by hydrogenolysis of both C–S bonds, while HHDBT and HHDMDBT underwent desulfurization by cleavage of the aryl C–S bond by hydrogenolysis, followed by cleavage of the cycloalkyl C–S bond by elimination as well as by hydrogenolysis. Ni promoted the C–S bond breakage of DBT, THDBT, and HHDBT strongly, but promoted the (de)hydrogenation only weakly. The methyl groups suppressed the desulfurization in the order DMDBT>THDMDBT>HHDMDBT and promoted hydrogenation. These different degrees of steric hindrance are due to the hydrogenation of a phenyl ring, which makes the THDBT and HHDBT rings flexible. H2S strongly inhibited the desulfurization rates in the order (DM)DBT>TH(DM)DBT>HH(DM)DBT, but inhibited the (de)hydrogenation rates only slightly. 2-Methylpiperidine inhibited the hydrogenation of all molecules. [Copyright &y& Elsevier]

Abstract: A combination of 27Al magic-angle spinning (MAS)/multiple-quantum (MQ) MAS, and 27Al–{14N} TRAnsfer of Population in DOuble-Resonance (TRAPDOR) nuclear magnetic resonance (NMR) was used to study aluminium environments in zeolite ZSM-5. 27Al–{14N} TRAPDOR experiments, in combination with 14N NMR were employed to show that the two tetrahedral peaks observed in the 27Al MAS/3Q-MAS spectra of as-synthesized ZSM-5 are due to aluminium atoms occupying crystallographically inequivalent T-sites. A 13C–{27Al} TRAPDOR experiment was used to study the template, tetrapropyl ammonium bromide (TPABr), in the three-dimensional pore system of ZSM-5. The inequivalency of the methyl groups of TPA was observed in the 13C–{27Al} TRAPDOR spectra of as-synthesized ZSM-5 and the motion of the methyl end of the propyl chain appeared to be more restricted in the sinusoidal channel than in the straight channel. [Copyright &y& Elsevier]

Abstract: Three methods were investigated to synthesize mesoporous mordenite. XRD, N2 physisorption, SEM, and TEM showed that the mordenite obtained by acid leaching followed by base leaching of a conventional mordenite is a crystalline mesoporous material with MOR framework. The higher diffusivity of toluene indicated that mesopores benefited molecule transport through the zeolite crystal. Measurement of the number of Brønsted acid sites by n-propylamine TPD and 27Al NMR showed that the mesoporous mordenite had less extra-framework aluminum and a large number of Brønsted acid sites, while the isomerization of 2-methyl-2-pentene indicated that the mesoporous mordenite possessed a higher reactivity than conventional mordenite. The mesoporous mordenite had a much higher catalytic activity than conventional mordenite in the alkylation of benzene with benzyl alcohol. At 353 K and under atmospheric pressure, the conversion of benzyl alcohol over hierarchical mesoporous mordenite was 100% in 3 h, whereas the conversion over conventional mordenite was less than 2%. Synthesis of mesoporous mordenite with amphiphilic organosilane and carbon as secondary template did not give real mesoporous mordenite. [Copyright &y& Elsevier]

Abstract: The hydrodesulfurization (HDS) of benzothiophene (BT) and dihydrobenzothiophene (DHBT) was studied over a sulfided Mo/γ-Al2O3 catalyst at 5MPa and 280 and 300°C. In the absence of H2S, benzothiophene reacted by hydrogenation to dihydrobenzothiophene and by hydrogenolysis to ethylbenzene (EB), and dihydrobenzothiophene reacted by hydrogenolysis to ethylbenzene. H2S inhibited both hydrogenation and hydrogenolysis, but the latter much more strongly. The reverse inhibition was observed for 2-methylpiperidine (MPi). In the presence of H2S and/or 2-methylpiperidine, dihydrobenzothiophene reacted to ethylbenzene as well as by total hydrogenation to octahydrobenzothiophene, and on to ethylcyclohexenes and ethylcyclohexane. Dihydrobenzothiophene did not react back to benzothiophene at and below 300°C, while the equivalent tetrahydrodibenzothiophene reacted fast to an equilibrium with tetrahydrodibenzothiophene, due to stabilization of the vinylic bond by the alkyl groups. The observed products and kinetic results were explained by a model in which the Cere mainly broken by hydrogenolysis. [Copyright &y& Elsevier]

The hydrodenitrogenation of 2-methylpiperidine and 2-methylpyrrolidine was studied over sulfided NiMo/γ-Al2O3 in the presence of dialkylamines, alkylamines, and alkenes to determine why N-pentylpiperidine is formed in the hydrodenitrogenation of pyridine. N-alkylated 2-methylpiperidine and 2-methylpyrrolidine were only formed as primary products by reaction with alkylamines and not by reaction with 2-methylpiperidine and 2-methylpyrrolidine, or by reaction with an alkene. This indicates that, in the hydrodenitrogenation of pyridine, N-pentylpiperidine is formed by the reaction of the secondary intermediate pentylamine with the primary intermediate piperidine, and not by reaction of two primary piperidine intermediates or by reaction of pentene, one of the final products, with piperidine. [ABSTRACT FROM AUTHOR]

