Ruthenium molybdenum sulphide catalysts : physicochemical characterization and catalytic properties in HDS, hydrogenation and HDN reactions.

Alumina supported RuMo sulphide catalysts having different weights of metal content and atomic composition ratios R=Ru/(Ru+Mo) were prepared by using ammonium heptamolybdate dissolved in water or a 10% (NH₄)₂S-H₂O solution and RuCl₃.3H₂O as precursor compounds. Their activities were studied in the hydrodesulphurization (HDS) of thiophene and in the hydrogenation (HYD) of biphenyl, and optimized in terms of the preparation method and the sulphidation process. Some hydrodenitrogenation (HDN) tests were also performed on these catalysts. Electron microscopy and XPS measurements were performed, and the nature of the active phase was discussed.     

CO-free hydrogen from steam-reforming of bioethanol over ZnO-supported cobalt catalysts: Effect of the metallic precursor

The ethanol steam-reforming reaction was studied over ZnO-supported cobalt catalysts (10 wt.% Co). Catalysts were prepared by impregnation of nitrate and carbonyl cobalt precursors. Characterization was accomplished by transmission electron microscopy (TEM), Raman spectroscopy, UV-Vis diffuse reflectance spectroscopy (DRS), X-ray diffraction (XRD), and in situ techniques: magnetic measurements, and diffuse reflectance infrared spectroscopy (DRIFT) coupled to mass spectrometry. The use of Co₂(CO)₈ as precursor produced a catalyst that was highly stable and selective for the production of CO-free hydrogen at reaction temperature as low as 623 K. The only by-product was methane and selectivity of 73% to H₂ and 25% to CO₂ was obtained. Under reaction conditions, the catalyst showed 92% of reduced cobalt, mainly as small particles.     

Preparation of niobates of rhodium and nickel and their catalytic behaviors during calcination and reduction treatments

Double oxides of Rh and Ni have been prepared by chemical mixing methods. Silica-supported and unsupported RhNbO₄ and NiNb₂O₆ catalysts exhibited strong metal-oxide interaction behaviors in ethane hydrogenolysis activities after the decomposition of the double oxides by H₂ reduction at 500°C. Silica-supported and zeolite-supported RhVO₄ catalysts showed high activity and selectivity for dehydrogenation of cyclohexane after the decomposition in H₂. The double-oxide catalyst systems can be used as starting materials to obtain high-performance metal catalysts (redispersion of metals by H₂ reduction and regeneration of catalysts by calcination at a high temperature).     

The role of molybdenum in Mo-doped V–Mg–O catalysts during the oxidative dehydrogenation of n-butane

A detailed study on the influence of the addition of molybdenum ions on the catalytic behaviour of a selective vanadium–magnesium mixed oxide catalyst in the oxidation of n-butane has been performed. The catalysts have been prepared by impregnation of a calcined V–Mg–O mixed oxides (23.8 wt% of V₂O₅) with an aqueous solution of ammonium heptamolybdate, and then calcined, and further characterised by several physico-chemical techniques, i.e. S_BET, XRD, FTIR, FT-Raman, XPS, H₂-TPR. MgMoO₄, in addition to Mg₃V₂O₈ and MgO, have been detected in all the Mo-doped samples. The incorporation of molybdenum modifies not only the number of V⁵⁺-species on the catalyst surface and the reducibility of selective sites but also the catalytic performance of V–Mg–O catalysts. The incorporation of MoO₃ favours a selectivity and a yield to oxydehydrogenation products (especially butadiene) higher than undoped sample. In this way, the best catalyst was obtained with a Mo-loading of 17.3 wt% of MoO₃ and a bulk Mo/V atomic ratio of 0.6. From the comparison between the catalytic properties and the catalyst characterisation of undoped and Mo-doped V–Mg–O catalysts, the nature of selective sites in the oxidative dehydrogenation of n-butane is also discussed.     

Selective removal of H2S from coke oven gas

The catalytic performance of some metal oxides in the selective oxidation of H₂S in the stream containing water vapor and ammonia was investigated in this study. Among the catalysts tested, V₂O₅/SiO₂ and Fe₂O₃/SiO₂ catalyst showed good conversion of H₂S with very low selectivity to undesired SO₂. Hydrogen sulfide could be recovered as harmless solid products (elemental sulfur and various ammonium salts), and distribution of solid products was varied with types of catalyst and compositions of reactant. XRD and FT-IR analysis revealed that the salt was mixture of ammonium–sulfur–oxygen compounds. It was noteworthy that V₂O₅/SiO₂ catalyst produced elemental sulfur and ammonium thiosulfate, and that elemental sulfur was principal product on Fe₂O₃/SiO₂ catalyst. Small amount of ammonium sulfate was obtained with the Fe₂O₃/SiO₂ catalyst. In order to elucidate the reaction path, the effects of O₂/H₂S ratio and concentration of NH₃ and H₂O are also studied with the V₂O₅/SiO₂ catalyst.     

