Preparation of MoO3/TiO2 Catalysts with Eggshell and Uniform Mo Distribution by Water-Assisted Spreading of MoO3

MoO₃/TiO₂ catalysts were prepared by reaction of TiO₂ extrudates (140 m²g⁻¹) with a MoO₃/H₂O slurry. The adsorption of molybdena species was strong; sharp, deep eggshell profiles of the Mo concentration were obtained. The hydrodesulfurization activity of saturated catalysts with a uniform Mo distribution (about 10 wt.% MoO₃) was at least the same as that of a sample prepared by conventional impregnation.     

Comparative preparation of MoO3/SiO2 catalysts using conventional and slurry impregnation method and activity in transesterification of dimethy oxalate with phenol

Silica-supported MoO₃ catalyst prepared by slurry impregnation method exhibits higher activity and dispersion capacity compared to the MoO₃/SiO₂ prepared conventionally. Slurry MoO₃/water is used instead of the solution ammonium heptamolybdate. Highly dispersed amorphous Mo catalysts are obtained, which is closely related the catalytic activities, without calcination, waste solutions, and calcining nitrogeous gases. The dependence of catalytic activity on Mo loading for the slurry prepared catalysts was similar to the samples prepared by the conventional impregnation method, indicating the slurry method is a simple and clean alternative to the conventional one.     

High surface area MoO3/MgO: preparation by the new slurry impregnation method and activity in sulphided state in hydrodesulphurization of benzothiophene

High surface area MoO₂/MgO was prepared by the reaction of MgO (250–300 m² g⁻¹) with a slurry of ammonium heptamolybdate in methanol or anhydrous ethanol at the alcohol boiling point. The low solubility of ammonium heptamolybdate was sufficient for its gradual transport to the support surface: molybdena species were deposited and ammonia was evolved. Catalytic activities in the hydrodesulphurization of benzothiophene of the MoO₃/MgO samples were comparable to the activity of the reference commercial MoO₃/Al₂O₃ catalyst. This revised version was published online in July 2006 with corrections to the Cover Date.     

The reduction behavior of Mo/TiO2-Al2O3 catalyst

The effect of TiO₂ modified Al₂O₃ surface on the reducibility of MoO₃ has been studied by TPR and XPS. The results show that Mo⁶⁺ in Mo/TiO₂-Al₂O₃ can be reduced to much lower valency, especially at low Mo loading. The influence of the calcination temperature on the reduction of Mo⁶⁺ on Al₂O₃ and TiO₂-Al₂O₃ carriers is different. The data reveals that the reducibility of Mo⁶⁺ on Al₂O₃ slightly decreased, while that on TiO₂-Al₂O₃ increased when the calcination temperature was raised. It is suggested that the stronger tetrahedral site of the Al₂O₃ surface was first occupied by TiO₂ and main octahedral Mo⁶⁺ in polymeric species-; and a small crystalline MoO₃ formed on TiO₂-Al₂O₃, whereas the formation of tetrahedral Mo⁶⁺ species and Al₂(MoO₄)₃ phase was inhibited.     

Deposition of CoO onto MoO3/Al2O3 hydrodesulfurization catalysts by solvent assisted spreading

Solvent assisted spreading of CoO over monolayer MoO₃/Al₂O₃ catalysts has been studied. CoCO₃ · Co(OH)₂ and CoCO₃ reacted with MoO₃/Al₂O₃ in water slurries. CoO deposition over MoO₃/Al₂O₃ extrudates was followed by EPMA. In the set of eleven MoO₃/Al₂O₃ catalysts, the amount of CoO adsorbed was roughly proportional to the surface area of MoO₃ monolayer. The adsorbed Co species efficiently enhanced the HDS activity.     

