Nature of surface carbon species and pathways of their formation in the heterogeneously catalysed acetoxylation of toluene

Abstract

The origins of surface carbon species in the acetoxylation of toluene to benzyl acetate over Pd–Sb/TiO₂ catalyst and their formation pathways were systematically investigated. To reach this goal, steady-state catalytic experiments were combined with in situ temperature programmed oxidation (TPO) of catalyst samples treated under different reaction conditions. Complementary in situ as well as ex situ infrared (IR) and X-ray photoelectron spectroscopic (XPS) measurements were also performed to derive deeper mechanistic insights. Our studies revealed that the formation of surface carbon species occurs directly from acetic acid and indirectly from toluene with the former being, however, the main coke precursor. The derived knowledge provides the fundamentals for tailored catalyst design.