Study On The Structure-Activity Relationship And Alkali Metal Poisoning Of V₂O₅/TiO₂ SCR Catalysts

Currently,selective catalytic reduction(SCR)denitration is the most widely used NOx removal technology in thermal power industry.Catalyst is the core of SCR denitration system,whose denitration activity essentially depends on its structural characteristics.Effects such as catalyst formulations,preparation techniques,and catalyst poisoning will change the microstructure,thus affecting the catalyst activity of denitration.Therefore,a deep understanding of the structure-activity relationship for both fresh and poisoned catalysts is of great theoretical significance for developing novel SCR catalyst and improving the catalyst poisoning resistance ability.In this work,firstly,effect of preparation condition on structure and performance of fresh SCR catalyst was investigated.A series of V-W-Ti and V-Mo-Ti catalysts were prepared through altering the conditions of active components content,pyrolysis temperature,loading sequence of active component,and cosolvent of ammonium metavanadate.The catalyst denitration activity was determined on a self-built testing platform.Characterizations of XPS,H2-TPR and NH3-TPD were conducted to elucidate the structure-activity relationship.Results showed that the denitration activity was closely related to the catalyst acidity and reducibility.The more acidic sites,the lower the vanadium reduction temperature,the better the denitrification activity of the catalyst.The Bronsted acidic sites rather than the Lewis acidic sites played the major role in the denitration reaction.In a certain range,the proportion of low valent vanadium species is positively correlated with the catalyst denitration activity.Using oxalic acid as the cosolvent is beneficial to increase the proportion of low valent vanadium and chemisorbed oxygen,the surface acidity of the catalyst,and the reducibility of vanadium,thereby enhancing the denitration activity of the catalyst.Furthermore,alkali metal poisoning of catalyst in thermal power plant was simulated in this work.Characterizations including NH3-TPD,H2-TPR and XPS were performed to study the effect of alkali metal type and poisoning method on catalyst structure and performance,and reveal the mechanism of alkali metal poisoning.Both alkali metal oxides and alkali metal chlorides would poison the catalyst through occupying the active sites on catalyst surface.The higher loadings of alkali metal resulted in longer poisoning time and lower Bronsted acidic sites,further leading to poorer catalyst denitration activity.Under identical molar ratio of K/V,solid diffusion method was more harmful to the catalyst.