Hydration effects of Al2(MoO4)3 and AlPO4 phases in hydrotreating catalysts studied by solid state nuclear magnetic resonance spectroscopy

Solid state nuclear magnetic resonance spectroscopy of²⁷Al,³¹P, and⁹⁵Mo nuclei was used to investigate species on a NiPMo/Al₂O₃ hydrotreating catalyst calcined at 750 °C before and after rehydration. The Al₂(MoO₄)₃ phase disappeared after rehydration in 100% relative humidity at room temperature. However, almost none of the observed crystalline AlPO₄ reacted with adsorbed water. The results show that the Al₂(MoO₄)₃ phase on an alumina surface reacts easily with moisture unlike Al₂(MoO₄)₃ in the bulk phase. It also suggests that the crystalline AlPO₄ phase is formed under the Al₂(MoO₄)₃ phase or that both species are formed as neighboring islands on the surface of the alumina but have different reactivities toward moisture.     

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.     

Pretreatment effects and NO x decomposition on alumina supported Rh/MoO3 catalysts

Rh-MoO₃/Al₂O₃, Rh/Al₂O₃ and MoO₃/Al₂O₃ catalysts have been prepared and subjected to various pretreatments including high temperature reduction, high temperature oxidation and oxidation/ reduction cycles. After each series of treatments, surfaces were analysed by XPS and FTIR of adsorbed NO. The effectiveness of these surfaces in dissociating NO was studied by TPRS in the temperature range 300–773 K. Reduction rates of Mo oxides in H₂ were determined gravimetrically while rhodium dispersion was determined from H₂ adsorption isotherms at 298 K. Results indicate that molybdenum and rhodium exist in close contact in both oxidised and reduced forms. H₂ chemisorption was suppressed following HTR of the catalyst due to coverage of rhodium by molybdenum oxide species but this could be reversed by HTO (773 K) followed by low temperature reduction. Although a small proportion of Mo could be reduced following HTR, cycles of HTR/HTO produced Rh/Mo oxide phases in which a proportion of Mo could be reduced to Mo° at 473 K. The presence of reduced Mo would appear to play an important role in the improved performance of Rh-MoO₃/Al₂O₃ catalysts.     

Characterization of hydrodesulfurization catalyst prepared by impregnating cobalt nitrate solution onto the sulfided MoO3/Al2O3 catalyst

CoMo/Al₂O₃ catalysts were prepared by impregnating Cobalt nitrate solution into oxidic or sulfided Mo/Al₂O₃. The properties of CoMo/Al₂O₃ catalysts were characterized by XRD, TPS, oxygen chemisorption and ESR. Catalytic activity of CoMo/Al₂O₃ catalyst was evaluated by thiophene HDS as a probe reaction. When CoMo/Al₂O₃ catalyst was prepared by impregnating Cobalt nitrate solution into sulfided Mo/Al₂O₃, the interaction between Mo and alumina became weaker and the formation of synergic phase was facilitated. These structural changes may explain higher HDS activity of CoMo/Al₂O₃ catalyst prepared by impregnating Cobalt nitrate solution into sulfided Mo/Al₂O₃.     

Preparation of alumina supported molybdena catalysts by new slurry impregnation method: MoO3/Al2O3 sulfide hydrodesulfurization catalyst

A new slurry impregnation method (SIM) of the preparation of a catalyst or catalyst precursor MoO₃/Al₂O₃ is described. Aqueous slurry of powdered MoO₃ is mixed with alumina extradátes and the mixture is refluxed. A low solubility of MoO₃ is sufficient for transport of MoO₃ from powder form via solution to the surface of the support. The catalysts were tested by hydrodesulfurization of thiophene at 1.6 MPa and 280–400°C. Their activity was similar to the activity of industrial and laboratory MoO₃/Al₂O₃ samples prepared by conventional impregnation with solution of ammonium heptamolybdate. The advantage of the SIM method is that calcination, producing nitrogeneous waste gases, is not required and that all deposited molybdenum species are adsorbed and not precipitated.     

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.     

