Single-Atom Manganese-Based Catalysts for the Oxidative Dehydrogenation of Propane

Combinatorial screening of 150 supported metal oxide (manganese and additives) catalysts was carried out via a high-throughput synthesis platform and parallel reactors for the oxidative dehydrogenation (ODH) of propane to propylene. Specifically, an organomanganese (0.05–2.5 Mn atoms/nm2) complex was grafted on metal oxide supports (Al2O3, SiO2, TiO2, and ZrO2) premodified with either Lewis acid (Al, Ti, Zn, and Zr) or redox-active (Cu, Cr, Ga Ni, V) additives at various surface coverages (25, 50, and 75%). Catalysts were characterized by high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Raman spectroscopy, and UV–vis spectroscopy. Catalysts 0.05 Mn/V(50%)/Al2O3 and 0.05 Mn/Ni(50%)/ZrO2 showed the highest combined propane conversion and propylene selectivities (31/41% and 15/85%), with excellent stability at 500 °C for 25 h. The presence of Ni in Mn/Ni/ZrO2 resulted in a 6-fold increase in turnover frequency (TOF) over the Mn/ZrO2. HRTEM identified single Mn atoms after 500 °C heat treatment. For the Mn/Ni/ZrO2 system, Mn was incorporated into the support lattice due to the similar ionic radius of Mn2+ and Zr4+, which was also enhanced by the presence of Ni. For the Mn/V/Al2O3 system, highly active MnO was prevalent as observed by Raman. Both V and Mn contributed to an increase in mutual dispersion, but both species remained on the surface. It is proposed that the highly dispersed atom and interactions between Mn with either Ni or V are responsible for the ODH performance and stability.