关键词: CO₂ dry reforming of methane, Low-temperature, Ni-based catalysts, Chemical speciations, Reforming reaction mechanisms

Abstract: The cognition of active sites in the Ni-based catalysts plays a vital role and remains a huge challenge in improving catalytic performance of low temperature CO₂ dry reforming of methane (LTDRM). In this work, typical catalysts of SiO₂ and γ-Al₂O₃ supported Ni and Ni-Ce were designed and prepared. Importantly, the difference in the chemical speciations of active sites on the Ni-based catalysts is revealed by advanced characterizations and further estimates respective catalytic performance for LTDRM. Results show that larger[Ni_n⁰] particles mixed with [Ni-O-Si_n]) species on the Ni/SiO₂(R) make CH₄ excessive decomposition, leading to poor activity and stability. Once the Ce species is doped, however, superior activity (59.0% CH₄ and 59.8% CO₂ conversions), stability and high H₂/CO ratio (0.96) at 600?℃ can be achieved on the Ni-Ce/SiO₂(R), in comparison with other catalysts and even reported studies. The improved performance can be ascribed to the formation of integral ([Ni_n⁰]-[Ce^III-□-Ce^III]) species on the Ni-Ce/SiO₂(R) catalyst, containing highly dispersed [Ni_n⁰] particles and rich oxygen vacancies, which can synergistically establish a new stable balance between gasification of carbon species and CO₂ dissociation. With respect to Ni-Ce/γ-Al₂O₃(R), the Ni and Ce precursors are easily captured by extra-framework Aln-OH groups and further form stable isolated ([Ni_n⁰]-[Ni-O-Al_n]) and [Ce^III-O-Al_n] species. In such a case, both of them preferentially accelerate CO₂ adsorption and dissociation, causing more carbon deposition due to the disproportionation of superfluous CO product. This deep distinguishment of chemical speciations of active sites can guide us to further develop new efficient Ni-based catalysts for LTDRM in the future.

Key words: CO₂ dry reforming of methane, Low-temperature, Ni-based catalysts, Chemical speciations, Reforming reaction mechanisms