Modifier Effect in Silica-Supported FePO4 and Fe-Mo-O Catalysts for Propylene Glycol Oxidation

Currently, catalytic processing of biorenewable raw materials into valuable products attracts more and more attention. In the present work, silica-supported FePO4 and Fe-Mo-O catalysts are prepared, their phase composition, and catalytic properties are studied in the process of selective oxidation of propylene glycol into valuable mono- and bicarbonyl compounds, namely, hydroxyacetone and methylglyoxal. A comparative analysis of the main routes of propylene glycol adsorption with its subsequent oxidative conversion into carbonyl products is carried out. The DFT calculations show that in the presence of adsorbed oxygen atom, the introduction of the phosphate moiety to the Fe-containing site strengthens the alcohol adsorption on the catalyst surface with the formation of the 1,2-propanedioxy (-OCH(CH3)CH2O-) intermediate at the active site. The introduction of the molybdenum moiety to the Fe-containing site in the presence of the adsorbed oxygen atom is also energetically favorable, however, the interaction energy is found by 100 kJ/mol higher compared to the case with phosphate moiety that leads to an increase in the propylene glycol conversion while maintaining high selectivity towards C-3 products. The catalytic properties of the synthesized iron-containing catalysts are experimentally compared with those of Ag/SiO2 sample. The synthesized FePO4/SiO2 and Fe-Mo-O/SiO2 catalysts are not inferior to the silver-containing catalyst and provide similar to 70% selectivity towards C-3 products, while the main part of propylene glycol is converted into methylglyoxal in contrast to the Ag/SiO2 catalyst featuring the selective transformation of only the secondary C-OH group in the substrate molecule under the studied conditions with the formation of hydroxyacetone. Thus, supported Fe-Mo-O/SiO2 catalysts are promising for the selective oxidation of polyatomic alcohols under low-temperature conditions.

Automated summary

The catalytic processing of biorenewable raw materials into valuable products is gaining increasing attention. In this study, silica-supported FePO4 and Fe-Mo-O catalysts were prepared and their phase composition and catalytic properties were studied in the selective oxidation of propylene glycol. The results showed that the supported Fe-Mo-O/SiO2 catalysts exhibit promising performance for the selective oxidation of polyatomic alcohols under low-temperature conditions.