Preparation Of Carbon-based Single Atom Catalysts Supported Pt Nanoparticles And Their Application In Aerobic Oxidation Of Glycerol

The valorization of glycerol,a byproduct of biodiesel production,is crucial to reducing the cost of biodiesel production and to utilizing biomass resources.Selective oxidation of glycerol is an important way to produce value-added chemicals.Glyceric acid(glyceric acid,GA),the product of oxidation of the primary hydroxyl group in glycerol,is a commonly used food additive.1,3-dihydroxyacetone(1,3-dioxyacetone,DHA),produced by the oxidation of the secondary hydroxyl group in glycerol,can be used as pharmaceutical intermediates and cosmetic additives.So far,the highly selective production of these chemicals from glycerol is still economically and scientifically challenging.Platinum nanoparticles supported on carbon materials are efficient catalysts for the oxidation of glycerol.However,it suffers from the deactivation by the acidic products of glycerol oxidation——GA.Meanwhile,it is highly challenging to selectively oxidize the secondary hydroxyl over carbon-supported Pt catalysts.In this study,we innovatively combined single atom catalysts(SACs)with Pt nanoparticles,by supporting Pt nanoparticles on carbon-based SACs.By doing so,the activity and selectivity of Pt catalysts for the oxidation of glycerol can be enhanced.To improve the catalytic activity,the Pt nanoparticles were loaded on carbon nanotubes containing MN_x SACs active sites(MNC@CNT,M=Fe,Co,Ni).The catalyst was applied to the oxidation of glycerol under alkali-free conditions.Multiple characterization results showed that the doping of MN_x increased the dispersion of Pt nanoparticles and doubles the TOF.Furthermore,through the kinetics study,it was proposed that the improvement of the activity of Pt catalyst came from the synergistic effect of Pt nanoparticles and Co NC@CNT on oxygen activation,rather than the metal-support interaction.Although the oxidation of primary hydroxyl is dominant,the synergistic effect also improves the ratio of primary hydroxyl oxidation product to secondary hydroxyl oxidation product.Further research was devoted to improving the selectivity of glycerol secondary hydroxyl oxidation to DHA by introducing Bi SACs.A method coupling defluorination and doping Bi was proposed,which employed fluorinated carbon nanotubes(FCNTs)as support and metallic Bi powders as Bi source.At high temperatures,the defluorination of FCNTs creates defects where the molten Bi is in-situ anchored to synthesize atomic dispersed Bi species.Pt nanoparticles were further loaded on the Bi SACs.The existence of the interface between Pt particles and Bi-containing support increased the selectivity of DHA by 3 times.Through the hydrophilic modification of the catalyst,the accessibility of the reaction substrate to the Pt-Bi interface was improved,the catalytic activity and selectivity were further improved.In order to simplify the preparation process of the Pt catalyst,we developed a facile molten-salt assisted method to co-load In SACs and Pt-In alloy NPs on CNTs for glycerol oxidation.The chloroplatinic acid solution dissolved in isopropanol was used as the platinum source,and indium acetate was used as the indium source.At high temperatures for defluorinating FCNTs,molten indium acetate improved the dispersion of Pt source on carbon nanotubes.It facilitated the formation of Pt In alloy nanoparticles on CNTs with In SACs.Compared with the 5Pt/CNT catalyst,the use of a composite catalyst can increase the DHA selectivity by nearly 4 times along with an increased conversion rate of glycerol.