Hydrogen adsorption temperature dependence

The above results for Pt supported on three different types of difficult to reduce supports show that high temperature reduction usually causes large decreases in hydrogen adsorption capacity. However, the reduction temperature required for hydrogen adsorption suppression depends on the support. Hydrogen adsorption capacities of catalysts reduced at high temperatures can be restored by oxygen treatment followed by low temperature reduction, i.e. the processes responsible for adsorption suppression are reversible. 

The temperature dependence of the extent of adsorption was not interpreted, except that the results were considered to be consistent with the magnetic measurements of Selwood (see Section II,C) which indicate that the number of carbon-metal bonds between adsorbed species and the surface increases threefold between 120°and 200°C due to extensive dissociative chemisorption. The authors proposed that two forms of chemisorbed benzene exist at the nickel surface, (i) an associatively adsorbed form which can be displaced by further benzene, and which may be w- or hexa-dissociatively adsorbed form that requires the presence of hydrogen to bring about its removal from the surface. 

The low-temperature physisorption (type I isotherm) of hydrogen in zeolites is in good agreement with the adsorption model mentioned above for nanostructured carbon. The desorption isotherm followed the same path as the adsorption, which indicates that no pore condensation occurred. The hydrogen adsorption in zeolites depends linearly on the specific surface areas of the materials and is in very good agreement with the results on carbon nanostructures [24]. 

The temperature dependence of conversion (a) and dimer selectivity (b) are shown in Figure 7 Raising the temperature decreases the conversion, suggesting that the rate determining step could coincide with or be preceded by an exothermal reaction, for instance a hydrogenation reaction or the adsorption of reactants on the metal surface. The same effect could be explained by a faster catalyst deactivation at higher temperatures. The decrease in conversion, however, exhibits nearly the same slope in all 4 experiments, not supporting this explanation. 

The adsorption of each of the reactants and products on cobalt molybdate was studied under conditions as close as possible to reaction conditions. Butene and thiophene both showed strong temperature dependence, adsorption of the latter in particular being slow at the lower reaction temperatures. The temperature coefficients were 8.5 and 9.5 kcal. per mole, respectively. H2S adsorbed quickly and desorbed at a rate proportional to coverage, and hydrogen apparently behaved in the same way. Only relatively weakly bound or free hydrogen appeared to be reactive, but adsorbed hydrogen probably modified the adsorption of thiophene and of butene. 

C.5.2. Hydrogen Adsorption Followed by CO Adsorption. When the gas dosing sequence was reversed, the coadsorption behavior became more complex and depended on the temperature and the palladium surface structure. We start with measurements at 100 K. On hydrogen-precovered Pd(l 1 1), no CO adsorption was... 

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