Rutile - A superior support for highly selective and stable Pd-based catalysts in the gas-phase acetoxylation of toluene

Pd,Sb particles supported on anatase (A) and rutile (R) were tested in the gas-phase acetoxylation of toluene to benzyl acetate (BA). On Pd,Sb-A, fast deactivation occurred after reaching maximum conversion (X-Tol approximate to 67%) and selectivity (S-BA approximate to 80%), while Pd,Sb-R was slightly less active (X-Tol approximate to 50%) but extremely selective (S-BA approximate to 100%) and highly stable during reaction. On rutile, coke-resistant, uniform, well-facetted particles (Pd/Sb approximate to 5, d approximate to P-180 nm) with neighboring Pd-0/Pd-x species are formed. On anatase, irregular particles of different size, a Pd/Sb ratio <= 3 and coexisting Pd-0/Pd delta- surface sites were detected, which were covered by coke during time on stream. The beneficial properties of Pd,Sb-R are related to Pd surface clusters of optimum size and valence states, to an optimum Pd/Sb ratio and to incorporation of carbon into the metal particles, which keep their surface carbon-free and active. (c) 2012 Elsevier Inc. All rights reserved.