The role of nickel in pyridine hydrodenitrogenation over NiMo/Al2O3

Al₂O₃ supported Mo, Ni, and NiMo/Al₂O₃ catalysts with various Ni contents were prepared to investigate the role of Ni as a promoter in a NiMo bimetallic catalyst system. The hydrodenitrogenation (HDN) reaction of pyridine as a catalytic probe was conducted over these catalysts under the same reaction conditions and the catalysts were characterized using BET surface area measurement, infrared spectroscopy, temperature programmed reduction, DRS and ESR. According to the results of reaction experiments, the NiMo/Al₂O₃ catalyst showed higher activity than Mo/Al₂O₃ catalyst in the HDN reaction and particularly the one with atomic ratio [Ni/(Ni+Mo)]=0.3 showed the best activity for the HDN of pyridine. The findings of this study lead us to suggest that the enhancement in the HDN activity with nickel addition could be attributed to the improvement in the reducibility of molybdenum and the formation of Ni-Mo-O phase.     

Characterization of hydrodenitrogenation catalysts by O2 chemisorption

O₂ chemisorption on sulfided NiMo/Al₂O₃ catalysts with Ni/Ni+Mo = 0 to 1 was measured at 273 K. The quantities of chemisorbed O₂ were compared to the activities of the catalysts in biphenyl hydrogenation and in 1,2,3,4-tetrahydroquinoline hydrodenitrogenation (HDN) at 623 K, 3.5 MPa.     

Hydrodenitrogenation of quinoline over Ni–Mo/Al2O3 catalyst modified with fluorine and phosphorus

In this paper, the effects of fluorine and phosphorus on the physical and chemical properties of Ni–Mo/Al₂O₃ catalysts and the hydrodenitrogenation (HDN) activity of quinoline were investigated. The acidity, pore structure, and dispersion of Mo of the catalysts were analyzed with TG-DTA, BET, and XRD techniques. The activities of hydrodenitrogenation and hydrogenation of the catalysts were investigated using hydrogenation of quinoline at high pressure in a micro-reactor. Experimental results verified that phosphorus can promote the formation of moderate and strong acidic sites, the dispersion of Mo, and the formation of the active phases; therefore, the hydrogenation activity of aromatic rings and the hydrogenolysis activity of C–N bonds increase. The hydrogenation and hydrogenolysis accelerate each other, which results in the increase of HDN activity. It is concluded that phosphorus is a promoter for HDN activity of the Ni–Mo/Al₂O₃ catalysts. Fluorine can promote the formation of weak and moderate acidic sites and the dispersion of Mo, but inhibit the formation of the active phases. Therefore, the hydrogenation activity of aromatic rings and the hydrogenolysis activity of C–N bonds decrease, which results in the decrease of HDN activity. It is concluded that fluorine is not a promoter for HDN activity of the Ni–Mo/Al₂O₃ catalysts. The possible promoting mechanism of fluorine and phosphorus for the Ni–Mo/Al₂O₃ catalyst is put forward and discussed.     

Mesoporous silica–alumina as support for Pt and Pt–Mo sulfide catalysts: Effect of Pt loading on activity and selectivity in HDS and HDN of model compounds

