Uncovering CO2-driven selective oxidation of HCN to N2 over Pt/Al2O3 during the gasification-regeneration of FCC catalysts

Hydrogen cyanide (HCN) is a hazardous nitrogenous pollutant formed during fluid catalytic cracking (FCC) catalyst regeneration, yet its mitigation under oxygen-lean, CO 2 -rich regeneration environments remains poorly understood. Here, we demonstrate for the first time that Pt/Al 2 O 3 catalysts enable a deep oxidation of HCN to N 2 by CO 2 , a pathway fundamentally distinct from O 2 -assisted HCN oxidation that leads to the formation of the secondary pollutant, NO x . Using industrial spent FCC catalysts as a case study, Pt/Al 2 O 3 was found to simultaneously promote the CO 2 -gasification of coke and reduce HCN emissions, overcoming the intrinsically slow kinetics of CO 2 -mediated HCN oxidation. Furthermore, through the implementation of a two-stage CO 2 and O 2 regeneration strategy, the emission of HCN was completely suppressed and the total NO emissions were reduced by ~76-92% compared with conventional air-fired regeneration, while preserving the physicochemical integrity of the regenerated catalyst. HCN oxidation experiments, XAS characterization, and DFT free-energy calculations together reveal that metallic Pt sites mediate a Langmuir-Hinshelwood mechanism in which HCN undergoes dissociative adsorption to form adsorbed H and CN species, followed by thermodynamically favorable coupling of CN* with weakly adsorbed CO 2 to form NCO* and CO. Subsequently, NCO* decomposes to N*, which recombines to yield N 2 . This work reveals a previously unrecognized catalytic function of Pt/Al 2 O 3 that enables simultaneous control of HCN and NO x emissions in a low-carbon FCC regeneration strategy.