Reductive regeneration of sulfated CuO/Al2O3 catalyst-sorbent in ammonia

Reductive regeneration of a sulfated CuO/Al2O3 catalyst-sorbent suitable for simultaneous SO2 and NOx removal from flue gases was carried out in 5 vol.% NH3/Ar. Effect of regeneration temperature on SO2 removal activity of the regenerated catalyst-sorbent was investigated. Chemical morphology and physical structure of the catalyst-sorbent before and after the regeneration were characterized using elemental analysis, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and physical absorption. The results show that copper sulfate, the main copper species in the sulfated catalyst-sorbent, can be effectively regenerated at 350–450 °C. Aluminum sulfate, resulted from the reaction between Al2O3 and SO2 in flue gas, is unreductable under the conditions, which leads to reduced SO2 removal activity of the regenerated catalyst-sorbent compared to the fresh catalyst-sorbent. The main copper species after the regeneration at 400 °C is Cu3N. The nonexistance of copper sulfide suggests that over-reduction occurring in H2 is avoided in NH3. BET surface area and pore size distribution of the regenerated catalyst-sorbent are almost the same as that of the fresh one when the reduction temperature is 400 °C or higher. Besides as a reductant, ammonia also reacts with SO2 formed in the regeneration to form hydroxyamine sulfate at the outlet of the reactor.