Morphology observation of carbon deposition by CH4 decomposition over Ni-based catalysts

We found a novel morphology variation of carbon deposition derived from CH4 decomposition over NI-based catalysts. By altering the chemical composition and particle size of Ni-based catalysts, carbon filaments, nanofibres and nanotubes were observed over conventional Ni/y-Al2O3, Ni-Co/gamma-Al2O3 and nanoscale Ni-Co/gamma-Al2O3 catalysts, respectively. The simple introduction of Co into a conventional Ni/gamma-Al2O3 catalyst can vary the carbon deposition from amorphous filamentous carbon to ordered carbon fibres. Moreover, carbon nanotubes with uniform diameter distribution can be obtained over nanosized Ni-Co/gamma-Al2O3 catalyst particles. In addition, the oxidation behaviour of the different deposited carbon was studied by using a temperature-programmed oxidation technique. This work provides a simple strategy to control over the size and morphology of the carbon deposition from catalytic decomposition of CH4.

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.

Vinylic polymerization of norbornene by neutral nickel(II)-based catalysts

Neutral Ni(II) salicylaldiminato complexes activated with modified methylaluminoxane as catalysts were used for the vinylic polymerization of norbornene. Catalyst activities of up to 7.08 x 10(4) kg(pol)/(mol(Ni) (.) h) and viscosity-average molecular weights of polymer up to 1.5 x 10(6) g/mol were observed at optimum conditions. Polynorbornenes are amorphous, soluble in organic solvents, highly stable, and show glass-transition temperatures around 390 degreesC. Catalyst activity, polymer yield, and polymer molecular weight can be controlled over a wide range by the variation of the reaction parameters such as the Al/Ni ratio, monomer/catalyst ratio, monomer concentration, polymerization reaction temperature, and time.

Oxidative dehydrogenation of ethane and propane over Mn-based catalysts

The catalytic performances of Mn-based catalysts have been investigated for the oxidative dehydrogenation of both ethane (ODE) and propane (ODP). The results show that a LiCl/MnOx/PC (Portland cement) catalyst has an excellent catalytic performance for oxidative dehydrogenation of both ethane and propane to ethylene and propylene, more than 60% alkanes conversion and more than 80% olefins selectivity could be achieved at 650 degrees C. In addition, the results indicate that Mn-based catalysts belong to p-type semiconductors, the electrical conductivity of which is the main factor in influencing the olefins selectivity. Lithium, chlorine and PC in the LiCl/MnOx/PC catalyst are all necessary components to keep the excellent catalytic performance at a low temperature.

Selective oxidehydrogenation of ethane with CO2 over CeO2-based catalysts

Ceria catalysts were found active and selective to the oxidehydrogenation of ethane (ODE) with CO2 and the actual contribution for C2H4 formation from heterogeneous catalysis was 75-55% in the range 953-993 K. The presence of calcium ions in solid solution in the ceria crystalline network increased significatively the selectivity to ethene and the efficiency of CO2 as oxidant in the heterogeneous reaction. (C) 2000 Elsevier Science B.V. All rights reserved.

Preparation of titania-based catalysts for formaldehyde photocatalytic oxidation from TiCl4 by the sol-gel method

Titania sols were prepared by acid hydrolysis of a TiCl4 precursor instead of titanium alkoxides. The effect of acid concentration on the particle size and stability of sol was investigated. Stable titania sols with mean particle size of 14 nm could be obtained when the H+/Ti molar ratio was 0.5. The titania sols were modified with Pt, SiO2, ZrO2, WO3 and MoO3 to prepare a series of modified catalysts, which were used for the photocatalytic oxidation of formaldehyde at 37 degreesC. They showed different photocatalytic activities due to the influence of the additives. Comparing with pure TiO2, the addition of silica or zirconia increased the photocatalytic activity, while the addition of Pt and MoO3 decreased the activity, and the addition Of WO3 had little effect on the activity. It is of great significance that the conversion of formaldehyde was increased up to 94% over the SiO2-TiO2 catalyst. The increased activity was partly due to higher surface area and porosity or smaller crystallite size. A comparison of our catalyst compositions with the literature in this field suggested that the difference in activity due to the addition of a second metal oxide maybe caused by the surface chemistry of the catalysts, particularly the acidity. (C) 2001 Elsevier Science B.V. All rights reserved.