The one-pot synthesis of 1,2-pentanediol from 1-pentene is a route featuring environmental benignity, cost-effectiveness, and high atom economy. In this study, a bifunctional zirconium sulfate-loaded titanosilicate molecular sieve (ZS/Ti-MWW) catalyst was prepared via the impregnation method and used in the one-pot synthesis of 1,2-pentanediol. The effects of reaction conditions, zirconium sulfate loading, and calcination temperature on the catalytic performance for the oxidative hydration of 1-pentene were systematically investigated. On the basis of the NH3-TPD characterization results, the acid amounts of different catalysts were quantitatively analyzed. The results confirmed that zirconium sulfate could introduce abundant acidic sites into the catalyst, and the acid amount varied with the loading amount of zirconium sulfate and the calcination temperature. With the increase in acid sites in the ZS/Ti-MWW catalyst, its catalytic activity in epoxide hydration was markedly improved. Thus, the 1-pentene epoxidation and epoxide hydration were efficiently carried out in one system without additional separation. Under the optimal reaction conditions, the conversion rate of 1-pentene, the selectivity, and the yield of 1,2-pentanediol reached 95.65%, 80.72%, and 77.21%, respectively. This work offers new insights into the design and preparation of bifunctional titanosilicate molecular sieve catalysts as well as the efficient and green synthesis of 1,2-diols from olefins.
The Ti-MWW zeolites with a layered morphology, synthesized by a conventional method, usually show low catalytic activities in the epoxidation of bulky alkenes due to the serious steric constraint imposed by the zeolite micropores and the adverse effects from some extra-framework octahedral Ti species. In the present work, the Ti-MWW zeolite was prepared by the reaction of an ultra-thin layered borosilicate MWW-type zeolite (D-ERB-1) with tetrabutyl orthotitanate (TBOT) in a HNO 3 aqueous solution, wherein D-ERB-1 was hydrothermally synthesized by introducing an organosilane into the synthetic gel. In combination with the results from extensive characterizations for the synthesized zeolites, it is found that the currently synthesized Ti-MWW zeolite without extra-framework octahedral Ti species has thinner nanosheets that are very helpful to the epoxidation of cycloalkenes with tert-butyl hydroperoxide (TBHP), and is more active than the conventional Ti-MWW and other titanosilicate zeolites. Moreover, the developed catalyst is recyclable after the regeneration of the deactivated zeolite by washing with acetonitrile (MeCN). Therefore, the present work provides some guidance in the development of an efficient titanosilicate catalyst for the epoxidation of bulky alkenes.
Chaosi Liu,Yijing Gao,Yixiang Niu,Yumei Zhang,Cheng Wang,Tengda Li,Chunhui Xu,Weidong Zhu,Xinqing Lu
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
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