Role of the Strong Lewis Base Sites on Glucose Hydrogenolysis

Abstract

This work reports the individual role of strong Lewis base sites on catalytic conversion of glucose hydrogenolysis to acetol/lactic acid, including glucose isomerisation to fructose and pyruvaldehyde rearrangement/hydrogenation to acetol/lactic acid. La2O3, Nd2O3, Sm2O3, and Pr6O11 were selected as representative oxides consisting of different base sites. The basicity of these lanthanide oxides was characterised by CO2‐TPD and DRIFT spectroscopy. It was found that lanthanide cation‐oxygen pairs, Brønsted OH group coordinated with one Lanthanide cation, and lanthanide cation near lanthanide cation‐oxygen pairs are the dominant base sites as compared to the other base sites on La2O3, Nd2O3, Sm2O3 and Pr6O11. In addition, the relative concentration of the base sites is different over the examined lanthanide oxides. These unique properties of lanthanide oxides are used to understand the individual role of base sites on the reactions mentioned above. Then, the catalytic results were correlated with the base properties of these lanthanide oxides. Based on this correlation, the base site requirements for each reaction were identified. In this regard, Brønsted OH group coordinated with one Lanthanide cation over Nd2O3 is found to be the suitable base site for glucose isomerisation. On the other hand, lactic acid is produced as the main product in glucose hydrogenolysis over lanthanide cation near lanthanide‐oxygen pairs on Pr6O11. Finally, lanthanide‐oxygen pairs over La2O3 are suitable base sites for retro‐aldol condensation of fructose to C3 chemicals.

Magnesium Oxide‐Catalyzed Conversion of Chitin to Lactic Acid

“…MgO is strongly basic, and thus in our system, isomerization of D‐glucose to fructose may have been enhanced either by MgO or by Mg(OH) 2 generated from MgO. Fructose is converted to glyceraldehyde and dihydroxyacetone by a retro‐aldol reaction, which involves C−C bond cleavage and is reported to be enhanced by base catalysts [35,36] . We previously reported that both dihydroxyacetone and glyceraldehyde can be converted to lactic acid in water in the absence of a catalyst even at 473 K [24] …”

“…Fructose is converted to glyceraldehyde and dihydroxyacetone by a retro-aldol reaction, which involves CÀ C bond cleavage and is reported to be enhanced by base catalysts. [35,36] We previously reported that both dihydroxyacetone and glyceraldehyde can be converted to lactic acid in water in the absence of a catalyst even at 473 K. [24]…”

Catalytic conversion of chitin to lactic acid in hot-compressed water

“…In addition, Mg(OH) 2 increased the isomerization reaction [103].In chitin conversion system, we used MgO and Mg(OH) 2 (MgO is hydrolyzed to Mg(OH) 2 ) could be increase isomerization reaction. In next step, glyceraldehyde and dihydroxyacetone were obtained from fructose by retro-aldol reaction, which enhanced by base catalyst [103,122]. From previous research lactic acid could be converted from dihydroxyacetone and glyceraldehyde in water solvent [31].…”