Chemical looping technology enables achievement of the simultaneous feedstock conversion and product separation without additional processes via circulating solid intermediates (so-called oxygen/nitrogen carriers) in a redox process, which contributes to the improvement of product selectivity and energy conservation. In general, methane, CO 2 , N 2 , ethane, propane, ethanol, and glycerol are typical gaseous and liquid fuels for producing syngas, pure H 2 , pure CO, NH 3 , ethylene, and propylene via the chemical looping process. Central to this technology is the solid intermediates that act as reservoirs for storing and releasing O or N in multiple sub-reactions to close the loop. This work comprehensively describes the chemical looping conversion of gaseous or liquid fuels for chemical production, covering chemical looping reforming of methane, chemical looping oxidative coupling of methane, chemical looping reforming of liquid fuels, chemical looping oxidative dehydrogenation, and chemical looping ammonia synthesis technologies. Specifically, this review mainly focuses on the development of oxygen/nitrogen carrier materials, especially the related research in China. The effects of composition, structure, and morphology on the performance and related reaction mechanisms are discussed.
The dry reforming of methane (DRM) reaction, which converts two greenhouse gases, CO 2 and CH 4 , into valuable syngas, offers a promising route to carbon sequestration. Nibased catalysts have been widely used for DRM due to the high activity, low cost, and high feasibility. Nevertheless, the rapid deactivation of Ni-based catalysts caused by carbon deposition and/or active metal sintering is the main drawback for large-scale application. In addition, its high energy demand poses additional difficulties due to the heat-absorbing nature of the reaction. The design of bimetallic alloy catalysts has been considered as an effective strategy to improve the activity and stability of Ni-based catalysts. This paper reviews recent advances in Ni-based bimetallic catalysts for DRM processes, which mainly focus on the synergistic effects of the two elements, the role of the second metal, and the reaction mechanism induced by different active species. Finally, the outlook for the development of high-performance catalysts for DRM is proposed. The discussions in the present work may provide helpful information to researchers in the CO 2 conversion fields to optimize catalyst design.
A promising approach is to transform carbon dioxide (CO2) into renewable, high value-added products with minimal environmental
impact and maximum efficiency. Many problems, including energy shortages
and environmental degradation, are caused by high CO2 levels,
but this can help. Photocatalytic reduction methods are a promising
technology for solving these problems. Cerium dioxide (CeO2) is one of the most important rare earth oxides, and cerium dioxide-based
photocatalysts have gained a lot of attention in recent years due
to their distinctive features, such as their tunable electronic structures
and their excellent photocatalytic performances. However, the wide
energy band of cerium oxide limits its utilization of light. This
review provides various strategies for the modification of cerium
oxide, encompassing external atom doping, heterostructure fabrication,
defect fabrication, and crystal plane modulation, to improve the catalytic
performance of CeO2. The fundamentals of the conversion
of CeO2-based photocatalysts into high value-added products
are also summarized. Finally, the challenges and prospects of CeO2-based catalysts for photocatalytic reduction of CO2 are presented.
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