Co/Al_2O_3催化剂制备及其合成重质烃的反应性能

以不同孔道结构Al_2O_3作载体,甲醇、乙醇和柠檬酸作分散剂,通过等体积浸渍法制备系列Co/Al_2O_3费托合成催化剂。采用XRD、TG-DSC和H2-TPR等考察制备方法对催化剂结构的影响,并在固定床反应器中对催化剂进行性能评价。结果表明,采用具有适宜孔道结构Al_2O_3作载体才能获得综合性能较好的催化剂,3种分散剂的加入,促进了钴物种在载体上的分散,增强了钴与载体间的相互作用,改善了催化剂费托合成反应活性,显著提高了重质烃时空收率。     

Preparation of Ru metal nanoparticles in mesoporous materials: influence of sulfur on the hydrogenating activity

Hydrogenating catalysts were prepared by inserting Ru into the pores of mesoporous Al-MCM-41 materials by selective adsorption of [Ru(NH₃)₆]³⁺. Ru/support catalysts were obtained after reduction with H₂. The activities of these catalysts in hydrogenation reactions were compared to those of Ru/HY and Ru/SiO₂. The catalytic properties in the absence of sulfur were tested in benzene hydrogenation, and the intrinsic activities of all the catalysts (either supported on mesoporous materials or on zeolites) were identical. It was concluded from this result that the dispersion of the Ru metallic phase was similar for all these catalysts. These samples were tested in the tetralin hydrogenation in pure H₂ and in the presence of H₂S (330 ppm of H₂S in H₂). They were found to be much less active than the zeolite-supported catalysts in the presence of H₂S. It is proposed that the lower activity of the catalysts supported on mesoporous materials is either due to their milder acidity, as evidenced by NH₃-TPD, cumene cracking and pyridine desorption experiments, or to the localization of the Ru nanoparticles on alumina islands.     

自搅拌下CoB/SiO2催化剂催化硼氢化钠水解制氢研究

采用浸渍-化学还原法制备了硼化钴/二氧化硅（CoB/SiO₂）催化剂,并考察了其催化硼氢化钠水解制氢的性能。研究了二氧化硅粒径、硝酸钴与二氧化硅物质的量比、硝酸钴与硼氢化钠物质的量比等条件对催化剂性能的影响,进而考察了催化剂用量、搅拌转速、反应温度等条件对硼氢化钠水解制氢性能的影响。结果表明,在二氧化硅粒径为15 nm、硝酸钴与二氧化硅物质的量比为0.08∶1、硝酸钴与硼氢化钠物质的量比为1∶5条件下,制备的催化剂催化硼氢化钠水解产氢的速率为45.6 mL/（min·g）;因为催化剂粒径很小,伴随硼氢化钠水解产氢产生的动量可以完全消除外扩散速率的影响,搅拌转速对硼氢化钠水解速率的影响很小,硼氢化钠的水解速率随着催化剂用量的增加而增大;随着温度的升高,硼氢化钠的水解速率增大,硼氢化钠水解反应的表观活化能为48.54 kJ/mol,硼氢化钠反应级数为零;催化剂具有良好的重复使用性能和稳定性。     

Strong rhodium–niobia interaction in Rh/Nb2O5, Nb2O5–Rh/SiO2 and RhNbO4/SiO2 catalysts: Application to selective CO oxidation and CO hydrogenation

The extent of Rh–niobia interaction in niobia-supported Rh (Rh/Nb₂O₅), niobia-promoted Rh/SiO₂ (Nb₂O₅–Rh/SiO₂) and RhNbO₄/SiO₂ catalyst after H₂ reduction has been investigated by H₂ and CO chemisorption measurements. These catalysts have been applied to selective CO oxidation in H₂ (CO+H₂+O₂) and CO hydrogenation (CO+H₂), and the results are compared with those of unpromoted Rh/SiO₂ catalysts. It has been found that niobia (NbO_x) increases the activity and selectivity for both the reactions.     

