Study On For VOCs Catalytic Combustion

Emissions of volatile organic compounds（VOCs）have caused serious damage to the public health and environment.Catalytic combustion is an efficient method for the VOCs elimination.The design and preparation of catalyst as well as the study of structure-activity relationship lie at the heart of this technology.Mn O_x-based catalysts with high-efficiency and satisfactory-stability were prepared for low-temperature catalytic VOCs combustion in this study.The relationship between the structure of manganese oxide and its catalytic performance was studied.Firstly,The effect of crystalline integrity on catalytic combustion activity over Mn O_xhas been investigated,and the amorphous Mn O_x with partial crystallization（Crystallinity=6%）shown higher activity than pure amorphous and intact crystal Mn O_x（Crystallinity=1%and 100%,respectively）.The amorphous Mn O_x has been prepared by glucose reduction method and the crystalline integrity has been adjusted by tuning the hydrothermal temperature and time.Besides,the various characterizations illustrated that the appropriate crystalline integrity can result in enhancing catalytic combustion reactivity due to the synergistic impact of amorphous and crystalline phase.The amorphous phase has abundant structure defects and unsaturated coordination bonds,which enhances adsorption ability of catalyst.Simultaneously,the crystalline phase drives electrons migration,which favors the adsorption and activation of oxygen and speed up the redox reaction rate.The synergy between amorphous and crystal phase gives catalyst the most of dominant adsorbed oxygen species,Mn⁴⁺species and the strongest oxygen supply capacity.Furthermore,mesoporous structures were formed in the early stage of crystallization of amorphous Mn O_x which gave the manganese oxides the largest specific surface area（192 m²/g）.This work shows a novel strategy to design and prepare efficient non-precious metal catalysts for VOCs catalytic combustion.Secondly,the porous silica supported amorphous Mn O_x was constructed that promoted the oxygen supply capacity.This catalyst presented excellent stability and high activity for toluene combustion,even under the high temperature and humidity(T₉₀=218^oC).The various characterizations and Quantum chemical calculation results suggested that the Mn-O-Si hybridization induced the weakening of Mn-O bond strength and the electron transfer from the catalyst to surface adsorbed oxygen(O_ads)species.The promoting effect of the Mn-O-Si interaction on the spillover of active O species was proposed for VOCs catalytic combustion.This research provides a convince way for the preparation of catalysts for VOCs combustion with high activity and satisfactory stability.Finally,the multi-component tolerance and moisture resistance of Mn O_x-based catalysts were studied.Thermogravimetric analysis shows that the existence of carrier Si O₂ reduces the competitive adsorption of H₂O and VOCs molecules on the active component due to Si O₂ has better hygroscopicity than Mn O_x,and then gives Mn O_x/Si O₂-250 better humidity resistance.In-situ DRIFTS analysis determined the reaction mechanism and revealed that the O_ads acted as the dominated oxygen species that can oxidize the adsorbed toluene to CO_2.The experimental results showed that the prepared AC-Mn O_x and Mn O_x/Si O₂-250catalysts can effectively catalyze VOCs low temperature combustion,which provides a theoretical basis and experimental basis for the efficient treatment of organic waste gas.