碳包钴-碳化钴纳米复合材料可控制备及其催化硼氢化物水解产氢

A highly active and stable catalyst is the key to the efficient hydrolytic dehydrogenation of borohydride. Decreasing of particles size, combining of Co and Co composites, increasing the electron density of Co in the Co composites and coating carbon are expected to achieve the excellent catalytic performances of Co-based catalysts. In this proposal, cobalt complexes with a ligand of Schiff base are used as the precursor due to the regulable structure, the poor thermal stability and the weak interaction among the metal center. Co-CoxC@C (x = 2 and 3) catalysts will be prepared by pyrolyzing and subsequent-treating. The composition, structure and size of Co-CoxC core, and structure, thickness and doping of carbon shell will be regulated and controlled by optimizing the molecular structure and element compositions of Co complexes, and the technological parameters during the preparation process. Then, the intrinsic mechanism of the effect of Co complexes and the preparation technology on the composition and microstructures of Co-CoxC@C will be elucidated by analyzing the evolution behavior of the chemical environment and the state of Co, C, N and other elements during the preparation process. Thereafter, the catalytic properties of Co-CoxC@C for hydrolytic dehydrogenation of borohydride will be tested. The adsorption sites, activation behavior and active intermediates will be studied by both in-situ spectrum and theoretical calculations, thereby confirming the active centers and the influence of electronic effect between Co and CoxC on the activity of the active centers. The structure-activity relationship at the molecular level will be clarified. Finally, the basic theory and the effective way to enhance the activity of the active centers will be proposed. The achievement of this proposal will not only provide the idea and implications for the reasonable design of the superior Co-based catalysts.

高活性、高稳定性催化剂是硼氢化物高效水解产氢的关键，减小颗粒尺寸、钴与钴化合物复合、提高化合物中钴电子密度和碳包覆有望实现钴基材料的高催化性能。本项目拟以结构可控、易热解且金属中心相互作用弱的席夫碱钴配合物为前驱体，热解及后处理制备Co-CoxC@C（x=2和3）催化剂；优化前驱体结构、组成和制备工艺参数，调控Co-CoxC组成、结构、尺寸和C层结构、厚度、杂原子，研究制备过程中Co、C和N等元素化学环境和存在状态的演化行为，阐明前驱体和制备工艺影响催化剂组成和微观结构的内在机制；测试Co-CoxC@C催化硼氢化物水解产氢性能，通过原位光谱分析和理论计算研究硼氢化物和水在催化剂表面的吸附位点、活化方式和活性中间体，明确活性中心和Co与CoxC间电子效应对其活性的影响，澄清分子水平上的构效关系，提出增强活性中心活性的基础理论和有效方法。项目的完成为高性能钴基催化剂理性设计提供思路和理论指导。

金属配合物、金属配位聚合物和金属有机框架等作为前驱体进行热解是构建碳包纳米颗粒的有效策略。碳包纳米颗粒或者负载型碳包纳米颗粒有望高效催化NH3BH3水解产氢。本项目以金属有机配位化合物、酚醛树脂等为前驱体，通过调整配合物分子结构、元素组成、热解和后处理工艺参数等，实现Co基纳米复合催化剂微观结构的有效调控。通过调节金属含量、引入不同金属元素、非金属元素、不同载体等来调节制备催化剂的物质组成，进而获得高活性和高稳定的Co-Co2C@C、Co-CoOx@C、CoCu-O@C、CoOxP@SiO2@CS、O-(CoP/Co2P)@SC等催化剂。另外以Al2O3、rGO和g-C3N4为载体，制备了Ni-Mo2C/Al2O3、富含缺陷的Co-CoOx/rGO和富含氧缺陷的Co3O4/g-C3N4催化剂。通过调节碳前驱体的引入含量以及比例、前驱体的热解温度和时间、合成物质的后处理相关参数等来控制碳层厚度以及碳层组成。优化了热解温度和时间、后处理时间、载体和负载工艺等参数，澄清了工艺参数对催化剂微纳结构的影响规律。分析了碳化温度、碳化时间等工艺参数对碳包纳米颗粒或者负载型碳包纳米颗粒催化剂的物相组成、碳层结构和颗粒尺度等微纳结构的影响规律；探究了金属种类、非金属种类、合金组成、颗粒尺寸和形貌等因素对催化产氢性能的影响规律，获得了催化NH3BH3制氢的高效催化剂；另外探讨了不同的载体对于催化性能的影响，阐明了金属-载体相互作用在催化反应中的重要作用；考察了碳包纳米颗粒或者负载型碳包纳米颗粒催化NH3BH3水解产氢性能，其中碳的存在阻止了纳米颗粒的聚集和团聚，增强了催化剂的催化活性和稳定性。理论计算研究表明，通过热解前驱体所设计的含有双活性位点的碳包纳米颗粒或者负载型碳包纳米颗粒催化剂，促进了NH3BH3和H2O分子的吸附、活化和解离过程，降低了NH3BH3和H2O分子的反应活化能垒，促进H自由基的生成，促进了催化反应的高效进行。基于以上工作，团队发表了标注基金资助的期刊论文9篇，其中SCI收录论文9篇，申请发明专利2项，参加国内外学术会议12人次。项目执行期间培养博士研究生1名，硕士研究生5名。