Constructing Ni-based confinement catalysts with advanced performances toward the CO2 reforming of CH4: state-of-the-art review and perspectives
In recent years, the global greenhouse effect has been receiving more and more attention due to the increasing emission of greenhouse gases. CO2 and CH4 have been widely considered as the main greenhouse gases causing global warming and climate change. The CO2 reforming of CH4 (CRM) reaction can simultaneously convert both CO2 and CH4 into value-added synthesis gas (H2 + CO) and also alleviate the emission of these two greenhouse gases. Ni-Based catalysts have been widely investigated as the most promising candidates for CRM owing to their advanced activities and low price. However, the Ni-based catalysts usually suffer rapid deactivation due to the thermal sintering of metallic Ni active sites and surface carbon deposition during the CRM reaction at high temperatures (>640 °C). To address this challenge, researchers worldwide have devoted great efforts to developing highly efficient and stable Ni-based catalysts. However, it is extremely difficult to achieve this aim by using the traditional supported catalysts because of the weak metal–support interaction. Therefore, the concept of Ni-based confinement catalysts, such as core–shell catalysts, mesoporous catalysts, layered catalysts, and Ni-containing crystalline compound catalysts, have been proposed and developed to address the challenge of the thermal sintering of the metallic Ni active sites by the space and/or lattice confinement effects of these structures. As a result, the metallic Ni active site can be firmly stabilized and the surface carbon deposition can be effectively inhibited owing to the size effect of the metallic Ni active sites. This review mainly summarizes the state-of-the-art progress of the Ni-based confinement catalysts with advanced performances for CRM. Specifically, the Ni-based catalysts with different confinement types, including pore channel confinement, core–shell structure confinement, interlayer structure confinement, and crystalline lattice confinement, have been summarized. The significant impacts of the confinement effect on the stabilization of the Ni-based CRM catalysts are discussed in detail. The influences of the preparation methods on the catalytic performance of the Ni-based catalysts are also discussed and their development trends have been determined.