| Popis: |
Temperature-programmed desorption (TPD) of coadsorbed H2 and CO was used to detect the presence of a H-CO complex on a Ni AI 2 O 3 catalyst, and isotope labeling was used to separate adsorbed species that were present on separate sites. The surface complex was shown to be present on the Al2O3 support and to have the stoichiometry of methoxy ( H CO3 ). The complex formed through an activated process carried out at 385 K. Much more CO and H2 adsorbed at 385 K than at 300 K. Both CO and H2 adsorbed on the Ni, after which they transferred to the Al2O3; activated adsorption of H2 appeared to limit the transfer. At high coverage, a new CO desorption state was detected on the Ni surface. During TPD following CO and H2 adsorption at 385 K, decomposition of the complex limited formation of CO and H2. During temperature-programmed reaction (TPR), the two CH4 peaks previously reported (Glugla et al. 1988) are shown to result from two forms of adsorbed CO: on the Ni surface and on the Al2O3 as a complex. Hydrogenation of the complex is limited by its decomposition, which is slower than CO hydrogenation on Ni. Good agreement is shown between TPD and TPR. |
