Effect of urea on the morphology of TS-1 and catalytic performance of Au/TS-1 for direct gas phase epoxidation of propylene

Direct gas phase epoxidation of propylene to propylene oxide (PO) over titanium silicalite-1 (TS-1) catalysts with H 2 and O 2 is a promising green and sustainable formation process. For TS-1with MFI structure, the shorter length along b-axis means that the reactants and products molecules have higher diffusion rate. By adding urea as crystal regulator into the synthesis system, the TS-1-S with layered structure was synthesized. TS-1 with the proper amount of urea added (urea/SiO 2 molar ratio of 0.15) shows good performance. When too much urea (urea/SiO 2 molar ratio of 0.35) is added into the synthesis system, the growth of the crystal along b-axis will be restrained, and the layered TS-1-S with the shortest b-axis length of 95 nm is obtained. But too much urea is harmful for titanium into molecular sieve skeleton and leads to more silicon hydroxyl structure, which has great influence on PO formation rate and PO selectivity.