Hydrogenolysis of ethane and exchange with D2 on rhodium during the build-up of hydrocarbon coverage

The isotope exchange and hydrogenolysis of C2H6 with D2 on evaporated Rh films were measured in a flow reactor during the build-up of hydrocarbon coverage and during displacement from the surface of chemisorbed hydrocarbon residues. The gaseous composition was continuously determined by mass spectrometry. The adsorption rate of light ethane, the rate of desorption of adsorbed C2 radicals by the mechanisms of both single and multiple exchanges, the hydrogenolysis rate and the hydrocarbon coverage Csub(S) were simultaneously measured. The value of Csub(S) is determined from the integrated in-out total mass balance. It is shown that all chemisorbed hydrocarbon radicals (Csub(S)) are reversibly chemisorbed and that the rate of methane formation is always simply proportional to the amount of Csub(S). On the contrary, the rate of single exchange is independent of Csub(S) but is simply proportional to the adsorption rate of ethane. (author)