抗烧结负载型金属纳米催化剂的制备机理研究和催化性能

The present research project focuses on the synthesis of well-dispersed supported metal nonacatalysts with high thermal stability by using a simple impregnation method with metal acetylacetonate compounds (Mn+(acac)n, M = metal) as precursors, and the investigation of the mechanism of catalyst preparation. The effects of various factors such as the types metal acetylacetonate precursor, impregnation solvent, support pretreatment on the nature of the metal precursor impregnated on the supports (SiO2, Al2O3), as well as on the mechanisms of precusor decomposition and metal (or metal oxide) particle formation in the calcination proceses (under air or other atmospheres) are to be investigated systematically by using various experimental techniques (including in situ spectroscopic techniques). The performance of the catalysts for catalytic partial oxidation of methane, reforming of methane or dehydrogenation of light alkanes will also be tested. It is expected that the studies will provide scientific bases for the design of supported metal catalysts and present promising applications in the synthesis of supported metal nanocatalysts with high performance and high thermal stability.

探究以乙酰丙酮金属化合物（Mn+(acac)n,M = 金属）为前驱体采用浸渍法制备高分散、抗烧结负载型金属纳米催化剂的方法和机理。通过改变浸渍溶剂或对载体进行预处理以及改变焙烧气氛等方法调变Mn+(acac)n化合物及其分解产物与载体表面的相互作用，使金属物种均匀分散于SiO2和Al2O3等载体表面。采用包括原位谱学技术在内的多种实验技术对催化剂的制备机理进行系统表征，揭示金属前驱物与载体的作用本质以及前驱物的焙烧分解机理及其与载体上生成的金属（或其氧化物）分散度和抗烧结性能的关系。以甲烷部分氧化、重整或轻质烷烃的脱氢等为目标反应评价催化剂的性能，为兼具高活性和高热稳定性的负载型金属催化剂的研制提供科学基础。

以乙酰丙酮化合物为前驱体，采用简单的浸渍法制备了兼具高分散和抗烧结性能的Ni/SiO2、Pd/SiO2、Rh-CeO2/SiO2和Rh-Sm2O3/SiO2等催化剂。经空气中800 °C焙烧和600 °C通H2还原后，催化剂上金属物种的平均粒径维持在2.5~3 nm，且在一定的负载量范围内，金属物种的粒径基本不随负载量的增大而改变。对甲烷部分氧化（POM）合成气反应，5%Ni/SiO2和0.5%Rh-Sm2O3/SiO2的催化活性、选择性分别在400和500 h保持稳定。前者对甲烷二氧化碳重整（DRM）制合成气反应也表现出良好的催化性能。对催化剂制备机理的表征结果表明，在浸渍过程中，乙酰丙酮化合物通过与SiO2表面硅羟基形成氢键而高分散吸附于载体表面，只要SiO2表面有足够的羟基且乙酰丙酮化合物的负载量不超过其在SiO2表面单层分散的阈值，均可保证负载于SiO2表面的乙酰丙酮镍、钯、铈、钐等化合物在空气中加热分解后生成高分散或平均粒径约3 nm且具有良好抗烧结性能的金属氧化物纳米粒子，并使纳米粒子的尺寸在一定的负载量范围内保持不变。高分散于SiO2表面的稀土氧化物与Rh之间存在的强相互作用可显著提高Rh的分散度，防止其在高温反应条件下烧结，进而使Rh负载量仅为0.025%的催化剂也表现出良好的甲烷部分氧化制合成气反应活性和稳定性。