Solid catalysts are prepared in many ways, generally through three steps:
First, the selection of raw materials and the preparation of raw material solutions, the selection of raw materials must take into account the purity of raw materials (especially the maximum limit of toxic substances) and the ease of separation or removal of by-products after the chemical interaction of raw materials in the preparation of catalysts;
Second, through methods such as co-precipitation, impregnation, high sub exchange, chemical cross-linking in one or more methods, the raw materials into particle size, pore structure, phase structure, chemical composition of the required basic materials;
Third, through physical methods (such as washing, filtration, drying, molding) and chemical methods (such as intermolecular condensation, heating decomposition, redox) to remove impurities in the basic material, and transformed into macrostructure, microstructure and surface chemical state are in line with the requirements of the finished product.
Currently, solid catalyst preparation methods commonly used in industry include precipitation, impregnation, sol-gel, hybrid and ion exchange methods.
Precipitation method is one of the most commonly used methods to prepare solid catalysts, which is widely used to prepare high content non-precious metals, metal oxides, metal salt catalysts and carriers.
The precipitation method involves the addition of a precipitant to an aqueous solution containing metal salts in order to generate crystals or gels of hydrated oxides, carbonates; the latter are then filtered, washed, dried and roasted to produce the corresponding catalyst precursors in powder form. This method is similar to the precipitation operation in inorganic and analytical chemistry, but must be more rigorous in its operation because it is necessary to obtain compounds with certain activity.
(B) the process of precipitation method
1. Preparation of metal salt solution
2. Neutralization of precipitation
3. Aging of precipitation
4. Filtration and washing
5. drying, roasting, activation
(C) the selection of metal salts and precipitating agents
1. Selection principles of metal salts
2. The principle of selection of precipitating agent
(D) the influence of precipitation conditions
2. precipitation temperature
3. PH value
4. The way of adding material and stirring intensity
(E) the classification of precipitation method
1. Single-component precipitation method
2. Co-precipitation method
3. uniform precipitation method and super uniform precipitation method
4. Impregnation precipitation method
5. Inverted crystal precipitation method
6. Complexation precipitation method