Ligation of Single-Site Ruthenium within Perovskite Oxides for Efficient Conversion of Thermodynamically Stable Molecules

Ru cation ligation in SrTiO3 perovskite and their migration to the surface through exsolution are investigated for the dry reforming of methane (DRM), a chemistry that requires activation of two thermodynamically stable molecules, CH4 and CO2. Compared to a supported 1 wt % Ru/SrTiO3 benchmark, doped and exsolved Ru-SrTiO3 demonstrate ≥3× higher CH4 turnover rates (873 K), with isolated, ligated Ru exhibiting higher reactivity. Reactor studies assert that CH4 and CO2 activation are both kinetically relevant for CH4 turnover rates on exsolved Ru-SrTiO3, unlike for supported Ru systems, where H-abstraction from CH4 is the sole kinetically relevant step. As such, exsolved and doped Ru architectures are responsive toward co-reactant activation strategies, with their consequent reaction networks showing marked departures from those established for supported Ru catalysts. In situ spectroscopy and kinetic analyses propose distinct sensitivity toward CO2 on Ru-SrTiO3 systems, where higher CH4 turnover rates result from O-assisted C─H bond activation pathways. These pathways occur on paired Ru-oxygen vacancy sites that are inherent to the perovskite structure and are not readily accessible on supported Ru catalysts. Here, CO2 is activated on oxygen vacancies directly adjacent to Ru active sites, which facilitates CH4 C─H bond activation through a surface methoxy intermediate. The high reactivity of Ru-SrTiO3 systems enables stable CH4 turnover rates at milder reaction temperatures (673 K), conditions under which the supported counterpart, Ru/SrTiO3, is inactive. Overall, this work demonstrates that ligation of catalytically active cations in perovskite oxides facilitates site engineering toward atom-efficient activation of thermodynamically stable feedstocks.