Tuning the oxidation of carbon monoxide using nanoassembled model catalysts

While the oxidation of CO has long been considered to be structure insensitive, nano-assembled model catalysts consisting of size-selected metal clusters (Au-n, Pt-n, Pd-n, and Rh-n, n = 1-20), supported on thin MgO(1 0 0) films, reveal distinct size-effects. When adding a single Pt atom to Pt-14,Pt- platinum clusters increase their reactivity by a factor of three. Rh-20 shows the highest reactivity of all the investigated clusters, oxidizing about 13 CO molecules per cluster at 350 K. While F-centers on MgO films transform Aug from an inert to an active catalyst, the reactivity of Pds is not suppressed when deposited on defect-poor films. These different catalytic properties are rationalized within simple frontier orbital models, whereas for AUg the reaction mechanism for the low temperature oxidation of CO is elucidated within first-principle calculations. (C) 2000 Elsevier Science B.V. All rights reserved.