Composite Cu-SSZ-13 and CeO2-SnO2 for enhanced NH3-SCR resistance towards hydrocarbon deactivation

The state-of-the-art Cu-SSZ-13 was mixed with CeO2-SnO2 to form a Composite catalyst which was resistant towards hydrocarbon poisoning of the NH3-mediated NOx-SCR reaction. The Composite was prepared via a solid-state synthesis through ball milling, which did not influence the final morphology. The resistance towards propylene poisoning was remarkably enhanced as the NOx conversion over the Composite catalyst decreased only 9% compared to 40 % over the unmodified Cu-SSZ-13. Transient and dynamic reactivity studies showed that the coke formed during the C3H6 protolytic polymerization was dispersed inside the zeolite pores and the addition of CeO2-SnO2 did not prevent its formation nor enhance its oxidation with O2. The ion-exchanged Cu was the principal active component for the coke and hydrocarbon oxidation and the hydrocarbon poisoning prevention was attributed to the complex interaction between the three primary active sites (Cu – CeO2-SnO2 – protonic sites). Propylene oxidation over Cu-SSZ-13 was inhibited when NO was included in the reaction stream, while over the H-Composite (mixture of H-SSZ-13 and CeO2-SnO2) it had the reverse effect, since C3H6 and NOx oxidation did not compete for the same active sites on CeO2-SnO2. Basing on reactivity studies coupled with IR analysis, a deactivation and poisoning prevention mechanism was proposed, whereby the HONO/nitrate intermediates formed over the CeO2-SnO2 catalyst re-activated the zeolitic copper for the SCR reaction.