Plasma-enhanced hydrolysis of urea and SCR of NOx over V2O5-MoO3/TiO2: Decrease of reaction temperature and increase of NOx conversion

Abstract

Plasma-enhanced hydrolysis of urea and selective catalytic reduction (SCR) of NOx over V2O5-MoO3/TiO2 were studied by temperature-programmed experiments using a packed-bed dielectric barrier discharge reactor. Urea over TiO2 and V2O5-MoO3/TiO2 could be hydrolyzed at 110–250 °C to NH3 and CO2 with yields of 79.0%–83.6% and 83.8%–88.6%, respectively. The catalyst type and presence of O2 in the carrier gas hardly affected catalytic urea hydrolysis performance. Introducing plasma reduced urea hydrolysis temperature over V2O5-MoO3/TiO2, without changing NH3 yield under O2-free condition while reducing NH3 yield to lower values at higher discharge power under O2-containing condition. Urea hydrolysis and NOx conversion temperatures decreased and NOx conversion increased after introducing plasma into the urea-SCR process. The presence of NO in the feed gas hardly affected and reduced urea hydrolysis temperature in urea-SCR and plasma-enhanced urea-SCR process, respectively. 5% O2 in the reaction gas favored NOx conversion in urea-SCR regardless of the presence of plasma. In the plasma-enhanced O2-containing urea-SCR process, N(-III) species (urea, NH3 and HNCO) were predominantly consumed in the conversion of NOx rather than being oxidized by oxidative plasma species. Minor slip of HNCO was observed at low temperatures during urea hydrolysis and urea-SCR over V2O5-MoO3/TiO2 and low-concentration N2O was detected during plasma-enhanced urea hydrolysis and urea-SCR process. The BET surface area and TiO2 crystal structure of V2O5-MoO3/TiO2 catalyst remained unchanged after urea hydrolysis and NOx conversion reactions no matter plasma was introduced or not. Plasma enhanced the conversion of NOx partially by enriching the catalyst surface with adsorbed oxygen.