高效低载量亚纳米/单原子Pt族金属催化剂的设计及其甲醛氧化反应研究

Catalytic oxidation is an effective strategy to eliminate formaldehyde in enclosed environment. Noble metal, especially Pt based catalysts have been extensively studied in this reaction due to its low temperature performance. However, these catalysts own high loadings, usually higher than 1 wt%. The recognition of the states of active species such as metal size, coordination environment, and valence status are still inconsistent. It is key to realize practical application through the design of low loading catalyst and the establishment of structure-function relationship in an atomic scale. In this application, we are planned to synthesize a series of Pt catalysts with dispersion of nano, subnano, single-atom based on the use of layered oxides rich of OH species as support and the control of metal precursors and strutural property of support. The aim is to decrease the metal loading to a level of 0.01-0.1 wt%. The metal-support interation and then dispersion and stability mechanism will be disclosed by the aberration-corrected scanning transmission electron microscopy, X ray absorption characterizations, in situ XRD and so on. Afterwards, the model of catalysts with different dispersion will be constructed. By a series of in-situ infrared, microcalorimetry, micro-kinetic methods, DFT calculations and so on, we will study the adsorption and reaction behaviors of formaldehyde oxidation over these catalysts, then explore the mechanism of this reaction. Furthermore, the differences among the oxidation of formaldehyde on the catalysts with various Pt group metals will be detected and compared. This application will provide guidance for the preparation of catalysts with low loadings but high performance.

催化氧化技术是消除甲醛的有效方法，贵金属尤其Pt催化剂以其低温活性受到关注；然而目前Pt载量较高（通常>1 wt%），活性中心状态如粒子尺寸、配位环境、价态等的认识不统一。设计制备低载量催化剂并从原子尺度上研究构效关系是甲醛消除催化剂实现应用的关键。本申请拟以富羟基层状氧化物为载体，基于调控金属前躯体状态及载体性质合成出具有纳米、亚纳米或单原子均一分散的Pt催化剂，将高效催化剂金属载量降至0.01-0.1 wt%。通过球差校正扫描透射电镜、X射线吸收光谱、原位XRD等手段研究载体与不同尺寸粒子间的相互作用，构建催化剂模型，并详细考察金属配位环境以揭示其稳定机制。在此基础上，借助原位红外、微量量热等手段并结合微观动力学、密度泛函理论计算等方法研究反应物的吸附、反应特征，探索反应过程中间物的形态及转化机理。进一步研究其它Pt族金属催化氧化甲醛的异同点，为高效低载量催化剂的开发提供借鉴与指导。

甲醛污染是公认的环境问题，采用催化氧化法具有能耗低、环境友好、实用性强等优点。本项目制备出室温条件下完全消除甲醛的具有特定尺寸的Pt基催化剂并降低Pt负载量至0.1 wt%以下，发现特定价态的Ir粒子能够实现室温下甲醛完全消除。.1. 超低负载量Pt/TiO2催化剂室温甲醛完全氧化。合成了不同尺寸分布的Pt/TiO2催化剂，分别为Pt-SAC（单原子）、均匀分散的Pt-NC（~1 nm）和Pt-NP（~2 nm）。在甲醛氧化反应中发现催化活性与Pt粒子尺寸呈火山型关系，Pt-NC表现出最佳的甲醛消除性能，20 oC下甲醛转化率为100%，而Pt负载量仅为0.08 wt%，比文献中报道的载量降低了一个数量级。并且该催化剂在高浓度甲醛（390~1300 ppm）、宽湿度范围（0~75%）内均表现出高活性和高稳定性。该类催化剂具有经济性以及一定的应用潜力。.2. 惰性载体Al2O3负载的Ir基催化剂用于室温甲醛消除。通过胶体-沉积法，制备出商业γ-Al2O3负载的亚纳米Ir催化剂（1.5IrAl-CD）。该催化剂的甲醛氧化性能优于传统沉积沉淀法制备的Ir基催化剂（1.8IrAl-DP），实现惰性载体担载的Ir基催化剂室温完全消除甲醛。研究发现Ir价态决定了催化剂的反应性能及路径。1.8IrAl-DP上Ir主要为正价并且与OH相连，遵循甲酸盐与OH反应的路径；而1.5IrAl-CD上Ir以零价存在，促进甲醛脱氢生成CO中间物种，并将CO氧化为CO2，具有更高的反应活性及更低的表观活化能。该工作表明Ir金属价态能够影响甲醛转化反应路径及其消除性能。.3. Pt/CAU-1催化剂上甲醛的室温“同步存储氧化”研究。以CAU-1-(OH)2金属-有机骨架材料为载体，制备了一种室温“同步存储氧化”甲醛的Pt基催化剂。室温下，CAU-1-(OH)2甲醛吸附量为1.6 mmol gcat-1，是文献中报道的几倍甚至十几倍。负载0.1 wt% Pt后，室温下可将305 ppm甲醛完全消除，该过程中一部分甲醛通过吸附的方式存储于载体，另一部分被氧化为CO2和H2O，实现了甲醛的同步存储与氧化，大大提高了消除效率。

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