What are the common catalyst preparation methods(2)

6. Immersion method

From the multi-component system, some of the substances are extracted with appropriate liquid agents (or water) to make catalysts with porous structures. For example, the skeleton nickel catalyst is made by melting a quantity of nickel and aluminum in an electric furnace, and the melt becomes an alloy after cooling. 

The alloy is broken into small particles and soaked in aqueous sodium hydroxide solution, and most of the aluminum is dissolved (to produce sodium meta-aluminate), which forms a porous and highly active skeletal nickel.

7. Ion exchange method

Certain crystalline substances (such as synthetic zeolite molecular sieve) can exchange metal cations (such as Na) with other cations. Put it into the solution containing other metal (such as rare earth group elements and some precious metals) ions, under the controlled concentration, temperature, pH conditions, so that the other metal ions and Na exchange.

New methods in development

① Chemical bonding method. This method is now used in large quantities to make polymerization catalysts. The purpose is to solidify the homogeneous catalyst. Carriers that can be chemically bonded to transition metal complexes have certain functional groups on their surface (or are chemically treated and attached to functional groups), such as -X, -CH2X, -OH groups. 

Such carriers are reacted with phosphine, arsine or amine to phosphorylate, arsenate or amine, and then the ligand complexes of phosphorus, arsenic or nitrogen atoms on the surface with the metal ions in the center of the transition metal complexes are used to make chemically bonded solid-phase catalysts, such as the manufacture of Ziegler-Natta catalysts, the carriers used for liquid-phase polymerization of propylene ontology.

②Fibrillation method. Used for the manufacture of carrier catalysts containing precious metals. For example, borosilicate is drawn into glass fiber filaments, etched with concentrated hydrochloric acid solution to turn into porous glass fiber carriers, and then impregnated with chloroplatinic acid solution to make them loaded with platinum components. 

Depending on the practical situation, the fibrous catalyst is pressed into various shapes and desired tightness, e.g. for automotive exhaust oxidation, it can be pressed into a short circular tube. If it is not an oxidation process, carbon fibers can also be used. The manufacturing process of fiber catalysts is more complex and costly.