The influence of MSI (metal-support interactions) on phenylacetaldehyde hydrogenation over Pt catalysts

TiO2-supported Pt, after a high-temperature reduction (HTR) at 773 K to induce the SMSI state, had a turnover frequency (TOF) for phenylacetylaldehyde hydrogenation that was 15-20 times higher than TOF values for Pt dispersed on either SiO2 or eta-Al2O3 and, since all supported catalysts had Pt dispersions of unity (1 nm crystallites), the TOF for Pt/TiO2 (HTR) based on complete dispersion was still 2-5 times greater than the other supported catalysts, More importantly, selectivity to 2-phenylethanol was markedly enhanced over Pt/TiO2 (HTR), comprising 70% of the product at conversions as high as 60%. Pt/TiO2 after a low temperature reduction (LTR) at 473 K gave neither the high TOFs nor the enhanced selectivity. Among these catalysts the highest activation energy of 12.4 kcal/mol was attained with Pt/TiO2 (HTR) and the reaction order on phenylacetaldehyde was between 0 and 1/2 while that on H-2 was around 1/2 or higher, At higher conversions (over 50%) significant hydrogenolysis activity to form benzene and toluene occurred on all Pt catalysts except Pt/TiO, (HTR). The higher hydrogenation activity and suppressed hydrogenolysis capability with the Pt/TiO2 (HTR) catalyst is attributed to TiOx species migrating onto the Pt surface to create active sites at the Pt-titania interface while simultaneously destroying large ensembles of Pt atoms required for hydrogenolysis reactions; however, competitive desorption/readsorption processes must also play a significant role in enhancing selectivity to the intermediate phenylethanol product.