The potential of mesoporous silica–alumina (MSA) material as support for the preparation of sulfided Pt and Pt–Mo catalysts of varying Pt loadings was studied. The catalysts were characterized by their texture, hydrogen adsorption, transmission electron microscopy, temperature programmed reduction (TPR) and by activity in simultaneous hydrodesulfurization (HDS) of thiophene and hydrodenitrogenation (HDN) of pyridine. Sulfided Pt/MSA catalysts with 1.3 and 2 wt.% Pt showed almost the same HDS and higher HDN activities per weight amounts as conventional CoMo and NiMo/Al₂O₃, respectively. The addition of Pt to sulfided Mo/MSA led to promotion in HDS and HDN with an optimal promoter content close to 0.5 wt.%. The results of TPR showed strong positive effect of Pt on reducibility of the MoS₂ phase which obviously reflects in higher activity of the promoted catalysts. The activity of the MSA-supported Pt–Mo catalyst containing 0.5 wt.% Pt was significantly higher than the activity of alumina-supported Pt–Mo catalyst. Generally, Pt–Mo/MSA catalysts promoted by 0.3–2.3 wt.% Pt showed lower HDS and much higher HDN activities as compared to weight amounts of CoMo and NiMo/Al₂O₃. It is proposed that thiophene HDS and pyridine hydrogenation proceed over Pt/MSA and the majority of Pt–Mo/MSA catalysts on the same type of catalytic sites, which are associated with sulfided Pt and MoS₂ phases. On the contrary, piperidine hydrogenolysis takes place on different sites, most likely on metallic Pt fraction or sites created by abstraction of sulfur from MoS₂ in the presence of Pt.     

CO2 Hydrogenation to Methanol Over Cu/ZnO/Al2O3 Catalysts Prepared by a Novel Gel-Network-Coprecipitation Method

A novel gel-network-coprecipitation process has been developed to prepare ultrafine Cu/ZnO/Al₂O₃ catalysts for methanol synthesis from CO₂ hydrogenation. It is demonstrated that the gel-network-coprecipitation method can allow the preparation of the ultrafine Cu/ZnO/Al₂O₃ catalysts by homogeneous coprecipitation of the metal nitrate salts in the gel network formed by gelatin solution, which makes the metallic copper in the reduced catalyst exist in much smaller crystallite size and exhibit a much higher metallic copper-specific surface area. The effect of the gel concentration of gelatin on the structure, morphology and catalytic properties of the Cu/ZnO/Al₂O₃ catalysts for methanol synthesis from hydrogenation of carbon dioxide was investigated. The Cu/ZnO/Al₂O₃ catalysts prepared by the gel-network-coprecipitation method exhibit a high catalytic activity and selectivity in CO₂ hydrogenation to methanol.     

Preparation,characterization and hydrotreating performances of ZrO2–Al2O3-supported NiMo catalysts

A series of Al₂O₃–ZrO₂ composite supported NiMo catalysts with various ZrO₂ contents were prepared. Several techniques including XRD, SEM, N₂ physisorption, H₂-TPR, and UV–vis DRS were used for typical physico-chemical properties characterization of the ZrO₂–Al₂O₃ composite supports and their NiMo/ZrO₂–Al₂O₃ catalysts. The test results showed that the composite supports prepared by the chemical precipitation method existed as amorphous phase in the samples with insufficient contents of ZrO₂, and the incorporation of ZrO₂ into supports provided a better dispersion of NiMo species, which made their reductions become easier. The pyridine-adsorbed FT-IR results indicated that the Lewis acid sites of catalysts increased significantly by the introduction of ZrO₂ into the supports. The activities of these catalysts for diesel oil hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) were evaluated in a high pressure micro-reactor system. The results showed that the ZrO₂–Al₂O₃-supported NiMo catalysts with suitable ZrO₂ contents exhibited much higher catalytic activities than that of Al₂O₃-supported one, and when the ZrO₂ contents were 15% and 5%, the NiMo/Al₂O₃–ZrO₂ catalysts presented the highest HDS and HDN activities, respectively.     

