Sequential dehydrogenation surface

The activation of methane or methane formation on metal surfaces is a cataly tically critical reaction. The sequential dehydrogenation of methane is important for CO production and the sequential hydrogenation of carbon are essential parts of the Fisher-TVopsch mechanism. 

Fig. 31. Hydrogen thermal desorption spectra illustrating the sequential dehydrogenation of ethylene, propylene, and cis-2-butene chemisorbed on the Pt(lll) crystal surface at 120 K. The rate of heating is 12 K/sec...

While adsorbed primary alcohols on the Pd( 111) surface dehydrogenate sequentially to form the corresponding adsorbed aldehyde and acyl species prior to their decarbonylation (23), we have found no evidence for aldehyde formation from primary alcohols on Rh(l 11) (2124). Instead, alcohol and aldehyde decarbonylation pathways on Rh(lll) appear to be non-intersecting. This surprising divergence of reaction pathways for such closely related molecules is demonstrated by two critical observations ... 

Yiwei Zhang et al prepared the La modified PtSnNa/ZSM-5 catalysts with various amounts of lanthanum by the sequential impregnation method, and studied the catalytic properties of La modified eatalysts for propane dehydrogenation. It was foimd that the La speeies were well dispersed on the both internal and external surfaces of ZSM-5 zeolite, and with the addition of La, the catalytic activity decreased slightly, but the catalytic active sites were stablizied. As a result, the increased catalytic selectivity and stability were obtained. When the 1.4% La was introduced into PtSnNa/ZSM-5 catalyst, the best selectivity and stability were observed, and 35.2%yield of propene at 590 °C for 80 h were achieved [162]. 

A diffusion-controlled process always involves various sequential steps. For example, the dehydrogenation of ethane on a single platinum crystal involves the diffusion of the ethane to the solid followed by the reaction on the solid surface. The reaction between protons and hydroxyl ions in water first has these species diffusing together, and then reacting. 

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