COMBINED DESOX DENOX REACTIONS ON A COPPER ON ALUMINA SORBENT CATALYST .3. DENOX BEHAVIOR AS A FUNCTION OF THE SURFACE COVERAGE WITH SULFATE SPECIES

The catalytic behavior of the copper on alumina sorbent-catalyst in NO reduction with NH3/O2 during the simultaneous oxidation-adsorption Of SO2 Was studied in a series of consecutive cycles of reaction-regeneration and as a function of the surface coverage with sulfate species. The behavior of a CUO/SiO2 system with simultaneous DeSO(x)/DeNO(x) reaction is also reported. Tests of thermal desorption for the analysis of residual adsorbed species after reaction and thermogravimetric tests of ammonia adsorption also were carried out. Results indicate that (i) there is an initial competition between the adsorption of ammonia to form an ammonium bisulfate species and the reaction of NH3 with NO, (ii) ammonia adsorption continues up to a complete 1:1 reaction with the surface sulfate species, (iii) these competition and adsorption phenomena give rise to the presence of an induction time in reaching the steady-state catalytic behavior, with a negative influence on the efficiency in NO removal, and (iv) the sulfate species induces a decrease in the activity of the copper-based active phase, with a reduction in NO conversion, but especially an increase in the formation of unwanted N2O. Furthermore, desorption tests showed that (i) the presence of adsorbed ammonia induces a desorption Of SO2 when the catalyst temperature is increased from about 570 to 720K and (ii) adsorbed ammonia thermally desorbs at higher reaction temperatures as such or as products of further transformation, specifically N2.