The role of surface properties of silicotungstic acid doped CeO2 for selective catalytic reduction of NOx by NH3: Effect of precipitant

• Silicotungstic acid located on the plane of CeO2 depended on the precipitans.
• Silicotungstic acid/CeO2 prepared by NH3·H2O exhibited the best SCR activity.
• Silicotungstic acid existed on the (1 1 1) plane of CeO2 contributed to surface acidity
• Medium Brönsted acid sites could improve the low-temperature SCR activity.

The present work elucidated the precipitants effect of pure CeO2 on the activity of silicotungstic acid supported on CeO2 catalysts toward NOx reduction. The results implied that the silicotungstic acid doped CeO2 prepared by the NH3·H2O precipitant showed the best SCR performance and nearly 100% NOx conversion was obtained at 225–450 °C. Silicotungstic acid doped CeO2 prepared by NH3·H2O (Cat-A) was enclosed by (1 1 1) and (2 2 0) planes; the catalyst with (NH4)2CO3 (Cat-B) predominantly exposed (2 2 0) and (2 0 0) surfaces, and the catalyst with the mixture of NH3·H2O and (NH4) 2CO3 (Cat-C) merely exhibited the (2 0 0) planes. Moreover, the aggregated WO3 was observed over the Cat-B and Cat-C, the BET surface areas and total pore volume of the two samples significantly decreased compared with Cat-A. Besides, the Brönsted (B) acid sites only appeared on the Cat-A catalyst and the intensity of Lewis acid was visibly stronger than that of Cat-B and Cat-C. Importantly, the Cat-A possessed its higher concentration of Ce3+ and surface chemisorbed oxygen Oα. As a result, the structure geometry and surface acidity were different on the (1 1 1) and (2 0 0) surfaces of CeO2, which were dependence on the different precipitants.

The CeO2 modified by silicotungstic acid with different precipitants were prepared and used for the NH3 selective catalytic reduction of NOx. The silicotungstic acid mainly located on the (1 1 1), (2 0 0) and (2 0 0) plane of CeO2 over 10SiW/CeO2 with different precipitants. The silicotungstic acid doped on the (1 1 1) plane of CeO2 was beneficial for the surface acidity (especially for medium Brönsted acid sites), resulting in the improvement of SCR activity.Figure optionsDownload high-quality image (160 K)Download as PowerPoint slide