Green synthesis of Tungsten-doped CeO2 catalyst for selective catalytic reduction of NOx with NH3 using starch bio-template

Abstract

Herein, a novel tungsten-doped CeO2 catalyst was fabricated via the spread self-combustion (SSC) method using sweet potato starch as bio-template. The doping of tungsten refines the pore diameter of CeO2 and restrains the growth of cubic CeO2 crystal formed in it. However, the annealing at 700 °C promotes the growth of cubic CeO2 crystal and the formation of Ce4W9O33 crystal instead of the amorphous tungsten species compared with the catalyst calcined at 550 °C. It is also found that the doping of tungsten increases the concentration of the adsorbed oxygen on the surface of CeO2-550 and enhances the reducibility of the surface oxygen of stoichiometric ceria and the acid sites. The as-prepared Ce4W2Oz-550 catalyst exhibits higher catalytic performance than Ce4W2Oz-CP-550 synthesized via the urea hydrothermal co-precipitation method due to the better dispersion of cerium species and the larger molar ratio of Oα/(Oα + Oβ). However, the enhancement of annealing temperature from 550 °C to 700 °C decreases the acidic and the redox properties of Ce4W2Oz, and thereby depresses the promotional effect of tungsten-doped on the NH3-SCR activity of CeO2-550. The suitable starch dosage (liquid/solid ratio), ion concentration, alkali titration and annealing temperature are 1 g (10 mL/g), 1 mol/L, ammonia water (pH ≈ 7.0) and 400–550 °C for the as-prepared Ce4W2Oz catalyst, respectively.