Synthesis and characterization of cobalt–molybdenum bimetallic carbides catalysts

Co₃Mo₃C, Co₆Mo₆C and MCM41-supported Co₃Mo₃C catalyst are prepared by a simple one-step thermal decomposition method without the conventional temperature-programmed carburization. The resultant carbides are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscope (HRTEM) and BET surface area measurements. The as-prepared Co₃Mo₃C/MCM41 catalyst exhibits good performance in both probe reactions of hydrodesulfurization (HDS) and hydrodenitrogenation (HDN), which proves the one-step decomposition method to be an effective route for the preparation of bimetallic carbide catalyst.     

Physico-chemical characterization and catalysis on SBA-15 supported molybdenum hydrotreating catalysts

SBA-15 supported Mo, CoMo, NiMo catalysts were prepared. The supports were characterized by surface area, pore size distribution, and X-ray diffraction. The finished catalysts in oxide state were characterized by surface area analysis and X-ray diffraction in the region where the molybdenum oxide lines are seen. The sulfided catalysts were examined by oxygen chemisorption at low temperatures. The catalytic functionalities of these catalysts viz hydrodesulfurization (HDS) and hydrogenation were evaluated on sulfided catalysts. The catalytic activities of these catalysts are compared with γ-Al₂O₃- and SiO₂-supported catalysts. An attempt is made to understand the relationship between oxygen chemisorption and catalytic activities with the help of other characterization results.     

Synthesis of mixed alcohols from CO2 contained syngas on supported molybdenum sulfide catalysts

The performances of active carbon supported molybdenum sulfide catalysts prepared by different procedures or promoted by different elements in the synthesis of mixed alcohols from CO₂ containing syngas were examined. The results showed that high alcohol activity and selectivity could be obtained by employing a rapid drying procedure and employing a H₂S---H₂ stream for (NH₄)₂MoS₄ decomposition. Addition of Co, Cr and Cl to K---Mo/C catalyst led to an increase in the alcohol activity or selectivity. The presence of CO₂ in the feed caused a greater amount of water to be produced but reduced the formation of CO₂. The product distribution was also strongly influenced by the presence of either CO₂ or H₂S in the feed. Addition of CO₂ reduces the formation of higher alcohols while H₂S increases higher alcohol formation.     

Conversion of methane to benzene over Mo2C and Mo2C/ZSM-5 catalysts

The activation and dehydrogenation of CH₂ on Mo₂C and MO₂C/ZSM-5 have been investigated under non-oxidizing conditions. Unsupported Mo₂C exhibited very little activity towards methane decomposition at 973 K. The main reaction pathway was the decomposition of methane to give hydrogen and carbon with a trace amount of ethane. Mixing Mo₂C with ZSM-5 support somewhat enhanced its catalytic activity, but did not change the products of the reaction. A dramatic change in the product formation occurred on partially oxidized Mo2C/ZSM-5 catalyst; besides some hydrocarbons benzene was produced with a selectivity of 70–80% at a conversion of 5–7%. Carburization of highly dispersed MoO₃ on ZSM-5 also led to a very active catalyst: the conversion of methane at the steady state was 5–6% and the selectivity of benzene formation was 85%.This laboratory is a part of the Center for Catalysis, Surface and Material Science at the University of Szeged.     

Preparation, characterization, and catalytic properties of the Mo2C/SBA-15 catalysts

A series of Mo₂C/SBA-15 catalysts with different Mo contents were prepared by temperature-programmed carburization (TPC). The materials obtained and their oxide precursors (MoO₃/SBA-15) were characterized by Nitrogen adsorption-desorption isotherms, X-ray diffraction (XRD), and Fourier transform-infrared (FT-IR) spectroscopy. The activities of the catalysts for deep hydrodesulfurization (HDS) of thiophene were evaluated. The results of N₂ adsorption-desorption isotherms indicated that the surface area and pore diameter of the oxide precursors increase after carburization. The XRD patterns show that Mo₂C particles are highly dispersed in the SBA-15 ordered mesoporous. The test results show that Mo₂C/SBA-15 catalysts have an excellent performance for the deep HDS under the lower temperature region.     

Aromatization of ethanol on Mo2C/ZSM catalysts

The reaction of ethanol was investigated on Mo₂C, Mo₂C/SiO₂ and Mo₂C/ZSM-5 catalysts at temperature ranging 573–973 K under atmospheric pressure. Mo₂C and Mo₂C/SiO₂ catalyzed only the decomposition of ethanol to H₂, ethylene, acetaldehyde and different hydrocarbons. The main reaction pathway on pure ZSM-5 is the dehydration reaction yielding ethylene, small amounts of hydrocarbons and aromatics. Deposition of Mo₂C on zeolite greatly enhanced the yield of benzene and toluene by catalyzing the aromatization of ethylene formed in dehydration process of ethanol.     

