Talk about platinum catalyst
Source:iotachem.com
PostTime:2024-12-03 14:19:05
Hydrosilane addition reaction refers to the addition reaction between organosilicon compounds containing hydrogen silicon bonds and compounds containing unsaturated bonds under certain conditions. It is the main form of silicon-carbon bonds and one of the most basic and important reaction types in organosilication. Unsaturated bonds can be carbon-carbon double bonds, carbon-carbon triple bonds, carbon-oxygen double bonds and carbon-nitrogen double bonds. Among them, the addition reaction of hydrogen silicon bond and carbon carbon double bond is the most common hydrogen silicon addition reaction in the silicone industry, and is the core reaction of many additive silicone products.
For hydrosilane addition reaction, in addition to hydrosilane compounds and unsaturated compounds, the catalyst is an indispensable component, which plays a role in speeding up the reaction speed, shortening the reaction time and reducing the reaction temperature. The catalyst of hydrosilane addition reaction is mainly the compounds and complexes of Group B transition metal elements platinum, palladium, nickel and rhodium in the periodic table, among which platinum catalyst has the highest catalytic activity and is the most widely used.
The platinum catalysts used to catalyze the hydrosilane addition reaction are mainly divided into homogeneous catalysts and heterogeneous catalysts. Among them, the homogeneous catalyst and the reactant are in the same phase, and there is no phase interface. In the reaction of hydrosilane addition, the homogeneous catalyst generally refers to the liquid catalyst.
There are three main homogeneous platinum catalysts: the first is to dissolve chloroplatinic acid (H2PtCl6▪6H2O) into ethanol, isopropyl alcohol and tetrahydrofuran and other organic solvents, so that they interact to form complexes, called "Speier catalyst", this catalyst is simple, quick and easy to use; The second type of platinum catalyst is the complex of platinum and vinyl double head, called Karstedt's catalyst, which has high reactivity, stable storage, and good compatibility with various types of polysiloxanes, and is the most widely used catalyst in the additive silicone release agent; The third type of platinum catalyst is chloroplatinic acid in addition to some other unsaturated compounds to form complexes, but also with ketones, cyclopentadienes, esters, alcohols, crown ethers, heteroatomic crown ethers and polysiloxanes to form complexes as catalysts.
Homogeneous platinum catalyst has high activity and reaction selectivity, but because it is in the same phase as the reactant, it is difficult to separate after the reaction and cannot be reused, so the cost is high, and it may bring heavy metal ion pollution. Therefore, researchers make heterogeneous catalysts by solidifying homogeneous catalysts. The so-called homogeneous catalyst is to combine the homogeneous catalyst with a solid carrier by physical or chemical methods to form a special catalyst. Heterogeneous platinum catalysts and reactants belong to different phases, and the common form of solid catalyst catalyzes the liquid mixed reactants to silane addition reaction.
Heterogeneous catalysts for hydrosilane addition can be divided into two types: traditional heterogeneous platinum catalyst and polymer metal complex catalyst. Among them, the traditional heterogeneous catalysts are formed by adsorbing transition metals on inorganic particles such as carbon black and alumina. Such catalysts have high stability and can be recycled, but their catalytic activity and selectivity are low, and the reaction process requires high temperature and pressure. Polymer metal complex catalyst consists of polymer carrier, ligand bonded to the carrier and transition metal. In general, although heterogeneous catalysts have the advantages of high stability and recycling, their application is limited due to their low activity and selectivity and complex preparation process, which reduces their catalytic activity when they are used again.
There are many substances that can make the platinum catalyst "toxic", causing its catalytic activity to decrease or even lose activity. For example, organic compounds containing nitrogen, phosphorus, sulfur and other elements and ionic compounds containing tin, lead, mercury, bismuth, arsenic and other heavy metals. Therefore, special attention needs to be paid to the use of platinum catalysts to avoid exposure to these substances that can make them toxic. There are many types and forms of platinum catalysts, so in the application process, the appropriate platinum catalyst should be selected according to the characteristics of the reaction system to achieve the best catalytic effect.
