There are mainly three types of nanoparticles catalysts. One is to directly use metal nanoparticles as a catalyst. This type of catalysts are mainly nano-powders of noble metals (AG, PD, PT, RH, etc.), and nano-powders of base metals such as FE, CO, and also NI have also been applied as catalyst. When some noble metal nanoparticles are used as catalysts, in addition to increasing the reaction rate, they also have good selectivity, and this selectivity is related to the particle size of the nanoparticles. The second is to load the metal nanoparticles onto the porous support as a catalyst. Commonly used carriers are porous carriers such as AL2O3, SIO2, MGO, TIO2 and activated carbon, and the supported metal nanoparticles have a particle diameter of about 1-20nm. A plurality of metal nanoparticles can be simultaneously loaded or formed into composite metal nanoparticles and loaded onto the same carrier, which can further increase the selectivity of the catalyst.
Application of nano gold catalyst
Gold has been considered as a low-activity catalytic material for a long time, but when gold is dispersed to the nano scale, it exhibits high catalytic activity. Therefore, nano gold catalysts have attracted widespread attention. Nano gold catalysts and become an important representative of nano catalysis technology. Let’s select some of the ions that have been successfully applied, which are summarized as follows:
1. Catalytic CO to CO2
The research in the past 10 years shows that when the nano Au particles are loaded onto the metal oxide by deposition or co-precipitation, the catalytic activity is very high, especially in the process of catalytic oxidation of CO to CO2 at low temperature, the catalytic ability and efficiency are better than other silicon. The metal is much higher.
2. Epoxidation of propylene
Propylene Oxide PO is an important chemical raw material used primarily in the production of polyurethane and polyol raw materials. For the gas phase in which O2 and H2 are present, the supported AU nanoparticles can catalyze the propylene to PO, and the epoxidation can be completed in one step, and no other by-products other than water.
Among the single metal oxide supports, only anatase TIO2 enables gold to selectively catalyze the oxidation of propylene to propylene oxide PO.
3. Hydrogenation of unsaturated hydrocarbons
A distinct feature of nano gold catalysts is that their partial hydrogenation is very selective: in the hydrogenation of unsaturated aldehydes, when the particle size of gold nanoparticles is greater than 2 nm, the hydrogenation selectivity ratio to C===O is C=== C is 40-50% higher. In the hydrogenation of acetylene on AU/AL2O3 and acrolein on AU/TIO2 and AU/ZRO2, the catalytic activity of the gold catalyst increases as the particle size of the AU nanoparticles decreases. This means that the metal nature of gold has an important influence on the hydrogenation of unsaturated hydrocarbons.
4. Liquid phase reaction
Ethylene glycol is oxidized to an acid in a MeOH-H2O (6:4) solvent. The gold/activated carbon catalyst is more active and selective than other precious metal catalysts and is used in the cosmetic and food industries.
5. Water-gas conversion reaction
The low temperature water-gas shift reaction has a good application prospect in polymer electrolyte fuel cells and civil electric heating systems for automobiles. A significant advantage of supported nano gold catalysts is their ability to catalyze at temperatures as low as 473K.