镍基催化剂的结构调控及其CH4-CO2重整反应的抗积碳机理

The catalytic carbon dioxide reforming of methane (CDR), which converts the two potent greenhouse gases (CO2 and CH4) into syngas, meets the principles of green chemistry and greenhouse gas reduction. However, the sintering of Ni and severe coke deposition are still the great challenge for the industrialization of CDR. Based on that the Ni particle sizes is the key factor for the coke deposition, herein, we proposed that using complex-impregnation method to adjust and control the interaction between Ni and support, and the influencing mechanism of the structure of complexing agents, the ratio of complexing agents to Ni and the atmosphere for calcination and reduction on the Ni-support interaction and Ni particle size will be determined. Consequently, the highly dispersed Ni-based catalysts with controllable Ni particle size and distribution will be realized. Moreover, based on the characteristic of structure-sensitive reaction for coke formation, and the different surface structures and distribution of active sites over two crystallographic phase Ni, namely, hexagonal close packed (hcp) phase and the face-centered cubic (fcc) phase, we proposed that using complex-impregnation method to adjust the Ni crystallographic structure, and overcome the problem of preparation of stable hcp Ni at high temperature. Consequently, using the CH4 decomposition and CO disproportionation as a probe reaction, the types and reaction performance of coke deposition will be studied for Ni-based catalysts with different Ni particle size and crystallographic structures. And these results will be quantitatively correlated with the CDR results and the particle size, distribution and crystallographic structures of Ni over different catalysts. The influencing mechanism of particle size, distribution and crystallographic structures of Ni on the resistance to the sintering of Ni and coke deposition will be determined, which will provide the theoretical direction for development of a high-performance CDR catalyst with high activity and stability.

甲烷-二氧化碳重整（CDR）同时将CO2和CH4两大温室气体转化成合成气，对温室气体减排具有重大意义。针对CDR反应中Ni基催化剂易烧结和积碳的问题，基于Ni颗粒尺寸是影响积碳的关键因素，本项目提出利用配位-浸渍技术来调控Ni与载体间相互作用，阐明配位剂结构和制备参数等因素对Ni与载体间相互作用及Ni颗粒尺寸的影响机制，实现高分散Ni催化剂颗粒尺寸和分布的可控制备；同时，基于积碳反应结构敏感性的特点及不同晶相结构Ni（fcc和hcp相）表面结构和活性位分布的差异，拟采用配位-浸渍技术来调控Ni的晶相结构，解决高温条件下稳定hcp相Ni的制备难题。以甲烷分解和CO歧化为模型反应，研究不同尺寸和晶相结构Ni表面积碳类型及反应性能，并与CDR反应结果及催化剂结构进行关联分析，揭示Ni颗粒尺寸、分布及晶相结构等因素影响其抗烧结和抗积碳性能的作用机制，为进一步优化设计高效CDR催化剂提供理论指导。

实现Ni基催化剂的Ni颗粒尺寸的高分散是调高CDR反应活性，尤其是稳定性的有效策略。但由于传统浸渍法制备的Ni基催化剂的Ni颗粒相对较大，且分布不均匀，导致Ni基催化剂在CDR反应中极易因积碳和高温烧结而失活。同时，基于CDR积碳反应结构敏感性的特点及不同晶相结构Ni（fcc和hcp相）表面结构和活性位分布的差异，以及高温hcp相Ni高温条件难于稳定存在等问题。本项目利用配位-浸渍技术来调控Ni基催化剂的结构，以具有规整结构的SiO2为载体，通过改变配位剂种类、配位剂与金属Ni比值等条件来调控Ni颗粒尺寸大小、分布以及与载体间相互作用；通过调变配位剂的分子结构、碳链结构及含碳量来调控Ni表面的碳的类型及与Ni的相互作用，同时通过改变催化剂的焙烧条件，如采用惰性气体、CO或H2、以及不同比例的CO和H2混合气作为焙烧气氛来调变Ni表面碳的类型和相互作用，制备一系列的Ni基催化剂。结合表征结果，揭示配位剂结构和制备参数对Ni与载体间相互作用及Ni颗粒尺寸和分布的影响机制，并明确配位剂结构以及焙烧条件下hcp相Ni的可控制备及形成机理。在CO2/CH4 = 1.0、GHSV = 60000 mL·g-1·h -1和T = 750 ℃条件下，对所制备的Ni基催化剂进行了CDR反应性能评价，获得了具有高活性和高稳定性的CDR Ni基催化剂。结合不同催化剂的XRD、物理/化学吸附、显微分析等表征结果，从微观水平上对Ni晶相结构、颗粒尺寸、分布以及与载体相互作用与CDR反应性能之间的关系进行了合理的关联分析，特别是明确了这些因素在影响催化剂活性及稳定性的作用机制。