Chemisorption of isobutane and neopentane on Ir(110)

摘要

Molecular beam techniques have been employed to investigate the chemisorption of isobutane and neopentane on Ir(110) at surface temperatures, T-s, from 85 to 1000 K. The beam translational energies, E-i, varied from 3.1 to 31 kcal/mol for isobutane, and 1.8 to 48 kcal/mol for neopentane. For T-s < 100 K, isobutane formed molecular multilayers, as did neopentane for T-s < 110 K. The initial adsorption probabilities. P-a, remained nearly independent of surface temperature between 100 and 300 K for isobutane, and 110 and 350 K for neopentane for different beam impact energies. For T-s = 100 K, isobutane adsorbs molecularly with an intrinsic trapping probability, xi, equal to 0.96 at E-i = 3.1 kcal/mol while neopentane adsorbs molecularly with xi = 0.94 at E-i = 1.8 kcal/mol and T-s = 110 K. In contrast, for isobutane with T-s between 300 and 1000 K, and for neopentane with T-s between 350 and 1000 K, the initial adsorption probabilities decrease with increasing T-s. For both molecules, the adsorption probabilities show characteristics of both trapping-mediated and direct dissociative chemisorption which dominate the kinetics for low and high impact energies, respectively. A kinetic model is proposed, which includes C-H bond cleavage reaction pathways. (C) 2000 Published by Elsevier Science B.V. All rights reserved. References: 43