The promoter function of molybdenum in Rh/Mo/SiO2 catalysts for CO hydrogenation

A series of Rh/Mo/SiO₂ catalysts with fixed Rh and different Mo contents were studied by FT-IR, chemisorption and CO hydrogenation. The FT-IR results at room temperature under CO atmosphere indicate that the addition of Mo to Rh/SiO₂ suppresses the linear and bridged CO species and promotes the twin CO species, which is consistent with the chemisorption results. It is suggested that the Mo promoter works via stabilization of Rh^1– ions and the coverage of Rh sites. The molybdenum promotes the formation of oxygenates and shifts the selectivity from hydrocarbons to oxygenates.     

Synthesis,characterization and hydrotreating performance of supported tungsten phosphide catalysts

Supported tungsten phosphide catalysts were prepared by temperature-programmed reduction of their precursors (supported phospho-tungstate catalysts) in H₂ and characterized by X-ray diffraction (XRD), BET, temperature-programmed desorption of ammonia (NH₃-TPD) and X-ray photoelectron spectroscopy (XPS). The reduction-phosphiding processes of the precursors were investigated by thermogravimetry and differential thermal analysis (TG-DTA) and the suitable phosphiding temperatures were defined. The hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) activities of the catalysts were tested by using thiophene, pyridine, dibenzothiophene, carbazole and diesel oil as the feedstock. The TiO₂, ?-Al₂O₃ supports and the Ni, Co promoters could remarkably increase and stabilize active W species on the catalyst surface. A suitable amount of Ni (3%–5%), Co (5%–7%) and V (1%–3%) could increase dispersivity of the W species and the BET surface area of the WP/?-Al₂O₃ catalyst. The WP/?-Al₂O₃ catalyst possesses much higher thiophene HDS and carbazole HDN activities and the WP/TiO₂ catalyst has much higher dibenzothiophene (DBT) HDS and pyridine HDN activities. The Ni, Co and V can obviously promote the HDS activity and inhibit the HDN activity of the WP/?-Al₂O₃ catalyst. The G-Ni5 catalyst possesses a much higher diesel oil HDS activity than the sulphided industrial NiW/?-Al₂O₃ catalyst. In general, a support or promoter in the WP/?-Al₂O₃ catalyst which can increase the amount and dispersivity of the active W species can promote its HDS and HDN activities.     

以大孔二氧化硅为载体的Cs／SiO2催化剂的制备及表征

提出一种以大孔SiO2为载体,负载碱金属的催化材料的制备方法。用无乳化剂乳液聚合法合成聚苯乙烯（PS）微球为模板剂,对SiO2进行扩孔,制备大孔SiO2载体,用微波负载法负载碱金属Cs,并对催化剂进行相关表征。结果表明,粒径为200～250nm左右的PS为较佳模板剂,扩孔后负载碱金属Cs量为13．28％,制得的Cs／SiO2催化剂孔径约为250nm,比表面积为2．965×10^2m^2·g^-1,总孔容积为1．806cc·g^-1,且在催化合成丙烯酸甲酯的反应中有较高的活性,酯收率在50％以上。     

Synthesis, characterization and hydrotreating performance of supported tungsten phosphide catalysts

Supported tungsten phosphide catalysts were prepared by temperature-programmed reduction of their precursors (supported phospho-tungstate catalysts) in H₂ and characterized by X-ray diffraction (XRD), BET, temperature-programmed desorption of ammonia (NH₃-TPD) and X-ray photoelectron spectroscopy (XPS). The reduction-phosphiding processes of the precursors were investigated by thermogravimetry and differential thermal analysis (TG-DTA) and the suitable phosphiding temperatures were defined. The hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) activities of the catalysts were tested by using thiophene, pyridine, dibenzothiophene, carbazole and diesel oil as the feedstock. The TiO₂, γ-Al₂O₃ supports and the Ni, Co promoters could remarkably increase and stabilize active W species on the catalyst surface. A suitable amount of Ni (3%–5%), Co (5%–7%) and V (1%–3%) could increase dispersivity of the W species and the BET surface area of the WP/γ-Al₂O₃ catalyst. The WP/γ-Al₂O₃ catalyst possesses much higher thiophene HDS and carbazole HDN activities and the WP/TiO₂ catalyst has much higher dibenzothiophene (DBT) HDS and pyridine HDN activities. The Ni, Co and V can obviously promote the HDS activity and inhibit the HDN activity of the WP/γ-Al₂O₃ catalyst. The G-Ni5 catalyst possesses a much higher diesel oil HDS activity than the sulphided industrial NiW/γ-Al₂O₃ catalyst. In general, a support or promoter in the WP/γ-Al₂O₃ catalyst which can increase the amount and dispersivity of the active W species can promote its HDS and HDN activities.     

