Microstructure of Porous V_2O-CeO_2-SiO_2 catalyst for SCR of NO with NH_3 at Low Temperature

摘要

Selective catalytic reduction (SCR) is a well-proven method to reduce NO emission. However, to choose the right catalyst that provides a surface for reaction between NO and ammonia at low temperatures is a challenging task for a catalyst's developers. In an earlier study, we prepared V_2O_5-CeO_2-SiO_2 catalyst with increasing V_2O_5 content by sol-gel route and found that the catalytic activity improved with increasing the V_2O_5 loading up to 0.5%. The catalytic activity, however, dropped when V_2O_5 loading was about 1% and increased back when the loading of V_2O_5 was about 5%. In this study, we looked into the microstructural relationship to explain these findings. The microstructures of the catalysts before and after exposure to NO gas revealed that the catalysts with 0.2% and 0.5% V_2O_5 were more porous after the reduction process possibly due to improved breakdown of (NH_4)HCO_3 to NH_3 by the possible interaction with the V_2O_5 and CeO_2-containing catalysts which consequently resulted in a more efficient NO reduction to N_2 and H_2O at low temperature. The microstructure of the catalyst with 1% V_2O_5 content to 5%, improved back the efficiency although clogging by CeVO_4 phase still possible due to its presence based on XRD. The well-ordered micropores before exposure to NO and the more efficient breakdown of (NH_4)HCO_3 could have contributed to increase back the catalytic activity at low temperature.