Catalyst reducibility, selectivity effect

In this paper, the selective conversion of methane to C2 hydrocarbons over ternary Ca0-Mn0/Ce02 catalysts in the CO2 OCM process are presented. The synergistic effect between catalyst reducibility and distribution of basic sites are highlighted. The most promising catalyst was then tested towards its stability. 

The pyrolytic reforming reactor was a packed bed in a quartz tube reactor. Quartz was selected to reduce the effect of the reactor construction material on the hydrocarbon decomposition rate. ° The reactor was packed with 5.0 0.1 g of AC (Darco KB-B) or CB (BP2000) carbon-based catalyst. The reactor was heated electrically and operated at 850—950 °C, and the reactants had a residence time of 20—50 s, depending on the fuel. The reactor was tested with propane, natural gas, and gasoline as the fuels. Experiments showed that a flow of 80% hydrogen, with the remainder being methane, was produced for over 180 min of continuous operation.The carbon produced was fine particles that could be blown out... 

Mobil ZSM-5 zeolite catalysts can be modified to reduce the effective pore and channel dimensions. These modified zeolites allow discrimination between molecules of slightly different dimensions. Because of this shape-selective action, p-ethyltoluene is able to diffuse out of the catalyst pores at a rate about three orders of magnitude greater than the two regioisomers. As a result, p-ethyltoluene is formed with very high (97%) selectivity.333... 

Both of these reactions have very important industrial uses (Section 14.3.9). In order to obtain alkene streams of sufficient purity for further use, the products of steam-cracking or catalytic cracking of naphtha fractions must be treated to lower the concentration of alkynes and alkadienes to very low levels (<5ppm). For example, residual alkynes and dienes can reduce the effectiveness of alkene polymerisation catalysts, but the desired levels of impurities can be achieved by their selective hydrogenation (Scheme 9.4) with palladium catalysts, typically Pd/A Os with a low palladium content. A great deal of literature exists,13,37 particularly on the problem of hydrogenating ethyne in the presence of a large excess of... 

Whenever the kinetics of a chemical transformation can be represented by a single reaction, it is sufficient to consider the conversion of just a single reactant. The concentration change of the remaining reactants and products is then related to the conversion of the selected key species by stoichiometry, and the rates of production or consumption of the various species differ only by their stoichiometric coefficients. In this special case, the combined influence of heat and mass transfer on the effective reaction rate can be reduced to a single number, termed the catalyst efficiency or effectiveness factor rj. From the pioneering work of Thiele [98] on this subject, the expressions pore-efficiency concept and Thiele concept have been coined. 

Because sulfur adsorbs very strongly on metals and prevents or modifies the further adsorption of reactant molecules, its presence on a catalyst surface usually effects substantial or complete loss of activity in many important reactions, particularly in hydrogenation reactions. Where the reaction network leads to two or more products, adsorbed sulfur can markedly affect the selectivity by reducing the rate of one of the reactions more than the other(s). In a few reaction systems these changes in selectivity are desirable however, in many others they are not. 

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