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Pure Appl. Chem., 2012, Vol. 84, No. 3, pp. 561-578

Published online 2011-11-23

Selective epoxidation of propylene to propylene oxide with H2 and O2 over Au/Ti-MWW catalysts*

Yingjie Ren, Le Xu, Liyan Zhang, Jianggan Wang, Yueming Liu, Mingyuan He and Peng Wu*

Shanghai Key Laboratory of Green Chemistry and Chemical Processes, Department of Chemistry, East China Normal University, North Zhongshan Rd. 3663, Shanghai 200062, China

Abstract: Direct epoxidation of propylene to propylene oxide (PO) with H2 and O2 has been performed on bifunctional catalysts, Au nanoparticles supported on novel Ti-MWW titanosilicate (Au/Ti-MWW). In comparison to conventional Au/TS-1 catalysts, Au/Ti-MWW exhibited a similar phenomenon with respect to PO formation, that is, the PO selectivity increased with increasing Si/Ti ratio of titanosilicate. However, at optimized Ti contents corresponding to Si/Ti ratio >140, the PO selectivity of Au/Ti-MWW catalysts was lower than 60 % in comparison to ca. 90 % achieved on Au/TS-1. A large number of boron species and defect-site-related hydroxyl groups contained in Ti-MWW were assumed to retard the desorption of PO from the channels or crystallite surface of zeolite, which favors side reactions such as over-oxidation and decomposition of PO. Poststructural rearrangement was then carried out on Ti-MWW with piperidine (PI) solution to improve effectively its hydrophobicity, leading to defect-less Re-Ti-MWW. This enhanced significantly the PO selectivity of Au/Re-Ti-MWW thus prepared, which reached as high as 92 % at Si/Ti ratio of 135. Au/Re-Ti-MWW(135) then gave the highest PO formation rate of 22.0 gPO kg–1 h–1.
*Pure Appl. Chem. 84, 411–860 (2012). A collection of invited papers for the IUPAC project 2008-016-1-300 “Chlorine-free Synthesis for Green Chemistry”.