Slurry Impregnation of ZrO2 Extrudates: Controlled EggShell Distribution of MoO3, Hydrodesulfurization Activity, Promotion by Co

Catalysts with eggshell/uniform Mo concentration profiles were prepared by a reaction of ZrO₂ and ZrO(OH)₂ extrudates with an aqueous slurry of MoO₃. The thickness of the shell was regulated by the amount of MoO₃. CoCO₃ was adsorbed onto MoO₃/ZrO₂ from its aqueous slurry. The ZrO₂-supported catalysts were compared to their TiO₂-supported and industrial reference Al₂O₃-supported counterparts in a model reaction of benzothiophene hydrodesulfurization.     

The effect of sodium on the catalytic activity of ZnO–Al2O3/ZSM-5 and SnO–Al2O3/ZSM-5 for the transesterification of vegetable oil with methanol

In order to elucidate the effect of sodium on the activity of ZSM-5 supported metal oxides catalysts (ZnO–Al₂O₃/ZSM-5 and SnO–Al₂O₃/ZSM-5) for the transesterification of soybean oil with methanol, ZSM-5 supported metal oxides were prepared with and without sodium hydroxide by impregnation. The metal compositions of the ZSM-5 supported metal oxide catalysts and the metal concentrations dissolved from the catalysts to the methylester phase were measured by SEM-EDS and inductive coupled plasma spectroscopy, respectively. The catalytic activity of ZnO–Al₂O₃/ZSM-5 and SnO–Al₂O₃/ZSM-5 containing sodium did not originate from surface metal oxides sites, but from surface sodium sites or dissolved sodium leached from the catalyst surface.     

Effects of sintering additives on dispersion properties of Al2O3 slurry containing polyacrylic acid dispersant

The effects of sintering aid adsorption on the dispersion properties of aluminum oxide slurries were investigated. We considered Al₂O₃ slurry without additives and Al₂O₃ slurry with a Mg additive with 0.1 mass% in oxide equivalent as a sintering aid. In this study, we evaluated the adsorption isotherm of polyacrylic acid (PAA) onto Al₂O₃ and the dispersion degree of Al₂O₃ slurries in sedimentation tests under gravity. The adsorption isotherm featured a characteristic adsorption isothermal line with a maximum value when Mg additive was present in Al₂O₃. In addition, the packing fractions did not correspond to the apparent viscosity. However, in slurry that was allowed to settle for several days, both of them agreed.Therefore, the disagreement between the packing fraction and the apparent viscosity immediately after preparation arose from changes of the dispersion state, such as the decrease of the distance between particles with time.     

Electrolytic deposition of Ni-Co-Al2O3 composite coating on pipe steel for corrosion/erosion resistance in oil sand slurry

To improve the resistance of the hydrotransport pipe steel to corrosion and erosion in oil sand slurry, a Ni-Co-Al₂O₃ composite coating was fabricated by electrolytic deposition on X-65 pipe steel substrate. Potentiodynamic polarization curve and electrochemical impedance measurements show that the deposited coating significantly improves the corrosion resistance of the steel in water-oil-sand solution that simulates the chemistry of oil sand slurry. The corrosion resistance of the coating increases with the increasing Al₂O₃ particle concentration in electrolyte, cathodic current density, electrode rotating speed and temperature. However, a maximum value of corrosion resistance as a function of the depositing parameters is observed, indicating that the optimal electrodepositing parameters and operating conditions are essential to the maximization of the corrosion resistance of the coated steel in oil sand slurry. The optimal depositing conditions are suggested in the given system. The morphology, structure and composition of the coatings were characterized by scanning electron microscopy and energy-dispersive X-ray analysis. The Ni-Co-Al₂O₃ composite coating develops a compact, uniform, nodular structure with an average thickness of 50-200 microns. The Al₂O₃ amount in the coating increases with the increasing Al₂O₃ concentration in electrolyte, which also enhances the co-deposition of Ni and Co. The micro-hardness and wear resistance of the composite coatings are much higher than the steel substrate and increase with the increasing Al₂O₃ particle amount in the coating.     

