Impact of Co-Components on the State of Pd and the Performance of Supported Pd/TiO2 Catalysts in the Gas-Phase Acetoxylation of Toluene

The effect of the co-components Mn, Co, Au, and Sb with a wide range of standard reduction potentials (Mn2+/Mn: E degrees=-1.18 V; Co2+/Co: E degrees=-0.28 V; Sb3+/Sb: E degrees=+0.2 V; Au3+/Au: E degrees=+1.52 V) on the catalytic performance of 10 wt% Pd, 8 wt% M/TiO2 (M=Mn, Co, Sb, Au) catalysts in the gas-phase acetoxylation of toluene to benzyl acetate has been studied. Co-components with low E degrees are more active, but less selective than those with high E degrees. Co-components with low E degrees (Mn, Co) stabilize Pd in its oxidized form, whereas those with high E degrees (Sb, Au) support the formation of metallic Pd. Sb and Au are incorporated into the Pd lattice, whereas Mn and Co are enriched at the surface during time on stream. Carbon is deposited on all catalysts during the reaction. However, for Mn- and Co-containing catalysts, carbon is incorporated into the metal particles, whereas it is deposited on top of Pd particles modified with Sb and Au, which leads to faster deactivation.