Automobile catalyst is a relatively new product in the rare earth application market, which is divided into oxidation catalyst and three-way catalyst. Oxidation can't solve the problem of nitrogen oxide emissions, which is out of date. The three-way catalytic converter works in a closed-circuit system with sensors. It can oxidize CO and HC into CO2, reduce water and nitrogen oxides into nitrogen, and control the air (gas)/fuel (oil) ratio in the internal combustion engine.
A stainless steel box is installed in the automobile exhaust system, and a catalytic purification converter is placed in the box. The automotive catalyst in the converter is made of honeycomb ceramics or metal, and the inner surface of the honeycomb is coated with an active coating composed of Al2O3, rare earth-based materials (mixed oxides of CeO2 and other metal oxides) and a small amount of precious metals (platinum, palladium or rhodium). Catalysis is mainly carried out by precious metals such as platinum.
CeO2 _ 2 in rare earth has excellent oxygen storage capacity, which can play an excellent dynamic adjustment role when the air-fuel ratio changes, that is, oxygen is supplied when the fuel is long, CO and HC are oxidized, and when the fuel is short, it plays a reducing role in the form of Ce2O3 to remove nitrogen oxides in the exhaust gas. Rare earth exists in the form of cocatalyst. Through the efficient redox coupling effect and high ion mobility of cerium, the catalytic activity of three-way catalyst is improved, precious metals are saved, and the heat resistance of Al2O3 carrier is improved. Especially, adding the solid solution formed by zirconia and ZrO2 into CeO2 can significantly improve the thermal stability and activity of CeO2, and improve the heat resistance of exhaust gas purifier at the temperature of automobile engine (up to 570℃). In recent years, Europe, the United States and Japan have made use of this achievement.
China needs to deeply study the basic theory of catalysis.
Since the introduction of automotive catalysts in the United States in the mid-1970s, more than 40 countries have implemented emission control laws. In 2000, the European Euro II standard required the allowable values of particulate matter emission as follows: CO 2.3 g/km, HC 0.20 g/km, NOx0. 15g/km/km. When the Euro IV standard is implemented in 2005, the allowable values of particulate matter emission will be further reduced by 40% ~ 50%. Obviously, environmental protection laws and regulations have promoted the increasingly strict control of particulate matter emissions, and also spawned new rare earth catalytic materials, forming an increasingly powerful market.
The number of cars in the United States exceeds 65.438+0.8 billion. By 654.38+0.996, the consumption of rare earth oxides in automobile catalysts has exceeded 6.5438+0.3 million tons, accounting for 46% of the total domestic consumption of rare earth, and has risen to 60% of the total consumption by 654.38+0.999. The annual output of automobile catalysts is nearly 50 million sets, and so is the consumption of rare earth in its petroleum cracking catalysts. 1996 has risen to 7300t, accounting for 25% of the total consumption of rare earths. However, the application of rare earth catalysis in China has obviously not reached the height of the United States. Petroleum catalytic cracking accounts for 18% of China's total rare earth consumption, while automobile catalysts representing high-tech industries account for less than 2% of the total consumption. It can be seen that there is still a long way to go for China's rare earth consumption structure to transform into high-performance, high-tech and high value-added products.
Compared with China, the application prospect of automotive catalysts in Europe is encouraging. Rona Planck, the world's largest manufacturer of rare earth separation and purification, changed its name to Rhodia Electronics and Catalyst Materials Company, which indicates that the downstream product catalyst materials have become the main pillar of industrial restructuring. These companies generally require the quality of rare earths supplied by China to be consistent, so as to ensure the high performance of their final products in 5-7 years.
Rhodia has also developed a new generation of catalyst Eolys for diesel vehicles. This is a kind of cerium oxide catalyst with fuel as carrier, which is used in diesel particulate filter system. The filtration system is a ceramic wall fluid filter (or filter catcher), and more than 90% or even 99% of particulate emissions from diesel engines can be removed by using rare earth. The filter can be regenerated by Eolys before the collected particles are completely blocked, that is, before the soot composed of particles is burned. Because CeO2 in Eolys is used to reduce the ignition temperature of soot and slow down the temperature rise caused by combustion, the whole regeneration process is mild and easy to control, which can avoid the formation of negative pressure and reduce the working performance of diesel vehicles. As it is a trade secret, we only know that Eolys is compatible with diesel oil and diesel oil additives, completely miscible with diesel oil, and forms a highly stable mixed liquid, which can be put in bottles like lubricating oil for diesel engines.
Compared with gasoline engines, diesel engines save fuel obviously, except that the oil price is lower. Diesel engines are becoming more and more popular in Europe and have been widely promoted. In China's oil product structure, diesel is 1.3 times that of gasoline, accounting for 27.2% of the total oil output. Diesel oil has been widely used in large transport vehicles, ships, tractors, railway locomotives and motorcycles, and solving the black smoke emitted by it has always been a major environmental problem to be solved urgently. Using Rhodia's technology as catalyst, CeO2 not only solves the problem of light rare earth, but also benefits the environmental protection of transportation industry.
The catalyst lacks the necessary basic theoretical research. In-depth study on how the interaction between CeO2 _ 2 and ZrO2 _ 2 and other metal oxides affects the catalytic behavior will directly affect the development of a large number of application markets involving the environment, from volatile organic compounds incineration to wastewater treatment.