氢气高温还原制备的负载型镍基催化剂用于苯酚加氢的性能

通过等体积浸渍法分别将Ni(NO₃)₂、NiCl₂、NiSO₄ 3种镍前体浸渍于A1₂O₃或SiO₂载体上,然后通过H₂高温还原法制备了负载型镍基催化剂,考察了镍前体、载体种类、镍负载量、反应条件等对镍基催化剂苯酚加氢性能的影响。结果表明,对比3种镍前体,在H₂高温还原体系中Ni(NO₃)₂最容易被还原,制备的镍基催化剂苯酚加氢活性最高。SiO₂负载的镍基催化剂活性远高于γ-Al₂O₃催化剂。适宜的Ni负载量有助于活性组分的分散和催化活性的提高。镍基催化剂的苯酚加氢产物以环己醇为主,相对缓和的反应条件更容易生成环己酮。在非极性溶剂正庚烷或环己烷存在下,苯酚加氢反应速率远远高于极性溶剂水或乙醇存在下的结果,而且环己酮的选择性更高。     

On the nature of the silver phases of Ag/Al2O3 catalysts for reactions involving nitric oxide

The nature of the silver phases of Ag/Al₂O₃ catalysts (prepared by silver nitrate impregnation followed by calcination) was investigated by X-ray diffractograms (XRD), transmission electron microscopy (TEM) and UV–VIS analyses and related to the activity of the corresponding materials for the oxidation of NO to NO₂. The UV–VIS spectrum of the 1.2 wt.% Ag/Al₂O₃ exhibited essentially one band associated with Ag⁺ species and the NO₂ yields measured over this material were negligible. A 10 wt.% Ag/Al₂O₃ material showed the presence of oxidic species of silver (as isolated Ag⁺ cations and silver aluminate), but the UV–VIS data also revealed the presence of some metallic silver. The activity for the NO oxidation to NO₂ of this sample was moderate. The same 10% sample either reduced in H₂ or used for the C₃H₆-selective catalytic reduction (SCR) of NO showed a significantly larger proportion of silver metallic phases and these samples displayed a high activity for the formation of NO₂. These data show that the structure and nature of the silver phases of Ag/Al₂O₃ catalysts can markedly change under reaction feed containing only a fraction of reducing agent (i.e. 500 ppm of propene) in net oxidizing conditions (2.5% O₂). The low activity for N₂ formation during the C₃H₆-SCR of NO (reported in an earlier study) over the high loading sample can, therefore, be related to the presence of metallic silver, which is yet a good catalyst for NO oxidation to NO₂. The reverse observations apply for the oxide species observed over the low loading sample, which is a good SCR catalyst but do not oxidize NO to NO₂.     

A comparative study of supported MoO3 catalysts prepared by the new “slurry” impregnation method and by the conventional method: their activity in transesterification of dimethyl oxalate and phenol

A new preparation method for supported MoO₃ catalyst, slurry impregnation, has been described and compared with the conventional impregnation method. Slurry MoO₃/water is used instead of the solution ammonium heptamolybdate, AHM [(NH₄)₆Mo₇O₂₄]. The MoO₃/γ-alumina, MoO₃/active carbon, and MoO₃/silica catalysts with different Mo loadings were prepared by slurry and by conventional method. The low solubility of MoO₃ was sufficient to transport molybdenum species from solid MoO₃ to the adsorbed phase. The equilibrium was achieved after several hours at 95 °C based on the loading amount of molybdenum. Only the process of drying was needed; calcination was not necessary and was left out. This is an important advantage for active carbon support because oxidative degradation of active carbon impregnated by molybdena starts at a relatively low temperature of about 250 °C during calcination on air. The activity was tested in the transesterification of dimethyl oxalate (DMO) and phenol at 180 °C. The dependences of catalytic activity on Mo loadings for the slurry prepared catalysts were similar to the dependences for the samples prepared by the conventional impregnation method with AHM. The activities of the slurry impregnation MoO₃/γ-Al₂O₃ catalysts were almost the same as those of catalysts prepared conventionally. Although the performances of slurry impregnation MoO₃/SiO₂ catalysts for transesterification of DMO were slightly better than those of the corresponding catalysts prepared by conventional impregnation, no waste solution and no calcining nitrogenous gases were produced. Therefore, we conclude that the new slurry impregnation method for preparation of supported molybdenum catalysts is an environmentally friendly process and a simple, clean alternative to the conventional preparation using solutions of (NH₄)₆Mo₇O₂₄. The present work will lead to a remarkable improvement in the catalyst preparation for the transesterification reaction.     

