On the Redox Mechanism of Low-Temperature NH3 -SCR over Cu-CHA: A Combined Experimental and Theoretical Study of the Reduction Half Cycle.

Cu-CHA is the state-of-the-art catalyst for the Selective Catalytic Reduction (SCR) of NOx in vehicle applications. Although extensively studied, diverse mechanistic proposals still stand in terms of the nature of active Cu-ions and reaction pathways in SCR working conditions. Herein we address the redox mechanism underlying Low-Temperature (LT) SCR on Cu-CHA by an integration of chemical-trapping techniques, transient-response methods, operando UV/Vis-NIR spectroscopy with modelling tools based on transient kinetic analysis and density functional theory calculations. We show that the rates of the Reduction Half-Cycle (RHC) of LT-SCR display a quadratic dependence on CuII , thus questioning mechanisms based on isolated CuII -ions. We propose, instead, a CuII -pair mediated LT-RHC pathway, in which NO oxidative activation to mobile nitrite-precursor intermediates accounts for CuII reduction. These results highlight the role of dinuclear Cu complexes not only in the oxidation part of LT-SCR, but also in the RHC reaction cascade.

Nitrogen-Doped Carbon-Assisted One-pot Tandem Reaction for Vinyl Chloride Production via Ethylene Oxychlorination.

A bifunctional catalyst comprising CuCl2 /Al2 O3 and nitrogen-doped carbon was developed for an efficient one-pot ethylene oxychlorination process to produce vinyl chloride monomer (VCM) up to 76 % yield at 250 °C and under ambient pressure, which is higher than the conventional industrial two-step process (≈50 %) in a single pass. In the second bed, active sites containing N-functional groups on the metal-free N-doped carbon catalyzed both ethylene oxychlorination and ethylene dichloride (EDC) dehydrochlorination under the mild conditions. Benefitting from the bifunctionality of the N-doped carbon, VCM formation was intensified by the surface Cl*-looping of EDC dehydrochlorination and ethylene oxychlorination. Both reactions were enhanced by in situ consumption of surface Cl* by oxychlorination, in which Cl* was generated by EDC dehydrochlorination. This work offers a promising alternative pathway to VCM production via ethylene oxychlorination at mild conditions through a single pass reactor.