Modification of the alumina‐supported Mo‐based hydrodesulfurization catalysts by tungsten

The incorporation effect of tungsten as an activity‐promotional modifier into the Ni‐promoted Mo/γ‐Al₂O₃ catalyst was studied. Series of W‐incorporated catalysts with different content of tungsten were prepared by changing the impregnation order of nickel and tungsten onto a base Mo/γ‐Al₂O₃. Catalytic activities were measured from the atmospheric reactions of thiophene hydrodesulfurization (HDS) and ethylene hydrogenation (HYD). The HDS and HYD activities of the WMo/γ‐Al₂O₃ catalysts (WM series) initially increased and subsequently decreased with increasing content of tungsten as compared with those of their base Mo/γ‐Al₂O₃. The maximal activity promotion occurred at the W/(W + Mo) atomic ratio 0.025. For the Ni‐promoted Mo/γ‐Al₂O₃ catalysts, the effect of W incorporation was greatly dependent on the impregnation order of tungsten. The catalysts prepared by impregnating Ni onto the WMo/γ‐Al₂O₃ catalysts showed the same trend of activity promotion as for the WM series, while those by impregnating W onto a NiMo/γ‐Al₂O₃ catalyst resulted in lower activities than their base NiMo/γ‐Al₂O₃ catalyst. To characterize the catalysts, temperature‐programmed reduction and low‐temperature oxygen chemisorption were conducted. The effects of W incorporation on the NiMo‐based catalysts were discussed in reference to those on the CoMo‐based catalysts. This revised version was published online in July 2006 with corrections to the Cover Date.     

Comparison of product selectivity during hydroprocessing of bitumen derived gas oil in the presence of NiMo/Al2O3 catalyst containing boron and phosphorus

A detailed experimental study was performed in a trickle-bed reactor using bitumen derived gas oil. The objective of this work was to compare the activity of NiMo/Al₂O₃ catalyst containing boron or phosphorus for the hydrotreating and mild hydrocracking of bitumen derived gas oil. Experiments were performed at the temperature and LHSV of 340-420 °C and 0.5-2 h⁻¹, respectively, using NiMo/Al₂O₃ catalysts containing 1.7 wt% boron or 2.7 wt% phosphorus. In the temperature range of 340-390 °C, higher nitrogen conversion was observed from boron containing catalyst than that from phosphorus containing catalyst whereas in the same temperature range, phosphorus containing catalyst gave higher relative removal of sulfur than boron containing catalyst. Phosphorus containing catalyst showed excellent hydrocracking and mild hydrocracking activities at all operating conditions. Higher naphtha yield and selectivity were obtained using phosphorus containing catalyst at all operating conditions. Maximum gasoline selectivity of ∼45 wt% was obtained at the temperature, pressure, and LHSV of 400 °C, 9.4 MPa and 0.5 h⁻¹, respectively, using catalyst containing 2.7 wt% phosphorus.     

Hydrogenation of phenol with supported Rh catalysts in the presence of compressed CO2: Its effects on reaction rate, product selectivity and catalyst life

Hydrogenation of phenol to cyclohexanone and cyclohexanol in/under compressed CO₂ was examined using commercial Rh/C and Rh/Al₂O₃ catalysts to investigate the effects of CO₂ pressurization on the total conversion and the product selectivity. Although the total rate of phenol hydrogenation with Rh/C was lowered by the presence of CO₂, the selectivity to cyclohexanone was improved at high conversion levels >70%. On the other hand, the activity of Rh/Al₂O₃ was completely lost in an early stage of reaction. The features of these multiphase catalytic hydrogenation reactions using compressed CO₂ were studied in detail by phase behavior and solubility measurements, in situ high-pressure FTIR for molecular interactions of CO₂ with reacting species and formation/adsorption of CO on the catalysts, and simulation of reaction kinetics using a simple model. The CO₂ pressurization was shown to suppress the hydrogenation of cyclohexanone to cyclohexanol, improving the selectivity to cyclohexanone. The formation and adsorption of CO were observed for the two catalysts at high CO₂ pressures in the presence of H₂, which was one of important factors retarding the rate of hydrogenation in the presence of CO₂. It was further indicated that the adsorption of CO on Rh/Al₂O₃ was strong and caused the complete loss of its activity.     

