Recently, Dr. Ping Chen and Dr. Jianping Guo have made important progress in catalytic ammonia synthesis research. The research team innovatively proposed the "dual activity center" catalyst design strategy, and thus developed a series of composite catalysts composed of transition metals and lithium hydride, and realized the low temperature catalytic synthesis of ammonia. The relevant research results were recently published in the journal Nature Chemistry.
Ammonia is one of the most basic chemical raw materials, and it is also the main source of fertilizer. From a thermodynamic point of view, the ammonia produced by the reaction of nitrogen and hydrogen can be carried out under normal temperature and pressure conditions. However, because nitrogen molecules are very stable and difficult to activate, the process of industrial ammonia synthesis can only be achieved under conditions of high temperature and high pressure (350°C-500°C, 50-200 atmospheres). With such harsh conditions, the ammonia industry needs to consume 1%-2% of the global energy supply each year. China is the largest producer of synthetic ammonia. The annual output of synthetic ammonia is close to 30% of the total amount of synthetic ammonia in the world. For China's national conditions, it is of great strategic significance to develop low-temperature, low-pressure and high-efficiency synthetic ammonia catalysts.
Although the research on synthetic ammonia has a history of more than 100 years, it still has not achieved low-temperature and low-pressure synthesis. Where is the difficulty?
Previous studies have shown that there is a limited relationship between the reaction energy barrier and the adsorption energy of the reaction species on the transition metal surface, making it difficult to achieve efficient synthesis of ammonia at a low temperature on a single transition metal catalyst.
In response to the above problems, Chen Ping's research team creatively introduced lithium hydride as the second component into the catalyst to construct a dual-active-center-composite catalyst system of "transition metal-lithium hydride" and proposed the "activated nitrogen transfer". The reaction mechanism makes the activation of nitrogen and hydrogen and the adsorption of intermediate species occur in different active centers, thus breaking the limit relation between the reaction energy barrier and adsorption energy on a single transition metal, making it possible to synthesize ammonia at low temperature and pressure. .
The experimental results show that the addition of lithium hydride has a significant role in promoting the activity of the transition metal of the third cycle, especially Fe-LiH (iron-lithium hydride) and Co-LiH (cobalt-lithium hydride) composite catalyst at 150 °C. The considerable activity of ammonia synthesis was demonstrated, demonstrating the effectiveness and universality of the "dual activity center" strategy.
Previously, Chen Ping's research team has accumulated more than 10 years of research in alkali metal hydrides, nitrides, and amino/imino compounds. This research is another new breakthrough after the successful application of this type of compound for hydrogen storage and catalytic ammonia decomposition.
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