Low-Temperature Selective Catalytic Reduction of NOx with Urea Supported on Carbon Xerogels

Low-temperature selective catalytic reduction (SCR) of NO x on urea-supported carbon xerogels is studied. The kinetics results show that the orders of reaction for NO and O 2 are 1 and 0.5 for NO reduction, while the orders of reaction for NO 2 and O 2 are 1 and 0.03 for NO 2 reduction, respectively. The apparent activation energies of NO and NO 2 reduction are calculated to be −14.0 and 0.79 kJ/mol, respectively. Possible mechanisms are proposed, based on the hypothesis that there exist two kinds of active sites on the surface of carbon xerogel, including nonreductive and reductive ones. Spillover of the NO 3 species generated on the nonreductive ones into the reductive ones which are subsequently oxidized by NO 3 and the migration of NO 3 species from nonreductive ones into the oxidized carbon sites are considered to be of great importance for the successive urea-SCR process and the formation of steady-state NO x removal period.