Selective propane dehydrogenation with single-site Co^II on SiO₂ by a non-redox mechanism

We report the synthesis, characterization, and catalytic performance for gas phase propane dehydrogenation of single-site Co²⁺ ions supported on silica. Spectroscopic characterization by resonance Raman, electron paramagnetic resonance, and X-ray near-edge and extended absorption fine structure revealed that tetrahedrally coordinated Co²⁺ ions are chemisorbed into the trisiloxane rings on the surface of amorphous silica. In situ XAS shows that Co is not oxidized by air nor reduced by hydrogen even at 650 °C. For catalytic propane dehydrogenation, single-site Co²⁺/SiO₂ exhibits selectivities >95% at 550 °C and >90% at 650 °C with stable activity over 24 h. Calculations with hybrid density functional theory support a non-redox mechanism for activation of C-H and H-H bonds by Co²⁺ similar to that previously reported for single-site Zn²⁺/SiO₂.