NO and CO adsorption studies on transition metal-exchanged silico-aluminophosphate of type 34 catalysts Original Research Article

Adsorption of nitric oxide (NO) and carbon monoxide (CO) and the co-adsorption of (NO+CO) and (CO+NO) over the transition metal-exchanged SAPO-34 have been studied by infrared spectroscopy. Novel manganese-, cobalt-, and copper-exchanged silico-aluminophosphate of chabazite type catalysts were prepared and characterized using techniques such as elemental analysis, X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, and nitrogen sorption capacity (BET). Detailed FTIR studies were carried out on the disproportionation reaction of NO and the decomposition of CO over the Mn-, Co-, Cu-SAPO-34 catalysts. The IR spectra indicated the formation of various CO/NO species or complexes with active metal species. NO adsorption leads to band formation of at least four metal-NOx complexes. In the case of Mn-SAPO-34, the four strong bands are attributed to the chemisorbed NO2, metal (NO)2 (di-nitrosyl) and Mn(II)-NO2 species. The species Mn(II)-NO2 is most abundant, followed by the metal (NO)2 species. In the case of the Co-SAPO-34, the Co-(NO2) species seemed to be the most abundant followed by the Co-(NO2), and Co-(NO3). Effects of the pressure, temperature and evacuation on these NO/CO species have been studied. Investigations on the influence of presorbed CO molecule on the adsorption of NO molecules over the catalysts indicated that the preadsorption of CO molecules strongly affects the NO adsorption. The concentration of NO/CO species varies with the NO/CO pressure, reaction temperature and evacuation.