The Study Of Cu-based Catalyst Synthesized By Ice Melting Method And Its Performance For Selective Catalytic Reduction Of NO With NH₃

The selective catalytic reduction（SCR）is the mainstream de NOx technology and widely used at present.Catalyst as the core of technology,the choice of synthesis method is the key point to influence the catalytic performance.In this study,the catalyst synthesis method was improved based on the traditional coprecipitation method.A series of Cu-based catalysts were synthesized by ice melting method,the influence of synthetic parameters was discussed and the de NOx activity of catalysts was tested.Characterization methods including XRD,BET,SEM,TEM,AFM,XPS,H₂-TPR and NH₃-TPD were used to analyze the physicochemical properties of catalysts.The mechanism of promoting the activity of catalyst synthesized by ice melting method was preliminarily studied.The specific research contents are as follows:First,a series of CuO/TiO₂ catalysts were synthesized by ice melting method.The influences of Cu content,calcination temperature,calcination time and precipitant type were investigated to determine the optimum reaction conditions.When the molar ratio of Cu/Ti is 0.05,the catalyst showed the best catalytic activity;The optimum calcination temperature and time of catalyst was 550℃for 3 h.The higher the calcination temperature was or the longer the calcination time was,the lower the activity of the catalyst showed.When oxalic acid and ammonia solution were used as precipitators,the catalyst activity was higher than that of ammonium carbonate.The restrict of mass transfer between catalyst particles has little effect on its catalytic activity at high GHSV condition.Then,compared with co-precipitation method,it was found that when the molar ratio of Cu/Ti was 0.005,the CuO/TiO₂ catalyst synthesized by ice melting method exhibited the highest catalytic activity.The NOx conversion was up to 90%at2850°C,30%higher than that synthesized by co-precipitation method and showed high N₂ selectivity.The grain size of catalyst decreased significantly,the active species were highly dispersed on support,the proportion of Cu²⁺and chemical absorbed oxygen increased.Meanwhile,the redox ability and surface acidity increased,which played an important role for the improvement of catalytic performance.Finally,the Cu-Ce/TiO₂ composite metal oxide catalysts were synthesized by ice melting method.When Ce/Cu molar ratio was 0.4,the catalyst showed the wide temperature window.The NOx conversion could be maintained over 80%at250-375℃,20%higher than that of catalyst synthesized by co-precipitation method.The N₂ selectivity was close to 100%.During the synthesis of ice melting method,the release concentration of precursor solution was low per unit time,which had an important impact on catalyst structure,including high specific surface area,low TiO₂grain size,uniform nano particles and nano pore structure.The proportion of Cu²⁺,Ce³⁺species and chemical absorbed oxygen on the catalyst surface increased.The catalyst surface has more acidic sites,which is conducive to the adsorption and activation of NH₃.The catalyst oxidation ability from NO to NO₂ was enhanced,which further accelerated the reaction process through"fast SCR"。Meanwhile,the NO species can react with coordinated NH₂ rapidly and promoted the NOx conversion at high temperature.