Jie Cen

The application of heterogeneous visible light photocatalysts in organic synthesis

The advantage of visible-light photocatalysis lies in its use of clean, renewable, cheap visible light as a driving force. Recently heterogeneous visible light photocatalysts have drawn much attention due to their nature of easy recycling and simple chemical work-up. Immense effort has been devoted to the application of solar energy in the field of energy regeneration such as hydrogen production and the reduction of carbon dioxide. Recently, solar energy has also captured much attention in organic synthesis due to its unique advantages. This paper will review the state-of-the-art progresses in the application of heterogeneous visible-light photocatalysis in organic synthesis through four sections: oxidation of alcohols, oxidation of amines, carbon–carbon bond formation reactions, and carbon–hetero bond formation reactions.

The effect of Si/Al ratio on the catalytic performance of hierarchical porous ZSM-5 for catalyzing benzene alkylation with methanol

Ethylbenzene is the major side product in benzene alkylation with methanol and it is difficult to be suppressed over hierarchical porous ZSM-5. Moreover, the separation of ethylbenzene from xylene still remains a great challenge. Our research indicated that ethylbenzene formation could be highly suppressed by changing the Si/Al ratio of the catalyst. Hierarchical porous ZSM-5 catalysts with different Si/Al ratios were prepared via reducing the amount of Al in the solvent evaporation assisted dry gel conversion method. In this method, tetra-n-propylammonium hydroxide was used as the direct agent to create micropores, and hexadecyltrimethoxysilane was added to create additional porosities by forming organic assemblies which occupied a certain space between zeolitic walls. The catalyst with a Si/Al ratio of 1800 could achieve high benzene conversion (59.5%) and high xylene selectivity (39.0%) as well as excellent suppression of ethylbenzene formation (<0.1%).

Catalytic Activity of Pt Modified Hierarchical ZSM-5 Catalysts in Benzene Alkylation with Methanol

Hierarchical ZSM-5 zeolite showed an improved performance as compared to conventional ZSM-5 catalysts in the alkylation of benzene with methanol. However, ethylbenzene yet remains as a major problem. In this study, we modified hierarchical ZSM-5 with Pt to evaluate the alkylation of benzene with methanol in a fixed-bed continuous flow reactor. It was found that Pt modified hierarchical ZSM-5 could successfully combine the catalytic advantages of hierarchical ZSM-5 and the high suppression of Pt to ethylbenzene formation. Moreover, employing direct reduction could improve the utilization of Pt by avoiding Pt particles sintering.Graphical Abstract.

Alkylation of benzene with methanol over hierarchical porous ZSM-5: synergy effects of hydrogen atmosphere and zinc modification

The competitive reaction of methanol to olefins is difficult to be suppressed in benzene alkylation with methanol over hierarchical porous ZSM-5. The influence of ZnO content and different atmospheres on the catalytic performance of hierarchical porous ZSM-5 catalyst was investigated. The results indicated that the introduction of ZnO could form the Lewis acid sites of zinc species (ZnOH+) at the expense of the Bronsted acid sites, and the reduction of strong Bronsted acid would help to suppress the side reaction of methanol to olefins. However, the presence of ZnOH+ could catalyze the dehydrogenation reaction of light hydrocarbons to olefins which would result in the formation of coke under the nitrogen atmosphere, while the hydrogen atmosphere could inhibit the dehydrogenation ability of ZnOH+.

Promoting effects of MgO and Pd modification on the catalytic performance of hierarchical porous ZSM-5 for catalyzing benzene alkylation with methanol

The effect of MgO and Pd modification on the catalytic performance of hierarchical porous ZSM-5 for benzene alkylation with methanol was investigated. The results indicated that the introduction of MgO could reduce the Bronsted acid sites which suppressed the side reaction of methanol to olefins and in turn effectively promoted the alkylation of benzene. However, the single modification of MgO could not completely suppress the formation of ethylbenzene and coke. Doping a small amount of Pd had a positive effect on inhibiting the generation of ethylbenzene and coke, which could be attributed to the hydrogenation of ethylene into ethane on Pd. The dual modified catalyst (MgO and Pd) exhibited high benzene conversion (56%) and xylene selectivity (39.1%), and the lowest ethylbenzene selectivity (0.13%) and coke content (0.4 wt%).

Thermal oxidation to regenerate sulfone poisoned Pd-based catalyst: effect of the valence of sulfur

Sulfur deactivation is a serious problem which largely limits the industrial application of noble metals as catalysts. Here we report a thermal oxidation method to regenerate sulfone poisoned Pd/C catalyst applied in the hydrogenation of sodium-m-nitrobenzene sulfonate (SNS). It was found that the initial activity of Pd/C catalyst could be substantially recovered after treating it in air at temperatures as low as 100 °C. And the catalyst could be reused for at least 20 times without the significant loss of activity. The properties of deactivated and regenerated catalysts were studied in detail by BET measurement, X-ray photoelectron spectroscopy (XPS), temperature programmed desorption (TPD), and Fourier transform infrared spectroscopy (FT-IR). The results indicated that the main surface sulfur species found on deactivated and regenerated Pd surfaces were Sn and sulfate (SO4), respectively. The change of the valence of sulfur species was found to be the key factor influencing the catalytic activity of the Pd-based catalyst.