有序介孔限域镍基高效甲烷化催化剂的构建及催化性能研究

Ni/Al2O3 catalysts prepared by the traditional methods such as impregnation or precipitation method have been widely used for CO/CO2 methanation reaction. However, there are still some critical issues to be addressed, such as poor activity at low temperature, easily sintering, coking, and deactivating of the catalysts at high temperature. Based on the excellent properties of the ordered mesoporous alumina (OMA), such as the superior confinement effect, adjustable regular mesoporous channels and feasible doping of heteroatom, a series of multivariate NiM1-M2O-Al2O3 metal oxide composites with ordered mesoporous structure and various Ni, M1 and M2O contents were rationally designed and facilely synthesized via a one-pot evaporation-induced self-assembly strategy for methanation reaction. On the basis of the controllable synthesis of the ordered mesoporous catalysts, this project will focus on the systematic investigation of the distribution of each component during the calcination and reduction processes, in which, how NiO, M1O and M2O nanoparticles distribute in the OMA frameworks and how Ni, M1 nanoparticles emerge from the OMA frameworks, as well as their individual characteristics and general rules, and the synergistic effects of multiple metal species. Furthermore, the interaction of active metal-promoter-support and the catalytic performances for CO/CO2 methanation, such as low-temperature activity, anti-coking and anti-sintering properties will be studied to understand the structure-composition-performance relationship of the catalysts, which will be helpful for developing new catalysts with both good low-temperature activity and high-temperature stability. The successful implementation of this project will be significant not only in developing the catalytic theories of multivariate ordered mesoporous catalysts but also in addressing some key issues occurred in traditional Ni/Al2O3 catalysts.

传统方法制备的Ni/Al2O3甲烷化催化剂存在低温活性差、高温易烧结、易积碳等问题。本项目基于有序介孔氧化铝材料卓越的限域效应、孔道规整可调以及可掺杂杂原子等优良特性，采用“一锅”溶剂蒸发诱导自组装法，通过掺杂金属（Ni和M1）以及助剂（M2O）等物种，制备NiM1-M2O-Al2O3多元复合有序介孔甲烷化催化剂。在实现催化剂可控合成的基础上，系统研究介孔氧化铝骨架上NiO、M1O、M2O纳米颗粒的分布和Ni、M1纳米颗粒的还原溢出分散机制以及不同金属组分还原过程的个性特征、共性规律及协同效应，探讨催化剂中金属-助剂-载体的相互作用机制以及对低温活性、抗烧结、抗积碳等性能的影响，明晰催化剂结构-组成-催化性能的构效关系，开发同时具有好的低温活性和高温稳定性的新型甲烷化催化剂。本项目的实施对于丰富多元复合型有序介孔材料的催化理论和解决传统Ni/Al2O3催化剂存在的问题具有重要意义。

针对浸渍法、沉淀法等传统方法制备的Ni/Al2O3甲烷化催化剂存在低温活性差、高温易烧结、易积碳等问题。本项目基于有序介孔氧化铝材料良好的限域效应、孔道规整可调以及可掺杂杂原子等优良特性，采用溶剂蒸发诱导自组装法（EISA），通过掺杂金属Ni和第二金属M1（M1 = Ru, Fe, Co）以及助剂M2O（M2O = CaO, La2O3, WO3, Sm2O3, MoOx等）物种，考察了物料配比、焙烧/还原温度和时间的影响，成功实现了高度长程有序NiM1-M2O-Al2O3催化剂的可控合成。通过系列表征系统研究了介孔氧化铝骨架上NiO、M1O、M2O纳米颗粒的分布和Ni、M1纳米颗粒的还原溢出分散机制以及不同金属组分还原过程的个性特征、共性规律及协同效应，探讨了催化剂中金属-助剂-载体的相互作用机制以及对低温活性、抗烧结、抗积碳等性能的影响。研究发现在有序介孔Ni-Fe/Al2O3催化剂中，NiO和FeOx物种均匀分散在Al2O3骨架中，形成固溶体形态。还原后Ni颗粒溢出，并锚定在氧化铝介孔孔道中，但是由于铁物种与载体具有强相互作用，很难被还原到金属态，而是以FeOx存在于到催化剂Al2O3骨架中。在有序介孔Ni-Co/Al2O3催化剂中，还原后金属以NiCo合金的形式存在；与此相反，在有序介孔NiRu-CaO/Al2O3催化剂中，还原后金属Ni和金属Ru单独存在而非形成合金。同时，CaO、Ni和Ru的加入并未影响催化剂的有序性，但显著提升了催化剂的催化活性。另外，La2O3, WO3和Sm2O3等物种的加入，也可以形成高度长程有序的介孔结构，还原后助剂以La2Ox, WOx和Sm2Ox (x<3)的形式存在，并显示出良好的催化性能。本项目的实施明晰了催化剂结构-组成-催化性能的构效关系，开发出同时具有好的低温活性和高温稳定性的新型甲烷化催化剂，对于解决传统Ni/Al2O3催化剂存在的低温活性差和高温稳定性低的问题起到了显著地提升效果。