The Research On The Preparations And CH₄-CO₂ Reforming Properties Of Nickel Based Catalysts Confined By Mesoporous Silica

Methane and carbon dioxide are generally considered as the least expensive Ci compounds. At the same time, both of them are the greenhouse gases, contributing to the global warming. CO2 (Dry) reforming of methane is a promising catalytic process for the conversion and utilization of C1 resource and solving the deteriorating environmental problems. However, the catalysts deactivation due to loss metal surface area by coking and sintering was still remains a major challenge. To solve these problems, two kinds of coking and sintering resistant nickel based catalysts were prepared by in situ and post-synthetic strategies, respectively. The main research results are listed as follows:The Ni/SBA-15 catalyst was prepared by ammonia evaporation (Ni-AE) under hydrothermal condition. The formation of Ni phyllosilicate was crucial to achieve the uniform distributed Ni nanoparticles. Dry reforming of methane reactivity results showed no observed decrease of activity for Ni-AE even reacted at 800℃ for 100 min or 700℃for 100 h. Compared with the catalyst prepared by impregnation, the Ni-AE catalyst possessed smaller nickel particle size, higher dispersion and more uniform Ni particle distribution, which should be responsible for its excellent resistance to coking. The anchored effect of the pore wall and the confinement effect of mesoporous channel paly a helpful role for stabilizing the catalyst.The Ni-HMS catalyst was prepared by one-pot synthesis at room temperature. It was found that the catalytic activities of Ni-HMS are well maintained after high-temperature test at 800℃ for 4 h and long-term test at 700℃ for 100 h. The strong metal-support interaction deriving from the strong anchor effect of silica matrix to Ni species plays a crucial role in suppressing sintering of Ni nanoparticles, and the homogeneously distributed Ni with a small size effectively suppress the carbon formation. Additionly, we made our attempt to recovery of the template from the as-synthesized Ni-HMS by solvent extraction instead of burned off by calcination (Ni-HMS-Extracted), and use the collected template to prepare a fresh Ni-HMS (Ni-HMS-Reused). The excellence catalytic performance of the Ni-HMS-Extracted and Ni-HMS-Reused catalysts was also confirmed.The comparative studies also showed that coking is not the only reason that lead to deactivation. Although the activity of the catalysts was well maintained after long-term test, that the carbon nanotube was indeed formed, which was revealed by TEM photo and TG-DSC patterns. However, singtering of catalyst not only cause a sharp decrease of the active site, but also facilitated the carbon formation and growth.