Impregnation Method: A highly porosimetric support (such as diatomaceous earth, alumina, activated carbon, etc.) is immersed in a solution containing one or more metal ions. While maintaining a certain temperature, the solution enters the pores of the support. The support is drained, dried, and calcined, resulting in a layer of the desired solid metal oxide or its salt adhering to the inner surface of the support.
Spray Drying Method: Used to prepare fluidized bed catalysts with particle diameters ranging from tens to hundreds of micrometers. For example, in the manufacture of a fluidized bed ammoniation oxidation catalyst for m-xylene to m-dicarboxynitrile, a given concentration and volume of metavanadate and chromium salt aqueous solution are thoroughly mixed, then mixed with a quantitative amount of freshly prepared silica gel. This mixture is pumped into a spray dryer, atomized by nozzles, and the water evaporates under the action of hot airflow, forming microsphere catalyst particles, which are continuously drawn out from the bottom of the spray dryer.
Hot Melting Method: This method is a special approach for preparing certain catalysts, suitable for a few catalysts that must undergo a melting process. It utilizes high temperatures to melt the components into a uniformly distributed mixture, which, combined with necessary subsequent processing, yields a high-performance catalyst.
Immersion Method: This method involves removing a portion of a multi-component system using a suitable liquid reagent (or water) to create a porous catalyst. For example, in the manufacture of skeletal nickel catalysts, a measured amount of nickel and aluminum is melted in an electric furnace. After cooling, the melt forms an alloy. This alloy is then broken into small particles and immersed in an aqueous sodium hydroxide solution. Most of the aluminum is dissolved (forming sodium aluminate), resulting in a porous, highly active skeletal nickel alloy.
Lon Exchange Method: The metal cations (such as Na) of certain crystalline substances (e.g., synthetic zeolite molecular sieves) can exchange with other cations. By immersing the substance in a solution containing other metal ions (such as rare earth elements and certain noble metals), and under controlled concentration, temperature, and pH conditions, the other metal ions exchange with Na.
