基于分子氧还原活化的甲烷低温直接催化转化

Given its tremendous abundance and availability, hydrocarbon gas mixture consisting primarily of methane has been considered a future alternative source for chemicals and materials in the post-oil era. The purpose of this project is to develop new catalytic routes for methane valorization. The objectives of this research were: 1) explore and develop new innovative processes that can deliver direct and selective catalytic conversion of methane to produce methanol; 2) demonstrate the feasibility to directly produce value-added methyl formate and its derivatives from simple feedstocks comprising methane and HCOOH. Special efforts will be dedicated to three aspects: investigate the catalytic behavior of the nanocomposite catalysts comprising both “metal” and “acid/base” surface species recently developed by our group for the selective reductive transformation of nitrobenzene using methane as the convenient and energy-efficient hydrogen source, establish several catalytic systems capable of producing value-added chemicals directly using methane as feedstock based on the concept of reductive activation of molecular O2, and conduct reaction/kinetic studies for understanding the essential physico-chemical aspects of the relevant processes. Efforts will also be directed to gain insight into the influence of metal dispersion, metal-support interactions, surface acidity/basicity and redox properties on the activity, selectivity and stability of the catalysts, understanding the mechanistic pathways involved in the relevant processes, exploiting the concepts of catalyst designing, seeking and fabricating new efficient catalytic system for methane valorization, thus providing the essential knowledge and skill required to develop a technically and economically feasible process.

以甲烷为主要成分的碳资源储量极其丰富，被认为是“后石油时代”的重要替代资源。本项目旨在寻求和发展甲烷直接转化新途径和新策略。拟以探索和开发甲烷直接制甲醇新工艺为目标，筛选和创制高性能催化体系；针对甲烷直接转化制甲醇及甲酸甲酯等高值化学品，探究本研究团队近年发展的具有“金属”及“表面酸/碱”等多活性位集成的复合催化材料的活性和选择性变化规律；建立以分子氧还原活化的甲烷直接制高值化学品的催化体系，研究其中的催化物理化学特点。系统认识催化剂表面多活性中心微/纳尺度上的协同/集成与甲烷直接制甲醇活性、选择性和稳定性的关系，催化体系中金属分散状态和金属-载体相互作用与甲烷活化或选择氧化反应的活性、选择性和稳定性的关系。明确相关催化反应体系的催化活性和选择转化作用的机理，拓展催化剂设计理念，发现和创制甲烷增值利用的高效催化体系，为发展相应催化新技术提供理论指导和科学基础。

本项目遵循采用分子氧（O2）还原活化策略实现甲烷低温直接转化总体思路，重点围绕具有“金属”及“表面酸/碱”等多活性位集成的复合催化材料的构建、O2还原活化制过氧化氢（H2O2）及甲烷与相关烃类化合物低耗直接转化等核心科学问题开展深入研究。在揭示并阐明相关功能材料催化O2还原活化制H2O2及后续甲烷及相关烃类直接羟化等过程的性能调控规律、反应机理和相关体系中金属-载体协同作用机制等方面进行了探索。针对O2还原活化制H2O2，发展了基于甲酸（HCOOH）及甲酸盐等为还原剂的高效H2O2直接合成体系，可有效避免传统氢氧直接合成面临的安全性低及与后续选择氧化反应直接集成困难等缺点。发展了TiO2等氧化物负载Au高效金属催化剂，通过金属与载体相互作用的调控，实现了在无外源助剂温和条件下以O2为氧源的H2O2直接清洁合成，H2O2合成效率高达665 h-1。针对甲烷等低碳烃在O2/HCOOH体系中的直接选择氧化，设计合成了Au/TiO2与钛硅分子筛的高效复合催化材料，两种组元间的协同作用（Au/TiO2组元的H2O2直接合成，钛硅分子筛组元的H2O2活化与甲烷转化）可有效活化O2、HCOOH与甲烷等分子，加快反应速率，获得高达7.7 mmolCH3OH(KgAuh)-1的初始甲醇合成速率。针对苯等重要芳烃基本化工原料的直接临氧转化，设计合成了仅基于Au/TiO2的简单负载金属催化剂，通过调控相关催化剂的表面酸碱特性、结构组成和H2O2生成与后续转化路径分析，高选择性获得收率达6%的苯酚产物，催化剂可多次连续使用不失活，具有较好的稳定性。上述利用O2还原活化策略实现甲烷低温直接制甲醇等若干临氧催化转化新体系的建立与发现，不仅开创了H2O2直接合成的新方法，对甲烷等碳基资源的低耗增值利用以及进一步发展相关环境友好新工艺可望起到良好的推动作用。