Abstract
Propylene epoxidation with O2 to propylene oxide is a very valuable reaction but remains as a long-standing challenge due to unavailable efficient catalysts with high selectivity. Herein, we successfully explore 27 nm-sized cubic Cu2O nanocrystals enclosed with {100} faces and {110} edges as a highly selective catalyst for propylene epoxidation with O2, which acquires propylene oxide selectivity of more than 80% at 90–110 °C. Propylene epoxidation with weakly-adsorbed O2 species at the {110} edge sites exhibits a low barrier and is the dominant reaction occurring at low reaction temperatures, leading to the high propylene oxide selectivity. Such a weakly-adsorbed O2 species is not stable at high reaction temperatures, and the surface lattice oxygen species becomes the active oxygen species to participate in propylene epoxidation to propylene oxide and propylene partial oxidation to acrolein at the {110} edge sites and propylene combustion to CO2 at the {100} face sites, which all exhibit high barriers and result in decreased propylene oxide selectivity.
Highlights
Propylene epoxidation with O2 to propylene oxide is a very valuable reaction but remains as a long-standing challenge due to unavailable efficient catalysts with high selectivity
We found that the densities of {110} edges are high on Cu2O cubes finer than 100 nm and the {110} edge sites on these fine c-Cu2O NCs, rather than the {100} face sites, are the dominant active site catalyzing the CO oxidation reaction[24]
Surface sites of various Cu2O NCs were probed by CO adsorption at 123 K with in-situ Diffuse reflectance infrared spectroscopy (DRIFTS) (Supplementary Fig. 4)
Summary
Propylene epoxidation with O2 to propylene oxide is a very valuable reaction but remains as a long-standing challenge due to unavailable efficient catalysts with high selectivity. We successfully explore 27 nm-sized cubic Cu2O nanocrystals enclosed with {100} faces and {110} edges as a highly selective catalyst for propylene epoxidation with O2, which acquires propylene oxide selectivity of more than 80% at 90–110 °C. Among various alternative technologies[4,5,6,7], propylene epoxidation with O2 to PO is considered most economic and environment-friendly It is one of the most challenging catalytic reactions due to unavailable efficient catalysts with high selectivity[8,9,10,11,12]. We report a successful exploration of fine cubic Cu2O nanocrystals (NCs) enclosed with {100} faces and {110} edges as a highly selective catalyst for propylene epoxidation with O2 to PO, guided by an experimental fundamental understanding of the active site. The reaction mechanism for PO production at the Cu2O{110} active site was found to switch from weakly adsorbed O2-participating Langmuir–Hinshelwood (LH) mechanism at low temperatures to surface lattice oxygen-participating Mars-van Krevelen (MvK) mechanism at high temperatures
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