Application of rare earth purification catalysis

Application of rare earth purification catalysis

Outer layers of the rare earth elements have special electronic structure, the coordination number of variability determines that they have a "backup chemical bond" or "remaining valence", and this ability is the catalyst must have the. Therefore, rare earth elements have catalytic activity not only in themselves, but also as additives or catalysts to improve the catalytic performance of other catalysts. The application of rare earth catalysts includes the following aspects: external combustion engine exhaust purification; Industrial waste gas and human settlement environment purification; Catalytic combustion; Fuel cell; Low - value paraffin utilization, etc.

1. Research and application of rare earth catalysis in automobile exhaust purification
The rare earth catalyst is used in automobile exhaust purification, with good effect, stable quality and reliable price, and is a developing rare earth application market. Since the 1980s, rare earth catalysts have gradually entered the market. In the United States, the demand for vehicle exhaust purification catalysts has increased rapidly and has become the largest market for rare earth applications. In 1996, the United States used 12, 000 tons of rare earths in the market, accounting for 46 percent of the total.

In the early 1980s, countries such as Japan and Europe improved the technology of catalysts, added rare earth to the catalyst, reduced the cost, improved performance and greatly promoted the application of rare earth catalysts. In 1996, the amount of rare earth used in automobile exhaust purification catalyst in Japan was 420 tons.

Europe has about 1,000 tonnes of rare earth in this market. Scientific workers in China in the early 70 s began to research and development work, automobile exhaust purification catalysts after 20 years of effort, applied research has the world frontier level, basic terms with the transformation of industrialization.

Especially on technology adopted with foreign different technical route, research and development is the main focus on pure rare earth catalyst or in rare earth based on the introduction of a small amount of precious metals technology direction, it is in the research and development of automobile exhaust purification of rare earth catalyst we have created a unique in our country and the world's advanced level of scientific research achievements.

The production of automobile exhaust purification catalyst will be one of the largest catalyst industries in China in the next century and will be one of the main users of rare earth. Research and development of natural gas bus and d iesel vehicle purification high performance high resistance sulfur rare earth oxide catalyst; Develop the Ⅱ and European Ⅲ standard new preparation technology of vehicle exhaust purification catalysts;

Development of natural gas to catalyze high temperature combustion of rare earth catalysts to improve the efficiency of combustion furnace and pollution-free discharge; Develop industrial sources to discharge pollutants such as toxic, harmful and organic pollutants. In 2002, the environment area included automobile catalyst, sensor industrial source purification catalyst, rare earth consumption of about 500 tons. At present, the domestic existing places such as Shanghai, Beijing, wuxi production of rare earth catalyst into the market, and gradually applied in the automobile exhaust purifier, its technology has reached the world advanced level in the 1990 s. It has been applied in more than 1000 vehicles, and has achieved obvious purification effect.

The application of rare earth in this field has not only developed new application fields, but also alleviated the air pollution of Chinese cities, which is of great significance for the sustainable development of economy and society. In the early 21st century, the application of rare earths in automobile exhaust purification catalysts will have a big leap and become a new hotspot of rare earth consumption. The development of rare earth - precious metal composite catalysts will be very promising. It is estimated that in 2005, China will need the automobile exhaust purification catalytic conversion device for 800 ~ 10 million sets, which will cost about 1,500 tons of rare earth. In 2010, the data will be 12 million and 1, 800 tons.

In China's large and medium-sized cities, especially in Beijing, Shanghai and guangzhou, automobile exhaust emissions have become the major air pollution sources. Of the total emission of air pollutants in Beijing, an average of 83% of carbon monoxide, 74% of hydrocarbons and 41% of nitrogen oxides are formed by vehicle exhaust emissions.

To solve the automobile exhaust emission pollution, by far, the most effective method of governance in China and abroad is the exhaust gas purifier, and the core technology of purifier is the catalyst. The foreign countries mainly use precious metals as catalysts, but even precious metal catalysts need a certain amount of rare earth to stabilize the high temperature phase of alumina in the dispersion layer of the base.

Since Libby proposed to apply the catalysts containing rare earth to automobile exhaust purification, the special catalytic performance of rare earth oxides has attracted the attention of researchers. The paramagnetism of rare earth oxides, the mobility of lattice oxygen, the variable valence of cationic ions, and the surface alkalinity are intrinsically linked to many catalysis. With the deepening of the research, the rare earth oxide not only can be used as a catalyst carrier and additives, and found that by adding rare earth oxide catalyst can improve coating the surface of the aspect ratio of thermal stability and mechanical strength, improve the precious metal dispersion of active components, resistance to poisoning and durable performance, improve the oxygen storage capacity and antioxidant performance of catalyst, etc.

