A chromium catalyst refers to an elemental chromium or chromium compound which has a catalytic function. Chromium is a silvery white shiny metal that is malleable. Chromium belongs to the VIB family in the periodic table. There is no free state of chromium in nature, and it mainly present in the form of FeCr2O4. Chromium is chemically inert and highly resistant to corrosion. In the air, even in hot condition, chromium oxidation is slow. Chromium is commonly present in the form of Cr6+, Cr5+, Cr3+ and Cr2+, so the types of chromium catalysts are abundant. Chromium catalysts can generally be classified into organic chromium catalysts and inorganic chromium catalysts. The chromium catalysts can also be classified into supported chromium catalysts and unsupported chromium catalysts depending on whether it has supported substance.
Figure 1. Inorganic chromium catalyst
Due to the wide variety, low cost and excellent performance of chromium catalysts, they have been widely used in various organic synthesis reactions.
Figure 2. Organic chromium catalyst
The chromium catalyst can be used as a cocatalyst to prepare 1,2-propanediol (PG). 1,2-Propylene glycol is an important basic chemical raw material for the production of unsaturated polyester resins, functional fluids, foods, pharmaceuticals, liquid detergents, paints and coatings. 1,2-propanediol can be produced by hydrogenolysis of glycerol. The addition of a certain proportion of the chromium catalyst to the copper-based catalyst not only affects the state of the copper component, but also functions to stabilize the copper particles. The construction of copper-chromium catalyst has good selectivity for the preparation of 1,2-propanediol by hydrogenolysis of glycerol.