Influence of attrition milling on V/Ti catalysts for the selective oxidation of ammonia

Abstract

Mechanochemical treatments can change the physicochemical characteristics of catalysts. Attrition milling was utilized in the preparation of catalysts from V2O5 and anatase TiO2, and the catalysts were applied for the study of selective catalytic oxidation (SCO). Catalysts comprising 2wt% V/Ti were prepared by mechanochemical methods using different milling times, and these catalysts were used for the SCO of NH3 to N2. The optimal calcination milling time was 3h. The 2wt% V/Ti catalyst prepared by attrition milling for 3h (VTi-A.M3; where A.M in the catalyst name denotes attrition milling, and 3 is the milling time applied) gave rise to the highest N2 yield (∼82%) at 250°C. The dry attrition milling method is a dry method for the synthesis of the SCO catalyst, involving a combination of V2O5 and TiO2 powder. The properties of the catalyst were studied using physiochemical analyses, including BET surface area, X-ray diffraction (XRD), transmission electron microscopy (TEM), NH3 temperature programmed desorption (NH3-TPD), X-ray photoelectron spectroscopy (XPS), and H2 temperature programmed reduction (H2-TPR). Anatase, which is a metastable phase, underwent transformation into TiO2(II) due to the milling effect. The highest N2 yield was achieved when the TiO2 crystallite size of the catalyst was 16nm. The content of pentavalent vanadium species increased due to the milling effect. A correlation was identified between the V5+ species and the catalyst N2 yield. VTi-A.M3 was found to lead to high-level selective catalytic oxidation of NH3, with active internal selective catalytic reduction (SCR) because of the presence of highly dispersed V5+ on the catalyst surface. The dry attrition milling method can be used to control the dispersion of vanadium on the catalyst surface, which can in turn improve the N2 yield activity by increasing the ratio of V5+ species.