In China since the 1970 s for the research of the automobile exhaust purification with rare earth catalyst, in using rare earth partly or fully replace the shortage of resources of precious metals used in automobile exhaust purification research level in the world, with perovskite rare earth complex oxides (regarding) fully or partially instead of precious metals to act as active components of catalysts, catalytic reduction of CO, HC, NO.

The development of automobile exhaust catalyst has good activity, good thermal stability, certain ability to resist sulfur, lead poisoning, in the life test has more than 50000 kilometers, the basic conditions to the transformation of industrialization. However, the study of catalytic properties of rare earth oxides and understand the catalytic chemical laws are relatively shallow, lack of detailed and in-depth research, understanding of rare earth oxide on the surface properties and catalytic properties far less detailed than for precious metals and transition metal oxides and in-depth.

The government has implemented the new emission standard gb14761-1999 on 1 January 2000. All motor vehicles can meet the new emission standards only by using the electric spray and the three-way catalytic converter. With the rapid development of automobile industry in our country, as well as the relevant departments of the government and the public is becoming more and more attention of environmental protection, automobile exhaust emission purification technology suitable for China's national conditions and the product market has started to form.

At present our country automobile exhaust purifier manufacturing enterprises more than 100, a few enterprises reached the annual output of more than 300000 sets of production capacity, product performance, quality, basic can satisfy the requirements of the current our country emissions control. But the influx of foreign purifiers into China's vehicle matching market poses a huge potential threat to China's purifier industry.

Apart from cars, China has been the world's largest motorcycle manufacturer since 1999, and the number of motorcycles has exceeded 10 million. Motorcycle exports to developed countries currently requirements must be installed exhaust gas purifier, domestic large and medium-sized cities have begun to require control of the motorcycle exhaust pollution, which is an important aspect of rare earths catalytic materials.

In the exhaust pollution treatment of d iesel vehicles, it is mainly relying on installing an oxidation purifier to purify the carbon smoke and some gas pollutants from d iesel vehicles. This is also an important field for the application of rare earth catalytic materials.
Since 2002, the production of fixed small fuel engine in China has also increased rapidly. At present, it is mainly used for household engine, yard mower, small irrigation equipment, water power equipment, etc.

In 2003, China exported more than 15 million small fuel engines, and some manufacturers have asked for the installation of purification devices. In 2003, China produced 3.2 million automobile exhausts. All kinds of rare earths, including catalysts, carriers and oxygen sensors, have been consumed by 910 tons. It is expected that in 2005, China will have more than 5.5 million car exhausts and 1,560 tons of rare earth consumption.

The research and application of rare earth catalysis in the purification of industrial waste gas and human habitation environment

China is a major producer of chemicals that can produce more than 37,000 chemicals (including 8% of toxic chemicals). With the rapid development of China's industrialization, the industrial production, such as petrochemical industry, shoe industry, leather industry, paint and coatings industry, etc) in the discharge of poisonous and harmful waste gas and use these chemicals produce the waste gas has become one of the city's main pollution source, especially volatile organic waste gas (VOC) emissions. The use of rare earth catalytic materials for industrial organic waste gas pollution control and human settlement environment purification is one of the driving forces for the catalytic application of rare earth.

It is one of the most active fields in recent years to develop economical and practical industrial sources to purify toxic pollutants. Catalytic combustion method has low operating temperature, high purification efficiency, without auxiliary fuel, less secondary pollutant generation, has long been regarded as the most effective and most application prospect of purification technology. The catalytic oxidation method mainly ADAPTS to the purification of organic waste gas. High performance oxidation catalyst is the key of purification technology. Due to its unique catalytic oxidation properties, rare earth catalytic materials have shown an increasingly obvious application prospect, and there have been many successful examples in this field. In 1997, the sales of the catalyst for the purification of VOCs in the United States amounted to about $1 billion, and the annual growth rate was 20% ~ 25%, which was the fastest growth in the field of environmental catalysts in recent years.

A modern day life, 80 to 90 percent of the time is spent indoors. Inhaling a large amount of air containing a variety of pollutants can cause a range of conditions that affect human health. The survey shows that 68 percent of the disease in modern humans is associated with indoor air pollution. So purifying the living environment and improving the indoor air quality have become the urgent needs of the residents. Indoor air pollution is there are many different kinds of pollutants, low concentration, since the net anti sex, so indoor air purification is much more difficult than industrial exhaust gas catalytic purification, at room temperature under the conditions of photocatalytic oxidation and coupling of room temperature catalytic oxidation technology.

Rare earth has complex energy level structure and spectral characteristics, doping modification of nano-tio2 can effectively improve the efficiency of photocatalysis, which is one of the most promising technologies to solve the visible utilization rate. Of low temperature oxidation catalyst, rare earth type catalyst at room temperature to eliminate the harmful gas such as CO, O3, with the synergy of photocatalyst, is one of the best way to purify living environment at room temperature.

