Research PaperNew insight into Cu/SAPO-34 preparation procedure: Impact of NH4-SAPO-34 on the structure and Cu distribution in Cu-SAPO-34 NH3-SCR catalysts

•The gas phase ion exchange synthesis was firstly utilized to prepare Cu-SAPO-34.•Traditional liquid NH4+ exchange could be substituted by gas phase exchange way.•NH4+ adsorption on Brønsted acid sites benefited x-Cu-SAPO integrity.•More adsorbed NH3 on precursors boosted more isolated Cu2+ and higher CuO/Cu2+.•The polydentate NH4+ in precursors promoted CuO formation.

Cu/SAPO-34 is a promising NH3-SCR catalyst and its precise preparations involving ammonia exchange, copper loading and copper distribution are still the challenges in exchange procedure of SAPO-34 support. In the present work, a new series of x-NH4-SAPO samples prepared by controlling NH3 adsorption temperature (x standed for NH3 adsorption temperature) were used to examine their impacts on the following Cu exchange compared with NH4-SAPO-34 by traditional liquid exchange. The TPD and DRIFTS experiments revealed that the NH4+ amounts on x-NH4-SAPO samples increased with the NH3 adsorption temperature decreasing. And 200-NH4-SAPO prepared by gas NH3 adsorption (GA) under 200 °C contained the similar NH4+ loading with L-NH4-SAPO prepared by the liquid ion exchange (LIE) method, but they presented different coordinations between NH4+ species and Si(OH)Al. After copper exchange, the H2-TPR and EPR results unveiled monodentate NH4+ on Si(OH)Al structure would facilitate isolated Cu2+ generation in Cu/SAPO-34, while the polydentate NH4+ would promote CuO formation via liquid Cu ion exchange. Therefore, it was found that the isolated Cu2+ content in 200-Cu-SAPO was lower than L-Cu-SAPO even under the same copper exchange condition for different NH4+ coordinations. In addition, the ex-situ IR and NMR results demonstrated that the SiOAl bonds without NH4+ protections unveiled bond breakage during the liquid Cu exchange. Finally, our study proposed NH4+ exchange mechanism on Brønsted acid sites in NH4-SAPO-34 and indicated their influences on the copper distribution and the support integrity for x-Cu-SAPO catalysts.

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