Hydrodenitrogenation Reactions Research Articles

Catalytic performances of platinum doped molybdenum carbide for simultaneous hydrodenitrogenation and hydrodesulfurization

The hydrotreating activity of molybdenum carbide doped with platinum (0.3 wt.%) was studied and compared to that of a pure, non-modified Mo 2C. 4,6-Dimethyldibenzothiophene (4,6-DMDBT, 300 ppm of S) and carbazole (100 ppm of N) were designated as model compounds and subjected to hydrodesufurization (HDS) and hydrodenitrogenation (HDN) processes either separately or simultaneously. In both cases the molybdenum carbide doped with platinum (Mo 2C-Pt) turns out to be more active than Mo 2C. The increase of the hydrotreating activity, owing to the presence of platinum in molybdenum carbide can be related to the raise of hydrogenation activity of the modified catalyst. The platinum modified molybdenum carbide was stable ( displays a long lifetime) under HDN and HDS reaction conditions. The predominant reaction products are bicyclohexyl (BCH) for the HDN process or 3,3′-dimethylbiphenyl (3,3′-DMBPh) and methylcyclohexyltoluene (MCHT) for the HDS process, respectively.

Preparation, Characterization, Hydrodesulfurization and Hydrodenitrogenation Activities of Alumina-supported Tungsten Phosphide Catalysts

Two series of WP/Al 2O 3 catalyst precursors with WP mass loading in the range 18.5%–37.1% were prepared using the impregnation method and mixing method, respectively, and the catalysts were then obtained by temperature-programmed reduction of supported tungsten phosphate (precursor of WP/Al 2O 3 catatlysts) in H 2 at 650°C for 4h. The catalysts were characterized by XRD, BET, TG/DTA, XPS and 31P MAS-NMR. The activities of these catalysts were tested in the hydrodenitrogenation (HDN) of pyridine and hydrodesulfurization (HDS) of thiophene at 340°C and 3.0MPa. The results showed that owing to the stronger interaction of the support with the active species, the precursor of WP/Al2O 3 catalyst was more difficultly phosphided and a greater amount of W species was in a high valence state W 6+ on the surface of the catalyst prepared by the impregnation method than that by the mixing method. 31P MAS-NMR results indicated that 31P shift from 85% H 3PO 4 of 2.55 × 10 −4 for WP and 2.57 × 10 −4 for WP/γ-Al 2O 3 catalysts prepared by mixing method. Such WP/Al 2O 3 catalysts showed higher HDN activities and lower HDS activities than those prepared by the impregnation method under the same loading of WP. WP/γ-Al 2O 3 catalysts with weak interaction between support and active species were favorable for HDN reaction while the WP/γ-Al 2O 3 catalysts with strong interaction were favorable for HDS reaction.

Effect of fluorine and boron modification on the HDS, HDN and HDA activity of hydrotreating catalysts

A series of fluorine- and/or boron-modified catalysts were studied, among which the catalysts simultaneously modified with fluorine and boron were prepared and studied for the first time. The hydrodesulfurization (HDS), hydrodenitrogenation (HDN) and hydrodearomatics (HDA) activities of all the catalysts were evaluated with model compounds, 4,6-DMDBT, pyridine and 1-methylnathphlene. The catalysts were also characterized by FT-IR, BET, X-ray photoelectron spectroscopy (XPS), and thermogravity/differential thermal analysis (TG/DTA) for acid type and acidity, pore structure, metal distribution on the surface of catalysts, existing state of hydrogenation metals, and decomposition of fluorine, boric and hydrogenation metal compounds. The experimental results showed that the catalyst simultaneously modified with borane isoproxyl and ammonium fluoride had the best HDN and HDA activities and good HDS activity, though the lowest acidity among the catalysts. The excellent hydrogenation activity of this catalyst may attribute to its highest dispersed active nickel and its large pore volume and surface area. The catalyst modified with NH 4F and H 3BO 3 showed a similar performance to the catalyst modified with H 3BO 3 only. The incorporation of boron led to a greater increase in hydrogenation activity than the addition of fluorine which presents a detrimental effect on the HDN reaction.

