An infrared and electrical conductance study of [formula omitted] catalysts active for the reduction of NO by NH 3

Abstract

A series of V 2O 5 SiO 2TiO 2 catalysts (vanadia content 2–30 wt%) was evaluated for the selective reduction of NO by NH 3. Activities at 200 °C determined on a per gram vanadia basis were nearly equal for catalysts containing 5–20% vanadia. The 10% catalyst exhibited the highest activity at 350 °C. Characterization of the catalysts with FTIR and XRD showed that the vanadia was highly dispersed on the carrier as an amorphous phase for all catalysts with 20% or less vanadia. Electrical conductance measurements were made to study the dispersion of the vanadia on the support and the effect of different gases on the degree of vanadia reduction. Conductances for the catalysts in 1.5% O 2 Ar carrier gas increased with increasing vanadia content for catalysts with 15% or more vanadia indicating a decreasing distance between V(IV) centers. Exposure of the catalysts to NH 3 in the carrier gas resulted in reversible increases in conductance for all vanadia concentrations. Exposure of the catalysts to NO resulted in reversible conductance increases for the 15, 20, and 30% catalysts. Exposure of the catalysts to NH 3 + NO resulted in conductance changes which indicated a reaction at 350 °C between adsorbed, laterally mobile NH 3 and gaseous NO for all catalysts with the most effective reaction occurring on the 10% catalyst. At 200 °C, the conductance measurements indicated a reaction between strongly bound NH 3, which exhibited little lateral movement, and gaseous NO.