CH4/CO2低温重整反应TaskerⅢ型表面金属氧化物纳米片负载镍基催化剂的设计制备与机理研究

Carbon dioxide reforming of methane is of great importance because two greenhouse gases CO2 and CH4 can be directly transformed to the extremely useful synthesis gas. This reaction normally needs high temperature. A traditional nickel-based catalyst was often employed to achieve this target. However, there still remained an intrinsic drawback of this kind of catalyst, that is, the catalytic activity of nickel-based catalyst is very low and the catalyst is subject to deactivation because of carbon deposition for the low-temperature carbon dioxide reforming of methane (<650℃). On the basis of preliminary work, this project aims to design and prepare novel nickel-based catalysts supported on metal oxide nanosheets with Tasker Ⅲ surface, such as MgO(111) and CeO2(200), which can overcome the drawback mentioned above. The designed nanosheets structure and the alternating ionic layers of MgO(111) or CeO2(200) surface can regulate the adsorption and activation of CO2 and CH4. Especially, it can prevent the deactivation resulted from the carbon depositin of nickel catalysts under low-temperature carbon dioxide reforming of methane. Therefore, the higher activity and higher stability of nickel-based catalyst for the low-temperature carbon dioxide reforming of methane can be realized. At the same time, in-situ DRIFTS combined with density functional theory calculations will be carried out to analyze the influence of the interaction between nickel and the Tasker Ⅲ surface of support on the kinetics of reaction. The carbon dioxide reforming of methane catalyzed by Ni/MgO(111) and Ni/CeO2(200) catalysts will be investigated to clarify the reaction mechanism as well. It is believed that this project will provide a theoretical and practical foundation at molecular level to the design of active and stable low-temperature reforming catalysts.

甲烷二氧化碳重整可以将CO2和CH4两种温室气体直接转化为合成气，通常需要高温反应。目前应用最为广泛的镍基催化剂在低温重整条件下（<650℃）的低活性和易积碳等问题至今仍未有效解决。本项目在前期工作基础上，设计制备Tasker Ⅲ 型表面定向生长的金属氧化物纳米片（MgO(111)、CeO2(200)）负载镍基催化剂，并用于催化低温甲烷二氧化碳重整反应。利用载体Tasker Ⅲ 型交替离子层的特殊表面，调控催化剂对反应物种的吸附活化能力，着力改善因低温下积碳而导致的失活问题，最终提高低温重整反应的活性和稳定性。采用原位光谱并结合密度泛函理论计算，研究载体Tasker Ⅲ型表面与活性金属之间的相互作用对反应动力学行为的影响机制，探索Ni/MgO(111)和Ni/CeO2(200)的催化反应机理，从而为在分子水平上设计制备具有优异性能的低温重整反应催化剂提供一定的理论和实践支撑。

甲烷二氧化碳重整可以将CO2和CH4两种温室气体直接转化为合成气，具有十分重要的理论意义和现实价值。然而，目前应用最为广泛的镍基催化剂在低温重整条件下的低活性和易积碳等问题至今仍未有效解决。本项目设计制备了四类新型镍基催化剂，如MgO(111)纳米片负载镍基催化剂Ni/MgO(111)、CeO2(200)立方体负载镍基催化剂Ni/CeO2(200)、TiO2(001)纳米片负载镍基催化剂Ni/TiO2(001)以及锆掺杂有序介孔氧化铝负载镍基催化剂Ni/ZrO2-Al2O3等，并用于催化甲烷二氧化碳重整反应。研究结果表明，这四类催化剂均表现出较为优异的催化活性和稳定性。究其原因，大致有以下几个因素：（1）载体的特殊形貌（如纳米片、立方体、有序介孔结构等）有利于提高活性金属镍的分散度，增强了催化剂对CH4和CO2的吸附活化能力，从而有利于催化反应活性的提高；（2）暴露的特殊晶面以及元素掺杂等特性，提高了载体表面的中等强度碱性位，增强了催化剂对CO2的吸附活化能力，从而有利于反应过程中积碳的及时消除，避免了碳的累积；（3）载体的特殊晶面以及元素掺杂等特性，还增强了活性金属与载体之间的相互作用，抑制了镍粒子的长大，从而改善了因纳米粒子高温烧结而失活的问题。总之，通过设计制备的新型氧化物负载镍基催化剂，最终实现了同时提高低温重整反应的活性和稳定性的目的。同时，采用原位红外光谱研究了不同的氧化铝载体负载镍基催化剂对反应物分子不同的吸附活化行为，为揭示催化重整反应的微观过程提供了有用的信息。另外，结合密度泛函理论模拟计算的方法，对MgO(111)表面负载Ni催化剂结构进行了从头算分子动力学(AIMD)模拟。为了探究Ni/MgO(111)催化甲烷二氧化碳重整反应机理，分别以NiO3和Ni3O为模型，计算了催化剂上CH4和CO2的吸附和解离反应，从而为在分子水平上设计制备具有优异性能的低温重整反应催化剂提供了一定的理论和实践支撑。