Two intermediates of dibenzothiophene (DBT)—tetrahydro-DBT (THDBT) and hexahydro-DBT (HHDBT)—were synthesized, and their hydrodesulfurization (HDS) mechanism was investigated over Mo/γ-Al2O3 at 300–340 °C and 5 MPa in the absence and presence of H2S and 2-methylpiperidine. The rate constants of all steps in the kinetic network of the HDS of DBT were measured. THDBT underwent desulfurization by hydrogenolysis to 1-phenylcyclohexene, followed by hydrogenation to phenylcyclohexane. The desulfurization of HHDBT occurred by hydrogenolysis of the aryl Cd then cleavage of the cycloalkyl C the resulting thiol by elimination to 1-phenylcyclohexene and by hydrogenolysis to phenylcyclohexane. H2S strongly inhibited the desulfurization of all three molecules but did not inhibit (de)hydrogenation. 2-Methylpiperidine also had a strong inhibitory effect, especially on (de)hydrogenation and, to a lesser extent, on desulfurization. The order of the inhibition of DBT, THDBT, and HHDBT was explained by the adsorption constants of these three molecules. [Copyright &y& Elsevier]

Abstract: The N2O decomposition activity of the Fe-ZSM-5 catalysts, prepared by chemical vapor deposition (CVD) and aqueous ion exchange (IE), was studied after steaming and high temperature treatment at 1218K (HT) and compared with the activity of the corresponding non-steamed catalysts after pretreatment at 873K. FTIR spectra showed that dehydroxylation and/or dealumination took place during steaming and high temperature treatment of the catalysts, which leads to the formation of oxygen vacancies (i.e. lattice defect). These lattice defects leads to a change in electronic properties of the iron sites, which are associated with electron withdrawing Al Lewis centers. The iron sites in close proximity of defects are responsible for the initial higher N2O decomposition (transient activity) of the steamed and HT catalysts. The increase in steady-state activity over steamed and HT catalysts can be mainly attributed to an increase in the number of active sites created by autoreduction of the iron centers during steaming and high temperature treatment. The above-mentioned trends are valid for both CVD and IE samples. [Copyright &y& Elsevier]

Abstract: Hierarchical mesoporous ZSM-5 (M-ZSM-5) was prepared using amphiphilic organosilane as a mesoporous structure-directing agent, and characterized by XRD, N2 sorption, 27Al and 29Si MAS NMR spectroscopy, and 2-methyl-2-pentene isomerization. The XRD and N2 sorption data indicate that M-ZSM-5 is a mesoporous material with ZSM-5 framework. 29Si MAS NMR spectroscopy revealed that M-ZSM-5 was highly crystalline, like conventional ZSM-5. 27Al MAS NMR spectroscopy showed that most of the aluminum atoms were in tetrahedral coordination and 2-methyl-2-pentene isomerization exhibited that M-ZSM-5 possessed strong acidity similar to conventional ZSM-5. The benzylation reaction of benzene by benzyl alcohol was used to evaluate the catalytic reactivity of the hierarchical zeolite catalyst in Friedel-Craft alkylations. The results showed that M-ZSM-5 had a much higher catalytic activity than conventional ZSM-5. The apparent rate constant for M-ZSM-5 is 23 times larger than that for conventional ZSM-5. Moreover, the catalyst could be reused and maintain the initial activity even after three cycles. These results indicate that hierarchical zeolites have potential application in Friedel-Crafts alkylations, especially of large molecules. [Copyright &y& Elsevier]

Pyridine and piperidine inhibited the hydrodesulfurization of 4,6-dimethyldibenzothiophene (4,6-DM-DBT) over alumina-supported Pt, Pd, and Pt–Pd catalysts. The Pd catalyst was least sensitive and the Pt–Pd catalysts were most sensitive to the nitrogen-containing compounds. Pyridine was a stronger inhibitor than piperidine at low initial pressure, but the reverse was true at high initial pressure. Hydrogenation of the tetrahydro to the hexahydro and on to the perhydro sulfur-containing intermediate as well as the removal of sulfur from these intermediates was slowed down by piperidine and pyridine. The hydrogenation pathway in the hydrodesulfurization of 4,6-DM-DBT was inhibited much more than the direct desulfurization pathway. The hydrogenation of the desulfurized products 3,3′-dimethylcyclohexylbenzene and 3,3′-dimethylbiphenyl over the Pt–Pd catalysts was suppressed by piperidine and pyridine. Piperidine and pyridine substantially decrease the ability of noble metal particles to convert refractory molecules like 4,6-DM-DBT and diminish the advantage of bimetallic Pt–Pd over monometallic Pt or Pd catalysts. [ABSTRACT FROM AUTHOR]

Abstract: Gold nanoclusters supported on γ-Al2O3 were more active and selective than platinum nanoclusters in the high-pressure liquid-phase hydrogenation of cinnamaldehyde to cinnamylalcohol, while in the hydrogenation of cyclohexene gold was less active than platinum. The differences in catalytic performance are ascribed to the weaker interaction of gold with the reactants and products compared to platinum. Gold clusters with a diameter below 2nm are essential to obtain a high activity and selectivity in the hydrogenation of cinnamaldehyde. The size dependence of the selectivity originates from the stronger dependence of the Cnation rate on cluster size compared to the Cnation rate. Small clusters exhibit an enhanced π backbonding, which favors Cion over Cion. [Copyright &y& Elsevier]

Abstract: The activities and selectivities of Pt, Pd, and Pt–Pd supported on amorphous silica–alumina (ASA) in the hydrodesulfurization (HDS) of 4,6-dimethyldibenzothiophene (4,6-DM-DBT) were investigated. The ASA-supported catalysts had much higher activities than alumina-supported catalysts, due to the creation of electron-deficient metal particles. Pd had a high hydrogenation activity for 4,6-DM-DBT, but the removal of sulfur from 4,6-DM-DBT and its HDS intermediates occurred faster over Pt than over Pd. Comparison of two Pt/ASA catalysts with different Pt loadings showed that the metal dispersion strongly influenced the product selectivity. Larger metal particles led to relatively faster hydrogenation and slower C–S bond breaking. Bimetallic Pt–Pd catalysts were much more active than the monometallic constituents, indicating that the metal particles were alloyed. Acid-catalyzed cracking and isomerization occurred especially over Pt/ASA. [Copyright &y& Elsevier]

