STRUCTURE REACTIVITY RELATIONSHIPS FOR ALKANE DISSOCIATION AND HYDROGENOLYSIS USING SINGLE-CRYSTAL KINETICS

The dissociative adsorption of several small alkanes has been studied on single crystalline surfaces of Ni. As well the hydrogenolysis of ethane and n-butane has been investigated on single crystalline surfaces of Ni and Ir. These studies have utilized a coupled high pressure reactor-ultrahigh vacuum analysis chamber, which permits the measurement of the specific rates of reaction and in situ pre- and post-reaction surface characterization. In general, the greater the corrugation of the Ni single crystal surface, the more active that surface is toward alkane dissociation and hydrogenolysis. Further-more, the activity/selectivity for hydrogenolysis on the "rough" or more open surfaces of Ni and Ir surfaces [Ni(100), Ir(110)-(1x2)] correlates well with analogous results for relatively small particles of Ni and Ir in supported catalysts. The results for the "smooth" Ni and Ir surfaces [Ni(111), and Ir(111)], on the other hand, correlate well with the analogous results for relatively large supported particles of Ni and Ir. Altogether these results are suggestive regarding the nature of the active sites on these catalytic surfaces for alkane dissociation and hydrogenolysis.