Hydrodenitrogenation and Hydrodesulfurization of Heavy Gas Oil Using NiMo/Al2O3 Catalyst Containing Boron: Experimental and Kinetic Studies

In this work, a systematic study has been conducted to optimize the process conditions and to evaluate kinetic parameters for hydrodenitrogenation (HDN) and hydrodesulfurization (HDS) of heavy gas oil derived from Athabasca bitumen using NiMo/Al 2 O 3 catalysts containing boron (B). In the catalyst, the concentrations of boron were varied from 0 to 1.7 wt %. Experiments were performed in a trickle-bed reactor at the temperatures, pressures, and liquid hourly space velocities (LHSVs) of 340-420 °C, 6.1-10.2 MPa, and 0.5-2 h -1 , respectively. H 2 flow rate and catalyst weight were maintained constant at 50 mL/min and 4 g, respectively, in all cases. Statistical analysis of all experimental data was carried out using ANOVA to optimize the process conditions for HDN and HDS reactions. Kinetic studies for HDN and HDS reactions were studied within the temperature range of 340-400 °C using a power law model as well as the Langmuir-Hinshelwood model. The power law model showed that HDN of heavy gas oil follows first-order kinetics while the HDS process follows 1.5-order kinetics. The activation energies for HDN and HDS reactions from power law and Langmuir-Hinshelwood models were 75 and 87 kJ/mol and 110 and 159 kJ/mol, respectively.

Investigation of the steric course of the C [sbnd]N bond breaking in the hydrodenitrogenation of alkylamines

The steric course of the hydrodenitrogenation reactions of 2-( R)- and 2-( S)-butylamine to 2-butanethiol and di- sec-butylamine was studied at 3 MPa and 300 °C over sulfided NiMo/ γ-Al 2O 3. After separation of the thiol from the dialkylamine and unreacted alkylamine, the chirality of the thiol and unreacted alkylamine was determined by analysis of the diastereomers formed by reaction with Moscher's acid chloride, ( S)-(+)- α-methoxy- α-(trifluoromethyl)phenylacetylchloride. The dialkylamine was analyzed by direct chiral chromatography without derivatization, using another type of chiral column. When 2-( S)-butylamine was used as reactant, the 2-butanethiol product was completely racemic, whereas the di- sec-butylamine consisted of 48% ( R, S), 32% ( S, S), and 20% ( R, R) isomers and the 2-butylamine of 70% ( S) and 30% ( R) isomers. These results cannot be explained by a classic S N2 substitution mechanism. Two similar mechanisms can explain all products and their configurations, as well as the racemization of the amine reactant. In one mechanism the amine first reacts by dehydrogenation to an imine, whereas in the other the amine first reacts by electron and proton transfer to an imine cation. Thereafter, the addition of H 2S or an amine molecule to the imine or to the imine cation occurs, and, after ammonia or amine elimination and hydrogenation, a thiol or a dialkylamine is formed.

Surface morphology of NiMo/Al 2O 3 catalysts incorporated with boron and phosphorus: Experimental and simulation

Three catalysts namely NiMo/Al 2O 3, NiMoB/Al 2O 3 and NiMoP/Al 2O 3 were prepared, extensively characterized and were used for hydrodenitrogenation (HDN) and hydodesulfurization (HDS) of heavy gas oil obtained from Athabasca bitumen. The hexagonal structure of MoS 2 of the catalyst at different stages of reaction was studied and quantified using transmission electron microscopy (TEM). The length and number of MoS 2 stack, the dispersion of edge and corner molybdenum atoms, number of MoS 2 stacks and number of MoS 2 layers per stack, which play important role on the HDN and HDS activities of these catalysts, were calculated. It was concluded that the decrease in MoS 2 slab length caused an increase in catalyst activity for HDN of heavy gas oil derived from Athabasca bitumen. Computer simulation was also performed in order to correlate the surface morphology with catalyst activity. Maximum edge and corner Mo atoms which were responsible for high HDN and HDS reactions, was obtained at an average MoS 2 slab length of approximately 20 and 10 Å, respectively.

