A commercial V2O5-WO3/TiO2 catalyst used at an NH3-SCR deNOx process in an oil-fired power plant: cause of an increase in deNOxing and NH3 oxidation performances at low temperatures

Abstract

The extent of both NOx removal and NH3 oxidation in the selective reduction of NOx by NH3 over a sample of a commercial V2O5-WO3/TiO2 catalyst that had been used for 20,000 h at an NH3-SCR deNOx process in a domestic heavy oil-fired power plant has been determined using an on-line IR-based system coupled with a modified White cell and the catalyst has been characterized to ascertain the reason why it possessed visibly different behaviors in the deNOx reaction, compared to a fresh sample. The on-site-used catalyst gave not only much higher deNOx activity at all temperatures less than 400 °C than that indicated for a fresh catalyst but also a greatly increased NH3 oxidation reaction. SEM-EDX measurements with samples of the used and fresh catalysts represented the presence of a huge amount of sulfur in the former sample, very consistent with sulfur amounts determined by a C/S analyzer; however, this did not create the measured enhancement in the low-temperature deNOx and NH3 oxidation performances. ICP measurements indicated a significant increase, by 1% as a basis of V2O5, in an amount of vanadium species after the on-site use and such vanadium species came from heavy oils used to generate electricity at the power plant and were in the form of polycrystalline V2O5 nanoparticles as acquired by XRD measurements. All these results propose that the increased V2O5 content might be associated with the noticeable difference in SCR activity and NH3 oxidation between both of the samples.