甲烷与二氧化碳加压重整制合成气反应机理及高性能镍基催化剂研究

The catalytic carbon dioxide reforming of methane (CDR) is a promising process for converting the two potent greenhouse gases of CO2 and CH4 into the valuable syngas, which can be a hydrogen source or a feedstock for synthesizing chemicals and fuels. Moreover, the direct utilization of the natural gas with high CO2 levels avoids the necessity of the costly and complex gas-separation processes, and CDR under pressurized conditions is industrially more desirable in terms of the higher process efficiency. However, CDR is still a challenge topic due to the quick deactivation of catalysts as a result of the severe coke deposition even under mild reaction conditions, i.e., the atmospheric pressure, higher CO2/CH4 molar ratios than the stoichiometric value, and a lower space velocity. Thus, the lacking of a stable catalyst is the bottleneck for the commercialization of the CDR process. .Based on our previously promising work, this project aims at revealing the catalytic mechanism and designing a highly active and stable Ni-based catalyst for the pressurized CDR. Thus, the study will focus on (1) the adsorption, activation, and surface reaction of methane and/or carbon dioxide over the Ce-ZrO2 solid solution promoted Ni-SiO2 catalyst; (2) the kinetics behavior of the coking and the removing of the deposited coke over the catalyst; (3) the mechanistic understanding on the formation and the transformation of active sites; (4) the effect of the coking on the development of the active site; (5) the catalytically promotional effect and mechanism of the Ce-ZrO2 solid solution as a promoter on Ni-SiO2; and (6) the impact of the interfaces between Ni and the Ce-ZrO2 solid solution on the coking and the removing of the coke over the catalyst. As a result, the intrinsic kinetics equation including the parameters will be obtained. Together with the characterization results of the fresh and used catalysts including the in-situ FT-IR and Raman results, the detailed CDR mechanism and the coking deactivation kinetics of the Ni-based catalyst will be revealed. With these theoretic understandings, a highly active and stable Ni-CeZrO2-SiO2 catalyst for the pressurized CDR is reasonably expected. The novelty of this proposal lies in (1) the reversibly high oxygen-storage capacity of the Ce-ZrO2 solid solution is applied to enhance the removing of the deposited coke over the catalyst, leading to a fast kinetic balance between the coking and the coke removing; and (2) the interaction between Ni and the support is easily regulated in a wide range by simply changing the complex used during the synthesis of the catalyst. The achievements of the proposal will lay a solid foundation for the industrialization of the pressurized CDR.

从储运或下游利用角度，将CH4和CO2两大温室气体加压重整制合成气，更具理论研究意义和应用价值，但现有催化剂在加压条件下失活更快，是其工业化的瓶颈。基于前期创新性结果，本项目主要研究CH4和CO2在镍基催化剂表面的吸附、活化和转化机制及催化剂的积炭和消炭动力学行为、催化剂活性中心和表面积炭物种的形成及其演化规律、Ce-ZrO2固溶体助剂与金属Ni界面性质对积炭和消炭的调控作用，以期建立本征动力学方程，阐明反应机理，揭示催化剂积炭失活机制，提供优化设计催化剂的理论依据，制备出CH4与CO2加压重整的高活性和高稳定性镍基催化剂。其中，提出利用Ce-ZrO2固溶体的氧化还原特性和储氧性能调控催化剂表面的积炭和消炭速率以形成快速动态平衡，并优化Ni与Ce-ZrO2-SiO2载体之间的相互作用，进而构建高性能催化剂模型是本项目的主要特色。本项目的完成将为CH4与CO2加压重整反应的工业化奠定基础。

甲烷和二氧化碳经干重整制合成气（CDR），将两大温室气体高效转化为高附加值的合成气，具有重要的理论研究和应用价值。但现有催化剂普遍快速失活，是其工业化应用的瓶颈。同时，从储运或下游利用的角度看，加压CDR更具优势，但加压条件下的催化剂更易失活，相关催化剂的研发极具挑战。本项目首先分析了加压CDR的热力学特点，特别是压力对积炭温度区域的影响规律。在优化配位剂种类和制备参数的基础上，采用配位-分解法制备了不同Ni含量、稀土氧化物种类及含量的Ni-稀土氧化物-SiO2催化剂。根据稳态CDR反应结果，结合催化剂表征结果，获得了Ni-Ce-ZrO2-SiO2催化剂。采用程序升温表面反应、甲烷（二氧化碳）脉冲、原位漫反射红外、原位透射电镜等手段，获得了二氧化碳/甲烷分子在Ni-Ce-ZrO2-SiO2催化剂表面的吸附、活化、积炭-消炭等规律，结合稳态动力学结果，提出了CDR的动态积炭-消炭反应机理，构建了相应的Ni基催化剂结构模型。基于上述理论认识，进一步优化了Ni、Ce-ZrO2和SiO2的含量及Ce/Zr摩尔比等参数。长周期反应评价结果表明，优化催化剂不仅具有高活性（接近热力学平衡转化率），而且在1.0 MPa时稳定运转大于500小时（0.1 MPa时大于2200小时），表现出很好的放大研究价值和工业应用前景。