Ethylene hydrogen coadsorption

The coadsorption of 0.222 mg/g H2 with ethylene accelerates the reaction and increases the relative amount of ethane produced. In another experiment the H2 dose was reduced by half. The rate and the amount of ethane produced are diminished. The initial rate for ethylene reaction on Ru-Na-Y zeolite is dependent upon hydrogen concentration to approximately first order. This agrees with previous studies of ethylene hydrogenation.(7 7) Table I lists the rate dependence of loss of ethylene on the initial concentration of hydrogen. 

All Ru exchanged Y zeolites were dehydrated in a glass vacuum line at 623 K and reduced under static hydrogen at the same temperature using a procedure similar to that of Uytterhoeven et al..(7,<5) Dispersions for all samples exceeded 0.9. For coadsorption studies of ethylene and hydrogen, ethylene was preadsorbed at 77 K and hydrogen was introduced immediately afterwards. 

In a separate series of experiments, the influence of sulfur on the decomposition of a mixture consisting of CO/C2H4/H2 over iron was investigated. Previous work [17] had shown that while iron did not catalyze the decomposition of ethylene, even in the presence of hydrogen, when a small fraction of CO was added to the reactant, a dramatic increase in the rate of decomposition of the olefin was observed. This behavior was rationalized according to a model in which the presence of coadsorbed CO resulted in what is believed to be reconstruction of the iron to form a surface, which favors dissociative chemisorption of ethylene. In the current study, we have extended this study to include the case where sulfur is preadsorbed on the metal surface in an attempt to determine how such adatoms modify the coadsorption characteristics of CO and C2H4 on iron. 

Fig. 16. Estimated surface coverage of hydrogen and ethylene coadsorption under Temkin conditions. Ethylene adsorption is assumed to occur on 4 ( , a ) or 2 (b, b ) sites. Hydrogen surface coverage, curves (o, b). Ethylene surface coverage, curves (a, b ). 2 A HCIO4 electrolyte P of ethylene, 1 atm.

Adsorption of ethylene on a hydrogen-covered Fe(lOO) surface occurs without reaction at 1 lOK, but at 160K reversible insertion occurs ro give surface Fe-Et groups. These do not react with further H2, but coadsorption of CO induces reductive elimination of ethane. Similar studies with other alkenes showed that the surface alkyls formed are predominantly teiminal. 1... 

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