Highly Selective Hydrogenolysis of Glycerol to 1,3-Propanediol

Glycerol is an organic compound with the chemical formula C₃H₈O₃ and a simple polyol compound. It is a colorless, odorless and sweet viscous liquid. The glycerol backbone is found in lipids called glycerides. Glycerol has antibacterial and antiviral properties, and it is also used as a bacterial culture medium. It serves as an effective marker of liver disease. It is also widely used as a sweetener in the food industry and as a humectant in pharmaceutical formulations. Due to its three hydroxyl groups, glycerol is miscible with water and hygroscopic.

In recent years, the rapid development of biodiesel has led to a continued excess of glycerol, the main by-product. Therefore, it is of great research significance to prepare 1,3-propanediol with high added value through selective hydrogenolysis of glycerol.

However, selective cleavage of secondary carbon hydroxyl groups to efficiently convert glycerol into 1,3-propanediol remains a huge challenge due to thermodynamic limitations and steric hindrance. Currently, supported Pt-WO_x-based catalysts with bifunctional active metals and Brønsted acid sites can simultaneously satisfy the hydrogenation and dehydration processes of glycerol molecules, thereby achieving selective hydrogenolysis of glycerol to produce 1,3-propanediol. However, the dispersion of Pt and WO_x species on the surface of the support and their interaction with the support has an important impact on the catalytic reaction. It is well known that mesoporous materials have large specific surface areas, rich pore structures, and controllable surfaces. Therefore, mesoporous materials are regarded as an excellent carrier that helps improve the dispersion of noble metal catalysts and are widely used in the field of catalysis. On the other hand, different active component/support interfaces will affect the electronic structure and coordination environment of active species, thereby affecting the catalytic reaction efficiency. However, the lack of surface Brønsted acid sites limits the application of Pt/ WO_x /TiO₂ catalysts in the hydrogenolysis of glycerol to 1,3-propanediol. At present, the introduction of SiO₂ carrier helps to generate active polytungstate species and significantly increases the number of Brønsted acid sites of the overall catalyst.

Based on this, constructing Pt/TiO₂ and WO_x/SiO₂ nano-interfaces on the surface of the mesoporous support can not only achieve a high degree of dispersion of active sites, but also promote the catalytic hydrogenation and dehydration process. It is of great significance to improve the catalytic efficiency of selective hydrogenolysis of glycerol to 1,3-propanediol.

Recently, the latest research has prepared a hollow mesoporous SiO₂-TiO₂ nanosphere carrier through a hydrothermal process. Subsequently, the final hollow mesoporous Pt/WOx/SiO₂-TiO₂ nanosphere catalyst was obtained. Under the pressure test conditions of 423K and 4MPa H₂, the hollow mesoporous Pt/WO_x/SiO₂-TiO₂ nanosphere catalyst exhibited excellent catalytic activity, far exceeding that of the single-component supported catalyst. In the 24-hour catalytic reaction test, the hollow mesoporous Pt/WO_x/SiO₂-TiO₂ nanosphere catalyst achieved a glycerol conversion rate of 85.0% and a 1,3-propanediol selectivity of 53.8%. In the tolerance test, the hollow mesoporous Pt/WO_x/SiO₂-TiO₂ nanosphere catalyst also showed good catalytic stability. Subsequently, through a series of catalytic tests and pyridine infrared characterization, the mechanism by which Pt/TiO₂ and WO_x/SiO₂ nanointerfaces synergistically improve catalytic performance was clarified. This hollow mesoporous nanosphere catalyst with Pt/TiO₂ and WO_x/SiO₂ nano-interfaces can effectively promote the diffusion, adsorption, activation and catalytic hydrogenation process of glycerol molecules.

Reference

1. Interfacial synergism of hollow mesoporous Pt/WO_x/SiO₂-TiO₂ catalysts enable highly selective hydrogenolysis of glycerol to 1,3-propanediol.
   Nano Research, 2023