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 (XTol ≈ 67%) and selectivity (SBA ≈ 80%), while Pd,Sb-R was slightly less active (XTol ≈ 50%) but extremely selective (SBA ≈ 100%) and highly stable during reaction. On rutile, coke-resistant, uniform, well-facetted particles (Pd/Sb ≈ 5, d ≈ 80 nm) with neighboring Pd0/PdOx species are formed. On anatase, irregular particles of different size, a Pd/Sb ratio ⩽3 and coexisting Pd0/Pdδ− 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.