Efficient Production of Hydroxypyruvic Acid from Glycerol Using Pt/ZrSn_1–<i>x</i>Bi<i>_<i>x</i></i>O_4−δ/SBA-16 Catalysts

Glycerol is generated as a byproduct during the biodiesel producing process, whereas the increase in biodiesel production causes an oversupply of glycerol. The upcycling of glycerol by converting it into value-added compounds has received increasing attention. Among them, hydroxypyruvic acid is highly valuable owing to its functionality; however, its production from glycerol is challenging because both the primary and secondary hydroxy groups in glycerol must be oxidized and further oxidation of hydroxypyruvic acid must be suppressed. In this study, novel catalysts of Pt/ZrSn1–xBixO4−δ/SBA-16 were developed for the oxidation of glycerol into hydroxypyruvic acid. By using the scrutinyite-type ZrSn1–xBixO4−δ promoters, the effective oxygen supply toward the catalytically active sites and the geometric effect among glycerol, Pt, and surface Bi3+ facilitated the oxidation of the primary and secondary hydroxy groups in glycerol, resulting in efficient hydroxypyruvic acid production. Moreover, the moderate reaction conditions (open-air atmosphere and 30 °C) suppressed further hydroxypyruvic acid oxidation. Among the prepared catalysts, the 7 wt %Pt/12 wt %ZrSn0.90Bi0.10O4−δ/SBA-16 catalyst exhibited the highest catalytic activity, reaching a yield of hydroxypyruvic acid of 58.0% and a glycerol conversion of 98.8% after 8 h of reaction at 30 °C in an open-air atmosphere.