【Frontiers in HaiChuan Chemical Technology】New mechanism for the structural evolution of propane dehydrogenation catalysts revealed

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Recently, the team led by Professor Zeng Jie from the University of Science and Technology of China, in collaboration with Researcher Li Xu from the University of Electronic Science and Technology of China, made new progress in understanding the structural evolution of metal catalysts in the propane dehydrogenation reaction, providing a new perspective for the rational design of high-performance propane dehydrogenation catalysts. 　　The researchers prepared a silica-supported platinum-indium alloy cluster catalyst and, for the first time, discovered that under the influence of high concentrations of propylene, the disordered platinum-indium alloy clusters transformed into platinum-indium intermetallic compounds, exhibiting propane dehydrogenation activity that surpasses that of most platinum-based catalysts. The relevant findings have been published in Nature Communications. 　　In heterogeneous catalytic reactions, the catalyst does not remain unchanged and often undergoes structural changes. Under the influence of temperature and atmosphere, the active metals and supports of the catalyst undergo a series of phenomena such as atomic rearrangement and crystal surface reconstruction, which in turn lead to significant changes in the catalyst’s performance. It goes without saying that revealing the structural evolution of catalysts is significant for identifying active sites and establishing structure-activity relationships. In the propane dehydrogenation reaction, high temperature and hydrogen are generally considered to be the factors driving the structural evolution of alloy catalysts, while the role of the product propylene in this structural evolution remains unclear. 　　The researchers used a stepwise strong electrostatic adsorption method in the solution phase to sequentially load indium and platinum on the surface of silica, and obtained alloy clusters through high-temperature hydrogen reduction. A series of spectroscopic experimental results indicate that only a small amount of indium was reduced and alloyed with platinum. In the formed platinum-indium alloy clusters, indium tends to be distributed on the surface. Meanwhile, the indium oxide species present between the platinum-indium alloy and the silica carrier have been shown to effectively suppress the sintering of the platinum-indium alloy. 　　Catalytic test results show that the platinum-indium alloy catalyst exhibits a significant activation induction period in a high-concentration propane atmosphere. Although the initial activity of the catalyst was very low, it increased rapidly as the testing time progressed and remained relatively stable. The activity of this catalyst in its stable state exceeds that of the vast majority of platinum-based catalysts reported in the literature, and is an order of magnitude higher than that of the platinum-indium alloys described so far. 　　By characterizing the structure of the catalyst after the reaction, the researchers found that under the influence of high concentrations of propylene product, large amounts of indium species volatilized from the catalyst and condensed at the ends of the quartz tubes, which led to the exposure of the platinum active sites and the occurrence of an induction period. The platinum-indium alloy clusters gradually transformed into platinum-indium intermetallic compounds with an average size of only 1.3 nanometers; this ultra-small size is attributed to the anti-sintering property provided by indium oxide species at the interfaces.