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.

Automated summary

Manganese-based catalysts, when doped with sodium and combined with platinum and cobalt, exhibit excellent resistance to sulfur dioxide in propane oxidation reactions, while maintaining high catalytic activity. The doping with sodium enhances the catalyst's tolerance to SO2, but inhibits its overall catalytic activity. The Pt1Co1/meso-NaxMnOy catalyst, which consists of well-dispersed Pt and Co atoms on the mesoporous sodium-doped manganese oxide, shows the highest catalytic activity among all the studied samples.