In recent years, air pollution has seriously affected people's health and quality of life. According to statistics, the exhaust gas emitted by motor vehicle exhausts accounts for 60-70% of the total air pollution in the city. Among them, the most harmful one is nitric oxide. (NO) and carbon monoxide (CO). NO is colorless, odorless and carcinogenic to humans at room temperature, and NO can be oxidized to NO2 in the air. NO2 has a strong stimulatory effect on the respiratory system. CO is inhaled. Can inhibit the ability of hemoglobin to transport oxygen, suffocate and even endanger life.
How do we purify vehicle exhaust? Researchers have come up with a method that uses a metal oxide catalyst. This catalyst can provide active oxygen for the oxidation of CO to CO2. In addition, it provides oxygen vacancies for the reduction of NO to N2 to store oxygen. Redox cycle, while removing CO and NO two harmful substances, so that the vehicle exhaust can be purified.
However, in this catalytic process, if the catalyst can not provide more active oxygen, or can not provide more oxygen vacancies, it will limit the oxidation and reduction cycle, reduce the removal effect of pollutants. Therefore, the metal oxide catalytic material Oxygen atoms can escape from the bondage of metal, and then successfully participate in the oxidation-reduction cycle, it becomes a key issue that restricts the efficiency of automobile exhaust gas purification.
How to weaken the role of metal-oxygen, enhance the activity of oxygen atoms, help oxygen atoms escape from the bondage of metal as much as possible, and participate in the reaction has become a problem that scientists must overcome.
However, under normal circumstances, the interaction between the metal atoms and oxygen atoms in the metal oxide, the coordination condition, etc. should completely follow the crystal structure of the oxide. Once this structure is formed, it will be very stable, and the oxygen atoms will be held in crystal lattice. In a few days ago, the Sun Jian and Yu Jiafeng research team of the Dalian Institute of Chemical Physics, Chinese Academy of Sciences, specially developed an 'escape plan' for oxygen atoms in metal oxides.
The core problem of this plan is to 'grab the time'!
They used a high-temperature quenching method to make a 'difference in time' with the oxides. They used the flame to burn the oxides at a high temperature of 2000°C to form oxides quickly. Then, after the oxide crystal structure was roughly formed, a strong interaction between metal and oxygen occurred. Before, quickly cool down, 'crawl' the middle transitional state!
At this time, the oxide crystal structure is basically formed, but the oxygen atoms have not yet been rearranged and form a strong interaction with the metal atoms, and they are in a disorderly metastable state. This process is very, very short, from the precursor to the oxide The whole process of collecting requires the scientific research personnel to control within seconds. This is the real “fight”.
In this way, the researchers successfully locked the oxygen atoms in a disordered state during the transition. The metal atoms have weaker binding to the oxygen atoms. Under milder reaction conditions, the oxygen atoms can escape from the bondage of the metal. Redox cycle, which accelerates the purification of automobile exhaust.
Oxygen atoms escape from metal binding
It was found that oxygen vacancies were not found in the Ce-Zr solid solution oxides prepared by this method, indicating that metastable oxygen atoms in the catalyst can be stably present before the reaction, and under relatively mild conditions, such as low temperature reduction, vacuum treatment. , Metals, etc., can release a large amount of active oxygen. Compared with the traditional co-precipitation method of Ce-Zr oxides, the oxides produced by the FSP method can increase the number of oxygen vacancies by 19 times.
The research results provide a technical basis for the development of low-temperature efficient automotive exhaust gas purification catalysts, and this catalytic material preparation technology provides new ideas for the design and application of new oxide catalytic materials. Related research results have been published online in the "Chemical Science". (Chemical Science, 2018, 9, 3386-3394) magazine.