Catalytic Properties of Cr2O3 Doped with MgO Supported on MgF2 and Al2O3

Catalytic properties of Cr₂O₃ supported on MgF₂ or Al₂O₃ have been modified by magnesium oxide. The catalysts have been obtained by the co-impregnation method and characterised by: BET, XRD and TPR. As follows from the results, the oxides supported on magnesium fluorine react with each other already at 400 °C, leading to formation of an amorphous spinel-like phase. On the Al₂O₃ support such an MgCr₂O₄ spinel has appeared at much higher temperatures. The addition of magnesium oxide has a significant effect on the activity and selectivity of the catalysts studied in the CO oxidation reaction at room temperature and in the reaction of cyclohexane dehydrogenation. The magnesium–chromium catalysts supported on MgF₂ have been found to show much higher activity and selectivity than the analogous systems supported on Al₂O₃.     

Mechanisms of hydrodenitrogenation of alkylamines and hydrodesulfurization of alkanethiols on NiMo/Al2O3, CoMo/Al2O3, and Mo/Al2O3

The simultaneous hydrodenitrogenation (HDN) of alkylamines and hydrodesulfurization (HDS) of alkanethiols, with the NH₂ and SH groups attached to primary, secondary, and tertiary carbon atoms, were studied at 270–320 °C and 3 MPa over sulfided NiMo/Al₂O₃, CoMo/Al₂O₃, and Mo/Al₂O₃ catalysts. Pentylamine and 2-hexylamine reacted by substitution with H₂S to form alkanethiols and with another amine molecule to form dialkylamines. Alkenes and alkanes were not formed directly from pentylamine and 2-hexylamine, but indirectly by elimination and hydrogenolysis of the alkanethiol intermediates, as confirmed by their secondary behavior and the similar alkene/alkane ratios in the simultaneous reactions of amines and thiols. Only 2-methyl-2-butylamine, with the NH₂ group attached to a tertiary carbon atom, produced alkenes as primary products by E1 elimination. NiMo/Al₂O₃ and CoMo/Al₂O₃ have a higher activity for the HDS of alkanethiols than does Mo/Al₂O₃; H₂S has a negative influence. This shows that the thiols react on vacancies on the catalyst surface (Lewis acid sites). Mo/Al₂O₃ is the best HDN catalyst; H₂S has a positive influence on the HDN of amines with the NH₂ group attached to a secondary and a tertiary carbon atom. This indicates that the HDN of alkylamines occurs on Brønsted acid sites.     

Enantioselective hydrogenation of ethyl pyruvate on tin promoted Pt/Al2O3 catalysts

The enantioselective hydrogenation of ethyl pyruvate has been studied on a Pt/Al₂O₃-dihydrocinchonidine catalyst promoted with different amount of tin. The surface reaction between hydrogen adsorbed on Pt and tin tetraalkyls is used for the tin introduction. This reaction leads to the formation of surface organometallic complexes (I), with SnR_(4-x) moieties anchored to the platinum surface. The enantioselectivity of the Pt/Al₂O₃-dihydrocinchonidine catalyst is found to change only slightly upon promotion with tin, while the rate of ethyl pyruvate hydrogenation depends strongly on the amount and the form of tin introduced. The hydrogenation activity is suppressed completely at relatively low tin coverage (Sn/Pt_s < 0.06). The highest hydrogenation rate is measured over catalysts containing complex (I) (Sn/Pt_s = 0.025) on the platinum surface. On Sn-Pt alloy type active sites, which are formed after decomposition of (I) in hydrogen, the rate of hydrogation is considerably lower than on the unpromoted reference Pt/Al₂O₃ catalyst.On leave from the Central Research Institute for Chemistry of the Hungarian Academy of Sciences.     

Promoting effect of NiAl2O4 for supported Ni particles on sprayed Ni/Al2O3 catalysts

Ni/Al₂O₃ catalysts were prepared by the spray reaction method. The NiO particles supported on NiAl₂O₄ were stabilized against the aggregation and converted into smaller Ni particles by H₂ reduction. The Ni particles stabilized on NiAl₂O₄ marked anomalous high activity for CO hydrogenation, due to the stronger interaction between Ni and NiAl₂O₄. This revised version was published online in July 2006 with corrections to the Cover Date.     

