Catalyst genesis studied by atomic force microscopy

Abstract

Atomic force microscopy has been used to study the genesis of realistic Ag–α-alumina model catalysts from an aqueous precursor (AgNO 3), using conditions identical to those used in the synthesis of practical dispersed catalysts. The various stages in the evolution of the final catalyst from the initially deposited precursor were successfully imaged. It is found that the structure of the alumina substrate exerts a dramatic influence on the structure and stability of the silver deposit. On Al 2O 3(0001), sintering in 1 bar oxygen at 780 K causes a quasi-2D network of metallic Ag to collapse to large well-formed hemispherical particles on the bare oxide surface. On Al 2O 3(112̄0), precursor decomposition leads initially to the formation of quasi-1D Ag nanowires that decorate the faceted step edges and extend for many hundreds of nanometres. This is entirely different from the behaviour of vacuum-deposited Ag. These nanowires are much more stable against sintering in 1 bar oxygen at 780 K. Their formation and stability suggest a particularly favourable wetting interaction between Ag and the (11̄02) plane of α-alumina.