Xubin Zhang

Surface-Active Hollow Titanosilicate Particles as a Pickering Interfacial Catalyst for Liquid-Phase Alkene Epoxidation Reactions

The design of catalyst particles bearing excellent catalytic activity and suitable surface wettability is the key to successful application of Pickering interfacial catalysis. In this study, the epoxidation of 1-hexene and cyclohexene with aqueous hydrogen peroxide over hollow TS-1 (HTS-1) zeolite was studied as a probe reaction to investigate the influence of catalyst surface wettability on catalytic activity. Hydrophobized HTS-1 particles were fabricated via a postsynthesis desilication treatment with tetrapropylammonium hydroxide and a postsynthesis silylation treatment with hexamethyldisiloxane (HMDSO). The successful preparation of HTS-1 particles was verified by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy, and Fourier-transform infrared spectroscopy. X-ray diffraction patterns and ultraviolet-visible spectra confirmed that the hydrophobic modification had no effect on the zeolite structure of HTS-1 particles. Stable Pickering emulsions of aqueous hydrogen peroxide in either 1-hexene or cyclohexene could be prepared using HTS-1 particles as emulsifiers and confirmed by cryo-SEM images. The catalytic behavior in the obtained Pickering emulsions revealed a parabolic distribution of turnover frequency values with respect to the hydrophobization degrees with 0.2-HMDSO/HTS-1 particles possessing the maximum values of 20.6 h-1 for 1-hexene epoxidation and 8.1 h-1 for cyclohexene epoxidation. In addition, these 0.2-HMDSO/HTS-1 particles showed good reusability for more than five cycles.

The preparation of Fe 3+ ion-exchanged mesopore containing ZSM-5 molecular sieves and its high catalytic activity in the hydroxylation of phenol

A series of Fe3+ containing catalysts were synthesized using ion-exchange technique over hierarchically porous ZSM-5 (M-ZSM-5) and micro-mesoporous composite ZSM-5/MCM-41 (ZSM-5/MCM-41), respectively. The prepared catalysts were characterized by X-ray diffraction, scanning electron microscope, transmission electron microscope, N2 adsorption–desorption, UV–Vis spectroscopy, temperature programmed reduction and inductively coupled plasma-optical emission spectroscopy. The characterization results exhibit that the hierarchically porous ZSM-5 was synthesized with intracrystalline mesopores, while the micro-mesoporous composite ZSM-5/MCM-41 was prepared with the well-ordered mesopores. Furthermore, the results also prove that the existence of iron in the catalysts was mainly presented in the form of Fe3+ ions. Catalytic performances of the samples for phenol hydroxylation were compared by using H2O2 as oxidant. Under the optimized conditions, Fe3+ ion-exchanged M-ZSM-5 (Fe-M-ZSM-5) shows that a phenol conversion of 42.3% obtained with 92.5% selectivity to dihydroxybenzenes, whereas Fe3+ ion-exchanged ZSM-5/MCM-41 (Fe-ZSM-5/MCM-41) give 46.2% phenol conversion and 90.1% dihydroxybenzenes selectivity, which are all better than most reported results. The recyclability tests show that Fe-ZSM-5/MCM-41 with ordered mesoporous structure and bigger surface area has better anti-deactivation performance than Fe-M-ZSM-5. The excellent catalytic performances were due to the improved diffusion performance with newly created mesopores and the highly active Fe3+ species obtained by ion-exchange technique.

Cooperative structure direction of organosilanes and tetrapropylammonium hydroxide to generate hierarchical ZSM-5 zeolite with controlled porous structure

Hierarchical ZSM-5 zeolite with short-range ordered mesoporosity and hierarchical ZSM-5 zeolite nanorods were obtained via a direct hydrothermal synthesis by the cooperative structure direction of dimethyloctadecyl[3-(trimethoxysilyl)propyl]- ammonium chloride (TPOAC) and tetrapropylammonium hydroxide (TPAOH). Dimethyloctadecyl[3-(dimethoxymethylsilyl)propyl]ammonium chloride (DPOAC) and octadecyltrimethylammonium chloride (OTAC) were also employed as structure directing agents (SDA) to further explore the role of methoxysilyl groups in organosilanes during the formation of hierarchical structure. The prepared materials were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), N2 adsorption–desorption, FT-IR, UV-vis and inductively coupled plasma-optical emission spectroscopy (ICP-OES). The characterization results showed that the use of TPOAC and DPOAC would generate short-range ordered mesopores and irregular mesopores, respectively. Hierarchical ZSM-5 zeolite nanorods with worm-like intracrystalline mesopores could be obtained by adjusting the amount of silicon source. The lack of methoxysilyl groups in OTAC however could lead to phase separation problems. Furthermore, the hierarchical Fe-ZSM-5 zeolite with short-range ordered mesoporosity showed enhanced catalytic activity and stability for the hydroxylation of phenol at room temperature.

Efficient and stable Ru(III)-choline chloride catalyst system with low Ru content for non-mercury acetylene hydrochlorination

Abstract Herein, we report an excellent, supported Ru(III)-ChCl/AC catalyst with lower Ru content, where the ionic complex ChRuCl4 serves as the active component for acetylene hydrochlorination. The prepared heterogeneous Ru-10%ChCl/AC catalyst shows excellent activity and long-term stability. In this system, ChCl provides an environment for the ChRuCl4 to be stabilized as Ru(III), thus suppressing the reduction of the active species and the aggregation of ruthenium species during the reaction. The interaction between reactants and catalyst species was investigated by catalyst characterizations in combination with DFT calculations to disclose the effect of the ChRuCl4 complex and ChCl on the catalytic performance. This inexpensive, efficient, and long-term catalyst is a competitive candidate for application in the hydrochlorination industry.