There have been many successful examples of the catalytic combustion of organic waste gas in China, but the purification of low concentration VOC has not been reported. Sensitization of photocatalyst is one of the hot research topic in the field of photocatalysis, modified by rare earth elements in order to improve the efficiency of titanium dioxide photocatalyst sensitization, although there have been some research reports in recent years, but has not obtained a breakthrough research results, the present study also involves less rare earth doped atomic energy level and the interaction between nano TiO2 semiconductor energy level research, less on rare earths spectral studies the relationship between photocatalytic performance.

Due to its excellent catalytic performance, unique low temperature activity and excellent anti-poisoning ability, rare earth catalytic materials have shown an increasingly superior prospect in the development of organic waste gas management. In this paper, the catalytic materials of rare earth compound are characterized by large surface area, suitable pore size distribution and stable structure, and have become one of the most promising catalytic materials in industrial organic waste gas purification. In addition, the development of advanced rare earth catalytic materials through the design of nano-level can ensure the efficiency of catalytic purification can be increased by a factor of 1.

Research and application of rare earth in catalytic combustion
Flame burning plays an extremely important role in human evolution and the development of human civilization. Modern scientific research shows that the traditional flame burning method has low thermal efficiency and serious pollution, which restricts the development of China's economy. The way to fundamentally solve the inefficient and high emission of flame combustion is catalytic combustion. Compared with usually combustion, catalytic combustion with high efficiency, stable combustion, pollutant (such as CO, NOx and incomplete combustion) advantages of ultra-low emissions, it is countries in the recent 20 years is committed to the cause of the catalytic combustion research.

The rare earth type high temperature combustion catalyst has the advantages of cheap price, easy material, stable process, good purification and long service life, and has some application prospect in high temperature catalytic combustion. Development of rare earth catalysts, development and research of international advanced high temperature catalytic combustion technology, improve our country's traditional combustion methods are in line with China's national conditions and development path.

The present study of catalyst has two kinds: one kind is precious metal catalyst, this kind of catalyst has high activity and stability, but precious metals sintering and evaporation loss, easily and easy by sulfur and lead poisoning, and shortage of resources, expensive, has yet to industrialization; The other kinds of catalysts are mainly concentrated in rare earth, alkaline earth, calcium titanite oxide, hexaluminate and other catalysts. The basic requirements of catalytic combustion for catalyst are good low temperature activity and high temperature and thermal stability. The experimental results show that the combustion catalyst has high thermal stability, but the combustion activity is relatively poor.

At present, there are a lot of research reports abroad, just entering the stage of catalytic burner research, and a distance from industrialization. China's research in this area is still in its infancy. Currently, catalytic combustion has not been widely used, mainly because the performance of catalytic materials cannot meet the requirements.

The excellent activity and stability shown in rare earth catalytic materials is one of the most likely ways to promote the large-scale practical application of f ossil fuels such as natural gas.

China has abundant natural gas resources, with a total resource volume of 38 trillion cubic meters and its proven reserves of 1.53 trillion cubic meters. With the west to east gas pipeline, the east China sea natural gas development and "in the east, north and south" five national key projects, such as natural gas base to solve the cities along the serious environmental pollution caused by coal, the effective use of natural gas to China is an urgent need to solve the problem.

At present, the gas flame furnace is widely used at home and abroad. According to statistics, the market demand in 2001 was more than 15 million, which will increase by 30% in 2002 ~ 2005. However, the fire burning furnaces sold in the current market are all products of "open flame combustion, direct emission of waste gas", all of which have the real problems of low thermal efficiency and serious pollution. Therefore, the market prospect of the catalytic combustion furnace of natural gas and other low-carbon paraffin is very good.

The research and application of rare earth in the utilization of low carbon alkane
One of the key components of low carb liquefaction to replace some petroleum resources is the preparation of cheap syngas to reduce the cost of liquefied products. The main technological processes for the preparation of synthesis gas by low carbon alkanes are: steam reforming method, steam reforming and secondary furnace oxidation, catalytic partial oxidation and carbon dioxide reforming. In the process of steam reforming and syngas, the use of water vapor is much higher than that of chemical metering in order to restrain the sintering of carbon dioxide and the active metal Ni grain. It is proved that rare earth additives have good anti-ni grain sintering and inhibition of carbon deposition.

In addition to the preparation of syngas, olefins are an effective means of utilization. Has achieved industrialization, the process is direct dehydrogenation catalyst mainly include platinum and chrome aluminum series two kinds, the fatal weakness is easy to carbon deposit catalyst deactivation, short service life, catalyst regeneration every few minutes or more than ten minutes at a time, and alkane conversion rate is not high also. In recent years, using rare earth as the auxiliary agent of chromium aluminum catalyst has achieved good results.