Abstract: The breaking of the C C2H5SH on the catalytically active (100) edge of 2H-MoS2 was studied by means of density functional theory. Two reactions of C2H5SH were investigated: hydrogenolysis to ethane and elimination to ethane, with H2S as second product in both cases. The adsorption geometry, involving a hydrogen atom of the methyl group of C2H5SH, conducted reactions to more strongly bound surface intermediate states. The Ceaking resulting in ethane formation proceeds with a lower energy barrier than in ethene formation when the energy of the barriers for desorption of the products from the surface is compared relative to the molecularly adsorbed C2H5SH state. [Copyright &y& Elsevier]

Abstract: The activity and selectivity of alumina-supported Pt, Pd, and Pt-Pd in the hydrodesulfurization (HDS) of dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DM-DBT) were investigated, and all final, hydrocarbon products and partially hydrogenated intermediates were analyzed. Pd had a high activity in the hydrogenation of 4,6-DM-DBT, whereas the removal of sulfur from DBT and 4,6-DM-DBT and their intermediates occurred faster over Pt than over Pd. Bimetallic Pt-Pd catalysts were much more active than the combination of their monometallic constituents, proving a chemical synergism between the noble metals and the presence of alloyed particles. New sites with high hydrogenation activity explain why the hydrogenation of the products -dimethylcyclohexylbenzyl and -dimethylbiphenyl in the HDS of 4,6-DM-DBT, as well as the hydrogenation of -dimethylbiphenyl in the presence of DBT, were significant only over the Pt-Pd catalysts. In contrast to the metal sulfide catalysts, the hydrogenation route over the noble metal catalysts was faster for 4,6-DM-DBT than for DBT, which almost compensated for the loss of activity via the desulfurization pathway. [Copyright &y& Elsevier]

Abstract: 2-Methylpyridine and 2-methylpiperidine strongly inhibited the hydrogenation pathway in the hydrodesulfurization (HDS) of dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene over sulfided NiMo/γ-Al2O3, CoMo/γ-Al2O3, and Mo/γ-Al2O3 catalysts at 340 °C, 4.8 MPa H2, and 35 kPa H2S. The direct desulfurization (DDS) pathway was inhibited by both amines over the Mo and CoMo catalysts as well, but the NiMo catalyst showed a promotion effect in the HDS of DBT at 300 °C and at low partial amine pressure. Experiments with other amines showed that only the more basic and stable heterocyclic amines promoted the DDS pathway of DBT over NiMo. This promoting effect of amines on NiMo is explained by the special location of the Ni promoter atoms, on the metal edge of the MoS2 particles with low sulfur coverage. The perpendicular adsorption of amines hinders especially the π adsorption of DBT and 4,6-dimethyldibenzothiophene and thus the hydrogenation pathway, whereas the filling of sulfur vacancies by H2S inhibits the DDS pathway. [Copyright &y& Elsevier]

Abstract: Mesoporous materials were synthesized from solutions containing ZSM-5 precursors in the presence of a micellar template (CTACl). The effect of different parameters like aluminum content, aging conditions and hydrothermal treatment conditions on the properties of the final materials was investigated by dynamic light scattering (DLS), N2 physisorption, XRD, 27Al MAS-NMR, TEM and IR. In addition two catalytic test reactions (cracking of isopropylbenzene and 1,3,5-triisopropylbenzene) and acidity measurements via pyridine adsorption were carried out. We observed a transition of the initially formed mesoporous structure containing protozeolitic seeds to a zeolitic phase during hydrothermal treatment. The rate of zeolitization strongly depended on the conditions of the aging period and on the composition of the synthesis solution: the more protozeolitic seeds were formed during the aging procedure the faster the zeolitization. Catalytic test reactions and acidity measurements showed that the XRD amorphous materials with protozeolitic seeds in the mesoporous structure are more active and more acidic than mesoporous materials prepared without ZSM-5 precursors, but far less active and acidic than zeolites. A combination of high activity and accessibility of most active sites was found for samples containing small zeolite crystals. [Copyright &y& Elsevier]

Abstract: The surface of mesoporous M41S silica material was functionalized with 3-aminopropyl and methyl groups and with mixtures of both. The ratio of the two groups on the silica surface could be adjusted by changing the molar ratio of the corresponding alkoxysilanes in the reaction mixture. The fraction of 3-aminopropyl on the surface was always larger than in the functionalization reaction mixture. Moreover, functionalization with the 3-aminopropyl group or with mixtures of the 3-aminopropyl and methyl groups led to higher molar coverages of the silica surface than functionalization with the methyl group alone. One reason for these effects is that the amino group base-catalyzes the hydrolysis of the alkoxysilanes and thereby enhances the reaction of the silanes with the silica surface. The 3-aminopropyl/methyl—functionalized materials showed a very high stability against hydrolysis in boiling water because the siloxane bonds of the silica framework were protected by the organic moieties. [Copyright &y& Elsevier]

