title: Conversion of CO2 into valuable fuels and chemicals using non-thermal plasma
Creators: name: Zeng, Y
Publisher: name: University of Liverpool Repository
Year: 2017

description: This project studies the conversion of CO2 into fuels and chemicals in a dielectric barrier discharge (DBD) reactor. CO2, H2 and CH4 have been used as reactants, and special attention has been paid on understanding the plasma-catalytic synergy when a catalyst is placed in a plasma discharge. CO2 and CH4 are major greenhouse gases, responsible for the global greenhouse effect and climate change. The overall aim of this project is to initiate CO2 hydrogenation and biogas reforming at ambient temperature and atmospheric pressure by using plasma-catalysis. In this project, non-thermal plasma has been generated in a DBD reactor with and without a packed-bed of catalyst, enabling the CO2 conversion to be investigated under three conditions: Plasma alone, thermal catalysis and plasma-catalysis. Transitional metal catalysts such as Cu, Co, Mn, and Ni supported on Al2O3 and SiO2 have been screened, and their performance in the CO2 hydrogenation and biogas reforming have been compared under the three conditions. The synergy between non-thermal plasma and catalysts has been clearly identified. The effects of a catalyst’s properties and operational parameters on the reactions have also been studied. The project starts by the investigation of CO2 hydrogenation with H2. Results showed that reverse water-gas shift reaction and CO2 methanation were dominant in the plasma CO2 hydrogenation process. Compared to plasma CO2 hydrogenation without a catalyst, the combination of plasma with Cu/Al2O3, Mn/Al2O3 and Cu-Mn/Al2O3 catalysts enhanced the conversion of CO2 by 6.7% to 36%. The Mn/Al2O3 catalyst showed the best catalytic activity, as it increased the CO yield by 114% and the energy efficiency of CO production by 116%. The Ni/Al2O3 was even better than the Mn/Al2O3 catalyst, while its presence in the DBD reactor has clearly demonstrated a plasma-catalytic synergy at low temperatures. In addition, the introduction of argon in the reaction has enhanced the conversion of CO2, the yield of CO and CH4 and the energy efficiency of the plasma process. The formation of metastable argon (Ar*) in the plasma has created new reaction-routes which made a significant contribution to the enhanced CO2 conversion and CH4 yield. Biogas reforming has also been initiated at ambient temperatures by non-thermal plasma. The combination of plasma with the Co/Al2O3, Cu/Al2O3, Mn/Al2O3 and Ni/Al2O3 catalysts significantly enhanced CH4 conversion and showed a plasma-catalytic synergy for CH4 conversion and overall energy efficiency of the process. The best CH4 conversion of 19.6% and syngas production have been achieved over the Ni/Al2O3 catalyst at a discharge power of 7.5 W and a gas flow rate of 50 ml min-1. Moreover, the addition of K-promoter into the catalyst has further improved the performance of the Ni/Al2O3 catalyst. A conclusion of the findings of this project and outlook for further work is presented in Chapter seven, where it is concluded that non-thermal plasma has initiated the CO2 hydrogenation and biogas reforming at lower temperatures, comparing with thermal catalytic processes. The combination of plasma and catalyst has further improved the performance of the hydrogenation processes, in terms of conversion, yield, and energy efficiency, while significant synergy between DBD plasma and catalysts has been observed. By upgrading the catalyst and adjusting the operational parameters (e.g. molar ratio of feed gas, preparation method of catalyst, composition of catalyst, and promoters), the plasma-catalytic CO2 hydrogenation and biogas reforming processes can be further optimised.