WO 3 and Cr–WO 3 powders were prepared by sol–gel process, with Cr: W atomic concentration ranging from 2% to 8.8%. WCl 6 was used as W precursor and reacted with methanol in presence of acetyacetone as stabilizer. The required amount of Cr 2-ethylhexanoate was then added to the resulting solution, which was subsequently dried. The resulting powder was heat-treated at temperatures ranging from 200 to 700 C. With increasing the Cr concentration, the samples heat-treated at 500 C contained an …