Synergism between unsupported Re and Co or Ni sulfide catalysts in the HDS and HDN of gas oil

Two series of unsupported Co–Re and Ni–Re binary sulfide catalysts with variable atomic ratio α = Me/(Me + Re) from 0 to 1 were prepared by the co-maceration method. The catalysts were characterized by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), and evaluated in the simultaneous hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) reactions of a real gas oil feed under industrial relevant conditions. The results showed a synergetic effect of the Co or Ni sulfide on the ReS 2 in both HDS and HDN reactions. A maximum in activity at the same atomic ratio α ∼ 0.5 was observed for both reactions and both Co–Re and Ni–Re catalysts. The magnitude of the synergy was generally superior for HDS than for HDN, and at low reaction temperature (598 K) larger for Ni–Re than for Co–Re catalysts, especially in HDS, while at high temperature (648 K) it was reverse. Moreover, the Co–Re catalysts exhibited higher HDN/HDS selectivity than the Ni–Re catalysts. Neither XRD nor XPS results evidenced the presence of a “Co–Re–S” or “Ni–Re–S” like phase. It is suggested that the synergism could be associated to the hydrogen activation and spillover from the Co or Ni sulfide to ReS 2.

An Investigation of the Deactivation Behavior of Industrial Mo/Al2O3 and Ni-Mo/Al2O3 Catalysts in Hydrotreating Kuwait Atmospheric Residue

The catalyst system for fixed-bed residue hydrotreating processes usually consists of different types of catalysts designed to promote hydrodemetallation (HDM), hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) reactions to desired levels. Overall catalyst life is determined by the performance of the individual catalysts in the different reactors. Therefore, information about the activity, stability, selectivity, and deactivation behavior of the individual catalyst is highly desirable to design improved catalysts that can prolong catalyst life, increase stream efficiency, and improve process economics. In the present work, residue hydrotreating experiments were conducted on two types of industrial hydrotreating catalysts, namely Mo/Al2O3 and Ni-Mo/Al2O3, that have been used as HDM and HDS catalysts, respectively, in an industrial ARDS process. The primary objective of the study was to compare the deactivation behavior of both types of catalyst. The characterization of the used catalysts by elemental analysis, surface area, pore volume, and pore size measurements along with TPO-MS, 13C NMR, and electron microprobe analysis showed significant differences in the nature of the coke and metal deposits on the two types of catalysts. The role of initial coking, the relative importance of the coke, and metal depositions on the deactivation of the two types of catalyst are discussed.

Inhibition effects observed between dibenzothiophene and carbazole during the hydrotreating process

The inhibition effect of carbazole (50–220 ppm as nitrogen) on the hydrodesulfurization (HDS) of dibenzothiophene (700 ppm as sulfur), at conditions commonly used in the hydrotreatment (HDT) of diesel feedstocks, has been experimentally determined. The inhibition behavior of this non-basic compound at this range of concentrations is non-linear, and was found to be weaker than the observed with other basic and non-basic nitrogen compounds also present in a diesel feedstock, like quinoline and indole, and than the one observed when carbazole is presented at lower concentrations (below 50 ppm as nitrogen). An inhibiting effect of dibenzothiophene over the carbazole hydrodenitrogenation (HDN) during the same process is also reported. Additionally, a retarding effect of carbazole over its own hydrodenitrogenation reaction during the dibenzothiophene hydrodesulfurization has been kinetically analyzed. The carbazole self-inhibiting effect was almost as strong as the observed for indole and ten times stronger than the observed for o-ethylaniline, according to the results reported elsewhere. The inhibitory effects described here were quantitatively represented by introducing apparent adsorption constants into the denominator of modified Langmuir–Hinshelwood (L–H) type rate equations.

Modification of Electronic Properties of Mo2C Catalyst by Potassium Doping: Impact on the Reactivity in Hydrodenitrogenation Reaction of Indole

The effect of potassium doping on electronic surface properties of molybdenum carbide (Mo2C) was investigated by species-resolved thermal alkali desorption techniques, work-function measurements, a...

Synthesis and reactivity of iridium complexes with pyridine and piperidine ligands: models for hydrodenitrogenation.

