Direct Cu2+ ion-exchanged into as-synthesized SAPO-34 and its catalytic application in the selective catalytic reduction of NO with NH3

Abstract

A facile and direct ion-exchange (DIE) method has been developed to prepare Cu-exchanged SAPO-34s, in which as-synthesized SAPO-34 is used as a precursor. This approach is simple and economical as compared with the conventional multistep ion exchange procedure. The ion exchange behavior of the as-synthesized SAPO-34s is found to be template-dependent. For SAPO-34s templated by smaller amines, they show a better Cu exchange ability than the corresponding NH₄⁺-SAPO-34 and the Cu loadings rise with the increasing template size. Coordination between amine and Cu²⁺ in the as-prepared DIE sample is clearly evidenced. However, oversized amine in the CHA cage may cause a failure of the DIE process due to the steric effect. An obvious surface Cu enrichment is observed for the as-prepared DIE sample, which migrates to the interior of the crystals upon calcination. The Cu-SAPO-34 catalyst prepared by DIE method displays excellent performance in the selective catalytic reduction of NO with NH₃ (NH₃-SCR). Its better low-temperature activity as compared with that of the conventional one is likely due to the higher isolated Cu²⁺ amount and surface Cu content. This promising strategy is expected to facilitate the large-scale industrial preparation of NH₃-SCR catalyst.