Tailoring the microenvironment of Ti sites in Ti-containing materials for synergizing with Au sites to boost propylene epoxidation

Abstract

Au sites supported on Ti-containing materials (Au/Ti-containing catalyst) are currently considered as a promising catalyst for the propylene epoxidation owing to the synergistic effect that hydrogen peroxide species formed on Au sites diffuses to the Ti sites to form the Ti-hydroperoxo intermediates and contributes to the formation of propylene oxide (PO). In principle, thermal treatment will significantly affect the chemical and physical structures of Ti-containing materials. Consequently, the synergy between tailored Ti sites with different surface properties and Au sites is highly expected to enhance the catalytic performance for the reaction. Herein, we systematically studied the intrinsic effects of different microenvironments around Ti sites on the PO adsorption/desorption and conversion, and then effectively improved the catalytic performance by tailoring the number of surface hydroxyl groups. The Ti^VI material with fewer hydroxyls stimulates a remarkable enhancement in PO selectivity and H₂ efficiency compared to the Ti^VI material that possessed more hydroxyls, offering a 7-fold and 4-fold increase, respectively. As expected, the Ti^VI+IV and Ti^IV materials also exhibit a similar phenomenon to the Ti^VI materials through the same thermal treatment, which strongly supports that the Ti sites microenvironment is an important factor in suppressing PO conversion and enhancing catalytic performance. These insights could provide guidance for the rational preparation and optimization of Ti-containing materials synergizing with Au catalysts for propylene epoxidation.