Qiming Zhu

Synergetic effect of Pd and Ag dispersed on Al2O3 in the selective hydrogenation of acetylene

An alloy of palladium and silver dispersed on Al2O3 has been used for the selective hydrogenation of acetylene. The activity of Pd–Ag catalyst is lower than that of pure metal Pd catalyst. But the selectivity of Pd–Ag catalyst is higher and less impaired by temperature increase than that of Pd catalyst. X-ray diffraction (XRD) indicates that metal Pd and Ag can form an alloy on the surface of alumina. X-ray photoelectron spectroscopy (XPS) shows that the Pd–Ag alloy is formed with enrichment of Ag on the surface. Results of hydrogen adsorption isotherm, temperature-programmed reduction (TPR) and temperature-programmed desorption (TPD) reveal that the bulk of palladium of Pd–Ag catalyst adsorbed a small amount of hydrogen, which is desorbed at a higher temperature than that in the case of Pd catalyst.

Rhodium-oxide species formed on progressive oxidation of rhodium clusters dispersed on alumina

Abstract Samples of rhodium crystallites finely dispersed on alumina were prepared by impregnating an alumina support with different amounts of rhodium chloride. Reduced samples were oxidized at different temperatures (To) in air and the oxidized rhodium crystallites were characterized by the temperature-programmed reduction technique (TPR). According to the reduction peaks found by TPR, five kinds of oxidation products, i.e., oxygen-chemisorbed rhodium (RhOc), surface rhodium-oxide (RhsO), bulk rhodium-oxides (RhOx), rhodium-oxides interacting with support (RhiOx) and rhodium aluminate [Rh(AlO2)y], have been progressively formed on increasing To temperature. The abundance of these products on oxidized samples varied with To temperature and the dispersion of supported rhodium crystallites. Rhodium atoms in the Rh(AlO2)y structure, formed on severe oxidation conditions, would segregate from the bulk to the surface of alumina upon reductions at temperature above 750°C.

Synthesis of isobutene from synthesis gas over nanosize zirconia catalysts

Abstract Performances of nanosize zirconium oxides prepared by precipitation, supercritical fluid drying (SCFD) and freeze-drying (FD) methods were evaluated for the selective synthesis of isobutene from synthesis gas (syn-gas). The crystal structure, particle size and specific surface area were measured by XRD, TEM and BET. The acidic and basic properties of the catalysts were studied by NH 3 - and CO 2 -TPD, respectively. The results showed that the crystal phases, acidic and basic properties of nanosize zirconia depend remarkably on the drying conditions. The catalysts over which the formation of isobutene is favored show a higher ratio of basic to acidic sites on their surfaces. The results of adding acidic and basic components into zirconia suggested that both the acidic and basic sites on the catalysts are required for the isosynthesis. The conversion of CO was increased by adding acidic component into zirconia, and the selectivity for i-C 4 H 8 was increased greatly by adding basic component into zirconia. It is suggested that the acidic sites are responsible for the activation of reactant molecules and the basic sites of the catalysts are significant for the formation of i-C 4 H 8 from CO hydrogenation.

In situ IR studies on the mechanism of methanol synthesis over an ultrafine Cu/ZnO/Al2O3 catalyst

Abstract Methanol synthesis from CO 2 and CO/CO 2 hydrogenation was carried out under real reaction conditions over an ultrafine Cu/ZnO/Al 2 O 3 (Cu/Zn/Al=60/30/10, molar ratio) catalyst. The formation and variation of surface species were recorded by in situ FT-IR spectroscopy. The mechanisms of methanol synthesis and RWGS reaction were discussed. The result revealed that methanol was formed directly from CO 2 hydrogenation for CO 2 /H 2 or CO/CO 2 /H 2 reaction systems. b-HCOO − s was the necessary intermediate for methanol synthesis. A scheme of methanol and RWGS reaction was proposed.

Carbon Dioxide Reforming of Methane Over Nanocomposite Ni/ZrO2 Catalysts

A systematic study of the “size effect” of zirconia nanocrystals on nickel-catalyzed reforming of methane with CO2 shows that extremely stable Ni/ZrO2 catalysts are obtainable by hydrogen reduction of impregnated nickel nitrate on zirconia particles with sizes less than 25 nm. The same preparation method with larger particles of zirconia results in catalyst samples that deactivate rapidly in the reforming reaction. Comprehensive characterization with XRD, TPR/TPD, and TEM shows that the stable Ni/ZrO2 catalysts are better described as nanocomposites of size comparable to Ni metal (9-15 nm) and zirconia (7-25 nm) nanoparticles. The high percentage of the Ni-zirconia boundary or perimeter in the nanocomposite catalysts is believed to be crucial for the extremely stable catalytic activity.

