UCR Assistant Professor of Chemical and Environmental Engineering Phillip Christopher has recently uncovered a method to tune chemical reactions to favor specific products through the use of a catalyst. With this technique of controlling both the pathways and the products created in certain chemical reactions, Christopher hopes to apply the same principle to other chemical reactions, and perhaps use it for environmental protection in the future.
Catalysts in general terms, are materials that facilitate reactions by lowering the activation barrier, or the amount of energy required to drive a reaction. These catalysts often help break down the structure of a reactant and convert it into a usable product. Christopher emphasized the idea that much of chemistry and arguably, daily life, is heavily reliant on catalysts. From collecting oil out of the ground and converting it into usable products like gasoline and plastics, to even the catalytic converters in our cars, “catalysts are the materials that drive all the chemical change that we make to use our everyday stuffs.
The idea of using a catalyst to drive reactions on the industrial scale has been a well-utilized process in the past. The Haber–Bosch process, which converts nitrogen to ammonia, was necessary during World War I in order to produce munitions. However, the novel aspect of the catalysts that Christopher developed is that he can select and tune what specific product is made in a reaction where multiple products would otherwise be made. These new and modified catalysts, according to Christopher, “not only do lower activation barriers, but they lower activation barriers for one particular reaction,” thereby allowing you to make the product that you want. Christopher’s research, which was recently published in the journal Nature Chemistry, studied the conversion of CO2 to methane and carbon monoxide, and hypothesized whether a product of one specific pathway could be made.
Christopher explained that a lot of the metal ions in catalysts used in research are quite expensive and rare. These metal ions, which include platinum, gold, palladium and rhodium, are made into smaller particles, and are surrounded by support molecules like titanium dioxide in an effort to increase the area of contact where reactions occur. As Christopher found in his experiment, when these metal ions are in contact with support molecules, the properties of the catalyst can change. Christopher’s research used rhodium along with titanium dioxide, and looked at tuning and modifying the connections between the two in order to test whether different products could be made.
He found that when flowing CO2 over this catalyst at 250 degrees celsius, carbon monoxide and methane were made depending on the tuning and modification of the interactions between the rhodium and the support molecules. This was visualized and confirmed using in situ spectroscopy and microscopy. As Christopher explained, “Selectivity is the most important thing and the hardest thing to control, and we showed a new way to be able to control selectivity.”
Christopher remains hopeful in the application of this type of catalyst, saying, “The dream, ultimately, is can we capture the CO2 from the atmosphere?” With all of the carbon dioxide in the atmosphere that is driving global warming, Christopher believes this catalyst could utilize the gas and efficiently convert it into useful products like methane and carbon monoxide, which are both chemical building blocks for many other processes. Additionally, Christopher is looking to apply his approach with tunable catalysts to other important chemical reactions where he could similarly select for specific products.