Study Of The Deactivation Causes And The Regeneration Methods For Commercial V₂O₅-WO₃/TiO₂SCR Catalyst

Nitrogen oxides（NOx）has become one of the key factors that affect the national airquality, coal-fired power plant, as one of a major contribution to the field, must strengthen thecontrol of NOx. Currently，selective catalytic reduction （SCR） is widely used to remove NOxin power plants at home and abroad because of its special advantages. While catalyst as thecore of the SCR system needs to change after being used for a period of time, this will greatlyincrease the operation cost of power plant. In addition, the used catalysts which containvanadium and other toxic substances will cause environmental pollution. Research suggeststhat the activity of catalyst can recover to normal level after regeneration, and the cost is onlya third of buying new catalyst, which greatly reduces the operation cost of power plant. So itis a better choice for the poisoning catalyst to be regenerated.This paper introduces the deactivated reasons of commercial catalyst which got from onepower plant in Guangdong province, and the poisoning was simulated by loading a certainconcentration of K through wet impregnation with KNO₃solution. The paper also discussesdifferent methods and process of catalyst regeneration and its catalytic performance.Firstly, the SCR activity tests were carried out in a fixed-bed reactor, and the catalystswere characterized by X-ray powder diffraction （XRD）, Fourier-transform infrared （FTIR）spectroscopy, X-ray photoelectron spectroscopy （XPS） and so on. The results show that thedeactivation of catalyst is attributed to a common effect of several factors. One of the maincauses is the active component loss and poisoning, and the effect of As is the biggest amongall the poisonous substances, followed by Na、Ca. The increasing of K also reduces theactivity of the catalyst to some extent, but the impact is limited.Secondary, the effects of washing time, washing methods, the type of acid, acidconcentration on selective catalytic reduction （SCR） of NO with NH₃were investigated.Results show that the activity of the catalyst recovered greatly after regeneration, and thecrystal structure of the catalyst was not changed but the toxic element K can be washed awayeffectively after acid washing. FTIR results show that Br nsted acid sites are activechemisorbed sites of NH₃, and surface adsorbed oxygen of the catalyst get a certain recoveredafter acid washing, also the acid sites of catalyst and its stability can get a certain restored.At last, in order to get a high resistance towards alkali metals poisoning, differentconcentrations of Ni or Zr were introduced to the commercial SCR catalysts through wetimpregnation. The catalysts before and after modification were characterized by different characterization methods. Results show that the modifications of the catalysts cansignificantly improve their resistance towards K poisoning, especially VWTi+Ni（0.5） andVWTi+Zr（1.0）. Ni and Zr can successfully enter the catalyst system and maintain thecrystalline structure of the catalysts, FTIR results show that the catalysts by loading a certainconcentration of Ni can form new Lewis acid sites, and Br nsted acid sites are strengthenedby loading Zr，these are the reasons that the catalyst after modifications have a high resistanceto K poisoning. H₂-TPR and XPS show REDOX properties of catalyst get a strengtheningwhich weaken the negative factor of the decreasing of specific surface area.