Promotional roles of ZrO2 and WO3 in V2O5-WO3/TiO2-ZrO2 catalysts for NOx reduction by NH3: Catalytic performance, morphology, and reaction mechanism

Abstract V 2 O 5 /TiO 2 -ZrO 2 catalysts containing various amounts of WO 3 were synthesized. The catalyst morphologies, catalytic performances, and reaction mechanisms in the selective catalytic reduction of NO x by NH 3 were investigated using in situ diffuse-reflectance infrared Fourier-transform spectroscopy, temperature-programmed reduction (TPR), X-ray diffraction, and the Brunauer-Emmett-Teller (BET) method. The BET surface area of the triple oxides increased with increasing ZrO 2 doping but gradually decreased with increasing WO 3 loading. Addition of sufficient WO 3 helped to stabilize the pore structure and the combination of WO 3 and ZrO 2 improved dispersion of all the metal oxides. The mechanisms of reactions using V 2 O 5 -9%WO 3 /TiO 2 -ZrO 2 and V 2 O 5 -9%WO 3 /TiO 2 were compared by using either a single or mixed gas feed and various pretreatments. The results suggest that both reactions followed the Eley-Ridel mechanism; however, the dominant acid sites, which depended on the addition of WO 3 or ZrO 2 , determined the pathways for NO x reduction, and involved [NH 4 + –NO–Bronsted acid site] * and [NH 2 –NO–Lewis acid site] * intermediates, respectively. NH 3 -TPR and H 2 -TPR showed that the metal oxides in the catalysts were not reduced by NH 3 and O 2 did not reoxidize the catalyst surfaces but participated in the formation of H 2 O and NO 2 .