Abstract: The hydrodesulfurization (HDS) reaction network of 4,6-dimethyl-dibenzothiophene (4,6-DM-DBT) was investigated over Pd/γ-Al2O3 at 300 °C and 5 MPa. 4,6-DM-DBT reacts almost exclusively through the hydrogenation pathway, with only 1% reacting via the direct desulfurization route. No significant further hydrogenation of the desulfurized compounds occurred. Three (partially) hydrogenated intermediates of the HYD pathway were observed: 4,6-dimethyl-1,2,3,4-tetrahydro-dibenzothiophene (4,6-DM-TH-DBT), 4,6-dimethyl-hexahydro-dibenzothiophene (4,6-DM-HH-DBT), and 4,6-dimethyl-perhydro-dibenzothiophene (4,6-DM-PH-DBT). These three intermediates were synthesized and their HDS studied. Hydrogenation and dehydrogenation reactions occurred readily between the intermediates. 4,6-DM-TH-DBT and 4,6-DM-HH-DBT interconverted rapidly and were in equilibrium in the HDS of 4,6-DM-DBT and close to equilibrium in the experiments starting from the intermediates. The partly saturated 4,6-DM-TH-DBT and 4,6-DM-HH-DBT intermediates could be desulfurized much easier than 4,6-DM-DBT. This shows that the molecule planarity must be removed to weaken the steric hindrance caused by the methyl groups and to provide better access to the sulfur atom. Temperature had a stronger promotional effect on desulfurization than on hydrogenation and enhanced sulfur removal from the reaction intermediates. [Copyright &y& Elsevier]

Abstract: The effect of triethylene glycol on phosphate-doped Co(Zn)Mo catalysts supported on γ-Al2O3 was studied by means of 31P magic angle spinning nuclear magnetic resonance (MAS NMR) and Raman spectroscopy. 31P MAS NMR experiments, carried out on ZnMo/γ-Al2O3 doped with phosphate and triethylene glycol, suggested that the species that formed in the impregnation solution decomposed to monophosphate and an Anderson-type aluminum molybdate species on contact with the support. The presence of triethylene glycol favored the formation of polyphosphate and heteropolymolybdate species, but no was detected. The use of paramagnetic cobalt instead of zinc cations had a paramagnetic effect on the 31P-NMR signal of the , indicating that the species are bound to the promoter atoms. The close proximity of the promoter and Mo allows a better decoration of MoS2 and improves the catalytic activity. [Copyright &y& Elsevier]

Abstract: The sulfidation of CoMo/γ-Al2O3 catalysts prepared in the presence of phosphate and triethylene glycol (TEG) was studied by in situ Mo and Co K-edge QEXAFS. In a classic CoMo catalyst, prepared without phosphate and TEG, MoS2 is formed through intermediate MoS3-like species. In the presence of phosphate, alone or with TEG, this intermediate species is not observed and the molybdenum is directly sulfided to MoS2. The additives increased the sulfidation degree of molybdenum with respect to the standard catalyst, leading to a better sulfur saturation of the MoS2 slabs and to a higher static order. Co K-edged QEXAFS showed that the sulfidation rate of Co increases in the presence of phosphate and TEG. [Copyright &y& Elsevier]

Abstract: γ-Al2O3-supported CoMo catalysts doped with phosphate and prepared in the presence of triethylene glycol (TEG), ethylene glycol (EG), and triethylene dimethyl ether (TEG-DME) were tested in the hydrodesulfurization (HDS) of thiophene. The catalyst containing TEG showed a higher catalytic activity than the catalyst prepared without TEG. Laser Raman spectroscopy and EXAFS demonstrated that the impregnation solution containing the metal salts and phosphoric acid contained HP2Mo5 diphosphopentamolybdate and that this anion was not affected by the presence of TEG. 31P NMR measurements of the impregnation solution showed a paramagnetic effect of cobalt, which proved that cobalt is complexed by the diphosphopentamolybdate, both in the presence and absence of TEG. DRIFT experiments with a γ-Al2O3 support treated with TEG proved that glycol interacts with the basic OHs groups and coordinatively unsaturated Al3+ sites. The diphosphopentamolybdate complexes are decomposed by these sites on the γ-Al2O3 support, but EXAFS of the dried catalyst precursor showed that in the presence of glycol this decomposition was partially prevented. This favored the precipitation in the alumina pores of clusters in which Co and Mo are in close proximity. Because of their high Co/Mo atomic ratio, these complexes lead to an efficient decoration of the MoS2 slabs by the promoter atoms during the sulfiding treatment, thus increasing the catalytic performance of the supported CoMo catalyst. [Copyright &y& Elsevier]

The hydrodesulfurization (HDS) of dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT) was studied over sulfided NiMo/γ-Al2O3, CoMo/γ-Al2O3, and Mo/γ-Al2O3 catalysts. The Ni and Co promoters strongly enhanced the activity of the Mo catalyst in the direct desulfurization pathway of the HDS of DBT and 4,6-DMDBT and in the final sulfur-removal step in the hydrogenation pathway, while the hydrogenation was moderately promoted. H2S had a negative effect on the HDS of DBT and 4,6-DMDBT, which was strongest for the NiMo catalyst and stronger for the direct desulfurization pathway than for the hydrogenation pathway. Because the direct desulfurization pathway is less important for the HDS of 4,6-DMDBT than the hydrogenation pathway, the conversion of 4,6-DMDBT was less affected by H2S than the conversion of DBT. The sulfur removal via the direct desulfurization pathway and the ultimate sulfur removal in the hydrogenation pathway were affected by H2S to the same extent over all the catalysts. This suggests that the removal of sulfur from tetrahydrodibenzothiophenes takes place by hydrogenolysis, like the direct desulfurization of DBT to biphenyl. The CoMo catalyst performed better than the NiMo catalyst in the final desulfurization via the hydrogenation pathway in the HDS of 4,6-DMDBT at all partial pressures of H2S. [Copyright &y& Elsevier]

