Effect of support on chromium based catalysts for the oxidative dehydrogenation of C2H6 with CO2 to C2H4

The oxidative dehydrogenation of ethane (ODE) with CO2 to C2H4 has been studied over a series of Cr-based catalysts using SiO2, Al2O3, (MCM-41 zeolite) MCM-41, MgO and Silicate-2 (Si-2) as the supports. TPR, NH3-TPD, and EPR characterizations of catalysts were carried out to investigate the reduction property of Cr species on different supports, the acidities of catalysts and Cr species of 6Cr/SiO2 catalysts, respectively.

On the induction period of methane aromatization over Mo-based catalysts

The behavior of different species during the temperature-programmed surface reaction (TPSR) of methane over various catalysts is traced by an online mass spectrometer, It is demonstrated that the transformation of MoO3 to molybdenum carbide hinders the activation of methane as well as the succeeding aromatization in the TPSR, If this transformation process is done before the reaction, the temperature needed for methane activation and benzene formation will be greatly lowered (760 and 847 K, respectively). On the basis of comparison of the catalytic behavior of molybdenum supported on different zeolites, it is suggested that the initial activation of methane is the rate-determining step of this reaction. For the cobalt catalysts supported on HMCM-22 or Mo catalysts supported on TiO2, no benzene formation could be observed during the TPSR, However, the prohibition of benzene formation is different in nature over these two catalysts: the former lacks the special properties exhibited by molybdenum carbide, which can continuously activate methane even when multiple layers of carbonaceous species are formed on its surface, while the latter cannot accomplish the aromatization reaction since there are no Bronsted acid sites to which the activated intermediates can migrate, although the activation of methane can be achieved on it. Only for the catalysts that possess both of these properties, together with the special channel structure of zeolite, can efficient methane aromatization be accomplished. (C) 2000 Academic Press.

Catalytic role of pre-adsorbed CO in platinum-based catalysts : the reduction of SO 2 by CO on Pt l Au m (CO) n

Using density functional theory, we have investigated the catalytic properties of bimetallic complex catalysts PtlAum(CO)n (l + m = 2, n = 1–3) in the reduction of SO2 by CO. Due to the strong coupling between the C-2p and metal 5d orbitals, pre-adsorption of CO molecules on the PtlAum is found to be very effective in not only reducing the activation energy, but also preventing poisoning by sulfur. As result of the coupling, the metal 5d band is broadened and down-shifted, and charge is transferred from the CO molecules to the PtlAum. As SO2 is adsorbed on the catalyst, partial charge moves to the anti-σ bonding orbitals between S and O in SO2, weakening the S–O bond strength. This effect is enhanced by pre-adsorbing up to three CO molecules, therefore the S–O bonds become vulnerable. Our results revealed the mechanism of the excellent catalytic properties of the bimetallic complex catalysts.

Co-and Ca-phosphate-based catalysts for the depolymerization of organosolv eucalytpus lignin

Depolymerization of purified organosolv eucalyptus wood lignin by the heterogeneous catalysts, cobalt polyphosphate (CoP2O6) and calcium phosphate (β-CaP2O6) was investigated. A total syringol yield of 16.7% was achieved with β-CaP2O6 in a methanol/water (50/50, wt/wt) solvent system after depolymerization at 300 ºC for 1 h, showing selectivity of the catalyst.

Catalytic Dehydration of Ethanol to Ethylene on TiO2/4A Zeolite Composite Catalysts

TiO2/4A zeolite composite catalysts were prepared by coating TiO2 on 4A zeolite via liquid phase deposition. The TiO 2/4A zeolite composite catalysts wtih higher surface weak acidity and lower mediate strong acidity exhibit much better catalytic performance on ethanol dehydration to ethylene compared with 4A zeolite. It is suggested that the TiO2 promoter could improve the effective Lewis acidity of composite catalyst which consequently enhanced the catalytic performance.