Ag-MnOx/SBA-15双组分催化剂构建及其对甲苯催化氧化的“协同催化作用”机制的研究

Volatile Organic Compounds (VOCs) have always been hazardous to human health and environment. Although high efficiency of noble metals has been proved in the catalytic elimination of VOCs, their high cost and limited availability have been encouraging their replacement by transition metal oxides (such as MnOx) with high stability and low cost for the practical application. Therefore, it is of great scientific and practical interest to investigate the properties of transition metals oxides and improve their catalytic activity. Aiming at the low activity of MnOx and Ag-MnOx bi-component catalysts, the poor dispersion of active components and the unclear synergetic effect between Ag and MnOx, the encapsulation of Ag-MnOx bi-component composites with high dispersion into the pore channels of short-rod SBA-15 will be done to increase the stability of active species and the toluene oxidation activity in this project. The use of the short-rod SBA-15 can obviously increase the adsorption and diffusion ability of toluene. The addition of Ag into MnOx will promote the structure of the MnOx and its redox properties, and the highly dispersed Ag-MnOx catalysts inside the channel and the synchronously increased interface area by the enhanced dispersity are highly beneficial to the synergetic effect enhancement between Ag and MnOx. Herein we will pay more attention on the effect of the synergetic catalytic effect in Ag- MnOx catalysts for the toluene oxidation, and Ag-MnOx catalysts with the different particles size and different position inside or outside surface of SBA-15 are prepared for elucidating the synergetic catalytic effect. The transfer pathway of active oxygen species on the surface and at the interface of Ag-MnOx for toluene oxidation is stressed, and the reaction mechanism for toluene oxygen on Ag-MnOx/SBA-15 catalyst is suggested. The obtained results will show critical effects to understand the effects of IB meta/oxide on the structure of transition metal oxide and the VOCs catalytic oxidation and the synergetic catalytic effect in Ag-MnOx catalyst, and consequently to be very significant for development of the novel transition metal oxide and dual functional adsorbent/catalyst system for VOCs elimination.

本项目主要针对甲苯催化氧化中MnOx及Ag-MnOx双组分催化剂活性不够理想、粒子尺寸不均匀及双组分间作用机制不够清晰等问题，利用短棒状SBA-15较好的甲苯吸附性能、分子扩散能力以及优良的粒子孔道限域性，在分子筛孔道中制备出高分散的Ag-MnOx双组分催化剂，并借助改性双组分锰氧化物的良好界面协同作用及优良的氧迁移能力，提高催化剂对甲苯的低温催化氧化性能；通过粒子尺寸及双组分不同落位的调控，着重研究Ag-MnOx双组分间协同作用对甲苯催化氧化性能的影响；系统探讨甲苯在Ag-MnOx/SBA-15双组分催化剂上的反应机理，明确双组分催化剂对甲苯催化氧化的"协同催化作用"，并建立完整的氧循环机制。为进一步深入理解多组分催化剂中组分协同作用对催化氧化反应活性调变本质、为今后推动贵金属取代、复合氧化物催化剂在VOCs催化氧化净化中的应用及吸附-催化双功能体系的建立和推广奠定实验和理论基础

项目中通过调控锰氧化物形貌、晶相结构、金属掺杂、SBA-15载体的形貌有效构建出具有大比表面积、高氧空穴浓度与可还原性氧物种的锰氧化物，研究中获得了氧化物形貌、晶相结构与甲苯催化氧化间的构效关系；短棒状SBA-15较传统的纤维状及颗粒载体表现出更好锰氧化物负载性能以及甲苯的氧化活性；研究中发现过渡金属Ce, Co与金属Ag对锰氧化物的掺杂作用机制是不同的，过渡金属对锰氧化物的掺杂更易形成固溶体，而金属银的掺杂更易于与载体间形成界面作用，银与锰氧化物间的相互作用是活性提高的关键，不同形貌锰氧化物对银的负载表现出不同的相互作用，纳米线状锰氧化物更有利于高分散银纳米粒子的形成，良好的界面效应提高了两组分间的相互作用，增加了锰氧化物的氧可还原性和含量，促进了甲苯的吸附和低温催化氧化反应。利用原位红外和同位素质谱实验系统研究了甲苯在锰氧化物以及Ag-MnOx上吸附、活化以及氧循环机制。银的加入促进了甲苯的吸附、中间物种苯甲酸和羧酸盐的形成。气相氧的存在加速了甲苯的氧化速率，吸附活化的甲苯主要与氧化物中的氧发生反应，解离的气相氧会迁移到氧化物中与催化剂中氧共同参与甲苯的氧化过程。