In recent years, the development of nanoscience has penetrated into the field of catalytic research and the most typical example is the emergence of nanometer catalysts (NCs) and the vigorous development of related research. NCs have the characteristics of large specific surface area and high surface activity, showing excellent properties that many traditional catalysts cannot match. In addition, NCs also exhibit excellent electrocatalytic, magnetic catalytic properties, and they have been widely used in the fields of petroleum, chemistry, energy, paint, biology and environmental protection.
At present, the research of nanotechnology is mainly carried out in two directions: one is to reduce the amount of currently used materials such as metal oxides through new technologies, and the other is to develop new materials such as composite oxide nanocrystals. Due to the large surface area of the nanoparticles and the large number of surface active centers, it is an excellent catalytic material. Ordinary iron, cobalt, nickel, palladium, platinum can be made into nanoparticles, which can greatly improve their catalytic effect. The use of nanocatalytic materials in the petrochemical industry can increase the efficiency of the reactor, improve product structure and quality and increase product yield. In addition, nanomaterials have a good photolytic effect in the treatment of pollution and degradation of toxic substances.
2 Properties of nanocatalyst
2.1 Surface effect
The parameters that describe the surface characteristics of the catalyst typically include particle size, specific surface area, pore size and its distribution. Studies have shown that when the particle size is reduced from 10 nm to 1 nm, the number of surface atoms will increase from 20% to 90%. This not only makes the coordination number of the surface atoms seriously insufficient, appears unsaturated bonds and surface defects increase, but also causes the surface tension to increase, so that the stability of the surface atoms is reduced, and it is easy to combine with other atoms to reduce the surface tension.
2.2 Volume effect
The volume effect means that when the size of the nanoparticle is comparable to or smaller than the de Broglie wavelength of the conduction electron, the periodic boundary condition of the crystalline material is destroyed, and the atom density near the surface of the amorphous nanoparticle decreases. So, chemical activity and catalytic activity of nanoparticles will change greatly compared to that of ordinary particles.
2.3 Quantum size effect
When the nanoparticle size decreases to a certain value, the electron energy level near the Fermi level will be split from a quasi-continuous state to a discrete energy level. At this time, the volatility of the electrons in the discrete energy level can make the nanoparticle have more prominent properties such as optical nonlinearity and catalytic activity. The quantum size effect can directly affect the boundary blue shift of the absorption spectrum of nanomaterials, and make the electron/hole pairs have a higher oxidation potential and can effectively improving the catalytic efficiency of the nano semiconductor catalyst.
3 Applications of Nanocatalyst
3.1 Application in the field of environmental protection
3.1.1 Photocatalytic degradation
NCs can completely degrade organic pollutants in water or air into carbon dioxide, water, and inorganic acids. They have been widely used in the treatment of wastewater and waste gases. The catalytic oxidation technology has more significant advantages than electrocatalytic and wet catalytic oxidation technologies in the mineralization decomposition of refractory organics.
3.1.2 Tail gas treatment
At present, 80% to 90% of the global urban exhaust gas is emitted by motor vehicles. Air pollution caused by major pollutants such as CO, NOx, and CH in automotive exhaust has become an urgent problem for human survival. Automobile exhaust gas purification mainly uses noble metal three-way catalysts with high catalytic conversion efficiency. However, precious metal catalysts are expensive and prone to Pb, S, and P poisoning. It has become an inevitable trend to look for new catalytic materials partially or completely replace precious metals.
3.2 The application of nano-catalysts in energetic materials
The catalyst can regulate the combustion performance of explosives and solid propellants. The addition of nanocatalysts to energetic materials is one of the best ways to improve the performance of energetic materials.
3.2.1 Elemental nanocatalysts
The simple nano-catalysts in energetic materials includes nano aluminum powder, nano nickel powder, nano magnesium powder, nano copper powder and nano boron powder. Due to its high energy performance, Al is the most used and studied metal. Aluminum powder is an energy additive in solid propellants. Adding aluminum powder can not only increase the energy of the solid propellant, but also improve the combustion stability.
3.2.2 Nanometer oxide catalyst
Nano-oxides are a promising class of catalysts, including non-metallic nano-oxides and metal nano-oxides. Monovalent metal oxides are frequently used in energetic materials and have been extensively studied due to their large specific surface area and high catalytic activity. At present, the studied nano-oxides include nano-sized Fe2O3, PbO, Bi2O3, Cu2O, Cr2O3, CuO, Al2O3, TiO2, SnO2, CeO2, and SiO2.
The development of nanotechnology will have an great influence on catalytic materials, lubricant additives, and process additives in the petrochemical industry. At present, research in this area is still in the laboratory stage and there is still a long way to go before it is actually applied.