The Promoting Effect of Mg on Propane Dehydrogenation over Co/Silicalite-1 Catalysts

Non-oxidative dehydrogenation of propane (PDH) is a well-established large-scale route for on-purpose propene production. Cobalt-based catalysts have attracted increasing attention due to their attractive performance as environmentally friendly and cost-efficient alternatives to commercially used catalysts containing chromium or platinum. However, their further development to reach an industrially attractive level is hindered by insufficient knowledge of the structure-activity-selectivity relationships for tailored catalyst design and preparation. In this work, magnesium (Mg) is introduced as a promoter to regulate the local structure of CoOx species on the surface of silicalite-1. Owing to the formation of Co−O−Mg bond(s) in the presence of the promoter, the formed CoOx species become isolated, less reducible, and less acidic. These changes are key to catalyst activity and propene selectivity. The promoter effectively decreases the amount of strong acidic sites, thereby facilitating propene desorption and accordingly suppressing undesired cracking and deep dehydrogenation reactions involving adsorbed propene. The optimized catalyst outperforms an analogue of commercial K-CrOx/Al2O3 and demonstrates durability in a series of five PDH/regeneration cycles under industrially relevant conditions. The space-time yield of propene formation reached 1.2 kgC3H6·kgcat−1·h−1 at 550 °C and 68% of the equilibrium propane conversion, being higher in comparison to that of most previously reported cobalt-based catalysts under comparable conditions. In view of this result, the structural and mechanistic knowledge obtained on the promoter effect can be used to prepare highly efficient PDH catalysts with supported metal-oxide species, including those beyond CoOx.