Zeolite crystal size effects of Au/uncalcined TS-1 bifunctional catalysts on direct propylene epoxidation with H2 and O2

Understanding the nature of Au-Ti bifunctional catalysis is important yet challenging for improving direct propylene epoxidation with H-2 and O-2 to propylene oxide (PO). Herein, we report a facile strategy to fabricate four different crystal sized TS-1 with the presence of highly active isolated Ti4+ species by adjusting the amount of TPAOH template. The resultant uncalcined zeolite samples, i.e., TS-1-B, are employed to load Au via deposition-precipitation with urea for obtaining similar sized Au immobilized on TS-1-B catalysts and thus excluding the size effects of Au active sites. The zeolite crystal size effects are further probed, and then decreasing the crystal size gives rise to the simultaneous promotion in PO formation rate and selectivity, as well as H-2 efficiency. These are attributed to the Au-Ti electronic synergy based on UV-vis and XPS measurements. The insights reported here could benefit the development of high-efficiency Au-Ti bifunctional catalysts for this reaction. (C) 2020 Elsevier Ltd. All rights reserved.