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.     

Hydrotreating of Heavy Gas Oil Derived from Athabasca Bitumen Over Co–Mo/γ-Al2O3 Catalyst Prepared by Sonochemical Method

Co–Mo/γ-Al₂O₃ oxide containing 9.8 wt% Mo and 2.9 wt% Co was prepared by high-intensity ultrasonic irradiation of Mo(CO)₆, Co₂(CO)₈, and γ-Al₂O₃ in decahydronapthalene under air flow. The oxidic Co–Mo catalyst thus formed was characterized by elemental analysis, BET N₂ adsorption and XRD. The surface sites on the sulfided Co–Mo/γ-Al₂O₃ catalyst were characterized by infrared spectroscopy of CO adsorption. Hydrodenitrogenation (HDN) and hydrodesulfurization (HDS) activities were evaluated for heavy gas oil derived from Athabasca bitumen in a trickle bed reaction system using the following conditions: temperatures ranging from 370 to 400 °C, a pressure of 8.8 MPa, a liquid hourly space velocity of 1 h⁻¹, and a H₂/feed ratio of 600 ml/ml. The dispersion, nature of active sites and hydrotreating activity of this catalyst were compared with the conventionally prepared Co–Mo/γ-Al₂O₃ catalyst containing similar wt% of Mo and Co. The Co–Mo catalyst prepared by sonochemical method has higher HDN and HDS rate constants than the conventional catalyst due to an improved dispersion of MoS₂.     

Effect of method of preparation on activity of Pd/Al2O3 monolith catalysts

Pd/Al₂O₃ monolithic catalyst of different washcoat thicknesses were prepared by two methods and tested for the activity of hydrogenation of α‐methyl styrene. These catalysts were prepared by two methods; either the palladium was impregnated on γ‐alumina and this Pd/Al₂O₃ powder was used to prepare the slurry for washcoating (Cat 1) or γ‐alumina washcoating was followed by impregnation of palladium (Cat 2). The effect of slurry concentration, pH of the slurry, and addition of binders on the catalyst properties was investigated. The monolithic catalysts were characterised by determination of metal dispersion, surface area, scanning electron microscopy, and weight loss of washcoat during ultrasonication. Well‐adhered washcoats were obtained with slurry prepared using milled γ‐alumina, whereas the adhesion of the washcoat prepared using Pd/Al₂O₃ powders was very poor. Addition of binders significantly improved the adhesion of the washcoats prepared from Pd/Al₂O₃. Metal dispersion for Cat 2 decreased with washcoat loading but did not change with loading for Cat 1. The activity tests were conducted at different washcoat loadings and the productivity of the monolithic catalyst prepared in both methods has been compared.     

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.     

Mechanistic Study of Selective Oxidation of Dimethyl Ether to Formaldehyde over Alumina-supported Molybdenum Oxide Catalyst

XPS and IR spectroscopies were used to investigate the surface intermediates of dimethyl ether (DME) oxidation to formaldehyde over MoOx/Al₂O₃ catalyst. The reaction performances were tested by employing three typical reaction conditions, depending on the O₂/DME ratio and the reaction temperature. When there was sufficient oxygen present in the reaction media, a terminal or bridged CH₃O* species formed by DME dissociation was highly active and rapidly reacted with lattice oxygen to produce formaldehyde, leading to higher selectivity of HCHO. When oxygen was consumed completely or only DME was present in the reaction media, CH₃O species bonded to more than two Mo atoms (μ-OCH₃) and CH_x (x=1–3) species attached to the Mo atoms were observed and the relative ratio of (μ-OCH₃) /Mo–CH_x was significantly dependent on the reduction degree of MoO_x domains. The (μCH₃O) species was related to the formation of CH₃OH or CO_x, and the Mo–CH_x species led to the formation of CH₄.