The hydrodesulfurization (HDS) of 4,6-dimethyldibenzothiophene (4,6-DMDBT) was studied at 340 °C and 5 MPa in the presence of 2-methylpyridine and 2-methylpiperidine. Both N-containing molecules inhibited the HDS. The inhibitory effect of 2-methylpiperidine on the direct desulfurization and hydrogenation pathways of the HDS was slightly stronger than that of 2-methylpyridine. The desulfurization of 4,6-dimethyltetrahydrodibenzothiophene, an intermediate in the hydrogenation pathway, was extremely difficult in the presence of N-containing molecules. 4,6-DMDBT, in turn, inhibited the hydrogenation of 2-methylpyridine to 2-methylpiperidine but did not affect the C&z.sbnd;N bond cleavage in the hydrodenitrogenation of 2-methylpiperidine. The use of toluene as an aromatic solvent had no effect on the HDS of dibenzothiophene and 4,6-DMDBT at 340 °C. Naphthalene inhibited the HDS of dibenzothiophene and 4,6-DMDBT without changing the product distributions. Both S-containing molecules suppressed the hydrogenation of naphthalene to the same extent. [Copyright &y& Elsevier]

The hydrodesulfurization (HDS) of dibenzothiophene (DBT) was studied at 300 °C, 4.8 MPa H2 and 35 kPa H2S in the presence of 0 to 6 kPa 2-methylpyridine and 2-methylpiperidine. 2-Methylpyridine suppressed the hydrogenation pathway by a factor of 6 to 30, depending on its partial pressure, and moderately inhibited the direct desulfurization pathway of the HDS of DBT (by a factor of 2 or less). 2-Methylpiperidine suppressed the hydrogenation by a factor of 10 to 50 but promoted the direct desulfurization of DBT at low partial pressures of 2-methylpiperidine. Both pathways were inhibited at high concentrations of 2-methylpiperidine. Structural and electronic factors may account for the promoting effect of 2-methylpiperidine. [ABSTRACT FROM AUTHOR]

The influence of 2-methylpyridine and 2-methylpiperidine on the hydrodesulfurization of dibenzothiophene (DBT) and the effect of DBT on the hydrodenitrogenation of 2-methylpyridine and 2-methylpiperidine were studied over a sulfided NiMo/Al2O3 catalyst at 5 MPa, 35 kPa H2S, and 300 and 340 °C. Both N-containing molecules strongly suppressed the hydrogenation pathway of the hydrodesulfurization of DBT and inhibited the direct desulfurization route at both reaction temperatures. The inhibitory effect on the direct desulfurization was stronger for 2-methylpyridine than for 2-methylpiperidine. H2S promoted the hydrogenation of 2-methylpyridine up to 10 kPa and inhibited it at higher partial pressures. H2S had a positive influence on the hydrodenitrogenation conversions of 2-methylpiperidine and 2-methylpyridine. DBT had a negative effect on the hydrogenation of 2-methylpyridine, but did not influence the C&z.sbnd;N bond cleavage of 2-methylpiperidine. Therefore, C&z.sbnd;N and C&z.sbnd;S bond breaking takes place at different active sites, whereas the hydrogenation sites for N- and S-containing molecules may be the same. [Copyright &y& Elsevier]

Heterogeneous catalytic diastereoselective hydrogenation is reviewed with a special emphasis on its application in the preparation of fine chemicals. [ABSTRACT FROM AUTHOR]

The different catalytic sites involved in hydrodenitrogenation (HDN) over supported sulfided Ni-Mo and Rh catalysts were investigated by means of four model reactions, the hydrodenitrogenation of methylcyclohexylamine (MCHA) and o-toluidine and the hydrogenation of cyclohexene (CHE) and toluene (TOL). By comparing the effects of the silica–alumina support and fluorination on the activity of these reactions, at least four sites were identified. The active site for C(sp3)&z.sbnd;N bond cleavage involves neighbouring acid and base sites. The site for C(sp2)&z.sbnd;N bond cleavage is highly unsaturated and accommodates aromatic amines in a flat adsorption mode. Hydrogenation of aromatics is favoured by high stacking of the MoS2 slabs with more edge and corner sites, whereas the hydrogenation of alkenes is favoured on catalysts with better dispersion and lower stacking of MoS2 slabs. [Copyright &y& Elsevier]

An unsaturated diketopiperazine derivative with a tricyclic α,β-dehydrodipeptide structure was isolated as a reaction intermediate in the hydrogenation of pyrazine-2-(methyl-(S)-prolinecarboxamide). The diastereoselective hydrogenation of this dehydrodipeptide was studied using various noble metals (Pd, Pt, Rh, and Ru) supported on charcoal. The hydrogenation over Pd, Rh, and Ru catalysts proceeded with a high diastereoselectivity (71–79%), and the diastereomer with the (S)-configuration on both chiral carbon atoms was formed preferentially. The reaction rates and diastereoselectivities of the hydrogenation over the Pd, Rh, and Ru catalysts were similar, while the platinum catalyst was much less active and selective (48% d.e.). The obtained results were compared with those of the hydrogenation of pyrazine-2-(methyl-(S)-prolinecarboxamide); two different pathways for the hydrogenation of this molecule were suggested. In one path, cyclization already occurs after hydrogenation to the tetrahydropyrazine molecule, and in the other path cyclization occurs after full hydrogenation of the pyrazine molecule. [Copyright &y& Elsevier]

