Inhibiting COx formation on WOx-loaded Au/TiO2 photocatalyst for selective oxidation of p-xylene to p-methyl benzaldehyde

Photocatalytic selective oxidation of p-xylene with O2 offers a mild pathway to synthesize p-methyl benzaldehyde (p-MBA), which is one of the primary precursors in the manufacture of fine chemicals. Here, we report that Au/WOx/TiO2 photocatalyst selectively catalyzes the oxidation of p-xylene to p-MBA with 88.6% selectivity at 1.0% conversion, the formation of COx is suppressed to 0.8%. Kinetic experiments indicate that p-methylbenzyl alcohol and p-MBA are initial products. p-Methylbenzyl alcohol is further oxidized to form p-MBA, p-methylbenzyl acid and COx; p-MBA is further oxidized to p-methylbenzyl acid and COx. On TiO2 surface, p-methylbenzyl alcohol is more prone to directly combust to COx by O2–. Loading of WOx can weaken the adsorption ability of p-methylbenzyl alcohol on the catalyst surface to avoid the combustion. Meanwhile, WOx and Au can facilitate the separation of photo-generated carriers to attain high activity and suppress the O2– formation to obtain high selectivity.