The complexes [Ir(H)2(eta1-N-L)2(PPh3)2]PF6, L = py (1), iQ (2) and pip (3) (py = pyridine, iQ = isoquinoline, pip = piperidine) have been synthesized in high yields by hydrogenation of [Ir(cod)(PPh3)2]PF6 in the presence of the appropriate nitrogen compound. When hydrogen is bubbled through 1,2-dichloroethane solutions of 1 or 2, two new species were formed in each case by C-Cl bond activation of the solvent, Ir(H)2Cl(eta1-N-L)(PPh3)2 (L = py, 4; iQ, 5) and IrH(Cl)2(eta1-N-L)(PPh3)2 (L = py, 6; iQ, 7). Reaction of 3 with py or iQ yielded complexes 1 and 2, respectively, while under a slow stream of carbon monoxide the complex [Ir(H)2(eta1-N-pip)(CO)(PPh3)2]PF6 (8) was produced. Complex 3 also reacts with halide and 4-bromothiophenolate anions leading to the corresponding neutral species Ir(H)2(X)(eta1-N-pip)(PPh3)2, X = Cl (9), I (10) and 4-BrC6H4S (11), or with [MoS4]2- to yield the hetero-bimetallic complex [Ir(H)(PPh3)2(mu-S)2MoS2]- (13). All the new complexes were characterized by analytical and spectroscopic methods. The X-ray structures of , 2 and 8 consist of distorted octahedra with a mutually cis disposition of the two hydrides and mutually trans phosphines. Complexes 1, 2 and 3 and their derivatives are of interest as models for the chemisorption step in hydrodenitrogenation reactions on solid catalysts.

Comparison of vanadium carbide and nitride catalysts for hydrotreating

Vanadium nitride and carbide were synthesized by the temperature-programmed reaction of ammonium vanadate (NH 4VO 3) with pure NH 3 and 20% CH 4 in H 2, respectively. Based on the XRD results, the catalysts showed VN and V 8C 7/V 4C 3 with an amount of V 2O 3 in the bulk after nitridation and carburization. The hydrogenation, hydrodesulfurization and hydrodenitrogenation reactions were studied and compared to vanadium sulfide catalyst. These catalysts (VC, VN) are stable under typical hydroprocessing conditions.

Active phase of Ni 2P/SiO 2 in hydroprocessing reactions

A series of Ni 2P/SiO 2 catalyst samples with loading from 6 to 22 wt% Ni 2P was prepared by the method of temperature-programmed reduction (TPR). The samples were characterized by BET, CO uptake, X-ray diffraction (XRD), and extended X-ray absorption fine structure (EXAFS) measurements. The activity of these catalysts was measured at 643 K and 3.1 MPa in a three-phase, packed-bed reactor for hydrodesulfurization (HDS), hydrodenitrogenation (HDN), and hydrodeoxygenation (HDO) using a model liquid feed containing 3000 ppm S as dibenzothiophene, 2000 ppm N as quinoline, and 500 ppm O as benzofuran. An optimum Ni 2P loading for HDS, HDN, and HDO activity was found around 18 wt% which gave an HDS conversion of 99%, an HDN conversion of 91%, and an HDO conversion of 80% at a WHSV of 2.1 h −1. These were much higher than those of a commercial Ni–Mo–S/Al 2O 3 catalyst which gave an HDS conversion of 76%, and an HDN conversion of 38% based on equal sites (70 μmol) loaded in the reactor. The sites were counted by CO chemisorption for the phosphide and by low-temperature O 2 chemisorption for the sulfide. XRD and EXAFS results confirmed that a Ni 2P phase was formed on the support. The crystallite size increased slightly from 7.7 to 9.8 nm when the loading was increased, and there was evidence from CO chemisorption that some crystallite agglomeration occurred in the higher loading samples. It was found that the HDS performance did not change appreciably with Ni 2P loading, but that the HDN activity and stability went through a maximum at intermediate loading. It was concluded that the HDS reaction is structure-insensitive, while the HDN reaction depends on the local arrangement of surface Ni, P, and S atoms, and is structure-sensitive. XRD and EXAFS analysis indicated that the active catalyst formed a surface phosphosulfide phase on top of a Ni 2P core in the course of hydrotreating.

Investigation of the mechanism of the hydrodenitrogenation of n-hexylamines over sulfided NiMo/ γ-Al 2O 3

The hydrodenitrogenation (HDN) of n-hexylamine, dihexylamine, and trihexylamine was studied between 300 and 340 °C, 3 and 5 MPa total pressure, 5 and 20 kPa amine pressure, and 10 and 150 kPa H 2S pressure over a sulfided Ni–Mo/ γ-Al 2O 3 catalyst. The conversion increased with the H 2 pressure and decreased with increasing partial pressure of the hexylamines. The conversion of hexylamine and dihexylamine decreased slightly with H 2S pressure, but that of trihexylamine increased substantially. The contributions of elimination and nucleophilic substitution to the HDN were determined by the initial product selectivities at short weight time. The initial alkene selectivities were low and accounted for only a minor part of the n-alkylamine conversion. Since the hexene/hexane branching ratio in the HDN of the alkylamines was almost equal to that in the hydrodesulfurization of pentanethiol in the presence of an alkylamine, it was concluded that the majority of hexene in the HDN of the hexylamines originates from hexanethiol. Nucleophilic substitution of the hexylamines with H 2S to give an alkanethiol is the predominant HDN reaction of all three n-hexylamines.

