Development of stable and efficient CeVO4 systems for the selective reduction of NOx by ammonia: Structure-activity relationship.

Bulk CeVO 4 catalysts prepared by hydrothermal synthesis have been developed for the ammonia-selective catalytic reduction of NO x to nitrogen. The catalytic properties were evaluated in standard- and fast-SCR conditions for stationary and mobile applications. The coexistence of low concentration of Ce 4+ species stabilized as CeO 2 with bulk CeVO 4 was found to be crucial for enhancing the intermediate formation of NO 2 from NO oxidation. Such cooperative effects impact on the rate of NO conversion to nitrogen regardless of the operating conditions. Aging processes under wet atmosphere at 500 °C and 600 °C did not destabilize the bulk zircon-type structure of CeVO 4 . No loss of vanadium was observed due to significant sublimation of vanadium. Despite poorer textural properties with regard to fresh CeVO 4 , aged CeVO 4 catalysts exhibit better catalytic properties in terms of rate of NO conversion and selectivity thus providing an alternative to less stable supported vanadia-based catalysts. Indeed, higher TOF values were measured in standard-SCR conditions at 200 °C on aged samples at 600 °C whereas an aging at 500 °C leads to selectivity enhancement at high temperature. All these changes can be rationalized based on the surface modifications of redox and acidic properties of vanadium species due to a slight extraction and stabilization of VO x species. [ABSTRACT FROM AUTHOR]