The Mechanism Of Simultaneous Removal Of NO And VOCs Over Modified Porous CuO-CeO₂-ZrO₂ Catalyst

Nitrogen oxides（NO_x）and volatile organic compounds（VOCs）are important precursors for the formation of ozone（O₃）and PM2.5.Non-electrical industries in our country,such as iron and steel smelting,domestic waste incineration,petrochemicals,have a large number of industrial furnaces and boilers,which are important sources of NO_x and VOCs emissions.Researching on the control of NO_x and VOCs in non-electrical industries is the key to realize the source control of ozone（O₃）and PM2.5 pollution.Using the existing SCR denitration unit to achieve efficient simultaneous removal of VOCs is one of the simplest,economical and highly competitive technical methods.But the commonly used commercial catalysts have some shortcomings,such as poor low-temperature activity and high toxicity of vanadium oxides,which make it difficult to meet the characteristics requirements of low exhaust gas temperature（<300℃）in non-electrical industries.However,the simultaneous removal of NO_x and VOCs by CuCeZr catalyst still faces some key issues:（1）the CuCeZr catalyst prepared by the traditional method has a small specific surface area and few exposed active sites,resulting in poor catalytic activity for simultaneous removal of NO_x and VOCs;（2）SO₂ in the flue gas can easily lead to catalyst poisoning and deactivation.Therefore,improving the performance of the CuCeZr catalyst for simultaneous removal of NO and VOCs at low-medium temperatures and exploring the mechanism of SO₂effect on CuCeZr catalyst for the simultaneous removal of NO_x and VOCs can provide a theoretical basis for the development of efficient and environmentally-friendly catalysts for simultaneous removal of NO_x and VOCs suitable for non-power plant industrial.In this paper,porous CuCeZr catalysts modified with different transition metal oxides M（M=Co,Fe,and Mn）were first prepared by the KIT-6 hard template method to investigate the effects on the performance of different transition metal oxides M（M=Co,Fe and Mn）modified porous CuCeZr catalysts for simultaneous removal of NO and toluene at low-medium temperature.The interaction mechanism between NH₃-SCR atmosphere and toluene oxidation was explored,and the reaction mechanism of CuMCeZr（M=Co,Fe and Mn）catalysts for simultaneous removal of NO and toluene was elucidated.On this basis,the various factors and internal relationships of SO₂ effect on the performance of Cu_1-xFe_xCeZr catalysts for simultaneous removal of NO and toluene was further studied by BET,XRD,H₂-TPR,TG-DSC,XPS and in situ infrared characterization methods.The specific composition of the deposits and the migration rule of the main elements on the catalyst surface were clarified.And the mechanism of SO₂ effect on the performance of Cu_1-xFe_xCeZr catalys for simultaneous removal of NO and toluene was explained.The main conclusions of this paper are as follows:（1）Different transition metal oxides M（Co,Fe and Mn）introduction can improve the texture and structural properties,supply abundant active sites and induce more reactive oxygen species formation.Also,the redox equilibrium of Mⁿ⁺+Cu⁺（?）M^（n-1）++Cu²⁺and Mⁿ⁺+Ce³⁺（?）M^（n-1）++Ce⁴⁺is important in promoting NO reduction and toluene oxidation.For CuFeCeZr and CuMnCeZr,toluene exhibits slightly inhibitive effect on NO conversion of the L-H reaction mechanism because toluene competes with NO for adsorbing on the Cu²⁺sites,while SCR atmosphere facilitates toluene oxidation owing to NO consumption and new Br（?）nsted acid sites formation for toluene adsorption.For CuCoCeZr,toluene and SCR atmosphere have mutual promoted effects,mainly attributing that Co addition provides Co³⁺sites for toluene adsorption which offset competitive adsorption on Cu²⁺sites between NO and toluene.（2）An appropriate amount of Fe doping can increase the specific surface area,cause structural distortion to generate more oxygen vacancies,and provide more active sites and reactive oxygen species.SO₂ exhibited an inhibition effect at low temperature（<300℃）but a facilitative effect at high temperature（≥300℃）for NH₃-SCR reaction.At the same time,an obviously inhibition effect on toluene removal was observed during the whole temperature range.The main reason is that the deposition of（NH₄）₂SO₄/NH₄HSO₄ at low temperature covers the active sites on the catalyst surface,leading to the decrease of NO reduction and toluene oxidation efficiency at low temperature.At high temperature,SO₂preferentially reacts with O₂ to form SO₃.Then the sulfates formed by the reaction of SO₃with Cu²⁺can provide additional acid sites to promote the adsorption and activation of NH₃,which is beneficial to the E-R reaction mechanism of NH₃-SCR.However,the formed stable sulfates can lead to deactivation of Cu sites,reduces the redox performance and oxygen transport rate,thereby inhibiting the oxidation of toluene.