氧空位增强的钙基CO2吸附剂及机理研究

Carbon capture/storage (CCS) is of great significance to constraining the problems of greenhouse effect, climate warming, environmental pollution and energy crisis. CaO-based sorbents have been identified as the most suitable candidates for large-scale CO2 capture at high temperatures in terms of high CO2 adsorption capacity, low material cost, fast CO2 carbonation/decarbonation kinetics and reversible carbonation/calcination process However, the major challenge for the CaO-based sorbents is the fast decay of CO2 capture performance with the number of cycles. Incorporation of refractory metals is regarded as a simple and effective method to improve the stability of calcium-based sorbents, which has been attracting increasing attention. Nevertheless, there are still some prolems, such as lack of deep analysis on the mechanism of adsorption, the design limitation of adsorbents and further improvement of the sorption capacity and stability. In this project, in order to introduce the high temperature resistant support and enhance the diffusion of CO2 and mobility of O2-, a series of CaO-based sorbents doped by inert materials (Zr-Ce, Ce-Mn, and Zr-Mn) are synthesized by a simple and facile method. The effect of microstructure, condition of desorption, oxygen vacancy and doping metal ions into the crystal lattice on the CO2 adsorption is discussed. The mechanisms of the promotion of the oxygen vacancy formation because of synergistic interaction between inert materials are investigated. The kinetics of CO2 adsorption is estimated by a double exponential method, revealing the relationship between rate-determining step (diffusion of CO2 and surface reaction) and the performance of CO2 adsorption. The influence of doping metal ions into calcium-based sorbent on the electron transfer in the process of CO2 adsorption is revealed.

有效捕集CO2对于缓解亟待解决的温室效应、气候变暖、环境污染和能源危机问题具有重大意义。掺杂改性钙基吸附剂作为一种简单易行、改善循环过程中易烧结问题效果显著的方法，得到广泛关注，但存在对掺杂促进CO2吸附的机理仍然缺乏深刻的认识、吸附剂的设计仅仅局限在改变材料的微观结构、吸附性能有待进一步提高等问题。 本课题从引入耐高温支撑骨架和氧空位、促进CO2的扩散和O2-的迁移同时出发，对钙基CO2吸附剂进行（Zr-Ce）、（Ce-Mn）和（Zr-Mn）复合掺杂改性，制备得到吸附容量高、稳定性强的吸附剂。通过实验和密度泛函理论（DFT）计算，探究微观结构、解吸条件和氧空位对CO2吸附性能的影响；剖释掺杂离子介入CaO晶格对CaO和CO2之间作用力的影响；阐明惰性组分之间协同作用对促进氧空位的生成机理；剖析反应控制和扩散控制与CO2吸附性能之间的耦合作用机制；揭示掺杂对CO2吸附过程中电子转移的影响。

有效捕集CO2对于缓解亟待解决的温室效应、气候变暖、环境污染和能源危机问题具有重大意义。掺杂改性钙基吸附剂作为一种简单易行、改善循环过程中易烧结问题效果显著的方法，得到广泛关注，但存在对掺杂促进CO2吸附的机理仍然缺乏深刻的认识、吸附剂的设计仅仅局限在改变微观结构、吸附性能有待进一步提高等问题。本课题从引入耐高温支撑骨架和氧空位、促进CO2的扩散和O2-的迁移同时出发，探究氧空位增强钙基吸附剂CO2捕集性能的作用机制以及掺杂离子介入CaO晶格对吸附性能的影响。基于变价金属氧化物之间协同更容易引入或促进氧空位的产生，进而提高CaO的CO2捕集性能，通过将变价双金属氧化物复合掺杂，制备得到（Fe-Mn）、（Fe-Ce）、（Mn-Cu）、（Fe-Cu）、（Ce-Cu）等复合掺杂的氧空位增强钙基吸附剂。结果表明复合掺杂（Fe-Mn）的吸附剂具有良好的循环稳定性，20个循环后CO2吸附性能和转化率分别保持在0.61 g-CO2/g-吸附剂和95%。性能的提高一方面归因于Fe2O3和Ca2MnO4颗粒的均匀分布阻止CaO微晶的生长和团聚；另一方面疏松多孔的、具有薄片结构和较大孔径的（Fe-Mn）复合掺杂吸附剂有利于CO2的扩散，并防止其烧结。同时，相邻Fe和Mn金属离子之间发生电子转移，促进氧空位的产生，有效提高钙基吸附剂的CO2亲和力。（Fe-Mn）复合掺杂样品在第20个循环中化学反应控制和扩散控制阶段速率常数均远大于纯CaO，Fe与Mn协同作用显著降低吸附反应的活化能。此外，采用溶胶凝胶法制备Mg离子掺杂介入CaO晶格的钙基吸附剂，剖析离子掺杂介入晶格对表面氧供电子能力及CO2吸附的作用机制。结果表明介入CaO晶格的Mg离子越多，CaO晶粒越小，且Ca-O-Mg物种的形成促进吸附过程中电子的转移和氧空位的生成。采用密度泛函理论计算发现Mg离子介入CaO晶格使得CaO中的O和CO2中C之间的作用力增强，提出掺杂离子介入晶格促进CO2吸附活化过程中电荷转移的机制。以上研究为钙基吸附剂的设计与开发提供新的思路与理论支撑。