The Nature of Active Sites of Co/Al2O3 for the Selective Catalytic Reduction of NO with C2H4

Abstract

The effects of Co loading and calcination temperatures on the catalytic activity of Co/Al 2 O 3 for selective catalytic reduction (SCR) of NO with ethylene in excess oxygen were investigated. Co/Al 2 O 3 showed high and low activities when calcined at high (800°C) and low (350°C) temperatures, respectively. The formation and dispersion of cobalt species for catalysts calcined at 350 and 800°C as well as for Al 2 O 3 were studied by XRD, UV-vis and FTIR spectra. Combined with DRIFTS results of ad-species and reaction experiments, it allowed us to correlate the catalytic activity with active sites of Co/Al 2 O 3 , and the catalytic functions of active cobalt species and support were clarified. Co 3 O 4 species contributed to the oxidation of NO to various nitrates and of C 2 H 4 to reactive formate species, even in the absence of O 2 , whereas the side reaction of ethylene combustion occurred simultaneously when excess oxygen was present. Tetrahedral Co 2? ions in CoAl 2 O 4 , which acted as the active sites, were responsible for the reaction between formate and nitrate species to form organic nitro compound.