Silicate-1 (TS-1) was developed nearly 40 years ago and has been successfully used as a catalyst to convert propylene to propylene oxide. This is an important commodity chemical, such as polyurethane. plastic. Now, a research team from ETH Zurich, the University of Cologne, Fritz-Haber-Institute and BASF has revealed surprisingly actual reaction mechanisms.
Propylene oxide is an important commodity in the chemical industry, used in the production of plastics, antifreeze and hydraulic oil. The annual production of propylene oxide exceeds 11 million tons, of which more than 1 million tons are generated by oxidation with hydrogen peroxide (H2O2). This chemical reaction is catalyzed by titanium silicate-1 (TS-1). Titanium silicate-1 is a porous crystalline material composed of silicon dioxide and contains a small amount of titanium atoms (about 1 to 4 titanium atoms per 100 silicon atoms). Water is the only by-product. Although this catalytic process has been successfully applied since TS-1 was developed nearly 40 years ago, the specific catalytic mechanism is still unclear. However, the consensus of the chemical research community is that the active site in TS-1 must be an isolated titanium atom, which provides the basis for the unique reactivity of the catalyst.
A research team from ETH Zurich, the University of Cologne, the Fritz-Haber-Institute in Berlin, and BASF questioned this hypothesis. In a study currently published in the journal Nature, researchers can show that in the catalytic process, two titanium atoms activate H2O2, which indicates that the titanium atoms are actually not isolated, but have a synergistic effect.
According to the 17O solid-state nuclear magnetic resonance spectrum, the researchers showed that in the oxidation process with H2O2, it will form a peroxide intermediate with two titanium atoms. Through computational modeling, the author further showed that these dinuclear sites can indeed promote the oxidation of propylene efficiently. Interestingly, the catalytic mode of this binuclear site is similar to the mature reaction mechanism of peracid, which is the oldest and most significant reagent for olefin oxidation. The study also shows that dinuclear sites are particularly effective in propylene epoxidation, and that development of improved catalysts should be considered.
"The methods we used in this study are not breakthrough new methods. However, many things must happen simultaneously for this study to be carried out," said Christophe Copéret, the corresponding author of the publication. "Our laboratory has only recently The development of a method for synthesizing 17O-rich hydrogen peroxide is one of the keys to our recent work. In addition, our research team has gained a lot of experience in low-temperature NMR spectroscopy in recent years, enabling us to conduct this research In addition, Dr. Henrique Teles of BASF is also a co-author of this study. He emphasized: "If you try to optimize the catalyst on the basis of false assumptions, it is very difficult and may lead you in the completely wrong direction. Therefore, it is important to study this hypothesis more carefully. "
"We have been working on explaining the reaction mechanism of homogeneous titanium catalysts for many years and have discovered-contrary to the assumptions in the literature-that hydrogen peroxide is activated by titanium pairs. Co-author Professor Albrecht Berkessel from the University of Cologne said:" We see in the current study that the results of homogeneous catalysis are also applicable to heterogeneous catalysis. This is really a special moment." Dr. Thomas Lunkenbein, co-author from the Fritz Haber Institute in Berlin, added: "We are very I am happy to contribute to this research and confirm these conclusions through our analysis. This research is of fundamental significance to the understanding of the two-atom active center and opens up new possibilities for catalyst research. "
The development of catalysts is often a black box, which relies on many experiments, large-scale screening and luck. Understanding the structure of the required active sites is critical to the rational development of the catalyst. It is very surprising to clarify the reaction mechanism of the heterogeneous catalyst TS-1, which provides new enlightenment for this 40-year-old catalyst, which will help to improve and develop other homogeneous and heterogeneous catalysts.
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