The effects of in situ fluorination on the hydrodenitrogenation of methylcyclohexylamine have been studied at 310–350°C and 5.0 MPa in a continuous microflow reactor over sulfided and fluorinated sulfided NiMo catalysts supported on alumina and silica–alumina. The silica–alumina-supported catalysts exhibit higher hydrodenitrogenation activity than their alumina-supported counterparts. In situ fluorination promotes hydrodenitrogenation activity mainly by enhancing the elimination of NH3 from methylcyclohexylamine, while less of an effect is observed for the direct reaction of methylcyclohexylamine to methylcyclohexane. Kinetic parameters were obtained for the reaction network by fitting the experimental results with Langmuir–Hinshelwood equations. After fluorination, the reaction rate constants of all catalysts increase substantially for the elimination step, but only slightly for the direct reaction. The activation energies and the heat of adsorption are about the same over all catalysts. This indicates that the intrinsic activity of the active sites is not influenced by the in situ fluorination or by the support, and only the number of sites active for hydrodenitrogenation is increased by a change of the dispersion of the active phase. [Copyright &y& Elsevier]

The diastereoselective hydrogenation of a chiral pyrazine derivative was used for the stereoselective preparation of piperazine-2-carboxylic acid, which is an important chiral building block. The study was focused on the diastereoselective hydrogenation with various noble metal catalysts (Pd, Pt, Rh, Ru) on different supports. It was found that intramolecular cyclization of the substrate takes place during the hydrogenation, forming an unsaturated diketopiperazine derivative. This intermediate was further hydrogenated to a mixture of saturated heterocyclic diastereomers. The influence of the reaction conditions (temperature, pressure of hydrogen, and type of solvent) on the diastereoselectivity was also studied. The highest diastereoselectivity (79%) was reached with 10% Pd/C and with water as solvent. The desired molecule of piperazine-2-carboxylic acid was finally obtained by acidic hydrolysis of the diastereomeric diketopiperazine adduct. [Copyright &y& Elsevier]

The effect of fluorine on the hydrogenation of cyclohexene over sulfided NiMo catalysts supported on Al2O3 and amorphous silica–alumina (ASA) was studied at 5.0 MPa and between 310 and 350°C. Fluorination was performed in situ after sulfidation of the catalyst. The hydrogenation of cyclohexene produced mainly cyclohexane over the Al2O3-supported catalysts. On the ASA-supported catalysts, large amounts of the isomerization products methylcyclopentene and methylcyclopentane were formed in addition to the hydrogenation product cyclohexane. At the applied partial pressure of cyclohexene between 16 and 100 kPa, the hydrogenation is between zero and first order in the partial pressure of cyclohexene on all catalysts. The Al2O3-supported catalysts showed higher conversions of cyclohexene than their ASA-supported counterparts. Fluorination mainly enhances the isomerization of cyclohexene to methylcyclopentene. Kinetic parameters were obtained by fitting the kinetic data with Langmuir–Hinshelwood rate equations in a wide range of conversions. The unchanged activation energy and heat of adsorption for the hydrogenation of cyclohexene to cyclohexane indicate that the active sites for hydrogenation are not influenced by in situ fluorination. The activation energy for the isomerization of cyclohexene remained constant after fluorination. In situ fluorination introduces more acid sites for the isomerization reaction over both the Al2O3- and ASA-supported catalysts. [Copyright &y& Elsevier]

Temperature‐programmed reduction of transition‐metal phosphate precursors is the most commonly used method for the preparation of transition‐metal phosphides (a new class of versatile metal catalysts), but the reduction processes are still not clear. Here we describe the construction of a temperature‐programmed reduction‐infrared spectroscopy apparatus (TPR‐IR) to analyze the gas flows during the reduction of nickel, molybdenum, and tungsten phosphates. PH3 and Pn+ species already appeared in the gas flows at low temperature (ca. 200 °C), and PH3 was involved in the formation of phosphides. The emission of PH3 and Pn+ during the reduction of the molybdenum and tungsten phosphates was smaller than that of the nickel phosphate. Ni2P drastically accelerated the formation of the PH3 and Pn+. These results explain why excess phosphorus is needed for the preparation of Ni2P, and also demonstrate that the TPR‐IR technique is an efficient method to understand the complex processes of catalyst preparation. [ABSTRACT FROM AUTHOR]

Temperature‐programmed reduction of transition‐metal phosphate precursors is the most commonly used method for the preparation of transition‐metal phosphides (a new class of versatile metal catalysts), but the reduction processes are still not clear. Here we describe the construction of a temperature‐programmed reduction‐infrared spectroscopy apparatus (TPR‐IR) to analyze the gas flows during the reduction of nickel, molybdenum, and tungsten phosphates. PH3 and Pn+ species already appeared in the gas flows at low temperature (ca. 200 °C), and PH3 was involved in the formation of phosphides. The emission of PH3 and Pn+ during the reduction of the molybdenum and tungsten phosphates was smaller than that of the nickel phosphate. Ni2P drastically accelerated the formation of the PH3 and Pn+. These results explain why excess phosphorus is needed for the preparation of Ni2P, and also demonstrate that the TPR‐IR technique is an efficient method to understand the complex processes of catalyst preparation. [ABSTRACT FROM AUTHOR]

