Introduction to precious metal catalysts

1.Characteristics of Precious Metal Catalysts
Changing the rate of chemical reactions
Not participating in the final product of the reaction
Almost all precious metals can be used as catalysts
Among them, the most commonly used precious metal catalysts include platinum, palladium, rhodium, silver, ruthenium, etc. Among them, platinum and rhodium are the most widely used. Due to their unfilled d-electron orbitals, their surfaces are prone to adsorbing reactants and have moderate strength, which facilitates the formation of intermediate "active compounds". Due to this characteristic, it has high catalytic activity and comprehensive excellent properties such as high temperature resistance, oxidation resistance, and corrosion resistance, making it an important catalyst material.
2,The main activity indicators of precious metal catalysts
01activity
Activity is the standard for measuring the effectiveness of a catalyst. In industry, it is usually expressed as the quantity of products obtained per unit volume (or weight) of catalyst under certain conditions and per unit time.
02selectivity
Selectivity refers to the specificity of a catalyst's action, that is, under certain conditions, a catalyst only accelerates a certain chemical reaction. Selectivity is usually expressed as a percentage of the ratio of the number of desired product molecules obtained after the reaction to the number of raw materials participating in the reaction.
03stability
Stability refers to the ability of a catalyst to maintain its activity and selectivity during use, usually expressed in terms of its service life. The good performance of catalysts depends not only on the inherent characteristics of active metals (such as the electronic structure of atoms), but also on factors such as their crystal structure, particle size, specific surface area, pore structure, and dispersion state. In addition, co catalysts and carriers also have a significant impact on the performance of catalysts.
3.Classification of Precious Metal Catalysts
According to different classification principles, catalysts belong to different categories.
01Divided by the shape of the carrier
Supported catalysts can be divided into particulate, spherical, columnar, and honeycomb shapes.
02Classified by the main active metals of the catalyst
Commonly used catalysts include silver catalysts, platinum catalysts, palladium catalysts, and rhodium catalysts.
03Classified by catalytic reaction category
Precious metal catalysts can be divided into two categories: heterogeneous catalysts and homogeneous catalysts:
Homogeneous catalysts are usually soluble compounds (salts or complexes), such as palladium chloride, rhodium chloride, palladium acetate, carbonyl rhodium, triphenylphosphine carbonyl rhodium, etc.
Multiphase catalysts are insoluble solids, mainly in the form of metal wire mesh and porous inorganic carrier loaded metal states. The vast majority of multiphase catalysts are carrier supported noble metal types, such as Pt/Al2O3, Pd/C, Ag/Al2O3, Rh/SiO2, Pt Pd/Al2O3, Pt Rh/Al2O3, etc.
In all catalytic reactions, heterogeneous catalytic reactions account for 80% to 90%.
03The difference between precious metal catalysts and traditional catalysts
4.Precious metal catalystsVSTraditional catalysts
01Precious metal catalysts are more stable and easier to store than ordinary metal catalysts
Precious metals are generally less prone to chemical reactions and have relatively stable properties (such as aluminum being easily oxidized and turned into alumina when exposed to air). They are not easily oxidized at room temperature and do not self ignite at high temperatures. Generally, acids and bases cannot corrode them. Therefore, after preparing with precious metal catalysts, they are more stable and easier to store than some ordinary metal catalysts.
02Precious metal catalysts exhibit higher activity and selectivity at low temperatures
Research has found that the interaction between nanoscale precious metal particles and carriers can alter their surface properties (geometric structure and surface electrons), accelerate reactions, and exhibit high catalytic activity.
03The synergistic effect of precious metal catalysts
Different precious metal catalysts can be used not only individually but also in combination.
When used in combination, there is a synergistic effect between different catalysts (when two catalysts are used together, their catalytic activity is greater than the sum of the two used separately), which greatly increases the catalytic activity of the reaction.
Moreover, precious metals can form composite catalysts with different content ratios and particle sizes with general metals, improving reaction selectivity and catalyst lifespan (the length of usable time), and reducing catalyst costs (the amount of precious metals in nature is very small, so their prices are much higher than those of general metals).
04The preparation method is simple and the recycling performance is good
The synthesis conditions of some precious metal catalysts are mild, the synthesis methods are simple, and the recycling performance of old catalysts is still very good, making them the most studied type of catalyst currently.
Precious metal catalysts are mainly used in hydrogenation and oxidation reactions, and so far, their research has mainly focused on preparation methods, particle size, and interactions with carriers (substances loaded with precious metal particles).
Although precious metal catalysts have various advantages, we also need to realize that they are not omnipotent. During use, precious metal catalysts may lose their activity due to various factors, generally divided into three categories: poisoning, sintering and thermal deactivation, coking and blockage.
5.The upstream and downstream of precious metal catalysts
01The upstream raw materials of precious metal catalysts rely on imports
The upstream of precious metal catalysts mainly involves precious metal minerals, carrier development, etc.
Precious metals are a scarce resource globally, and the main raw materials for precious metal catalysts are platinum, palladium, and other precious metal raw materials. However, China is a country with extremely scarce platinum group metal resources, mainly relying on imports. Prices are influenced by global and downstream industry economic cycles, and have the characteristics of rapid change and large fluctuations.
There are various types of carriers for precious metal catalysts, mainly silicates, metal oxides, and carbon carriers.
02Precious metal catalysts are widely used downstream
It involves various fields such as petrochemicals, coal chemicals, pharmaceuticals, pesticides, food, dyes, pigments, new chemical materials, environmental protection, new energy, electronics, etc.