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Design of Efficient Catalysts and Mechanism Study for Photothermochemical Dry Reforming of Methane
Abstract
The world's growing demand for energy has led to over-reliance on fossil fuels and increased emissions of greenhouse gases, which contributed to severe global warming. Dry reforming of methane (DRM) is a valuable technique that holds great promise in mitigating two main greenhouse gases (GHGs), CO2 and CH4 in the atmosphere and producing syngas (CO and H2), a valuable industrial feedstock to produce liquid fuels through Fischer-Tropsch processes. However, considerable thermal energy input from burning fossil fuels will be needed due to the endothermic characteristic of DRM, which leads to the reemission of GHGs. Instead, solar energy is a more sustainable and promising energy source to drive DRM while novel catalyst design can efficiently promote the synergy of thermal catalytic and photocatalytic activities. The long-term stable and efficient catalytic activities and fundamental mechanisms study remain a challenge for solar-driven DRM to be commercially applied. The major goals in this research are to design novel catalysts to maximize the DRM activities and to investigate photochemistry and reaction mechanisms. Firstly, the origin of photocatalytic effects from solar irradiation were systematically probed on a photoactive CeO2 supported Pt catalyst (Pt/CeO2) with Pt/ZrO2 as a photo-inactive control. It was found that the contributions of photocatalysis were mainly from lights less than 435 nm in wavelength, and photo-irradiation regenerated surface oxygen vacancies, thus boosting CO2 activation and promoting formate and carbonate intermediates conversion to final products. Based on the understanding of the photocatalytic effect on CeO2, CeO2 was then incorporated in ZrO2-supported Ni NPs (Ni-CeO2/ZrO2) and propelled PTC-DRM performance. Ni-CeO2/ZrO2 accumulated less coke and exhibited elevated and stable PTC-DRM activities. Furthermore, a Ce-substituted LaNiO3 perovskite catalyst was synthesized, and it was found light irradiation induced photocatalytic activities on La0.9Ce0.1NiO3 and enhanced CO2 adsorption and formation of active lanthanum oxycarbonates intermediates, making the CO2 and CH4 conversion among the top-performing literature. Additionally, a metal-organic framework (MOF) confined bimetallic Ni-Cu nanoparticles (9Ni1Cu/MOF) was developed and investigated. 9Ni1Cu/MOF offered full nanoconfinement of Ni-Cu NPs by the MOF-derived tetragonal-ZrO2/C (t-ZrO2/C) nanostructure, which provided large surface area, featured strong metal-support interaction, and hindered the detrimental filamentous carbon deposition and metal aggregation. As a result, the 9Ni1Cu/MOF catalyst delivered high and stable DRM activities, with an average of CO2 and CH4 conversions and H2/CO molar ratio of 76.5%, 76.7%, and 1.07 over the 100-h DRM reaction, which are among the top performing catalysts for DRM process. It is envisioned that this work about fundamental mechanism investigation and material innovation will lead to future large-scale commercial applications of DRM technology and bring scientific advancement into other catalytic and energy-saving processes.
Citation
Du, Zichen (2023). Design of Efficient Catalysts and Mechanism Study for Photothermochemical Dry Reforming of Methane. Doctoral dissertation, Texas A&M University. Available electronically from https : / /hdl .handle .net /1969 .1 /198861.