Hydrogenation of CO2 to formic acid on supported ruthenium catalysts

We report on the preparation and application of novel heterogeneous supported ruthenium catalysts. The catalysts are active in the synthesis of formic acid from the hydrogenation of carbon dioxide and are characterized by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, X-ray powder diffraction analysis and transmission electron microscopy. Abundant hydroxyl groups, which interact with the ruthenium components, play an important role in the catalytic reactions. Highly dispersed ruthenium hydroxide species enhance the hydrogenation of CO₂, while crystalline RuO₂ species, which are formed from the relatively high ruthenium content or the pH of the solution during preparation of the catalyst, restrict the production of formic acid. Optimal activity of ruthenium hydroxide as a catalyst for the hydrogenation of CO₂ to formic acid is achieved over a γ-Al₂O₃ supported 2.0 wt% ruthenium catalyst, which is prepared in a solution of pH 12.8 with NH₃·H₂O as a titration solvent. A possible hydrogenation mechanism for the hydroxide ruthenium catalyst is proposed.     

Performance and characterization of supported metal catalysts for complete oxidation of formaldehyde at low temperatures

Activities of a series of metals (Pt, Pd, Rh, Cu, Mn) supported on TiO₂ were investigated for the catalytic oxidation of formaldehyde. Among them, Pt/TiO₂ was found to be the most promising catalyst. Nitrogen adsorption, hydrogen chemisorption, X-ray diffraction (XRD), transmission electron microscopy (TEM) and temperature programmed reduction (TPR) by H₂ were used to characterize the platinum catalysts. Using Ce_0.8Zr_0.2O₂, Ce_0.2Zr_0.8O₂, SiO₂ as supports instead of TiO₂, the activity sequence of 0.6 wt.% platinum with respect to the supports is TiO₂ > SiO₂ > Ce_0.8Zr_0.2O₂ > Ce_0.2Zr_0.8O₂, and this appears to be correlated with the dispersion of platinum on supports rather than the specific surface areas of the catalysts. Platinum loading on TiO₂ has a great effect on the catalytic activity, and 0.6 wt.% Pt/TiO₂ catalyst was observed to be the most active, which could be attributed to the well-dispersed platinum surface phase. The reduction temperature greatly affects the particle size and, consequently, the catalytic activity. The smaller particle size of platinum, due to its high dispersion on support, has a positive effect on catalytic performance. Increasing formaldehyde concentration and space velocity exhibits an inhibiting effect on the catalytic activity.     

New synthesis technique of supported ZSM-5 using organo-alumino-silicic gels

This contribution deals with the synthesis of a silicon-rich ZSM-5 obtained from an amorphous organo-alumino-silicic gel. The gel was formed by reacting a mechanical mixture of RHA (rice hull ash), silica’s source, and of natural clinoptilolite, source of alumina, with glycerol during 2 h at 200 °C. After a maturation period of one day at 60 °C, the reaction product was hydrolyzed by a tetra-propyl-ammonium (TPA) solution and then aged for two days at 135 °C in a stainless steel autoclave. After washing and drying, the X-ray pattern showed a well crystallized ZSM-5. The textural analysis of the slowly calcined solid at 500 °C for 4 h, and the SEM micrographies evidence that the zeolite was supported on mesoporous silica. The proportion of both components depends on the tunable hydrolysis conditions.     

Zirconocene silanolate complexes and their heterogeneous siliceous analogues as catalysts for phenylsilane dehydropolymerization

The efficient catalytic dehydropolymerization of phenylsilane by homogeneous zirconocene bissilanolates ([{(c-C₅H₉)₇Si₈O₁₂O}₂Zr(η⁵-C₅H₅)₂] (1a); [{(c-C₅H₉)₇Si₈O₁₂O}₂Zr(η⁵-C₅H₄Bu)₂] (1b) [{(c-C₅H₉)₇Si₇O₉(OSiMe₃)O₂}Zr(η⁵-C₅H₅)₂] (4); [{(Me₃CO)₃SiO}₂Zr(η⁵-C₅H₅)₂] (5)) and chlorosilanolates ([{(c-C₅H₉)₇Si₈O₁₂O}ZrCl(η⁵-C₅H₄Bu)₂] (2); ([{(c-C₅H₉)₇Si₇O₉O₃}Zr₂Cl(η⁵-C₅H₅)₄] (3a); [{(c-C₅H₉)₇Si₇O₉O₃}Zr₂Cl(η⁵-C₅H₄Bu)₄] (3b)) has been demonstrated. The presence of at least one silanol ligand in the zirconocene moiety was found essential for high catalytic performance. Solid state structure of complex 1a was determined by single crystal X-ray diffraction analysis. A series of nine zirconocene-siliceous catalysts were prepared by grafting of zirconocene moiety onto silica using three general methods: (a) reaction of [(η⁵-C₅H₅)₂ZrCl₂] with silica in the presence of NEt₃; (b) reaction of [(η⁵-C₅H₅)₂ZrMe₂] with silica; (c) reaction of solely [(η⁵-C₅H₅)₂ZrCl₂] with silica. Supported catalysts were characterized by ICP-MS, FT-IR, TGA and selected examples by XPS analysis. Those catalysts prepared by method (a) and (b) were found efficient in the phenylsilane polymerization although a higher Zr/monomer ratio had to be used in comparison with homogeneous analogues. The low concentration of residual silanol groups in supported catalysts was found essential for their high catalytic performance. Advantageous reusability of supported catalysts was demonstrated using SiO₂₍₅₀₀₎/Cp₂ZrCl₂/NEt₃(5.8). The catalytic performance was retained in three consecutive cycles producing polymers with almost identical properties.     

