2021-06-30

Scientists can now design single-atom catalysts for important chemical reactions

By yqqlm yqqlm

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Scientists can now design single-atom catalysts for important chemical reactions

The annual demand for propylene is about 100 million tons (worth about US$200 billion), and there are simply not enough resources to meet the surge in demand. After sulfuric acid and ethylene, its production involves the third largest conversion process by scale in the chemical industry. The most common method for producing propylene and ethylene is steam cracking, and its output is limited to less than 85%. It is one of the most energy-intensive processes in the chemical industry. The traditional feedstock for the production of propylene is a by-product of oil and natural gas operations, but the shift to shale gas has limited its production.

The typical catalyst used for the production of propylene from propane found in shale gas is composed of a combination of metals, which may have random and complex structures at the atomic level. Reactive atoms usually come together in many different ways, making it difficult to design new reaction catalysts based on basic calculations of the chemical’s possible interaction with the catalytic surface.

In contrast, the single-atom alloy catalyst discovered by Tufts University and reported for the first time in the “Science” magazine in 2012 disperses a single active metal atom on a more inert catalyst surface with a density About 1 active atom is more than 100 inert atoms. This allows a clear interaction between a single catalytic atom and the chemical being processed without being complicated by irrelevant interactions with other active metals nearby. Reactions catalyzed by monoatomic alloys tend to be clean and efficient, and, as the current research shows, they can now be predicted by theoretical methods.

Charles Sykes, a professor of chemistry at Tufts University and the corresponding author of the study, said: “We have adopted a new approach to run the first supercomputer on a supercomputer with collaborators from University College London and the University of Cambridge. A principle calculation, which allows us to predict what is the best catalyst to convert propane to propylene.”

These calculations that lead to predicting the reactivity of the catalyst surface through atomic-scale imaging and reactions running on model catalysts It was confirmed. The researchers then synthesized a single-atom alloy nanoparticle catalyst and tested it under industrially relevant conditions. In this particular application, the rhodium atoms dispersed on the copper surface are most effective in the dehydrogenation of propane to propylene.

The co-corresponding author of the study, Michail Stamatakis, an associate professor in the Department of Chemical Engineering of the University of London, said: “The improvement of commonly used heterogeneous catalysts is mostly a trial and error process. Single-atom catalysts allow us to learn from the first One principle is to calculate how molecules and atoms interact on the catalytic surface to predict the outcome of the reaction. In this case, we predict that rhodium will very effectively pull hydrogen from molecules such as methane and propane-this prediction is similar to Common sense is the opposite, but it is incredibly successful when put into practice. We now have a new method of rationally designing catalysts.”

Monoatomic rhodium (Rh) catalysts are very efficient. The product propylene can be selectively produced by 100%, while the current industrial propylene production catalyst is only 90%. The selectivity here refers to the proportion of the reaction that leads to the desired product on the surface. Stamatakis said: “If adopted by the industry, this level of efficiency may result in substantial cost savings and millions of tons of carbon dioxide not being emitted into the atmosphere.”

Monatomic alloy catalysts are not only more efficient. High, and they also tend to run the reaction under milder conditions and lower temperatures, so they require less energy than traditional catalysts. They may be cheaper to produce, requiring only a small amount of precious metals, such as platinum or rhodium, and these metals may be very expensive. For example, the price of rhodium is currently about US$22,000 per ounce, while the price of copper, which accounts for 99% of the catalyst, is only 30 cents per ounce. The new rhodium/copper monoatomic alloy catalyst is also resistant to coking-a common problem in industrial catalytic reactions, that is, intermediate products with high carbon content-basically soot-accumulate on the surface of the catalyst and start Suppress the desired response. These improvements are the secret to “greener” chemistry that reduces the carbon footprint.

Stamatakis said: “This work further proves the huge potential of monoatomic alloy catalysts in solving the inefficiency of the catalyst industry, which in turn has very large economic and environmental returns.”