Aromatization of n-hexane on Mo2C catalysts

The deposition-precipitation method was used to prepare gold catalysts based on different supports. Their catalytic activities for combustion of carbon monoxide (CO) and formaldehyde (HCHO) were investigated. All these catalysts showed good activity for the two reactions and the Au/CeO₂-a catalyst exhibited the highest activity for the two reactions. Furthermore, catalysts derived from the as-precipitate hydroxides exhibited higher activity than that from corresponding oxide supports. The BET, XRD, TEM and XPS were carried out. The results indicated that the gold dispersed more homogeneous on the as-precipitate hydroxide supports than that on the corresponding oxide supports.     

油溶性纳米MoS2加氢催化剂的合成、表征和应用

传统MoS₂加氢催化剂粒径大、油溶性差而催化效率相对较低。纳米粒子合成方法很多，其中液相化学合成技术尤其水(溶剂)热、微乳液、单层二硫化钼重堆积和微波液相介电加热法等更为便捷、高效。在油溶性纳米MoS₂的合成中，表面修饰剂的选择最为关键。综述了油溶性纳米MoS₂的合成、表征和应用研究进展，提出了高稳定性、高活性和油溶性纳米MoS₂加氢催化剂高效合成优化参数，为实现工业应用提供了参考。     

Studies on physico-chemical characterization and catalysis on high surface area titania supported molybdenum hydrotreating catalysts

A series of titania supported molybdenum catalysts were prepared by incipient wetness impregnation method and characterized by BET surface area, XRD, TPR, FTIR, ESCA, and low temperature oxygen chemisorption. Thiophene, cyclohexene and tetrahydrofuran were taken as model compounds for evaluating catalytic activities for hydrodesulfurization (HDS), hydrogenation (HYD), and hydrodeoxygenation (HDO) reactions, respectively. XRD results indicate that molybdenum oxide species are dispersed as a monolayer on the support up to 8 wt.% Mo and the formation of crystalline MoO₃ is observed above this loading. FTIR and TPR results showed that molybdenum oxide species were present predominantly in tetrahedral form at lower loading and polymeric octahedral forms are dominant at higher loading. Both oxygen chemisorption and rates of reaction were found to increase with increasing Mo loading up to 8 wt.% and then decrease with further increase in loading. HDS and HYD activities are more or less same but HDO activity is two times higher than HDS and HYD activities. The results are also interpreted with the help of other parameters, like dispersion, equivalent molybdenum surface area, surface coverage, crystalline size, quasi-turnover frequencies and intrinsic activities. ESCA results suggest that electron transfer is taking place from support to metal.     

Hydrodesulfurization of thiophene on carbon nanofiber supported Co/Ni/Mo catalysts

Co, Mo, NiMo and CoMo catalysts supported on alumina, fishbone and platelet carbon nanofibers (CNFs) have been prepared. The dispersion of the oxide phases was qualitatively studied and compared using X-ray diffraction (XRD) and transmission electron microscopy (TEM). The reducibility of the catalysts was studied by temperature programmed reduction (TPR). Hydrodesulfurization (HDS) of thiophene was used as a model reaction to compare the activity of different catalysts. The activity tests showed that the alumina supported catalysts exhibited higher activity compared to the corresponding CNF supported catalysts, and the NiMo catalysts were more active than the corresponding CoMo catalysts. The thiophene HDS activity was correlated with the dispersion of the molybdenum species and the reducibility of different catalysts. Interestingly, the CNF supported Co catalysts have higher thiophene HDS activity than the CNF supported Co(Ni)Mo catalysts.     

Activity and stability of laser-photoreduced supported molybdenum oxide metathesis catalysts

Photoreduction of MoO₃/SiO₂ and MoO₃/SiO₂·Al₂O₃ catalysts in CO with a laser beam at 308 nm resulted, after addition of cyclopropane to form the active sites, in a high activity for alkene metathesis. Both catalyst systems are active for normal alkenes, e.g. propene, and for functionalized alkenes, e.g. methyl oleate, already at room temperature.     