• CoP and Co 2 P were prepared with stoichiometric P/Co ratios. • Hydrodesulfurization (HDS) reactions over CoP and Co 2 P followed different kinetics. • CoP was much more active and more nitrogen-tolerant than Co 2 P. • The network of the HDS of dibenzothiophene over CoP and Co 2 P was determined. • The cobalt phosphosulfide phases were formed in the HDS reactions. CoP and Co 2 P were prepared by temperature-programmed reduction of the mixtures of Co(OH) 2 and H 3 PO 3 with stoichiometric P/Co ratios, but their surfaces were still enriched in phosphorus. Based on the product distributions of the hydrodesulfurization (HDS) of dibenzothiophene (DBT), 1,2,3,4-tetrahydro-dibenzothiophene (TH-DBT), and 1,2,3,4,4a,9b-hexahydro-dibenzothiophene (HH-DBT), a reaction network of DBT HDS was proposed and the mechanisms of the cleavage of different C S bonds in DBT and its hydrogenated intermediates were discussed. CoP was much more active and more nitrogen-tolerant than Co 2 P, which make it a promising HDS catalyst. The HDS reactions over CoP and Co 2 P followed a pseudo-first-order kinetics and a pseudo-zero-order kinetics, respectively. Piperidine strongly inhibited the hydrogenation/dehydrogenation reactions and the direct desulfurization of DBT, but its inhibition on the desulfurization of TH-DBT and HH-DBT were less pronounced. The active surfaces of CoP and Co 2 P in HDS reactions can be cobalt phosphosulfide phases. [ABSTRACT FROM AUTHOR]

• Desulfurization networks of 2-phenylcyclohexanethiol (2-PCHT) under H 2 and Ar. • β-Elimination dominated the hydrodesulfurization of 2-PCHT over Ni 2 P. • MoP and WP showed much higher hydrogenolysis activity than Ni 2 P. • Dehydrogenation of 2-PCHT occurred over the phosphide catalysts. • The phosphosulfide phases were formed both under H 2 and Ar. The desulfurization of 2-phenylcyclohexanethiol (2-PCHT) was studied over Ni 2 P, MoP, and WP under 4.0 MPa H 2 or Ar at 240 °C. The hydrodesulfurization of 2-PCHT proceeded through three parallel pathways: β-elimination, hydrogenolysis, and dehydrogenation. Under Ar, the parallel pathways were β-elimination, hydrogenolysis or homolytic C–S bond cleavage, and dehydrogenation. MoP and WP were more active than Ni 2 P. β-Elimination dominated the hydrodesulfurization of 2-PCHT over Ni 2 P, while hydrogenolysis was as fast as β-elimination over MoP and WP. Under Ar, β-elimination and dehydrogenation pathways were about equal over Ni 2 P, whereas β-elimination was the major pathway over MoP and WP. The inhibiting effects of piperidine depended on the reaction and catalyst. Phosphosulfide phases were formed under both H 2 and Ar, but the sulfidation behavior of Ni 2 P was different from that of MoP and WP. Ni 2 P was more difficult to sulfide than MoP and WP under H 2. [ABSTRACT FROM AUTHOR]

Review: 165 refs. [ABSTRACT FROM AUTHOR]

[Display omitted] • Desulfurization networks of 2-phenylcyclohexanethiol under H 2 and Ar were obtained. • Hydrogenolysis and β-elimination were the two main reaction pathways under H 2. • Ni and Co mainly accelerated the β-elimination pathway under H 2. • The two main reaction pathways under Ar were β-elimination and dehydrogenation. • Both pathways under Ar were enhanced by Ni and Co. The desulfurization of 2-phenylcyclohexanethiol (2-PCHT) was studied over sulfided Mo/γ-Al 2 O 3 , Ni-Mo/γ-Al 2 O 3 , and Co-Mo/γ-Al 2 O 3 catalysts under 5.0 MPa H 2 or Ar at 240 °C. Under H 2 , the desulfurization of 2-PCHT proceeded mainly through the hydrogenolysis and β-elimination pathways. The former was faster than the latter over Mo/γ-Al 2 O 3. Ni and Co accelerated the β-elimination pathway but hardly affected the hydrogenolysis pathway. The activity of Mo/γ-Al 2 O 3 was enhanced by Ni, whereas Co did not show any promoting effect. Under Ar, the desulfurization of 2-PCHT occurred mainly through the β-elimination and dehydrogenation pathways. The β-elimination pathway was faster than the dehydrogenation pathway. Both pathways were enhanced by Ni and Co. Ni and Co promoted the dehydrogenation pathway mainly by promoting the dehydrogenation-ring closure reaction. The inhibiting effects of piperidine depended on the reaction and catalyst. Under Ar, Ni-Mo/γ-Al 2 O 3 was more sensitive to piperidine inhibition. [ABSTRACT FROM AUTHOR]

Abstract: The hydrodesulfurization (HDS) of dibenzothiophene (DBT), tetrahydrodibenzothiophene (THDBT) and hexahydrodibenzothiophene (HHDBT) was studied over Co–MoS2/γ-Al2O3 and Ni–MoS2/γ-Al2O3 catalysts, and the HDS of 4,6-dimethyldibenzothiophene (4,6-DMDBT) over metallic Pt–Pd catalysts supported on mesoporous NaH-ZSM-5. The desulfurization of DBT at 300°C was faster than that of THDBT and HHDBT, both over Co–MoS2/γ-Al2O3 and Ni–MoS2/γ-Al2O3. Desulfurization of THDBT occurred directly to CHEB and CHB, but desulfurization of HHDBT occurred mainly by dehydrogenation to THDBT and subsequent desulfurization of THDBT. In most cases C–S bond breaking occurred by hydrogenolysis. Pt–Pd/mesoporous NaH-ZSM-5 was much more active than Pt–Pd/γ-Al2O3, Pt–Pd/NaH-ZSM-5 and single metal Pt and Pd catalysts in the HDS of 4,6-DMDBT. The much higher rate of the Friedel–Crafts reaction of benzylalcohol with benzene demonstrated that mesoporous NaH-ZSM-5 had accessible mesopores. Noble metals on mesoporous zeolites are very active HDS catalysts and might be considered as catalysts in the second stage of a deep HDS process. [Copyright &y& Elsevier]

