Ni/半焦催化剂的构筑及其催化生物质气化焦油水蒸气重整反应机理

Tar has long been impeding the development and application of biomass gasification technologies severely. Steam reforming, as one of the prevalent technologies for tackling the tar problem, can convert tar into clean syngas for various types of downstream utilization. Biochar can be in-situ prepared with low cost, nevertheless, it consumes extremely fast under high temperatures but displays low catalytic activities under low temperatures. Therefore, in this project, external Ni nanoparticles will be introduced onto biochar via carbothermal reduction to fully utilize the synergistic effects between Ni and the inner alkali and alkaline earth metals. In that way, tar can be efficiently transformed under relatively low temperatures, and the consumption issue of biochar can be solved simultaneously. Experimental research work together with operando characterization techniques will be carried out to reveal the interactions and function matching among Ni nanoparticles, alkali and alkaline earth metals, surface oxygen-containing functional groups and lattice defects. Furthermore, the relationship between the amount, the chemical forms of alkali and alkaline earth metals and the water adsorption capability of catalysts will be illuminated as well. Combined with DFT calculations, the steam reforming characteristic of tar will be studied under different reaction environments. The reaction pathways will be obtained, based on which, the intrinsic reaction kinetics model will be established. Finally, the structure-property relationships between the composition and the structure of Ni/char catalysts and their catalytic efficacy will be clarified. This proposed project is expected to not only enrich the catalysis theories for metal loaded char catalysts, but also provide the theoretical basis for developing char-based tar reforming technologies and catalyst preparation methods.

焦油问题严重制约了生物质气化技术的推广应用，通过水蒸气重整将焦油转化为洁净燃气/原料气，是解决该瓶颈问题的重要技术之一。普通生物质半焦作为重整催化剂具有价格低廉、可原位制备的优点，但也存在高温迅速消耗而低温活性不足的矛盾。本项目通过碳热还原在半焦上引入外源活性Ni纳米颗粒，利用其与半焦中碱/碱土金属间协同作用，在较低温度下实现焦油高效转化的同时解决半焦自身消耗问题。通过实验研究结合原位动态测试表征，揭示Ni/半焦催化剂中Ni颗粒、碱/碱土金属、半焦表面含氧官能团与缺陷位间交互作用和功能匹配规律，阐明碱/碱土金属含量、形态与催化剂对水吸附能力间关联机制。结合理论计算，研究焦油在不同体系下重整反应特性，获取焦油重整转化路径，建立机理型本征动力学模型，揭示催化剂组成、结构要素与其催化性能间构效关系。研究将丰富金属负载型半焦催化理论，为开发基于半焦催化的焦油重整工艺和催化剂制备方法提供理论依据。

焦油问题严重制约了生物质气化技术的推广应用，通过水蒸气重整将焦油转化为洁净燃气/原料气，是解决该瓶颈问题的重要技术之一。普通生物质半焦作为重整催化剂具有价格低廉、可原位制备的优点，但也存在高温迅速消耗而低温活性不足的矛盾。本项目分别制备了Ni/半焦和Ni/有序介孔氧化铝（Ni/OMA）两类型催化剂用于生物质焦油水蒸汽重整反应，结合理论计算，建立了催化剂组成、结构要素与其催化焦油重整反应性能间构效关系。主要发现包括：（1）降低热解制备温度和Ni负载量，有利于制备具有高分散Ni纳米颗粒的Ni/半焦催化剂，提高了Ni/半焦催化剂的催化活性。生物质焦油模型化合物甲苯的水蒸汽重整反应是结构敏感型反应，在具有较多边和角位点的小颗粒Ni上更容易进行。将Ni/半焦催化剂用于真实焦油重整，降低焦油总量的同时，也促进了焦油裂解为更小的分子。（2）Ni/半焦催化剂上半焦载体中固有K增强了催化剂对水的吸附。在较低温度下，由于Ni颗粒周围水浓度的增加，甲苯转化率随着K含量的增加而显著增加。但在较高温度下，对水的强吸附导致半焦载体被迅速气化消耗。构建了掺杂B的Ni/半焦催化剂，B的掺杂有效猝灭了半焦中的固有K，降低了半焦的气化反应性，提高了Ni/半焦催化剂在甲苯水蒸气重整反应中的稳定性。（3）通过制备OMA负载Ni催化剂，有效抑制了Ni颗粒烧结。构筑了双金属Ni-Fe/OMA催化剂，通过原位漫反射红外表征手段结合DFT理论计算结果获得了甲苯重整反应机理，主要为甲苯裂解反应和水煤气变换反应组成的连串反应，甲苯裂解反应产生的碳基碎片与解离活化后的水反应生成COOH，COOH继续反应生成CO、H2等产气。（4）基于半焦中K可以促进水的吸附活化的发现，构筑了K掺杂Ni/OMA催化剂，降低了催化剂表面的总酸量，减少了积碳的形成，并使积碳主要以无定形形式存在。研究结果丰富了金属负载型半焦催化理论，为开发高效的生物质焦油催化重整工艺和催化剂制备方法提供了重要理论依据。