Silica Based Catalyst Supports Are Inert, Aren’t They? – Striking Differences in Ethanol Decomposition Reaction Originated from Meso- & Surface Fine Structure Evidenced by Small Angle X-ray Scattering

Abstract

6.6 nm Pt nanoparticles with narrow size distribution were anchored on mostly identical, amor-phous silica supports (SBA-15, MCF-17, Silica Foam) and were tested in ethanol decomposition reactions at < 300 °C. The reaction on the Pt/SBA-15 was ~2 times faster (0.073 molecules·site-1·s-1) compared to Pt/MCF-17 (0.042 molecules·site-1·s-1) and Pt/SF (0.040 molecules·site-1·s-1) at 300 °C. In the case of Pt/SF, selectivity towards acetaldehyde was ~2 times higher compared to the Pt/MCF-17 and Pt/SBA-15 catalysts. In the case of Pt/MCF-17 and Pt/SBA-15, the methane to acetaldehyde ratio was ~ 4 times higher compared to the Pt/SF catalyst. The ethene selectivity was ~1.5 times higher in the case of Pt/SBA-15 compared to Pt/MCF-17 and Pt/SF. Small Angle X-ray Scattering (SAXS) studies showed striking differences in the nature of the surface of the different silica supports, which may be responsible for the activation, and selectivity deviation in ethanol decomposition reactions. The SBA-15 has the most disordered mesostructure and SF has a fine surface structure with a diffuse phase boundary may resulted in the high activity and varying selectivity, respectively