After the introduction of rare earth into the catalyst, the activity and selectivity can be maintained within two hours. After repeated regeneration dozens of times, the performance is basically the same. The performance of the catalyst has also been significantly improved. The conversion rate of propane is greater than 50%. The selectivity of propylene is greater than 90%, which is the best catalyst for the current report. With low carbon alkane to syngas catalyst is similar, to improve the performance of rare earth on its research is still preliminary, the mechanism of the difference with other additives and multivariate mixed rare earth additive synergy research has not reported.

5. Research and application of rare earth in fuel cell
The solid oxide fuel cell (SOFC) has attracted more and more attention due to its characteristics such as high power generation, low pollution and sustainable power generation. It is regarded as the green energy of the 21st century. The research and development of rare earth in SOFC mainly focuses on the following aspects: the development of cathode materials, such as strontium doped submanganate (LSM); Development of anode materials, such as nickel-ysz metal ceramics; Bipolar connective plate materials, such as calcium or strontium doped lanthanum calcium titanate materials (LCC) : La1- xCaxCrO3; But more are applied to the electrolyte materials, such as YSZ (zirconium doped with yttrium oxide), the adulterated gallium gallium, thorium oxide, cerium oxide, rare-earth calcium titanite compound oxides, etc.

At present, it is found that the oxygen ion conductors of SOFC mainly include the ZrO2 basis, CeO2 base, Bi2O3 base material and LaGaO3 base materials of perovskite structure. Finding new good solid oxide electrolyte is still one of the key tasks to promote the practical application of SOFC in the new century. Since Cook, Ishihara et al. reported that the calcium titanite oxides based on LaGaO3 have high conductivity, the research of calcium titanite solid electrolyte has been widely valued. ABO3 not only has the stable crystal structure, but also for the A and B ion radius change has strong tolerance, and can through low metal ion doping, the introduction of A large number of oxygen vacancy in structure.

Perovskite oxide can accommodate a large number of oxygen ion vacancies and has a high electrical conductivity, such as La0.8 Sr0.2 Ga0.83 Mg0.17 O3 in 800 ℃ the electrical conductivity of 0.17 S/cm, except the Bi2O3 highest oxygen ionic conductivity of ceramic materials. The rare earth oxide has good ion and electron conductivity, which has no substitute for improving the performance of the solid oxide fuel cell. By selecting the appropriate oxide composition, the ion conductivity of electrode material can be improved, and the activation energy of oxygen reduction can be reduced.

By studying the composition, structure and form, the relationship between electrical conductivity and the doping ions to the structure of the design and synthesis of new compound of rare earth oxides, obtain high electric catalytic activity and high conductivity of rare earth electrode materials, is a solid oxide fuel cell current research hot spot, is also an important application of rare earth in this field.

The application of rare earth catalysis in the purification of coking sewage
Coal in high temperature and dry distillation temperature, gas purification and chemical products produced in the process of refining wastewater is a kind of extremely complex composed of pollutants, high concentration and toxicity of large and difficult treatment of industrial wastewater. Not only contains a large number of inorganic substances, but also contains a large number of organic compounds, including a large number of aromatic hydrocarbons and PAH, such as BaP.

At present, most of the coking wastewater treatment adopts ordinary biochemical method, which can effectively remove the phenol and cyanide, so as to meet the emission standard, and the removal of COD (COD) is also effective. However, as people's understanding of the environment continues to deepen, the state's requirements for environmental protection are becoming more and more strict, and it is difficult to meet the new requirements. Catalytic wet oxidation is treatment of coking wastewater purification technology in modern times, the method is wastewater under high temperature and high pressure in a liquid state, into the air, using our country to develop a new type of efficient bi-component catalyst (precious metals and rare earth element), oxidative decomposition of pollutants thoroughly, making them into harmless substances, so that sewage get deep purification method.

The application of rare earth catalysis in flue gas desulfurization
In recent years, due to the large number of mining and coal combustion directly, causing the content of SO2 in the atmosphere continuously on the rise, "acid rain", according to the statistics, in 1995 amounted to 23.7 million tons of sulfur dioxide released into the atmosphere, the world in the first place.

Therefore, the problem of desulphurization of coal flue gas has become a hot topic in various countries. The catalytic gasification of coal with rare earth was studied in Japan, and the gas rate of the load on the raw coal with lanthanum nitrate, cerium nitrate and samarium nitrate was significantly higher than that used in the past. Easily occur in rare earth type desulfurizer desulfurization reaction temperature range is wide, 150 ~ 150 ℃, tallies well with the actual flue gas temperature (160 ℃), and the desulfurization efficiency can reach 90%; Desulfurizer can also be reused and reused, so the rare earth desulfurizer is suitable for the removal of SO2 in flue gas.