Selective Catalytic Reduction of NOx with Ammonia over Copper Ion Exchanged SAPO-47 Zeolites in a Wide Temperature Range

Copper-exchanged H-SAPO-47 zeolites were synthesized by an aqueous solution ion exchange method and applied in the selective catalytic reduction of NO with NH3 (SCR). The microporous chabazite (CHA) structure of the catalysts was characterized and confirmed using synchrotron X-ray diffraction and nitrogen adsorption-desorption experiments. The synthesized Cu-x-SAPO-47 catalysts exhibited excellent SCR activity and nearly 100% N-2 selectivity in a wide temperature range. The Cu-0.1-SAPO-47 sample exhibited higher activity than the other samples below 250 degrees C. The weak Lewis acid sites originating from the introduction of Cu2+ were more active than the BrOnsted acid sites of the zeolites framework at low temperature. Two types of isolated Cu2+ species with different coordination surroundings were found, namely, Cu2+ cations bonded with the six-membered rings and those bonded in the CHA cages. The former species exhibited good stability and activity at high temperature, whereas the latter ones were more active at low temperature. The Cu-0.1-SAPO-47 catalyst provided a considerable amount of isolated Cu2+ bonded in the CHA cages. These results indicated that active Lewis acid sites and isolated Cu2+ species are responsible for their excellent SCR activity.