Support-shape dependent catalytic activity in Pt/alumina systems using ultra-small (USANS) and small angle neutron scattering (SANS)

Abstract

The correlation between the morphology of catalyst supports and their effect on catalyst dispersion was investigated. The structure of two types of gamma-alumina (gamma-Al2O3) crystallite particles, rod-like and platelet-like alumina, were measured in 4 orders of length scales, from nanometer to micrometer, using ultra small angle neutron scattering (USANS) and SANS and quantitatively characterized with Hammouda's Generalized Guinier-Porod model. Pt nanoparticles tended to deposit in finer particles and had narrower particle size distribution on the rod-like alumina supports compared to the plate-like alumina supports due to geometrically restricted deposition areas and higher surface curvatures of the rod-like supports. The high diffusion barrier for Pt particles on the highly curved surfaces of the rod-like supports was attributed to be the reason why Pt particles were prevented from diffusing and clustering. While aggregates of the rod-like alumina supports were randomly dispersed without any specific orientation, resulting in high surface area, aggregates of the plate-like alumina supports consisted of a stack of 2-3 layers due to the high van der Waals forces between planar layers, resulting in low surface area. Pt/rod-like alumina supports showed more than 100% higher catalytic activities than Pt/platelet-like alumina supports in model three-way-catalyst (TWC) reactions of CO, NO, and C3H6 conversions at 200-250 degrees C. Control of shape and aggregation of catalytic support materials in nano-micrometer scale can be an important parameter to improve catalytic performance. (C) 2015 Elsevier B.V. All rights reserved.