Highly selective catalytic hydrodeoxygenation of guaiacol to cyclohexane over Pt/TiO2 and NiMo/Al2O3 catalysts

Catalysts Pt/TiO₂ and NiMo/Al₂O₃ are highly active and selective for the hydrodeoxygenation of guaiacol in a fixed bed reactor at 300 °C and 7.1 MPa, leading to the hydrogenation of aromatic ring, followed by demethylation and dehydroxylation to produce cyclohexane. For a complete hydrodeoxygenation of guaiacol, metal sites and acid sites are required. NiMo/Al₂O₃ and Pt/Al₂O₃ are more active and selective for cyclohexane formation as compared with Pt/TiO₂ at 285 °C and 4 MPa. However, Pt/TiO₂ is stable while the other two catalysts deactivate due to the nature and amount of coke formation during the reaction.     

Reactivity of surface isocyanate species with NO, O2 and NO+O2 in selective reduction of NOχ over Ag/Al2O3 and Al2O3 catalysts

Reactivity of surface isocyanate (NCO(a)) species with NO, O₂ and NO+O₂ in selective reduction of NOχ over Ag/Al₂O₃ and Al₂O₃ catalysts was studied by a pulse reaction technique and an in situ diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy. The NCO(a) species on Ag/Al₂O₃ reacted with O₂ or NO+O₂ mixture gas to produce N₂ effectively above 200°C, while the reaction of NCO(a) with NO hardly produced N₂ even at 350°C. In the case of Al₂O₃ alone, less N₂ was detected in the reaction of NCO(a) with NO+O₂, indicating that silver plays an important role in the N₂ formation from NCO(a). These behaviors of the reactivity of NCO(a) species with reactant gases were in good agreement with the changes in NCO(a) bands shown by in situ DRIFT measurements. Based on these findings, the role of NCO(a) species in the selective reduction of NOχ on Ag/Al₂O₃ and Al₂O₃ catalysts is discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Catalytic Activities of Al2O3-promoted NiSO4/TiO2 for Acid Catalysis

A series of catalysts, NiSO₄/Al₂O₃–TiO₂, for acid catalysis was prepared by the impregnation method, where support, Al₂O₃–TiO₂ was prepared by the coprecipitation method using a mixed aqueous solution of titanium tetrachloride and aluminum nitrate solution followed by adding an aqueous ammonia solution. The addition of nickel sulfate (or Al₂O₃) to TiO₂ shifted the phase transition of TiO₂ from amorphous to anatase to higher temperature because of the interaction between nickel sulfate (or Al₂O₃) and TiO₂. 15-NiSO₄/5-Al₂O₃–TiO₂ containing 15 wt% NiSO₄ and 5 mol% Al₂O₃, and calcined at 400°C exhibited maximum catalytic activities for both reactions, 2-propanol dehydration and cumene dealkylation. The catalytic activities for both reactions were correlated with the acidity of catalysts measured by the ammonia chemisorption method. The charge transfer from Ti atoms to the neighboring Al atoms strengthens the Al–O bond between Al and the surface sulfate species. The addition of Al₂O₃ up to 5 mol% enhanced the acidity, thermal property, and catalytic activities of NiSO₄/Al₂O₃–TiO₂ gradually due to the interaction between Al₂O₃ and TiO₂ and consequent formation of Al–O–Ti bond.     