Microstructural investigations of tubular α-Al2O3-supported γ-Al2O3 membranes and their hydrothermal improvement

γ-Al₂O₃ meso-porous membranes supported by tubular α-Al₂O₃ substrates were prepared by using the sol-gel method and their nanostructural characterizations were performed for the first time with high-resolution transmission electron microscopy (HRTEM) before and after hydrothermal treatment at 500 °C. The HRTEM images and pore size distribution (PSD) analyses revealed that the morphologies as well as the characteristics of the powder and membrane samples prepared from the same boehmite are not identical. γ-Al₂O₃ and La₂O₃-Ga₂O₃ doped-γ-Al₂O₃ (LGA) membranes supported by α-Al₂O₃ were also fabricated and characterized under thermal and hydrothermal conditions for the purpose of comparisons. Finally, two type α-Al₂O₃/γ-Al₂O₃/SiO₂ (AA-SiO₂) and α-Al₂O₃/La₂O₃-Ga₂O₃-γ-Al₂O₃/SiO₂ (ALGA-SiO₂) membranes have been synthesized and the gas permeance of the membrane were measured in the temperature range 100–500 °C.     

The catalytic activity of FeOx/ZrO2 for the abatement of NO with propene in the presence of O2

FeO_x/ZrO₂ samples, prepared by impregnation with Fe(NO₃)₃, were characterised by means of DRS, XRD, FTIR, redox cycles and volumetric CO adsorption. Volumetric CO adsorption, combined with FTIR, showed that 45% of iron in the sample containing 2.8 Fe atoms nm⁻² was capable of forming iron carbonyls. DRS evidenced Fe₂O₃ on samples with Fe-content≥2.8 atoms nm⁻². The selective catalytic reduction of NO with C₃H₆ in the presence of O₂ was studied with a reactant mixture containing NO=4000 ppm, C₃H₆=4000 ppm, O₂=2%. The dependence on iron-content suggests that only isolated iron, prevailing in dilute FeO_x/ZrO₂, is active for NO reduction, whereas iron on the surface of small oxide particles, prevailing in concentrated FeO_x/ZrO₂, is active for C₃H₆ combustion.     

The adsorption characteristics of two Mo sites on a sulfided MoO3/γ-Al2O3 surface

The surface structure of the oxidized and ammonia dissolved MoO₃/-Al₂O₃ samples and the adsorption characteristics of the sulfided samples were investigated by Laser Raman Spectroscopy (LRS) and Low Temperature Infrared Spectroscopy (LTIR) techniques.It was verified that there were two kinds of coordinated unsaturated Mo sites (denoted as Mo_A(CUS) and Mo_B(CUS)) on the surface and the precursors of Mo_A(CUS) and Mo_B(CUS) were Mo(O) and Mo(T), respectively. It was also concluded that Mo_A(CUS) sites could adsorb NO and CO, while Mo_B(CUS) could adsorb CO only. The surface concentration of Mo_A(CUS) might be far smaller than that of Mo_B(CUS).     

Preparation and characterisation of vanadium catalysts supported over alumina-pillared clays

Supported vanadium-containing catalysts were prepared by impregnation of Al-pillared clays with NaVO₃ precursor aqueous solutions. A montmorillonite and a saponite, both natural as well as previously pillared with Al₁₃-Keggin polycations, were used as supports, being impregnated with solutions of the precursor by means of the incipient wetness technique. The layered structure of the supports is maintained after impregnation, and even after calcination of the impregnated solids at 500 °C, although with a significant worsening of the textural properties of the solids, in particular, a loss of specific surface area. Three crystalline vanadium-containing phases were identified in the impregnated solids, namely, NaV₃O₈, AlVO₄ and V₂O₅ (shcherbinaite). The reduction of these phases to V³⁺ species was observed as wide processes in the 450–750 °C range, all of them centred at ca. 600 °C.     

负载型Pd催化剂

介绍了制备负载型钯催化剂的几种方法,以及它在反应中的应用。阐述了几种催化剂载体的优点,最后对这种催化剂的前提提出展望。     

Supported honeycomb monolith catalysts for high-temperature ammonia decomposition and H2S removal

Catalysts that have potential in simultaneous removal of H₂S and NH₃ decomposition were developed. The monolith supports of high surface area and acceptable mechanical strength based on titania and silica–alumina precursors were prepared and tested. Preparation routine and composition of Mn, Fe and Cu oxides supported honeycomb catalysts have been optimized. Impregnated and washcoated monolith catalysts were tested in ammonia high-temperature decomposition.