Kinetic study of the hydrodenitrogenation of carbazole over bulk molybdenum carbide

Hydrodenitrogenation (HDN) of N-containing compounds (carbazole in this paper) in the presence of a small amount of sulfur (50 ppm) requires a strong catalytic hydrogenating function. Bulk molybdenum carbide, Mo 2C, behaves like a noble metal and has strong hydrogenating properties and can catalyse deep HDN if the S content is not too high. A kinetic investigation monitored both the hydrogenating function through carbazole consumption and the HDN of carbazole through two kinetically coupled cycles. Biphenyl was not observed. Kinetic coupling occurs by means of adsorbed orthocyclohexylaniline. The first route is the direct HDN reaction, leading to cyclohexylbenzene, while the second hydrogenation route leads to bicyclohexyl. At 633 K, a zero-order reaction is observed with respect to carbazole; total HDN is observed for 0.4 s, and the selectivity ratio of bicyclohexyl to cyclohexylbenzene is equal to 9.

Effect of Phosphorus Content in Nickel Phosphide Catalysts Studied by XAFS and Other Techniques

A series of novel, high-activity supported nickel phosphide hydroprocessing catalysts (Ni 2P/SiO 2) was synthesized by means of temperature-programmed reduction (TPR), and the effect of phosphorus content on hydroprocessing performance and catalyst structure was studied. The catalysts were characterized by BET surface area determinations, CO uptake titrations, X-ray diffraction (XRD) analysis, elemental analysis, and extended X-ray absorption fine structure (EXAFS) measurements. The activity of the catalysts was studied in a three-phase trickle-bed reactor operated at 3.1 MPa and 643 K in the hydrodenitrogenation (HDN) and hydrodesulfurization (HDS) of a model liquid feed containing 2000 ppm nitrogen (quinoline), 3681 ppm sulfur (dibenzothiophene), 500 ppm oxygen (benzofuran), 20 wt% aromatics (tetralin), and balance aliphatics (tetradecane). The samples were prepared with initial Ni/P ratios of 2/1, 1/1, 1/1.8, 1/2, 1/2.2, and 1/3, but the samples with excess P lost some of their P content during reduction and the main phase obtained was Ni 2P. Activity and stability of the catalysts were affected profoundly by the phosphorus content, both reaching a maximum with an initial Ni/P ratio of about 1/2 (actual Ni/P=1/0.57 after reaction). At this optimal P content, the activity was excellent, with steady state HDS conversion of 100% and HDN conversion of 81%, which were much higher than that of a commercial Ni–Mo–S/Al 2O 3 catalyst with corresponding HDN conversion of 76% and HDN conversion of 38%. The stability of the optimal composition was also high, with no deactivation observed over 90 h in HDS and only a slight deactivation in HDN. EXAFS analysis of the catalysts indicated the formation of a Ni 2P phase for the sample with an initial Ni/P ratio of 1/2, which was retained after reaction. At lower P content some Ni metal and Ni 12P 5 was obtained, and at higher P content, the Ni 2P active phase was blocked by excess P. The activity results indicate that on these novel catalysts, the HDN reactions are structure sensitive while the HDS reactions are structure insensitive.

