Scanning tunneling microscopy and spectroscopy of silver and platinum catalysts

Abstract

Scanning tunneling microscopic studies of silver catalysts dispersed on highly oriented pyrolitic graphite (HOPG) with 2, 5 and 10 wt% metal loading prepared by wet impregnation and hydrogen reduction show spherical crystallites, with the 2 wt% catalysts having an average crystallite size of ~2 nm and the 5 and 10 wt% catalysts with size distributions of 2-5 and 4-12 nm respectively. The Ag catalysts prepared by NaBH₄ reduction show a narrower size distribution. Pt/HOPG catalysts with 2 and 5 wt% metal loading prepared by wet-impregnation and hydrogen reduction show large (2-11 nm) raft-like crystallites; small crystallites (~1 nm) could be obtained by NaBH₄ reduction. Tunneling spectroscopic measurements reveal the nonmetallic nature of crystallites on the surface of Ag(2 wt%)/HOPG as well as Pt/HOPG prepared by NaBH₄ reduction.