Why Is Platinum Curing Agent Not Vulcanized?

- Apr 01, 2021-

Answer: The platinum vulcanizing agent will not vulcanize in the case of platinum poisoning. The phenomenon that the catalytic activity of a catalyst is degraded or lost due to the action of certain substances is called catalyst poisoning. These substances are called poisons. Poisons are usually impurities carried in the reaction raw materials, or some impurities in the catalyst itself; reaction products or by-products may also poison the catalyst.

One is that the poison is adsorbed on the active center of the catalyst, and the number of active centers is reduced due to the covering; the other is that the poison and the substance constituting the active center undergo a chemical reaction to transform into an inactive substance. According to the degree of the poison and the catalyst, it can be divided into temporary poisoning (reversible poisoning) and permanent poisoning (irreversible poisoning).

Platinum metal is a transition metal, which is a soft base element in theory, and easily reacts with soft acid elements to cause platinum poisoning. It is more common that the reaction between mercury and sulfur is similar. Therefore, when using platinum catalysts, it is best to remove or clean compounds containing sulfur, phosphorus, arsenic, etc.

There are three types of poisons:

1. The non-metallic elements of groups VA and VIA in the periodic table and their compounds (such as elemental compounds of sulfur, nitrogen, and phosphorus). These elements or compounds have lone pairs of electrons, which are easy to combine with the d orbital electrons of platinum metal to form strong adsorption bonds and poison the platinum catalyst.

2. Poisons with unsaturated bonds: The principle of toxicity is that the electrons on the π bond enter the d orbital of Pt, which reduces the d hole of Pt.

3. Metal or metal ions: If Au interacts with Pt, the electrons on the inner and outer layers of S of Au are filled into the inner d orbital of Pt, so that the d holes of Pt are reduced. We have injected 1.0 μL of a mixture of carbon disulfide and cyclohexane (1:200) or 1.0 μL of a mixture of thiophene and cyclohexane (1:100) in the catalytic addition reaction of platinum. The activity of the catalyst drops rapidly because carbon disulfide and thiophene poison the platinum catalyst.