有序介孔碳化硅包覆镍纳米粒子的组装及其催化性能

Coal to Synthetic Natural Gas (SNG) is currently being emphatically developed in China. The main barrier of this technology is the deactivation of conventional Ni-based methanation catalysts, which is caused by the sintering of Ni particles and carbon deposition. To overcome these technical barriers, in this research, we proposed a strategy for assembling ordered mesoporous silicon carbide encapsulated nickel nanoparticles (denoted as Ni@OM-SiC) for methanation. The confinement effect of the mesoporous channels could effectively prevent the migration and aggregation of Ni particles, suppress the coke deposition on the active nickel surface as well, and the high heat conductivity of SiC support are beneficial to decrease the generation of hot spots in the catalyst bed, which endowed the catalyst with prospective catalytic performance. The main components of this research proposal are as follows: The structural properties of the support involving the size, morphology, quantity and distribution of the nickel nanoparticles will be well controlled, the evolutions of the chemical composition, phase structure and texture properties at micro-scale will be explored to make the chemical mechanisms of directed assembly and synthesis clear; the mass transfer process and interaction for reactant molecules will be analyzed systematically, the qualitative relation in multi-scale between catalyst structure and catalytic performance will be established; the inherent characteristic of the catalytic active center will be clarified, while the reasonable reaction kinetic model is to be proposed to ascertain the catalytic mechanism; the sintering behaviour of the confined Ni particles will be understood; and the scientific evidence that the confinement environment provided by the mesoporous channel exerts a spatial restriction on metal particles, hampering their sintering as well as coke formation and finally promote the catalytic activity will be investigated in detail, the bases for controlling the effect of confinement and its role played in designing catalyst are going to be revealed, which will lay scientific foundation to prepare highly efficient catalysts for methanation.

煤制天然气是我国重点发展的现代煤化工技术，烧结和积碳是导致镍基甲烷化催化剂失活的根本原因。本项目组装合成有序介孔碳化硅包覆镍纳米粒子Ni@OM-SiC催化剂，利用介孔孔道的限域效应限制镍颗粒的迁移和聚并、抑制镍表面的积碳现象，借助SiC强导热性减少催化剂床层中热点的产生，进而获得理想的催化效果。主要内容包括：控制载体的结构性质及镍纳米粒子的尺寸、形貌、数量和分布，发现微观层次化学组成、晶相结构、织构特性的演变过程，阐明定向组装合成的化学机制；分析反应物分子在催化剂微观结构的传递过程、相互作用规律，建立多尺度范围内催化剂活性与结构的关系；明确催化活性中心的本征结构，探明催化作用机理，建立详细的反应动力学模型；认识受限体系中金属镍的烧结行为；发现纳米孔道限制金属烧结、改变催化活性、抑制积碳反应的科学证据，揭示“限域效应”的调控基础及其在催化剂设计中的作用，为制备高性能甲烷化催化剂奠定科学基础。

镍基催化剂在强放热的甲烷化反应中易发生烧结、积碳等现象而导致催化剂失活，极大限制了催化性能。本项目通过设计制备具有三维有序介孔结构的镍基甲烷化催化剂，通过控制载体形貌、添加助剂等手段调变催化性能，进而获得理想的催化效果。主要研究内容和结果如下：.（1）采用纳米浇铸法，以有序介孔二氧化硅（KIT-6）为硬模板剂合成了有序介孔SiC，通过浸渍法负载镍制得Ni/OM-SiC催化剂。高比表面积的OM-SiC有效提高了活性组分Ni的分散度，且其三维有序介孔结构显著增强了金属-载体间的相互作用力；此外，碳化硅的强导热性能够快速移出反应热，有效抑制了催化剂的烧结和积碳现象，提高催化剂的稳定性。.（2）探讨了助剂（Zr、Fe、Ce和Mg）的添加对催化剂性能的影响机制。Mg助剂的添加明显提高了WO3负载Ni催化剂在高温条件下的溢氢能力，提高了催化剂的活性；同时降低了Ni颗粒尺寸，提升Ni电子云密度，提高了CO解离能力，改善了CH4的选择性。此外，Zr、Fe和Ce助剂的添加均有利于Ni/Al2O3表面Ni的分散，提高催化剂吸附解离H2的能力，不同程度的改善了Ni/Al2O3催化剂的低温活性与选择性。.（3）将数据挖掘技术引入了镍基甲烷化催化剂的助剂筛选工作中，快速精确筛选出甲烷化催化剂的潜在活性助剂、抗烧结性能助剂和抗积碳性能助剂，且实验结果证实了预测结果的准确性。数据挖掘技术的引入，减少了试错实验的时间和经济成本，为新型高效催化剂的开发提供了有效方法。.（4）纳米浇铸法具有很好的普适性，可以制备出不同有序介孔结构材料，如三氧化钨WO3在该反应中也表现出优异活性。本方法为有序介孔材料负载镍催化剂的设计开辟了新的合成策略，可广泛应用于催化、电池等领域。