Abstract: The promoting effect of an acidic support on the hydrodesulfurization (HDS) of 4,6-dimethyldibenzothiophene (DMDBT) was studied by comparing the activity and selectivity of Pt/HZSM-5 with those of Pt/γ-Al2O3 and Pt/SBA-15. Pt/γ-Al2O3 and Pt/SBA-15 hydrogenated DMDBT fast to the intermediate hexahydro-4,6-dimethyldibenzothiophene and removed sulfur from DMDBT somewhat slower, giving 3,3′-dimethylbiphenyl. The dodecahydro-4,6-dimethyldibenzothiophene intermediate was not observed, indicating that it was very quickly desulfurized. The conversion of DMDBT over Pt/HZSM-5 was low, probably because of the high hydrocracking of the decane solvent and coking of the catalyst by the cracking products. Decreasing the bifunctional hydrocracking by lowering the temperature was not successful, because of a too low HDS activity. Poisoning of the acid sites by co-feeding pyridine suppressed the hydrocracking, but brought the HDS activity down to the level of Pt on a non-acidic support like SBA-15. [Copyright &y& Elsevier]

Abstract: The effect of the Si/Al ratio of the framework on the intrinsic activity of Brønsted acid sites in Y zeolite was investigated by monomolecular cracking of propane and physicochemical characterization. Samples with different Si/Al ratios were obtained by synthesis and by post-synthesis treatments. Two samples with Si/Al ratios of 3.3 and 3.6 exhibited characteristic features similar to those of commercial Y zeolite with a Si/Al ratio of 2.6, but they were more stable. An ultrastable Y (HUSY) was treated with ammonia and ethylenediaminetetraacetic acid (EDTA) to remove extra-framework aluminum (EFAl). The rates per gram increased with Si/Al ratio, but the activation energies did not depend on the Si/Al ratio or on the presence of EFAl. This implies that the intrinsic activity of the Brønsted acid sites that participate in the reaction is identical in all the samples. The enhanced activity of the samples with Si/Al ratios up to 5.0 is attributed to the creation of more isolated Brønsted acid sites, which are active in this demanding reaction. The removal of EFAl did not affect the intrinsic catalytic activity but increased the number of catalytically active framework Brønsted acid sites. [Copyright &y& Elsevier]

Abstract: The reaction network and mechanism of the hydrodenitrogenation (HDN) of 2-methylpyridine and 2-methylpiperidine were studied at 280–340 °C and 1–3 MPa in the absence and presence of H2S over sulfided NiMo/γ-Al2O3. By the addition of 2-ethylpiperidine to the HDN of 2-methylpyridine and of 2-ethylpyridine to the HDN of 2-methylpiperidine, the mutual inhibiting effects of 2-methylpyridine and 2-methylpiperidine could be determined. 2-Ethylpyridine hardly affected the HDN of 2-methylpiperidine, but 2-ethylpiperidine strongly retarded the hydrogenation of 2-methylpyridine and promoted its denitrogenation at low partial pressure and inhibited it at high partial pressure. Substantial amounts of 2,3,4,5-tetrahydro-6-methylpyridine were detected in the HDN reactions; thus, its HDN was studied. This imine intermediate reacted very rapidly to 2-methylpiperidine by hydrogenation. 2-Methylpiperidine reacted to 1-hexylamine and even more strongly to 2-hexylamine. The final hydrocarbon products were 1-hexene, 2-hexene, and hexane. Based on these results and on previous HDN studies of dialkylamines, we propose that 2-methylpyridine first reacts by hydrogenation to 2-methylpiperidine and that both react to the imines 2,3,4,5-tetrahydro-2-methylpyridine and 2,3,4,5-tetrahydro-6-methylpyridine. Breaking of the first Cd ring opening of the imines occurs as a result of the addition of H2S, elimination, and hydrogenation, forming amino-hexanethiols. The amino-hexanethiols react by hydrogenolysis to hexylamines, and the second C broken by hexylimine formation, H2S addition, and NH3 elimination. [Copyright &y& Elsevier]

Abstract: An unsupported nickel phosphide catalyst with high surface area (130 m2/g) and high hydrotreating activity was prepared in the presence of a polymer surfactant (Triton X-114) and ethylene glycol. The resulting catalyst was characterized by XRD, SEM, TEM, CO and O2 chemisorption, and 31P MAS NMR spectroscopy. Both polymer surfactant and ethylene glycol are necessary to obtain good texture properties and hydrotreating activities of bulk nickel phosphide catalysts. [Copyright &y& Elsevier]

Abstract: Silica-supported nickel phosphide particles with high dispersion were obtained by treating nickel metal particles on a support with 10% PH3/H2. Because the phosphidation occurred at relatively low temperature, the small nickel phosphide particles had the same size as the metal particles, and this size was maintained. The resulting catalysts were characterized by CO and O2 chemisorption, XRD, and 31P MAS NMR spectroscopy. The influence of the nickel source on the metal dispersion of the catalysts was investigated. The resulting silica-supported nickel phosphide catalysts proved to be very active in the hydrodesulfurization of dibenzothiophene and the hydrodenitrogenation of o-methylaniline in the presence and absence of H2S. [Copyright &y& Elsevier]