A series of CuO/Al2O3 catalyst−sorbents have been subjected to a large number of reaction−regeneration cycles and their physical and chemical properties compared before and after operation. The reaction phase of the cycle involved exposing the catalyst−sorbents to a mixture of SO2, NO, NH3, O2, and steam at 350 °C, during which time NO conversion was always greater than 90% and the SO2 was converted into CuSO4. The regeneration phase involved reduction of CuSO4 to copper metal by CH4 at 500 °C, followed by oxidation in air at 450 °C. In some tests the reaction or regeneration conditions were made more severe in an attempt to accelerate deactivation. The SO2 sorption capacity of one sample, which had been subjected to 1525 cycles, was reduced by about 25%, but generally there was no significant change in reactivity. Small changes in physicochemical properties are interpreted in terms of redispersion of the supported copper phase.

Some aspects of the industrial development of copper-on-alumina catalytic materials for the combined removal of SO2 (DeSOx and NOx (DeNOx) from flue gas of power plants are discussed. Applications of these catalytic materials for the recovery of sulfuric acid from diluted aqueous solutions of ammonium sulfate are also outlined. In particular, the following specific topics are analyzed: (i) the relationship between textural and reactivity properties. (ii) the problem of the design of samples with improved DeSOx properties in relation to the stability of the samples over extended operations, and (iii) the optimization of the regeneration characteristics of the samples. Details on the flow sheet of the technology are also given.

A study of the reductive regeneration of sulfated 4.3% CuO/Al 2 O 3 catalyst-sorbents suitable for the simultaneous removal of SO 2 and NO X from flue gases was carried out with various reductants. H 2 demonstrated a propensity to form CuS (ca. 20% CuS at 400°C) and subsequent formation of H 2 S above 550°C. Surface aluminum sulfate species are slowly reduced with H 2 to the sulfide at temperatures in excess of 450°C. Subsequently, H 2 S forms at higher temperatures, while bulk aluminum sulfate species were found to reduce in H 2 directly to Al 2 O 3 with the formation of H 2 S above 550°C. Although a much weaker reducing agent, regeneration with CH 4 leads to significantly less CuS formation and no H 2 S production. The formation of CuS, which was not reduced by CH 4 , occurred via the readsorption of product SO 2 gases on the catalyst-sorbent. Interestingly, no CuS was formed when water vapor was added to the CH 4 reductant gases and more SO 2 evolved in these conditions.

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