Effects of iron precursors on the structure and catalytic performance of iron molybdate prepared by mechanochemical route for methanol to formaldehyde

Mechanochemical synthesis has been applied for many novel material preparations and gained more and more attention due to green and high-efficiency recently. In order to explore the influences of iron precursors on structure and performance of iron molybdate catalyst prepared by mechanochemical route, three typical and cheap iron precursors have been used in preparation of iron molybdate catalyst. Many characterization methods have been employed to obtain the physical and chemical properties of iron molybdate catalyst. Results indicate that iron precursors have the significant impact on the phase composition, crystal morphology and catalytic performance in the conversion of methanol to formaldehyde. It is hard to regulate the phase composition by changing Mo/Fe mole ratios for Fe_2(SO_4)_3 as iron precursor. In addition, as for Fe_2(SO_4)_3, the formaldehyde yield is lower than that from iron molybdate catalyst prepared with Fe(NO_3)_3·9H_2O due to the reduction in Fe_2(MoO_4)_3 phase as active phase. Based on mechanochemical and coprecipitation method, the solvent water could be a key factor for the formation of MoO_3 and Fe_2(MoO_4) for FeCl_3·6H_2O and Fe_2(SO_4)_3 as precursors. Iron molybdate catalyst prepared with Fe(NO_3)_3·9H_2O by mechanochemical route, shows the best methanol conversion and formaldehyde yield in this reaction.     

Investigation of bio-ethanol steam reforming over cobalt-based catalysts

The catalytic performance of cobalt catalysts supported on γ-Al₂O₃, TiO₂, ZrO₂ were studied for bio-ethanol steam reforming (BESR) reaction. The supported catalysts (10 wt%Co) were prepared by impregnation and characterized through Thermogravimetric analysis (TGA), H₂ chemisorption, laser Raman Spectroscopy, Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS), and temperature-programmed reaction (TPRxn). The metallic cobalt sites were found to correlate with the BESR reaction activity. The reaction and H₂ chemisorption showed that ZrO₂ supported catalyst showed the best dispersion and best catalytic activity. Over the 10% Co/ZrO₂ catalyst, using a H₂O:EtOH:inert molar ratio of 10:1:75 and a GHSV = 5000 h⁻¹, 100% ethanol conversion and a yield of 5.5 mol H₂/mol EtOH were obtained at 550 °C and atmospheric pressure.     

Selective oxidation of cyclopentene with H_2O_2 by using H_3PW_(12)O_(40) and TBAB as a phase transfer catalyst

The selective oxidation of cyclopentene by aqueous H_2O_2 using H_3PW_(12)O_(40) and tetrabutyl ammonium bromide(TBAB) as a phase transfer catalyst has been investigated. The results show that the presence of TBAB significantly improved the oxidation selectivity of cyclopentene. The effects of the reaction conditions on the conversion of cyclopentene were investigated in detail. The optimal reaction conditions are as follows: the H_3PW_(12)O_(40) to TBAB molar ratio, 1:1–1:3; H_3PW_(12)O_(40) to cyclopentene molar ratio,0.54:100–0.64:100; and molar ratio of H_2O_2 to cyclopentene, 1.6:1. The conversion reached to 59.8% in 4h at 35.0 °C, while the selectivity of glutaraldehyde was 38.0% and the selectivity of 1,2-cyclopentanediol was 55.6%. In addition, a route for oxidation of cyclopentene by aqueous H_2O_2 using a heteropoly acid and quaternary ammonium salt as a phase transfer catalyst was proposed.     

Metal sols as a useful tool for heterogeneous gold catalyst preparation: reinvestigation of a liquid phase oxidation

Differently stabilised metal sols have been used as precursors in the preparation of heterogeneous gold catalysts for liquid phase oxidation in water solution. The methodology of sols generation appears to be fundamental to obtaining nanoparticles; the support, instead, plays an important role in maintaining particle dimension and morphology.

Three different materials (γ-Al₂O₃, SiO₂ and activated carbon) have been used as the supporting agents for different gold sols that were obtained by reducing HAuCl₄ with NaBH₄ in the presence of polyvinylalcohol (PVA) or polyvinylpirrolidone (PVP) and with the tetrakis(hydroxymethyl)phosphonium chloride (THPC)/NaOH system. During the immobilisation step, the maintenance of the particle dimension observed in solution depends on both the support and the type of sol. The gold particle mean size of the colloidal suspension is more easily maintained on oxidic supports than on carbon, the latter apparently needing both steric and polar stabilisation of the gold particle.

