Study On Preparation And Poisioning Mechanism Of MnO_X/TiO₂Catalytic Material For SCR Of NO_x With NH₃at Low Temperature

Cement industry, as one of the three sources of industrial nitrogen oxide, the taskof cement kiln NOx emission reduction is particularly urgent. Selective catalyticreduction (SCR) technology is the most efficient technology in the cement kiln NOxemission reduction, which is of great significance for solving the cement kiln of NOxemission reduction. The core of SCR technology is the denitration catalyst at lowtemperature. MnOx/TiO2catalyst is widely studied as its good activity during lowtemperature (90oC~180oC). Therefore, MnOx/TiO2catalyst is particularly applicableto the low temperature flue gas denitration in the cement kiln after the waste heatpower generation. However, some ultra-fine fly ash is rich in alkali metal or alkalineearth compounds，such as the K, Na, Ca and so on. Researchs have shown that thealkali metal and alkaline earth compounds deposited on industrial catalyst andinhibitted the adsorption of NH3on the catalyst surface, which resulted to thereduction of the SCR activity of the catalysts. Therefore, the study of poisoningmechanism of MnOx/TiO2catalysts can provide basis and guidance for thepreparation of catalysts which are suitable for cement kiln denitration at lowtemperature.The denitration catalyst of different kinds of carriers were prepared byimpregnation method, the denitration activity test, XRD and BET were employed toanalyse the catalysts. The results showed that the composite carrier can help toimprove the denitration activity of catalysts; the MnOx mainly existed as the form ofMn3O4and Mn2O3crystals.The MnOx-M/TiO2catalyst materials doped with different trace elements wereprepareed by sol-gel method. Besides, the MnOx/TiO2-SiO2catalyst materials ofcomposite carrier were prepard by sol-gel method. The results showed that the dopingof Ni can improve denitration activity; While the composite carrier of TiO2-SiO2goagainst to the denitration activity for sol-gel method; XRD and XPS test resultsshowed that the MnOx mainly existed as the amorphous form of MnO2.MnOx-M/TiO2-SiO2catalyst materials were prepared by sol gel-dippingcomplex method. An orthogonal experiment of three levels and three factors wasdesigned to study the effect of carrier composition, MnOx content and trace dopingelements. The resuls showed that the carrier has the greatest effect to the denitration activity of catalytic materials, the optimal experiment scheme is50%SiO2, Mn:(Ti+Si)=0.8, Ni as a dopant.MnOx/TiO2catalyst materials prepared by sol-gel method were used to study theposioning effect of alkali metal compounds and H2O. BET, XRD, SEM, XPS,NH3-TPD, H2-TPR and DRIFTS were employed to investigate the mechanism of K2Oposioning on MnOx/TiO2catalyst. The results showed alkali metal compounds andH2O could cause different degrees of poisoning effect to catalytic materials, while theH2O poisoning to catalytic material process is reversible. The K2O poisoning onMnOx/TiO2catalytic materials include two aspects of reasons including the physicsinfluence and the chemical influence, the physics influence is that the K2O reduce thespecific surface area of catalyst and pore volume, blocking the pore structure, whichresult to a decline in denitration activity. The chemical influence were that the K+ofK2O bond with acid sites of catalyst and hinder the adsorption of NH3on the surfaceof catalyst, which results to the decrease of the efficiency of denitration.