Investigation of the sulfidation of Mo/TiO2-Al2O3 catalysts by TPS and LRS

A series of Mo/Al₂O₃ and Mo/TiO₂-Al₂O₃ catalysts were investigated by temperature programmed sulfiding (TPS) and laser Raman spectroscopy (LRS). The effect of TiO₂ on the sulfidability of molybdena was studied in detail. It is found that Mo/Al₂O₃ catalysts can be partially sulfided by O-S exchange at low temperature, forming molybdenum oxysulfide. The Mo-S bond subsequently ruptures in the presence of H₂ to produce H₂S. At 530–550 K deep sulfiding of molybdenum oxysulfide occurs forming crystalline MoS₂. When the surface of Al₂O₃ was covered by a monolayer of TiO₂, the sulfiding rate of molybdena at low temperature was not only greatly increased, but H₂S produced in the reduction of Mo-S species caused deep sulfiding of the catalyst which resulted in a decrease of the TPS peak temperature by 80–100 K. The results indicate that this promotion of the sulfiding of molybdena is enhanced with TiO₂ loading. The function of TiO₂ is explained by the weakened interaction between MoO₃ and Al₂O₃ due to the coverage of the Al₂O₃ surface by TiO₂.     

The effect of Pd/Al2O3 pretreatment on catalytic activity in cyclopentane/deuterium exchange

Big variations in overall activity and product selectivity in the cyclopentane/deuterium exchange reaction were found in effect of various pretreatments of two chlorine‐free Pd/γ‐Al₂O₃ catalysts. The most important changes are observed when severely prereduced (at 600 °C) Pd/Al₂O₃ catalysts have been reoxidised and mildly rereduced: the multiple type of exchange, typical of mildly pretreated Pd catalysts, is replaced by a stepwise mode, and a big increase in catalytic activity occurs. At this state, the Pd/γ‐Al₂O₃ catalysts retain some water (as surface hydroxyls) generated by reoxidation and mild reduction. Deuterium spillover from Pd onto alumina and changes in acidity of alumina are invoked to rationalize the kinetic results. Changes in the state of Pd after various pretreatments, as probed by temperature‐programmed hydride decomposition, can hardly be correlated with changes in the catalytic behaviour in the exchange reaction. This revised version was published online in August 2006 with corrections to the Cover Date.     

Synergetic effect of combined use of Cu–ZnO–Al2O3 and Pt–Al2O3 for the steam reforming of methanol

Commercial Cu–ZnO–Al₂O₃ catalysts are used widely for steam reforming of methanol. However, the reforming reactions should be modified to avoid fuel cell catalyst poisoning originated from carbon monoxide. The modification was implemented by mixing the Cu–ZnO–Al₂O₃ catalyst with Pt–Al₂O₃ catalyst. The Pt–Al₂O₃ and Cu–ZnO–Al₂O₃ catalyst mixture created a synergetic effect because the methanol decomposition and the water–gas shift reactions occurred simultaneously over nearby Pt–Al₂O₃ and Cu–ZnO–Al₂O₃ catalysts in the mixture. A methanol conversion of 96.4% was obtained and carbon monoxide was not detected from the reforming reaction when the Pt–Al₂O₃ and Cu–ZnO–Al₂O₃ catalyst mixture was used.     

Determination of the nature of distinct catalytic sites in hydrodenitrogenation by competitive adsorption

The inhibitive effect of nitrogen-containing compounds on hydrodenitrogenation was studied over NiMo(P)/Al₂O₃ catalysts. From the differences in the adsorption constants it is concluded that at least four distinct catalytic sites are involved in the elementary hydrodenitrogenation steps. The catalytic site for the cleavage of aliphatic C(sp³)-N bonds is acidic and most probably an SH species on a surface Mo or Ni site. The catalytic site for the hydrogenation of a phenyl group is different from that for alkene hydrogenation, the former being more coordinately unsaturated than the latter, with two or three sulphur vacancies. A fourth site is responsible for the hydrogenolysis of the C(sp²)-N bond of anilines. It is characterised by a more reduced environment of Mo and by phosphorus promotion. This revised version was published online in July 2006 with corrections to the Cover Date.