Comparison of Au/γ-Al₂O₃ and Au/C catalyst activity in the liquid phase oxidation of ethylene glycol to glycolate highlighted the peculiarity of gold on carbon catalysts; in fact, the normally observed trend of reactivity is partially reversed, medium sized gold particle being the most active.     

Fischer–Tropsch synthesis over Re-promoted Co supported on Al2O3, SiO2 and TiO2: Effect of water

The activity and selectivity of rhenium promoted cobalt Fischer–Tropsch catalysts supported on Al₂O₃, TiO₂ and SiO₂ have been studied in a fixed-bed reactor at 483 K and 20 bar. Exposure of the catalysts to water added to the feed deactivates the Al₂O₃ supported catalyst, while the activity of the TiO₂ and SiO₂ supported catalysts increased. However, at high concentrations of water both the SiO₂ and TiO₂ supported catalyst deactivated. Common for all catalysts was an increase in C₅₊ selectivity and a decrease in the CH₄ selectivity by increasing the water partial pressure. The catalysts have been characterized by scanning transmission electron microscope (STEM), BET, H₂ chemisorption and X-ray diffraction (XRD).     

THE KINETICS OF H2S DECOMPOSITION OVER PRECIPITATED COBALT SULPHIDE CATALYST

Cobalt sulphide catalyst prepared via a new method involving the precipitation reaction between cobaltous acetate and ammonium sulphide solutions has been shown to be favourably active for the catalytic decomposition of H₂S when compared with data for other transition metal sulphides.

The BET surface area of this unsupported catalyst is about an order of magnitude higher than cobalt sulphide formed by direct sulphidation of cobalt oxide with H₂S gas. XRD, SEM and TEM analyses were used to obtain bulk composition and morphological characteristics. Catalyst specimen calcined at 823 K showed the best activity.

The kinetics of the decomposition reaction has been studied over this new preparation. Experiments conducted at atmospheric pressure between 933-983 K using about 11 feed compositions showed that below 40% H₂S/Ar the reaction was essentially 1st order with respect to H₂S partial pressure. Beyond this point, rate remained invariant with feed composition. A mechanism involving catalysis via co-ordinative unsaturation sites on the CoS was proposed and kinetic model based on the cleavage of the surface H-S bond as the rate-determining step appeared to be the most adequate representation of the rate data. Hydrogen production rates at all temperatures also paralleled the behaviour seen for H₂S decomposition. Activation energy for H₂S decomposition and H₂ production rates were estimated as 111 kJ mol^-1 and 88 kJ mol^-1 respectively     

Support effects on the catalytic behavior of NiO/Al2O3 for oxidative dehydrogenation of ethane to ethylene

Six representative Al₂O₃ supports with different specific surface areas and pore volumes were used to prepare NiO/Al₂O₃ catalysts with two NiO loadings. Oxidative dehydrogenation of ethane (ODE) to ethylene was investigated over these catalysts. The yield of ethylene was found to be approximately proportional to the pore volume/surface area ratio of the support used for that catalyst. X-ray diffraction analysis (XRD), TEM and H₂-TPR were employed to characterize their structure differences. It was found that the physical properties of the Al₂O₃ supports were crucial to the dispersion of NiO. More large crystal NiO was found on the Al₂O₃ supports with lower pore volume, while more highly dispersed NiO was formed on the Al₂O₃ supports with higher pore volume. An interpretation based on the pore volume of the supports and the physical properties of salt precursors was proposed.     

CO and CO2 hydrogenation study on supported cobalt Fischer–Tropsch synthesis catalysts

The conversion of CO/H₂, CO₂/H₂ and (CO+CO₂)/H₂ mixtures using cobalt catalysts under typical Fischer–Tropsch synthesis conditions has been carried out. The results show that in the presence of CO, CO₂ hydrogenation is slow. For the cases of only CO or only CO₂ hydrogenation, similar catalytic activities were obtained but the selectivities were very different. For CO hydrogenation, normal Fischer–Tropsch synthesis product distributions were observed with an of about 0.80; in contrast, the CO₂ hydrogenation products contained about 70% or more of methane. Thus, CO₂ and CO hydrogenation appears to follow different reaction pathways. The catalyst deactivates more rapidly for the conversion of CO than for CO₂ even though the H₂O/H₂ ratio is at least two times larger for the conversion of CO₂. Since the catalyst ages more slowly in the presence of the higher H₂O/H₂ conditions, it is concluded that water alone does not account for the deactivation and that there is a deactivation pathway that involves the assistance of CO.