Dispersion and reactivity of molybdenum oxide catalysts supported on titania

A series of MoO₃ catalysts with Mo loadings ranging from 2 to 10 w/w% supported on TiO₂ were prepared and investigated by X-ray diffraction (XRD), temperature programmed reduction (TPR) and oxygen chemisorption measurements. Dispersion of molybdena was determined by the oxygen chemisorption at 623 K and by static method on the samples prereduced at the same temperature. At low Mo loadings, i.e. below 6% Mo, molybdenum oxide was found to present in a highly dispersed amorphous state. TPR profiles of MoO₃/TiO₂ samples suggest that the reduction of MoO₃ to Mo proceeds in two stages and the reducibility of MoO₃ increases with Mo loading in the catalysts. The catalytic properties were evaluated for the vapor-phase ammoxidation of toluene to benzonitrile and are related to the oxygen chemisorption sites.     

Hydrodesulfurization of dibenzothiophene over supported and unsupported molybdenum carbide catalysts

A series of γ-Al₂O₃ supported molybdenum carbides [carbided Mo/γ-Al₂O₃ (MCS), Co-Mo/γ-Al₂O₃ (CMCS), and Ni-Mo/γ-Al₂O₃ (NMCS)] and unsupported molybdenum carbide (MCUS) were prepared by the temperature-programmed carburization of their corresponding molybdenum nitrides with 20 % CH₄/H₂. XRD and SEM studies show that unsupported molybdenum carbide catalyst possesses a typical crystalline Mo₂C (FCC structure), while supported molybdenum carbide catalysts possess highly dispersed surface molybdenum carbide species on an alumina oxide support. The results of dibenzothiophene (DBT) hydrodesulfurization over molybdenum carbide catalysts show that the reactivity is strongly dependent on the type of catalyst. Supported molybdenum carbide catalysts possess a higher reactivity than the unsupported molybdenum carbide catalyst. In addition, Co or Ni promoted, supported molybdenum carbide catalyst possesses a higher reactivity than the unpromoted, supported molybdenum carbide catalyst. The reactivity, which is also dependent on the reaction conditions, increases with increasing reaction temperature and pressure and contact time. The CO uptakes of the molybdenum carbide catalysts correlate well with overall activity (total rate) for DBT hydrodesulfurization. The major reaction product is biphenyl, with cyclohexylbenzene next in abundance regardless of the type of catalysts and reaction conditions. It was also found that the molybdenum carbide catalysts exhibit stable initial reactivity due to the stable and weak acidic characteristics of these catalysts.     

CO methanation over supported Mo catalysts in the presence of H2S

The effect of various Mo catalyst supports, i.e., γ-Al₂O₃, SiO₂, SiO₂–Al₂O₃, ZrO₂, yttria-stabilized zirconia (YSZ), CeO₂, and TiO₂, on CO hydrogenation in the presence of H₂S was examined. At 5 wt.% Mo loading, Mo/ZrO₂ was determined to be the most active catalyst for this reaction; its activity was dependent on the number of active sites, as determined via NO chemisorption. Raman spectroscopy revealed that MoO₃ transforms into MoS₂ during the reaction.     

Synthesis, characterization and cyclohexene hydrogenation activity of high surface area molybdenum disulfide catalysts

An ammonium tetrathiomolybdate (ATTM) catalyst precursor is synthesized and then thermally decomposed at different temperatures in N₂ or H₂ atmosphere. Characterization of the resulting compounds by powder X-ray diffraction (XRD) and surface area analysis indicates the formation of MoS₂–2H with a surface area of 5–9 m²/g. When ATTM is treated with cetyltrimethylammonium chloride and then decomposed in N₂ at 723 K, the resulting material has a surface area nearing 200 m²/g. If treatment also includes hydrazine, the surface area of the resulting MoS₂–2H reaches 215 m²/g. Analysis by XRD and electron microscopy shows a noticeable dispersion in the layers of the resulting MoS₂. The catalytic activity of the materials is tested in a batch reactor for cyclohexene hydrogenation, where the highest activity sulfides are those obtained by thermal decomposition of the chemically treated precursors in N₂.     

Hierarchical macro-mesoporous Mo/Al2O3 catalysts prepared by dual-template method for oxidative desulfurization

Journal of Porous Materials - A series of Al2O3 materials with hierarchical macro-mesoporous structure were synthesized by a dual-template method, using surfactant Pluronic P123 and polystyene (PS)...