高负载单原子催化剂的设计及其低温水煤气变换反应行为研究

Supported noble metal catalysts have attracted widespread attention in low-temperature water gas shift, which is an important step in the production of clean hydrogen industrially. The single atoms were the maximum of dispersion for the noble metals; however, the actual loadings were usually low, only a few tenths of a percentage point of the total weight. To prepare the single atom catalysts with high loading is an effective way to enhance the activity of low-temperature water gas shift reaction. In this application, we are planned to synthesize Pt, Pd, Ir-based single atom catalysts with loading higher than 1 wt% based on the coordination between hydroxyl, alkali metal promoter and the noble metal atoms. The dispersion and stability mechanism will be disclosed by the aberration-corrected scanning transmission electron microscopy, in-situ X ray absorption characterizations and so on. Then the model of single atom catalysts with high activity and stability for water gas shift at temperatures <200 oC will be constructed. By a series of in-situ infrared, Raman, pulse calorimetry, micro-kinetic methods and so on, we will study the adsorption and reaction behaviors of water gas shift reaction over these high-loading single atom catalysts, then explore the mechanism of this reaction. The aim of this application is to open a new avenue for developing water gas shift catalysts with high low-temperature activity and stability.

低温水煤气变换是工业生产洁净氢气的重要环节，负载型贵金属催化剂因其独特的优越性能受到广泛关注。单原子为贵金属分散的极限，然而现有催化剂单原子质量含量偏低，设计制备高负载单原子催化剂是提高低温水煤气变换活性的有效途径。本申请拟采用表面羟基、碱金属助剂与贵金属进行配位的方法获得高负载量（>1 wt%）的Pt、Pd、Ir等单原子催化剂。借助球差校正扫描透射电镜、原位X射线吸收光谱等手段研究单原子分散与稳定机制，并构建低温（<200 oC）高活性及高稳定性的单原子催化剂模型。在此基础上，结合原位红外、拉曼、脉冲量热及微观动力学等方法研究水煤气变换过程中反应物的吸附与反应行为，阐明高负载单原子催化剂上水煤气变换反应机理，探索单原子催化的本质。本项目申请将为开发低温高活性、高稳定性的水煤气变换催化剂提供一条新途径。

低温水煤气变换是工业生产洁净氢气的重要环节，负载型贵金属催化剂因其高活性与稳定性引起了人们的关注。本项目制备出适用于水煤气变换的原子Ir、Pt、Pd、Rh等单原子催化剂。进而提高单原子的负载量，并详细研究单原子与纳米分散对反应机制的影响。主要研究内容、代表性成果和科学意义如下：.（1）高效FeOx、TiO2分散Rh催化剂研究。研究可还原载体与金属物种间的相互作用，成功制备出高载量的亚纳米尺寸分散Rh催化剂，并发现该催化剂在低温CO消除如CO氧化、CO选择氧化中表现出优异的催化活性和稳定性，为高负载单原子催化剂的制备提供指导。代表性结果发表于Angew. Chem. Int. Ed. 2016, 55, 2820-2824；Appl. Catal. B 2016, 184, 299-308。.（2）较高载量、高选择性单原子催化剂的研制。采用沉积沉淀并借助HCl/H2O2溶液洗涤方法制备出TiO2负载较高载量单原子Rh催化剂，不仅可以实现较高的CO转化率，而且有效避免了甲烷化副反应，进而提高制氢效率。研制出单原子Pd催化剂，并发现单原子Pd与FeOx的强相互作用有利于该催化剂具有较高的水煤气变换活性。代表性结果发表于AIChE J. 2017, 63, 4022-4031；AIChE J. 2017, 63, 2081-2088。.（3）单原子与纳米催化剂水煤气反应机制的对比研究。分别采用共沉淀方法以及乙二醇还原及负载方法制备出单原子与纳米Pt/FeOx催化剂。研究了单原子与纳米尺寸分散的贵金属催化剂上反应物种的吸附、反应状态、中间物种形成以及分解过程，提出粒子尺寸影响反应机制，单原子催化剂上有利于氧化还原机理，而纳米催化剂上反应主要是经过甲酸盐中间物种形成与分解的缔合机理。该尺寸效应与反应机制的关联在Pt/TiO2上甲醛氧化过程的研究得以体现。代表性结果发表于ACS Catal. 2018, 8, 859-868；Commun. Chem. 2019, 2, 27.