Variations in the physicochemical properties of spent honeycomb V2O5-WO3/TiO2 catalysts from PC and CFB boilers SCR denitration systems

Abstract

The massive production of spent honeycomb V2O5-WO3/TiO2 catalysts has caused serious environmental hazards. Revealing the physicochemical property variations of the spent catalysts is of great significance to clarify the deactivation mechanism of catalysts and the recovery of the spent catalysts. This study focused on the changes of typically spent catalysts, selected from pulverized coal (PC) and circulating fluidized bed (CFB) boiler deNOx systems, morphologies, pore structure, chemical composition, carrier, and active components properties, etc. The activities of most spent catalysts could be to more than 95% at 300–400 °C after vibration cleaning. The pore blockage caused by fly ash and sulfur deposition is the major deactivation factor of the catalysts from the two furnace systems. The catalysts from CFB furnaces are more easily deactivated, which is owing to they are more prone to occur severe pore structure loss. The transformation of anatase to rutile TiO2 as one of the major factors causing the pore structure loss would form the irreversible deactivation of the catalysts. The valence state of the active component V has shifted. The spent catalysts from PC systems typically exhibit higher V4+/Vn+ ratios. However, those from CFB systems display a noticeable decrease, which may be attributed to the formation of CaWO4, resulting in the destruction of dispersed active sites on the surface. Finally, the deactivation mechanism of the spent catalysts from different furnaces of coal-fired power plants was summarized. This research is beneficial for further modification of SCR catalysts under different application conditions and provides valuable insights into the classification and recycling of the spent catalysts.