Can rare earth materials really cure urban smog?

Introduction: In recent days, the rare smog in history has hit Beijing City again. At around 18:00 on November 30, the PM2.5 concentration in the southwestern part of Beijing has reached 1000 μg/m3, which is close to the 1952 London fog incident.

Since 2013, "Smog" has become the key word of the year. In January of this year, four smog processes enveloped 30 provinces (autonomous regions and municipalities). In Beijing, only five days were not foggy days. According to reports, less than 1% of China's 500 largest cities meet the World Health Organization's recommended air quality standards. At the same time, 7 of the 10 most polluted cities in the world are in China.

Beijing City with ten sides

This reminds us of the fog of London that lasted for five days in December 1952. At that time, the visibility was only a few meters. The only way to find the road was to walk along the road barriers and houses. People simply can't see the traffic situation, and crossing the road must rely on hearing. The most direct cause of pollution is coal power plants and automobile exhaust and general home use.

In 1952, the number of direct deaths caused by heavy fog in London reached 4,000 to 6,000, mainly children and people with respiratory diseases. This is a national disaster. If converted according to the size of China's population, it is equivalent to 80,000 deaths. The serious impact of heavy fog has also exacerbated the existing conditions, and not all deaths have been registered immediately, so the final death toll is estimated at 12,000.

London fog

The following picture shows the environmental conditions of Beijing and Shanghai, respectively. Among them, Beijing's motor vehicle pollution accounted for 31.1%, and Shanghai's mobile source, that is, motor vehicle exhaust pollution accounted for the largest proportion of 25.8%.

The main hazard of motor vehicle exhaust

1. The particle size of PM2.5 emitted by motor vehicles is very small, at 0.04-0.3 microns (diesel car 0.3, gasoline car 0.1, motorcycle 0.04), far less than 2.5 microns, not only can enter the lungs, but also can enter the blood, right The human body is extremely harmful.

2. The chemical composition is highly toxic. The PM2.5 emitted by motor vehicles contains 16 kinds of highly carcinogenic substances such as polycyclic aromatic hydrocarbons (PAHs) (the limit of carcinogenic threshold is not the amount of carcinogenicity), which is the most toxic and harmful pollution. Object.

PM2.5 emitted by automobile exhaust contains 16 kinds of aromatic high carcinogens and human organs contaminated by automobile exhaust

Regarding automobile exhaust gas purification, taking gasoline vehicles as an example, the main one is the purification technology of three-way catalyst. The three-way catalyst consists of a honeycomb body and a catalyst coating. The catalyst coating consists of a rare earth oxygen storage material (oxidized by cerium oxide). preparation of lanthanum and zirconium oxide), rare earth stabilized aluminum oxide material and a noble metal composition. The rare earth element lanthanum in rare earth oxygen storage materials is a variable valence element, and its oxide has special storage and oxygen release functions. It combines with precious metals Pt, Pd and Rah to store oxygen during lean combustion and oxygen during rich combustion. Pollutants such as hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx) emitted from automobile exhausts are efficiently converted into nitrogen and water that are harmless to humans. Due to the high performance of rare earth oxygen storage materials, the performance of the three-way catalyst has been greatly improved. Now, foreign countries have reached the level of quasi-zero emission, and finally will basically achieve no emission of pollutants.

Since the automobile is equipped with an exhaust gas purification device, why is the domestic urban pollution still continually exploding? The main reason is that there are problems with the exhaustion of the exhaust gas purifier in a large number of domestic automobiles.

According to Professor Chen Yaoqiang, director of the Institute of Catalytic Materials at Sichuan University, our country now has only expired catalyst replacement for gasoline vehicles. In 2000, the national I emission standard for gasoline vehicles was implemented, and the catalyst was loaded onto the vehicle. The life of the catalyst was 80,000. Kilometer mileage. The taxi mileage is about 200,000 kilometers per year, so the taxi must be replaced twice a year to ensure the discharge is up to standard. According to this calculation, the taxi purchased in January 2000 should be replaced twice in 2000. From 2000 to now, there is no catalyst change in the country in 2015. How many high-emission vehicles can be imagined here.

By the end of 2014, China’s car ownership was 150 million, including 130 million gasoline vehicles. How many gasoline vehicles exceed the standard? The service life of the catalysts for the country I to the country III gasoline vehicles is 80,000 km or 5 years, whichever comes first, that is, no matter half a year, one year, two years, three years, four years. As long as the driving distance reaches 80,000 kilometers, the catalyst must be replaced. If it is less than 80,000 kilometers in 5 years, the catalyst must be replaced. For the national IV gasoline vehicle, the service life is 80,000 kilometers or 5 years, whichever comes first. .

According to the life of the catalyst of 8 (10) million kilometers or 5 years, more than 66 million gasoline vehicles produced in 2010 and before can be judged that the emissions have exceeded the standard, and 5 million bought before June 2014. Taxi must exceed the standard. More than 20 million of the more than 60 million gasoline vehicles produced between 2011 and 2014 have exceeded the standard. In addition, more than 90 million vehicles have exceeded the standard, that is, at least 130 million gasoline vehicles. 90 million vehicles have exceeded their emissions, which is the discharge of gasoline vehicles in our country.

The life span of the catalyst (80,000 km or 100,000 km) is experimentally calculated. When the vehicle travels more than 80,000 km, the emissions are basically exceeded, so the large-scale and large-scale pollution is caused by the lack of regular catalyst replacement. That is to say, PM2.5, hydrocarbons, carbon monoxide and nitrogen oxides can reach the emission standard by several tens to hundreds of times as the mileage is increased. This has been confirmed by the measurement results of gasoline vehicles with different mileage.

According to Professor Chen Yaoqiang, the failure of the catalyst itself will cause the pollutant emission to increase by about 3 times, and the deposition of phosphorus , zinc and the like in the lubricating oil in the catalyst pores will increase the exhaust resistance (back pressure), resulting in deterioration of engine combustion. The main reason for the increase in pollutant emissions by tens of times. It was confirmed by SEM and elemental analysis of the expired catalyst that the longer the catalyst expired, the more serious the catalyst pore blockage and the higher the pollution discharge.

From the measurement results, PM2.5 can be reduced by at least 60% to 80% for gasoline vehicles after catalyst replacement.

Therefore, only the government strongly advocates that the participation of all the people can make small rare earth elements continue to shine and heat in the process of controlling urban smog, and the blue sky of my city.

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