The Surprising Discovery By Chemists of Nanoconfined Reactions Might Support The Catalytic Design

The Surprising Discovery By Chemists of Nanoconfined Reactions Might Support The Catalytic Design

Georgia State University's chemistry researchers have uncovered one of the puzzles of catalytic reactions on a microscopic scale that enable the development of more efficient industrial processes. Nanoconfined Reactions

Catalysts accelerating chemical reactions, from food digestion to automotive internal combustion engines - are critical to converting raw materials into useful industrial products, including petroleum, plastics, paper, pharmaceuticals, and breweries. Knowing how reactions work will help scientists develop better catalysts that are more energy efficient and environmentally friendly. Nanoconfined Reactions

The researchers developed a new imaging strategy that allows individual molecules to be traced while flickering through tiny pores in the shells of silica spheres, and monitoring chemical reaction dynamics at catalytic centers in the nucleus. Thus, the first quantitative measurements of the actual inclusion could be performed on the nanoscale accelerating catalytic reactions. Nanoconfined Reactions

Understanding this surprising "nanoconfection effect" could help to develop more efficient industrial catalysts that can save energy. Nanoconfined Reactions

"You want to make a specific product and have a choice of different porous materials from which to make different things, which one offers the best conversion rate and the highest speed?" said Ning Fang, associate professor of chemistry at Georgia State, who published the findings of the research in Nature Communications. "Now we have a theory based on experimental evidence that we add to simulations to better predict what the result of using certain catalysts might be." Nanoconfined Reactions

The study of catalytic reactions has been limited to theoretical and computational models. Developed by Bin Dong, a Georgia postdoctoral fellow, and published in Nature Catalysis, the single-molecule imaging system allows researchers to observe and measure responses to a tiny, multi-layered porous sphere created by Iowa State University staff Led by Professor Wenyu Huang and postdoctoral fellow Yuchen Pei. 

The reactant molecules must align in a particular direction to pass through nanopores - openings about 100 times smaller than the width of a strand of hair. The nanopores are comparable in diameter to the size of the reactant molecule, and when their tip reaches the active core, it immediately triggers the first step of the reaction upon contact. However, the generated intermediate is trapped by the nanopore while the reaction continues in three steps to form the final product molecule. Catalytic Design

In contrast to conventional theory, this "nanoporous barrier" accelerates the reaction rather than slowing it down, based on Fang's experimental measurement of the activation energy. Although molecular motion is limited by the presence of a porous shell, the process is actually increased by the limitation, the study found. Catalytic Design

"Instinctively, one would expect decreasing activity if catalytic centers are shielded by a nanoporous envelope of reactant molecules," Fang said. "However, our experimental evidence shows a different story and, surprisingly, the catalytic activity for catalysts with longer and narrower nanopore structures is further enhanced until the benefits of nanoconfusion are overcome by the limited molecular transport in the nanoporous shell." Catalytic Design

This discovery could have significant implications for the development of new catalysts. For example, with an equivalent of more than 500 million barrels of gas per year, ethane and propane are converted into alkenes, which are used to make plastics, detergents, and other products. The use of more efficient catalysts on a large scale could save a lot of energy. Catalytic Design

Journal Reference
Bin Dong, Yuchen Pei, Nourhan Mansour, Xuemei Lu, Kai Yang, Wenyu Huang, Ning Fang. Deciphering nanoconfinement effects on molecular orientation and reaction intermediate by single molecule imaging. Nature Communications, 2019; 10 (1) DOI: 10.1038/s41467-019-12799-x

News Source