Enhanced catalytic performance of PdSn/Ti-MWW for the low-temperature epoxidation of propylene with H2 and O2 to propylene oxide

Develop Pd-based catalysts for propylene epoxidation with H 2 and O 2. • Sn species in PdSn/Ti-MWW increase the electron density of Pd. • Increased electron density of Pd enhances the H 2 utilization. • Sn significantly promotes the catalytic propylene epoxidation. The low-temperature epoxidation of propylene with H 2 and O 2 to propylene oxide (PO), commonly referred to as the low-temperature HOPO process, over titanosilicate zeolite-supported Pd catalysts is economically attractive and environmentally friendly. However, PO selectivity remains a major challenge for these systems and is comparatively low, because this process is commonly accompanied with propylene hydrogenation to propane. In the present study, a novel and efficient Ti-MWW-supported PdSn catalyst (PdSn/Ti-MWW) was developed for this low-temperature HOPO process, displaying a substantially high PO selectivity. The results on extensive characterizations, in combination with Density Functional Theory (DFT) calculations, for PdSn/Ti-MWW and Pd/Ti-MWW verify that the introduction of Sn species into Pd/Ti-MWW can boost the electron density of Pd species while does not affect the coordination states of Ti species and the textural properties of the zeolite. Interestingly, the enhanced Pd electron density will weaken the adsorption of propylene on the Pd active sites, resulting in inhibiting propylene hydrogenation, which is beneficial for the selective production of PO. Catalytic tests reveal that the optimal 0.33Pd0.22Sn/Ti-MWW catalyst achieves a PO selectivity of 68.4 % and a maximum PO productivity of 7.5 mol g Pd -1 h −1 , far exceeding monometallic Pd/Ti-MWW, while the undesired propane selectivity drops sharply. Moreover, PdSn/Ti-MWW shows an excellent stability and reusability as key catalytic traits. Thus, this work establishes an effective electronic modulation strategy for designing high-performance bimetallic Pd catalysts, and lays solid experimental and theoretical foundations for the industrial application of sustainable low-temperature HOPO technology. Download: Download high-res image (81KB) Download: Download full-size image