ABSTRACT
Zeolitic imidazolate frameworks (ZIFs) bearing rich accessible Lewis acidic/basic active sites and hierarchical pores are favorable to catalyze the cycloaddition of CO2 and epoxides with high yields of the target product under mild conditions. In this context, a facile etching and regrowth method is developed here to convert unstable leaf-like zinc-based ZIF-L to one kind of bimetallic ZIF (namely, ZnFe-ZIF) with a rough surface, a porous and accessible three-dimensional structure, and abundant Lewis acidic sites. Owing to the high Fe-doping content functioning as rich Lewis acidic sites and the high CO2 adsorbing capability together with the structural advantages to favor the mass diffusion, the yield of target cyclic carbonate can be up to >99% for the cycloaddition of CO2 and epichlorohydrin by ZnFe-ZIF at 6 h under mild conditions (0.1 MPa and 80 °C) with the selectivity of 100%. More importantly, unlike ZIF-L, which is unstable in the reaction system, the synthesized ZnFe-ZIF displays a satisfactory chemical stability without a loss in catalytic activities after five recycling runs as well as good substrate tolerance, making ZnFe-ZIF a potential high-performance catalyst for CO2 conversion.
ABSTRACT
Pyridine is a basic heterocyclic compound with high toxicity, widely found in liquid waste from industrial processes. The treatment of highly-concentrated pyridine was demonstrated using a novel mist-type water thermal plasma torch. Decomposition rate and TOC removal rate were more than 94% in all conditions, while the max energy efficiency reached about 23 g/kWh. With a high temperature of 5500-7500 K, more than 95% of carbon content in pyridine was converted into valuable gas products, while a little amount of formic acid and acetic acid were observed as liquid by-products. The production of hydrogen cyanide (HCN) during the thermal decomposition of pyridine was observed, which can be inhibited by increasing the input power. Based on the experimental results, detailed decomposition mechanisms in the high-temperature and the downstream region were discussed respectively. Water plasma shows significant potential in the treatment of non-biodegradable industrial liquid waste.
