Nano-characterization of Rh-Sn bimetallic catalysts

Abstract

Bimetallic catalysts are of considerable importance because they possess both high activity and selectivity. Recently, there has been considerable interest in bimetallic catalysts produced by surface organometallic chemistry on metals. A detailed description of the structure and composition at the nanometer level is critical to fully understand the behavior of such catalysts. We have undertaken a study of the microstructure of Rh-Sn/SiO2 bimetallic hydrogenation catalysts.A Rh-Sn precursor was prepared by reacting tetrabutyltin with a silica supported Rh parent catalyst (1 %Rh/SiO2). The bimetallic catalysts were produced by thermal decomposition of the precursor in flowing hydrogen at 623 K. Five different catalysts were produced with a range of different Sn loadings from Rh(1%)/SiO2 to Rh(1%)-Sn(1.85%)/SiO2. The resulting bimetallic catalysts were able to selectively hydrogenate isolated and conjugated C=O functional groups. In situ XPS showed that the Sn and Rh were in the fully reduced state. Mossbauer spectroscopy studies confirmed that Sn was present in the zerovalent state indicating that no oxidized Sn was present. Preliminary IR data suggests that most of the Rh atoms are isolated from their neighbors (presumably by Sn).