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

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.

Copper chromites catalysts have been prepared by the sol–gel process. Their catalytic activity is superior to that of the corresponding commercial catalysts. The simultaneous addition of silver and manganese to the reference catalyst has profound influence both on ammonia conversion and selectivity to nitrogen.Figure optionsDownload as PowerPoint slideHighlights
► Generation of acid sites in copper chromites by using Sol Gel process.
► Enrichment of catalysts surface with high valence chromium species (Cr6+).
► Crucial role of catalysts phase composition on NH3 conversion and N2 selectivity.