Search

Abstract: Rh-Mn-Li catalysts supported on SiO2, ZrO2 and SiO2-ZrO2 mixed oxides with various molar ratios of Si/Zr were prepared and tested for the synthesis of C2-oxygenates from syngas. Compared with pure SiO2 and ZrO2 supported catalysts, catalysts supported on SiO2-ZrO2 mixed oxides showed higher activity and C2-oxygenates selectivity, in which Rh-Mn-Li/SiO2-ZrO2 (molar ratio of Si/Zr=1:3) exhibited the best yield of C2-oxygenates. The effect of the support on the performance of the Rh-based catalysts was investigated comprehensively by XRD, N2 adsorption-desorption, H2 and CO uptakes, FT-IR, XPS, H2-TPR, TPSR and CO-TPD techniques. The results indicated that the chemical state of Rh, CO adsorption species, dispersion of Rh and the ability of CO hydrogenation varied over catalysts supported on SiO2, ZrO2 and SiO2-ZrO2 mixed oxides, which led to the diverse catalytic activity toward C2-oxygenates synthesis. [Copyright &y& Elsevier]

Abstract: The effect of calcination temperature (500–700°C) on the performance of B2O3/TiO2–ZrO2 catalyst for vapor-phase Beckmann rearrangement of cyclohexanone oxime to caprolactam was investigated. Catalysts were characterized by adsorption of nitrogen, X-ray diffraction and ammonia temperature-programmed desorption. The results indicated that the percent of acid sites of medium strength within the total acid sites and the pore size both increased with calcination temperature. Such increases led to increases of the oxime conversion and caprolactam selectivity. However, a large amount of crystalline B2O3 appeared after calcination at 700°C and caused the decrease of the total amount of acid sites, which resulted in remarkable decrease in the activity of the catalyst. Another part of this work focused on the effect of solvent on the catalytic performance of B2O3/TiO2–ZrO2. Solvents with various polarities were investigated for the reaction. It was found that acetonitrile, which has the highest polarity for solvents examined here, was the most effective for the formation of caprolactam. The solvent with high polarity increases the desorption rate of produced caprolactam from catalyst surface, resulting in a high selectivity to caprolactam and low catalyst deactivation rate. FT-IR measurements confirmed the efficient desorption of caprolactam induced by the attack of the acetonitrile molecule. [Copyright &y& Elsevier]

The effects of calcination temperature and preparation method of TiO2–ZrO2 mixed oxide on catalytic performance of B2O3/TiO2–ZrO2 catalysts were investigated. TiO2–ZrO2 mixed oxides with the same molar ratio of 1:1 were prepared by co-precipitation method, homogeneous precipitation method, sol–gel method and physical mixing method; each oxide was calcined at a temperature between 110 and 700 °C. Catalytic synthesis of #x03B5;-caprolactam from cyclohexanone oxime was evaluated in a fixed-bed flow microreactor at 300 °C and atmosphere pressure. Characterization of catalysts was carried out using adsorption of nitrogen, X-ray diffraction (XRD), Fourier transform-infrared spectroscopy (FTIR) and temperature-programmed desorption of ammonia (NH3-TPD) techniques. The experimental results reveal that the calcination temperature in the range of 110–500 °C had only a slight effect on the catalytic performance, but after calcination at 700 °C, the ZrTiO4 crystallite was formed and accounted for the decrease of acidity and catalytic performance. The co-precipitation method provided the catalyst with the highest reactivity while the physical mixing method resulted in the worst catalyst. Catalytic performance of the B2O3/TiO2–ZrO2 catalyst was closely related to its acid strength distributions and pore size. [Copyright &y& Elsevier]

Pure TiO2, ZrO2 and TiO2-ZrO2 mixed oxides with various compositions were prepared by the co-precipitation method. Catalysts containing 12 wt.% boria were prepared using these oxides and their catalytic performance for vapor-phase Beckmann rearrangement of cyclohexanone oxime to ϵ-caprolactam was determined. With increasing zirconia content in the mixed oxide, the specific surface area and the temperature of the phase transformation increased; maximum values were obtained for a mixed oxide having a Ti and Zr molar ratio of 1/1. XRD results indicated that TiO2-ZrO2 became amorphous after calcination at 500 °C if neither the content of TiO2 nor that of ZrO2 was less than 25%. The yield of lactam increased with increasing zirconia content in mixed oxide and reached a maximum value for the B2O3/TiO2-ZrO2 (1/1) catalyst. With further increase in zirconia content, the lactam yield decreased; the lowest value was observed for the pure ZrO2-supported catalyst. The acidic property and the pore characteristics of the catalyst were key factors that affected its performance. The influences of the operating parameters on the performance of B2O3/TiO2-ZrO2 (1/1) catalyst were also investigated. [Copyright &y& Elsevier]

A series of CuO-ZnO-MO x (M = Zr, Al, Cr, Ti) catalysts were prepared by co-precipitation method and characterized by ICP-OES, XRD, N 2 adsorption, N 2 O titration, H 2 -TPR, and XPS. The CuO-ZnO-ZrO 2 catalyst exhibits the highest BET surface area and Cu surface area. For all the CuO-ZnO-MO x catalysts, Cu 0 was the predominant copper species detectable on the surface of both reduced and spent samples. As-prepared CuO-ZnO-MO x catalysts were mixed physically with HZSM-5 zeolite to synthesize dimethyl ether (DME) via biomass-derived syngas. The highest CO conversion and DME yield were obtained over a CuO-ZnO-ZrO 2 /HZSM-5 hybrid catalyst. The CO conversion increases with the increase in the Cu surface area, but the relationship between them is not linear. Due to the H 2 -deficient characteristic of biomass-derived syngas, the water-gas shift reaction, by which H 2 can be produced in-situ for the hydrogenation of CO, plays an important role in the direct DME synthesis. [ABSTRACT FROM AUTHOR]