Support effects on the chemisorption of CO on small nickel clusters

Abstract

Spin-polarized self-consistent-field-local-spin-density-scattered-wave calculations for small Ni and Ni-Cu clusters, either alone or interacting with an adsorbed CO molecule have led to a detailed mechanism for the experimentally observed decrease in the saturation magnetization of Ni catalysts following chemisorption. It was also found that the magnetic response of Ni atom(s) directly involved in the chemisorption is highly sensitive to its (their) nearest-neighbor environment. Here this work is extended to small (Ni 9, Ni 9 + CO) clusters either alone or interacting with models (Al 5O 8, Al 5O 8H) of a supporting medium in order to examine the possible influence of the support on (i) the Ni magnetic moments, (ii) the effect of CO chemisorption on these moments and (iii) support effects on the NiCO and CO binding. The calculations predict a decrease of the Ni moments for the supported (Ni 9) cluster compared with the unsupported aggregate. This support effect may be traced to a strong mixing between Ni 3d and O 2p Orbitals. In contrast to the situation for unsupported Ni clusters, chemisorption of CO on a supported Ni 9 cluster causes only minor changes of the magnetism. Furthermore, the CO-derived levels in the “ supported” case are very different from those calculated for Ni 9CO.