Performance And Mechanism Studies For Synergistic Elimination Of VOCs And NO_x Over Bifunctional V-Ti Based Catalysts From Coal-fired Flue Gas

Volatile organic compounds（VOCs）are significant precursors of ozone and particulate matter PM_2.5.VOC emissions contribute to photochemical haze,climate change,and environmental toxicity,which have collectively sparked widespread concern.In addition to typical pollutants such as NO_x,the coal combustion process contributes significantly to VOCs emissions.VOCs entail a substantial ecological threat due to their low concentration,high total volume,and high toxicity in coal combustion flue gas.The most techno-economic control strategy is achieving the synergistic control of VOCs and NO_xin the SCR section.However,given that coal-fired flue gas has a high concentration of SO₂,NO,NH₃and H₂O,conventional catalytic oxidation methods and materials for VOCs from industrial sources cannot be applied.Meanwhile,the synergistic elimination of VOCs and NO_xhas been complicated by an obscure mechanism that has not been comprehensively delved into.Therefore,it is scientifically significant and practically meaningful to explore the synergistic removal mechanism of VOCs and NO_xand to create essential materials that can be tailored to the flue gas environment of coal combustion and remove both NO and VOCs concurrently.Based on a study conducted on the reaction mechanism and constitutive connection between V-W（Mo）/Ti O₂catalysts for NO and VOCs removal,Cu-VWT bifunctional catalysts for synergistic control of VOCs and NO_xin coal combustion flue gas were effectively created in this study.The monolithic catalyst was manufactured using a combined extrusion-impregnation technique and tested on a medium scale in the flue gas of a coal-fired boiler with a capacity of 1200 m³·h^-1.The following illustrates the main results yielded.V-W（Mo）/Ti O₂demonstrated excellent catalytic oxidation activity and stability for toluene alone.However,it demonstrated extremely low selectivity for CO₂and CO_xin the simulated coal-fired flue gas.NO,NH₃,and SO₂alone or in combination with coal combustion flue gas attenuate the rate and selectivity of toluene catalytic oxidation for CO₂and CO_xelimination,with NH₃being the primary inhibitory gas.The findings of in situ DRIFTS and GC-MS analysis suggest that the addition of NH₃occupies the active site,inhibiting benzene ring oping reaction and following oxidation process.At the same time,the interaction of NH₃and by-product from toluene oxidation continued to form nitrile species,which prevented the generation of benzoic acid,nitrobenzene,and maleic acid.Additionally,the largest concentrations of benzonitrile and naphthalene were identified in the tail gas.These findings show that the V-W（Mo）/Ti O₂catalyst requires an additional modification to boost the selectivity and oxidation efficiency of catalytic oxidation of VOCs while minimizing environmental risks.The Cu-VWT catalyst showcased excellent catalytic oxidation performance for VOCs in a flue gas atmosphere,it can effectively prevent the generation of PAHs.Cu-VWT displayed excellent performance and stability in the synergistic removal of VOCs and NO_x.The reasons for the effective performance include the presence of highly dispersed Cu and V active sites,a high proportion of surface reactive oxygen,alongside desirable oxidation and reduction properties of the Cu-VWT catalyst.In situ DRIFTS results showed that,compared with the VWT catalyst,on which NO,NH₃and SO₂react with toluene to form several by-products such as benzonitrile,the Cu-VWT catalyst with a bifunctional effect can simultaneously remove more NO_xand VOCs.Site Cu and site V are mainly used as the active site for catalytic oxidation and the site for NO reduction on Cu-VWT,respectively.Toluene is preferentially adsorbed on-site Cu for oxidation reaction,while NH₃is preferentially adsorbed on-site V for reaction with gaseous NO.Toluene oxidation and NO reduction occur synchronously,which are synonymous with the simultaneous removal of toluene and NO_x.Based on the study on the formulation of the powdered Cu-VWT catalyst,a scale-up study on the preparation of monolithic Cu-VWT catalyst upon laboratory optimization was performed,and the Cu-VWT-MC2 monolithic catalyst was prepared.The catalyst’s performance was investigated in flue gas at 1200 m³·h^-1.The results demonstrate that by using the Cu5-VWT-MC2 monolithic catalyst,the overall removal rate of VOCs from coal-fired flue gas reached 97.9%,the removal efficiencies of total hydrocarbon and non-methane total hydrocarbon were 91.94%,and 95.76%,indicating that the Cu-VWT-MC2 monolithic catalyst was an excellent candidate due to its performance in flue gas.