Characterization and reactivity of Re( x)/γ-Al 2O 3 catalysts in hydrodesulfurization and hydrodenitrogenation of gas oil: effect of Re loading

A series of Re( x)/γ-Al 2O 3 catalysts containing 1.69–6.76 wt.% Re 2O 7 were prepared by wet impregnation and characterized using X-ray diffraction (XRD), BET surface area, diffuse reflectance spectroscopy (DRS), electrophoretic migration (EM), X-ray photoelectron spectroscopy (XPS) and surface acidity techniques. The catalysts were tested for simultaneous hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) of commercial gas oil under typical industrial hydrotreating conditions. In general, the activities for both HDS and HDN reactions increased almost linearly with increasing Re loading, reaching maxima at about 0.5 Re atoms nm −2 and then leveled off. These activity trends resemble that observed for the Re dispersion as measured by EM (in the oxided state) and XPS (in the sulfide state), which resulted in a monolayer-type deposition up to about 0.5 Re atoms nm −2 and then in multilayers or small aggregates. The magnitude of the catalytic effect was, however, different for HDS and HDN, and strongly depends on the Re content and reaction temperature. This led to a marked increase in the HDN/HDS selectivity with decreasing temperature (values above 1.5 at 325 °C), due to the large differences in the apparent activation energies of HDS and HDN found for all catalysts. A gradual increase in the HDN/HDS selectivity with increasing Re loading was also found. Such selectivity increase was ascribed to the parallel increase of catalyst acidity observed.

Catalytic elimination of nitrogen organic compounds from the coal-liquid and structural properties of NiMo catalysts supported on NaX and NaY zeolites modified with transition metal cations

Changes in the crystal structure of faujasite (X and Y) type zeolites occurring as a results of sodium ions exchange into transition metal cations (TMC) and impregnation with Mo(VI) and Ni(II) ions are described. The catalysts obtained were studied in hydrodenitrogenation reaction (HDN) of coal-liquid. Both ion exchange and surface impregnation were found to cause a destruction of the crystal structure of zeolites. The degree of destruction was proved to depend on the kind of TMC. The NiMo catalysts supported on X type zeolites were less active than those supported on Y type zeolites, which means that the molar ratio SiO 2/Al 2O 3 plays an important for the catalysts performance. The catalysts with Y type zeolite containing a divalent cations show a similar activity in HDN, while this activity for the catalysts with trivalent TMC decreases in the sequence NiMo/NaFeY>NiMo/NaLaY>NiMo/NaCrY>NiMo/NaY. The greatest catalytic activity revealed the NiMo catalysts supported on Y type zeolite in which sodium ions were in 44% exchanged for Fe(III). Moreover, as follows from the results obtained, in the preparation conditions applied Mo(VI) ions are built into the zeolite structure.

Silica and alumina impregnated with dimethylformamide solutions of molybdophosphoric or tungstophosphoric acids for hydrotreatment reactions

Heteropolyacid (HPA) based catalysts were prepared by impregnation of silica and alumina with dimethylformamide solutions of molybdophosphoric and tungstophosphoric acids. This solvent allows the preservation of the Keggin unit during the impregnation independently of the nature of the support. Ni-promoted catalysts were prepared by impregnation with nickel nitrate solutions of the supported HPA. The stronger interaction of the HPA with alumina than with silica allows a better dispersion of the polyoxometallate species on the former one whereas the formation of bulk oxides is observed on silica. The performance of these HPA–Ni/support catalysts for hydrodenitrogenation and hydrodesulfurization reactions is related to the precursor–support interaction.

Reaction network of pyridine hydrodenitrogenation over carbide and sulfide catalysts

A series of carbide and sulfide catalysts comprising NbMo 2C, Mo 2C, NbC and MoS 2/SiO 2 was used to study the pyridine hydrodenitrogenation (HDN) network below at high pressure (3.1 MPa) as a function of temperature. pyridine → k 1 piperidine → k 2 n- pentylamine → k 3 hydrocarbons All the catalysts showed the same trend in activities for the three molecules: the reactivity of n-pentylamine was high, while those of piperidine and pyridine were relatively low, especially at low temperatures. The carbide catalysts showed higher selectivity towards HDN products than the sulfide catalyst at the same conversion levels. The higher selectivity was related to the higher ratio ( r= k 2/ k 1) between the rate constants of the two consecutive reactions, hydrogenation of pyridine ( k 1) and ring opening of piperidine ( k 2). The order of activity of the carbides and sulfide differed considerably depending on the substrate. At the same temperature, the sulfide was more active for pyridine HDN when compared to the carbide catalysts, but it was much less active for quinoline HDN, suggesting that the HDN reaction mechanism depends greatly on the structure of the N-containing molecule. However, for the pyridine reaction network the similarity in product distribution suggested that the active surface of the carbides and sulfide was similar at reaction conditions.