高稳定担载型低维过渡金属碳化物的表面催化机理和增强机制研究

Rising atmospheric concentration of CO2 is forecasted to have potentially disastrous effects on the climate from its role in global warming and ocean acidification. Ethane comprises approximately 10% in shale gas and natural gas, and is underutilized. A process that utilizes CO2 as a feedstock coupled with selective scission of C-C and C-H bond in ethane to make valuable oxygenates and hydrocarbons is considered to be more desirable and of great importance academically and industrially. .Transition metal carbides (TMCs) are attractive alternatives because they have similar properties to precious metal catalysts. Based on the unique properties of TMCs as well as its dual functionality: 1) the particular pathway in CO2 activation without using oxide supports through the carbide-oxycarbide catalytic cycle, 2) selectively breaking C-H bonds of ethane while preserving the C-C bond to produce ethylene, the primary motivation of the current proposal is the fabrication and design of high stable transition metal carbides (TMCs) supported noble metal (M/TMCs) catalyst, using ethane and CO2 as feedstock to produce higher value products. .The proposal will devote most of the initial efforts to the mechanistic understanding and the enhanced synergetic effect of CO2 activation by ethane over M/TMCs, a primary focus on identifying key descriptors that control the ethane dry reforming (C2H6+2CO2→4CO+3H2) and oxidative dehydrogenation of ethane by CO2 pathways (C2H6+CO2→C2H4+CO+H2O) will be illustrated in detail using various in-situ techniques coupled with physiochemical characterizations. In an effort to kinetically control C-C and C-H scission as well as CO2 activation for the two pathways. Combined density functional theory (DFT) calculations and Kinetic Monte Carlo (KMC) simulations will also be applied to help understand the binding energies of key intermediates or the activation barriers of key reaction steps..The recent shale gas boom combined with the requirement to reduce atmospheric CO2 has created an opportunity to use the two raw materials in a single process. To determine the mechanisms and identify distinct types of catalysts that can 1) efficiently break the C-C bond to produce synthesis gas, or 2) selectively break C-H bonds of ethane while preserving the C-C bond to produce ethylene. Understanding the thermodynamics and kinetics of the possible pathways to design new and improved catalysts represents a promising opportunity for both fundamental understanding and practical applications.

CO2含量升高是全球变暖和海洋酸化等灾难性气候变化的主要因素。乙烷广泛存在于天然气和页岩气等中，很难直接利用。选择性剪裁乙烷C-C和C-H键，将CO2温和转化为高附加值基础化工品，对于资源化利用CO2和乙烷意义重大。本项目基于碳化物的类贵金属性质和活化CO2的特殊路径，设计高稳定担载型低维过渡金属碳化物催化剂，利用原位反应监测手段和物理化学表征技术，结合DFT和KMC，研究乙烷C-C和C-H键断裂规律，调控CO2在催化剂表面的吸附和活化，揭示乙烷重整（C2H6+2CO2→4CO+3H2）和乙烷温和氧化脱氢（C2H6+CO2→C2H4+CO+H2O）竞争机制的表面催化机理及贵金属和过渡金属碳化物的协同作用对乙烷C-C、C-H键的选择性剪裁和CO2温和活化的增强机制，从微观层面优化催化剂，实现绿色利用CO2和乙烷制备高附加值的烯烃，为CO2和乙烷的资源化利用提供新途径。

随着我国2030年碳达峰目标的提出，CO2作为一种弱氧化剂在乙烷氧化脱氢反应(CO2-ODHE)中受到了化工行业的广泛关注。设计制备高稳定低维担载型低维过渡金属碳化物（Mo， W）催化剂，开展乙烷温和氧化脱氢反应的基础研究具有重要的理论研究价值。开发出具有自主知识产权气高稳定贵金属担载型过渡金属碳化物催化剂具有重要的应用背景。其中，调控乙烷C-H和C-C键断裂，提高催化剂活性、寿命和稳定性，抑制结焦，实现在乙烷的可控转化，提高产物中基础化学品乙烯的含量，是乙烷和二氧化碳绿色、资源化利用的新途径，且极具挑战。.本项目从基础理论入手催化剂设计和优化，共制备了40余种过渡金属碳化物或氧化物催化剂，搭建了用于评价高稳定低维担载型过渡金属碳化物催化剂的在线反应和检测平台，并对其中性能优异的催化剂进行了深入优化和性能测试，较大幅度提升了反应的选择性和转化率。考察了催化剂表面物理化学特性对乙烷C-H和C-C键断裂的影响，通过原位表征手段和物理化学结构分析技术，并提出了可能的反应路径。初步揭示了在所研制催化剂上乙烷C-H和C-C键选择剪切规律，通过调控催化剂表面Mo物种，实现了对乙烷的高效催化转化；通过改变催化剂表面Mo晶相，有效提高了乙烯的选择性和产率。通过强化载体与活性位点的相互作用，抑制了乙烷C-C键裂解，并研制了形貌可控的锌基催化剂，表现出了优异的性能，相关研究还在继续深入。证明了物种及其浓度、价态及其分布、载体及其表面性质、形貌等关键因素对于反应性能的重要影响，提高了催化剂活性、寿命和稳定性，实现了对乙烷的高效催化转化，对于更深入认识乙烷C-H和C-C键选择断裂规律和表面竞争反应机制提供了较为关键的积累和数据，确认了未来工作方向。人才培养和科研工作都将伴随着基金工作的深入开展，继续进行。