Mesoporous NaxMnOy-Supported Platinum-Cobalt Bimetallic Single-Atom Catalysts with Good Sulfur Dioxide Tolerance in Propane Oxidation

Manganese-based catalysts show a tremendous potential in propane oxidation due to their low cost and good catalytic activity but are easily deactivated by SO2. In this work, we first synthesized the mesoporous sodium-doped manganese oxide (meso-NaxMnOy) using the mesoporous silica (KIT-6) as a template after washing with a concentrated NaOH aqueous solution and then prepared the platinum-cobalt bimetallic singleatom (Pt1Co1/meso-NaxMnOy) catalyst using the polyvinyl pyrrolidone-protecting one-pot strategy. It was found that the doping of 13.8 wt % Na dramatically enhanced the SO2 tolerance of meso-NaxMnOy but inhibited its catalytic activity due to the alkali metal poisoning. Among all of the samples for the oxidation of propane, Pt1Co1/meso-NaxMnOy showed the highest catalytic activity (a propane conversion of 90% was obtained at 282 degrees C and a space velocity of 30 000 mL g-1 h-1, and apparent activation energy, specific reaction rate, and turnover frequency at 250 degrees C were 76.0 kJ mol-1, 78.9 x 10-5 mol gPt-1 h-1, and 193.7 x 10-3 s-1, respectively), which was associated with the Pt and Co double active sites with good dispersion, abundant electron deficiency, outstanding lattice oxygen mobility, good low-temperature reducibility, and large capacity and weak strength of propane adsorption. More importantly, the Pt1Co1/meso-NaxMnOy sample possessed the excellent resistance to sulfur dioxide. Propane oxidation occurred via different reaction routes over the MnO2, meso-NaxMnOy, and Pt1Co1/meso-NaxMnOy samples, with the Langmuir- Hinshelwood mechanism being dominated. Propane oxidation over Pt1Co1/meso-NaxMnOy might follow a pathway of propane -> acetone and isopropoxide -> carboxylate and fatty ether -> CO2 and H2O. Pt and/or Co single atoms are highly dispersed on mesoNaxMnOy. SO2 is preferentially adsorbed at the Na site in Pt1Co1/meso-NaxMnOy, which protects the active Mn, Pt, and Co from being poisoned by SO2, hence making Pt1Co1/meso-NaxMnOy show good SO2 resistance in propane oxidation.