New 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

Abstract Cu/SAPO-34 is a promising NH 3 -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-NH 4 -SAPO samples prepared by controlling NH 3 adsorption temperature (x standed for NH 3 adsorption temperature) were used to examine their impacts on the following Cu exchange compared with NH 4 -SAPO-34 by traditional liquid exchange. The TPD and DRIFTS experiments revealed that the NH 4 + amounts on x-NH 4 -SAPO samples increased with the NH 3 adsorption temperature decreasing. And 200-NH 4 -SAPO prepared by gas NH 3 adsorption (GA) under 200 °C contained the similar NH 4 + loading with L-NH 4 -SAPO prepared by the liquid ion exchange (LIE) method, but they presented different coordinations between NH 4 + species and Si (OH) Al. After copper exchange, the H 2 -TPR and EPR results unveiled monodentate NH 4 + on Si (OH) Al structure would facilitate isolated Cu 2+ generation in Cu/SAPO-34, while the polydentate NH 4 + would promote CuO formation via liquid Cu ion exchange. Therefore, it was found that the isolated Cu 2+ content in 200-Cu-SAPO was lower than L-Cu-SAPO even under the same copper exchange condition for different NH 4 + coordinations. In addition, the ex-situ IR and NMR results demonstrated that the Si O Al bonds without NH 4 + protections unveiled bond breakage during the liquid Cu exchange. Finally, our study proposed NH 4 + exchange mechanism on Bronsted acid sites in NH 4 -SAPO-34 and indicated their influences on the copper distribution and the support integrity for x-Cu-SAPO catalysts.