Ammonia removal in selective catalytic oxidation: Influence of catalyst structure on the nitrogen selectivity
Chengxiong Wang1, Dezhi Ren1, Gavin Harle2
1State Key Laboratory of Advanced Technologies for Comprehensive Utilization of Platinum Metals, Kunming Institute of Precious Metals, Kunming 650106, China; State-Local Joint Engineering Laboratory of Precious Metal Catalytic Technology and Application, Kunming Sino-platinum Metals Catalysts Co. Ltd., Kunming 650106, China.
Abstract:
Selective catalytic oxidation is regarded as an effective and favored method for the removal of hazardous ammonia. A number of M-Pt/USY (M=Mn, Fe, Ce and Pr) catalysts were prepared and the resulting materials were characterized using N2 adsorption/desorption, XRD, TEM, NH3-TPD, XPS and H2-TPR. It was found that the addition of non-stoichiometric metal oxides to Pt/USY leads to the generation of additional acid sites for ammonia chemisorption and that N2 selectivity improved with increased strong acidity of the bi-functional catalysts. The oxidation state of active Pt could be adjusted by the introduction of non-stoichiometric metal oxides with increased concentrations of oxidized Ptδ+ species observed in the order of FeOx >CeO2-x >MnO2-x >Pr6O11. High valence platinum surrounded by atomic oxygen that can act as a proton scavenger to drive ammonia activation, inhibiting O2 dissociation and therefore improve N2 selectivity. Fe-containing USY zeolite is demonstrated to be a preferred catalyst for the removal of ammonia, due to its high N2 selectivity and good hydrothermal stability.
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