Investigation of inherent differences between oxide supports in heterogeneous catalysis in the absence of structural variations

Oxide supports in heterogeneous catalysts can profoundly influence the catalytic properties of the metal or alloy active phase. Supports prepared by conventional methods can have not only different chemical properties but also different structural properties depending on the oxide. These structural differences can in turn affect the dispersion, distribution, and accessibility of the active phase. In this study, we apply an atomically-controlled synthesis method to isolate the effects arising from the different chemical properties of three oxide supports -titania, alumina and silica -used in Rh catalysts for syngas conversion reactions. We perform atomic layer deposition of titania and alumina to chemically modify the surface of silica gel, without changing its structural characteristics such as surface area and porosity. An inverse catalyst structure is also fabricated by depositing titania and alumina as overlayers onto silica-supported Rh. Titania is found to increase syngas conversion activity and higher hydrocarbon selectivity as both a support layer and an overlayer. An alumina support layer increases Rh nanoparticle dispersion and activity whereas an alumina overlayer decreases the activity of Rh. No significant increase in higher oxygenate selectivity was observed with either titania or alumina. (C) 2017 Elsevier Inc. All rights reserved.