Comparatively high yield methanol production from gas phase partial oxidation of methane

Gas phase partial oxidation of methane to methanol has been carried out in a specially designed reactor. A comparatively high yield of methanol (ca. 7–8%, methanol selectivity of 60% at methane conversion 13%) was obtained over a quite wide temperature range of more than 40 ◦ C at 5.0 MPa and CH4/O2/N2 = 100/10/10 (ml/min). The effects of the total flow rate, CH4/O2 ratio and pressure were examined and the superiority of the new reactor is discussed.

Condensation of formaldehyde and methyl formate to methyl glycolate and methyl methoxy acetate using heteropolyacids and their salts

Abstract Catalytic performances of heteropolyacids and their salts in the condensation of formaldehyde and methyl formate to methyl glycolate and methyl methoxy acetate have been studied. H 3 PW 12 O 40 and H 4 SiW 12 O 40 were found to have high activities for the formation of methyl glycolate and methyl methoxy acetate. The acidic salts of heteropolyacids also showed the activities in the condensation reactions, but the neutral salts of H 3 PW 12 O 40 and of H 4 SiW 12 O 40 were inactive. Thermal treatment of heteropolyacids was found to show a positive effect on the catalytic activities, and the most suitable pretreatment temperature was 300°C in the range 100–350°C. The investigating results of the influence of the reaction conditions showed that the molar ratios of formaldehyde to methyl formate and the reaction temperatures greatly affected the reaction. It was also found that the coexistence of water in the reaction system showed a negative effect on the catalytic activity.

Direct partial oxidation of methane to methanol: Reaction zones and role of catalyst location

Abstract Direct partial oxidation of methane to methanol was investigated in a specially designed reactor. Methanol yield of about 7%–8% was obtained in gas phase partial oxidation. It was proposed that the reactor could be divided into three reaction zones, namely pre-reaction zone, fierce reaction zone, and post-reaction zone, when the temperature was high enough to initiate a reaction. The oxidation of methane proceeded and was completed mostly in the fierce reaction zone. When the reactant mixture entered the post-reaction zone, only a small amount of produced methanol would bring about secondary reactions, because molecular oxygen had been exhausted in the fierce reaction zone. A catalyst, if necessary, should be placed either in the pre-reaction zone, to initiate a partial oxidation reaction at a lower temperature, or in the fierce reaction zone to control the homogeneous free radical reaction.

B2O3/ZrO2 for Beckmann rearrangement of cyclohexanone oxime: optimizing of the catalyst and reaction atmosphere

Abstract Optimization of zirconia-supported boria catalyst for the Beckmann rearrangement of cyclohexanone oxime was studied with the control of three preparation parameters: the temperature of support pre-calcination (PCT: 110–700°C), the calcination temperature for the catalyst activation (CAT: 250–600°C), and the load level of boria. When the CAT is limited no higher than 500°C, the lactam yield increases with the PCT and shows maximum numbers with PCT=350–500°C. This effect of PCT seems not important for the catalyst preparation when the late catalyst activation is done with CAT as high as 600°C. Catalyst preparations with CAT=600°C agrees with the model that the optimized catalyst has, on the average, about two surface overlayers of boria on the support. Another part of this work focused on effects of the reaction solvents and carrier gases. A remarkable benefit for the lactam synthesis is observed with proper combination of the solvents and carrier gases.

Influence of acidic and basic properties of ZrO2 based catalysts on isosynthesis

Abstract Zirconium dioxide based catalysts were synthesized by mechanical mixing method and evaluated for the direct synthesis of isobutene and isobutane (i-C4) from CO hydrogenation. The experiments of temperature-programmed desorption of ammonia and carbon dioxide indicated that both the amount of acid–base sites and the strength of acid and base of the catalysts varied with the incorporation of promoters including various calcium salts, Al2O3 and KOH in ZrO2. The test results indicated that the activity and selectivity of the zirconia based catalysts depended on the acid–base properties of the catalysts. An appropriate amount of moderately strong acid–base sites and ratio of basic to acidic sites on the catalysts are significant for an active catalyst to selectively produce isobutene and isobutane from CO hydrogenation.