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Definition of catalyst: Also known as a catalyst. According to the definition established by the International Union of Pure and Applied Chemistry (IUPAC) in 1981, a catalyst is a substance that can alter the rate of a reaction without changing the standard Gibbs free energy change of that reaction. Based on their application, they can be classified into hydrogenation catalysts, oxidation catalysts, isomerization catalysts, etc. Hydrogenation nickel catalysts can be further divided into: 1. Skeletal nickel catalysts (nickel-aluminum alloy powder) ； 2. Loaded nickel carbonate and copper carbonate catalysts ； 3. Supported nickel catalysts. The catalysts we commonly use include palladium on carbon, Raney nickel, German 6504K, C207 (copper-based) catalyst, KT-02 nickel catalyst, etc. First, the advantages and disadvantages of each catalyst are listed below for reference by those of you engaged in catalytic hydrogenation. (1) From a price perspective, palladium-carbon is the most expensive; the price for 3% concentration is around 20,000 yuan per kilogram ； The price of Reni nickel is around 200,000 yuan per ton ； The price of the 6504K catalyst is 300,000 yuan per ton ； The price of the C207 catalyst is unknown, but since its main catalytic component is copper, it is estimated to be the cheapest among them ； The price of the KT-02 type nickel catalyst is around 400,000 yuan. (2) In terms of activity, Pd/C > KT-02 > Raney nickel > 6504K > C207. (3) From the perspective of the catalytic reaction temperature, the temperature for the palladium-carbon reaction is very low; the catalytic reaction can take place at room temperature as well ； The KT-02 nickel catalyst can carry out catalysis at around 40 ； The reaction temperature for the Raney nickel catalysis is slightly higher, around 60 degrees ； The catalytic reaction temperature for 6504K is around 80 degrees ； The catalytic reaction temperature for C207 is generally not lower than 150 degrees. (4) Analysis from the perspective of safety in use: The KT-02 nickel catalyst does not self-ignite in air at 150 degrees Celsius ； 6504K can also be stored in air at 120 degrees Celsius ； Palladium on carbon tends to catch fire spontaneously when exposed to air at room temperature ； Raney nickel ignites easily when exposed to air. (5) From the perspective of catalytic reaction selectivity, palladium-carbon systems have too high activity, resulting in low selectivity when multiple functional groups are present and the formation of by-products ； The KT-02 nickel catalyst has excellent selectivity ； Raney nickel has a better hydrogenation selectivity than palladium on carbon, but it is slightly inferior to KT-02 ； C207 has good selectivity. (6) From the perspective of conversion rate: Pd/C > KT-02 > Raney nickel > 6504K > C207. (7) From the perspective of ease of use, neither KT-02 nor 6504K requires activation before use; they can be directly added to the reaction system to carry out catalysis ； Palladium on carbon does not require a catalyst, but it must be stored in an airtight container to stay protected from air ； Before use, Raney nickel and C207 must be activated by treating them with an alkali to remove aluminum before they can be used for catalysis in reactions; moreover, Raney nickel also needs to be kept away from air during storage. (8) Analysis through separation from the product: After catalytic hydrogenation is complete, it is necessary to separate the product from the catalyst. In terms of the ease of separation, the order is KT-02 > Raney nickel > 6504K > palladium on carbon; C207 is generally used in fixed-bed hydrogenation, where separation does not present too many difficulties. (9) In terms of number of reuse cycles: KT-02 > Reney nickel > 6504K > Pd/C > C207. Here, the deactivation during the reaction process and the losses during the subsequent separation process are taken into account comprehensively. The KT-02 can be reused at least 100 times ； The number of reuse cycles for Reni nickel is around 70 times ； The number of reuse cycles for 6504K is 30-35 times ； C207 is used in a fixed-bed system ； Generally, the catalyst is replaced after being used for a period of time ； It is difficult to estimate the specific number of uses; palladium on carbon generally needs to be activated after use. (10) Catalyst form: Palladium carbon, KT-02, 6504K, and C207 are supported catalysts, while Raney nickel is a nickel-aluminum alloy. The above mainly compares the characteristics of various catalysts; please feel free to offer any suggestions if there are any issues. Friends can choose the appropriate catalyst based on the characteristics of the feedstock and product they intend to hydrogenate.