Selective oxidation of gas phase ammonia over copper chromites catalysts prepared by the sol–gel process

Abstract

Abstract Selective gas phase oxidation of ammonia at atmospheric pressure was studied over a series of undoped and doped (Mn, Ag) copper chromites prepared by sol–gel process (SG). The catalysts were characterized by elemental analysis, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and by adsorption microcalorimetry (AMC). A comparative study was made with a commercial copper chromite catalyst. The surface of the sol–gel undoped catalyst was found to be enriched in high valence chromium species with respect to the commercial one (Cr6+/Cr3+ = 0.56 versus 0.39 for commercial catalyst). From XPS, the Cu2+/(Cu° + Cu+) ratio was the same (ca. 5) in both catalysts but the sol–gel sample, contained twice more surface copper species (8.3 at.%) than the commercial one (17.6 at.%). Ammonia AMC experiments showed both a higher ammonia uptake and a wider strength distribution of adsorption sites on the sol–gel-prepared sample than on the commercial one. Improved catalytic performance in selective oxidation of ammonia at low temperature was obtained by simultaneous addition of silver and manganese to the sol–gel-prepared copper chromite.