Water-Enabled Conversion of NO and CO to NH3 over CuO x Clusters via Hydrolysis of Surface –NCO Intermediates

Abstract

Abstract The catalytic conversion of gaseous NO to NH3 offers a promising dual-benefit strategy for environmental remediation and sustainable chemical synthesis. Herein, CuO/Al2O3 catalysts with varied CuO loadings (x wt %, xCu/Al) were developed for the possible NH3 production from NO reduction by CO with the assistance of H2O. While increasing CuO loading (1–12 wt %) monotonically improved NO conversion to N2 under dry conditions, the introduction of H2O dramatically boosted NO conversion on 5Cu/Al with highly dispersed CuOx clusters, raising its NO conversion comparable to that of 12Cu/Al. Further analysis revealed that NH3 was generated on xCu/Al catalysts under wet conditions, with NH3 generation on 5Cu/Al initiating at the lowest temperature (275 °C) and being the most vigorous. Combined experimental and theoretical analysis suggested that, on CuOx clusters, H2O facilitated the conversion of the NCO* intermediate to NH3 with a much lower activation barrier compared to its CO-mediated pathway to N2, well explaining the boosted NO conversion and NH3 yield on the 5Cu/Al catalyst upon H2O addition to NO + CO flow. This work highlights that a simple, earth-abundant Cu catalyst enabled the efficient and cost-effective synthesis of NH3 from air pollutants of NO and CO under mild conditions, underscoring a sustainable strategy that simultaneously addresses pollution abatement and resource recovery.