碳酸酐酶/介孔MOFs催化胺吸收CO2的构效关系及反应机制

Dosage of carbonic anhydrase (CA) into the tertiary amine solution can not only enhance CO2 absorption rate but also keep its superior thermodynamics, resulting in a significant decrease in energy penalty of CO2 capture. The main issue related to the application of CA enzyme for the practical application is its stability at the typical flue gas conditions. Enzyme immobilization is regarded as a promising method to address this issue. With the traditional carbon-based materials as carriers, the immobilized CA enzyme featured moderate stability, low enzyme loading, and activity retention, resulting in a high operation cost of CO2 capture. This proposal aims to develop a novel CA-mesoporous MOFs composite biocatalyst with high enzyme loading, activity, and stability to enhance the CO2 absorption into tertiary amine solution. The structure, pore distribution, and surface functional group of the MOFs will be tuned for the biocatalyst preparation via molecular design and assembling. The relationship between the spatial conformation of CA enzyme and structure of mesoporous MOFs will be investigated to interpret the structure-activity relationship of the biocatalyst. Furthermore, the transfer of CO2 in the gas, liquid, solid phases and their interfaces will be investigated to explore the synergistic enhancement mechanism of CO2 absorption by the mesoporous MOFs and CA enzyme. Moreover, the law of the mass transfer with reaction in the heterogeneous catalytic system will be clarified. This proposal will provide significant insight into the development of the novel biocatalyst with high activity and stability, and green technology of CO2 capture in the future.

向三级胺中添加碳酸酐酶（CA）可强化吸收CO2，且能发挥其热力学优势，因而能大幅降低CO2捕集能耗。如何确保CA酶的高稳定性是实现该过程的关键，其中酶固定化是提升稳定性的重要途径。然而，以常规载体（如活性炭等）制备的固定化酶，其稳定性欠佳、载酶量小且活性较低，难以满足工业应用需求。本项目拟研制载酶量大、高效、稳定的CA/介孔MOFs复合生物催化剂，用于强化三级胺吸收CO2的反应过程。通过对介孔MOFs的分子设计、组装及表面改性，调控其孔结构及物化特性；考察MOFs孔结构及物化特性对酶分子空间构象的影响，揭示催化剂微观结构与催化活性及稳定性的构效关系；基于CO2在气、液、固三相迁移转化过程的研究，探明介孔MOFs与酶协同强化CO2吸收的反应机理；探索该非均相催化体系的相间传质与相内反应的内在关联，阐明CO2的传质-反应规律。研究结果可为开发高效、稳定的生物催化剂及绿色CO2捕集技术提供参考。

向吸收剂中添加碳酸酐酶（CA）可强化吸收CO2，且能发挥其热力学优势，因而能大幅降低CO2捕集能耗。如何确保CA酶的高稳定性是实现该过程的关键，其中酶固定化是提升稳定性的重要途径。然而，以常规载体（如活性炭等）制备的固定化酶，其稳定性欠佳、载酶量小且活性较低，难以满足工业应用需求。本项目通过研究以化学组分相同但物理结构特性不同的硅基介孔分子筛为载体制备得到固定化CA酶，当载体孔径若大于CA酶尺寸则其主要分布在载体孔道内，而孔径若小于CA酶尺寸则主要分布在载体界面，探明了硅基介孔分子筛的理化性质与酶负载量及其催化性能与稳定性的内在构效关系，证实了CO2在载体孔道的内扩散效应是吸收过程的限速步骤。通过比较不同类型介孔ZIFs材料固定CA酶的催化性能，揭示了载体的亲/疏水性及官能团类别对CA酶稳定性和催化活性的影响机制，证实了载体的疏水性是影响CA酶活性的主要原因之一，明晰了载体醛基上的醛氧原子与CA酶活性中心亲水区的苏氨酸（Thr 198）侧链的交互作用，以及载体的有机配体中苯环与CA活性中心的组氨酸（His 93）形成π-π相互作用，均会导致酶的二级分子构象改变，进而降低酶活性。开发了一种低能垒、高催化性能的CA/ZIF-L复合生物催化剂，通过SEM、CLSM、XRD等表征手段，证明了CA酶包裹在ZIF-L骨架结构内并主要分布在颗粒内表面，探明了CA酶与沸石咪唑酯骨架材料（ZIF-L）协同强化吸收CO2的作用机制，证实了ZIF-L的界面吸附作用可提高CO2迁移至催化中心的传质速率，强化了CO2从液相到固相的传质过程。相比游离酶，该复合生物催化剂的吸收速率提升了50%。