The Elements of Catalysis
Ian Harrison and Matthew Neurock
Photos by Tom Cogill
Every high school chemistry student learns the definition of a catalyst. It’s a substance that changes the speed of a chemical reaction without undergoing any change itself. Yet even the most sophisticated chemists lack a clear understanding of how catalyst surfaces work on a molecular level. This is the task that Ian Harrison and his colleagues in chemistry and chemical engineering are seeking to remedy.
This work is crucial because catalysts are ubiquitous. They make it possible to process petrochemicals into a host of products, they are used in automobiles and factories to reduce pollution, and they drive the chemical reactions that power fuel cells. Attain the highly refined understanding of catalysis that Harrison hopes to achieve, and these catalysts can become more effective enablers of chemical transformations, more selective, and more energy efficient.
“Historically, the development of catalysts has relied heavily on trial and error,” says Harrison. “Our goal is to define structure and reactivity relationships and energy flow pathways that occur during catalysis. This kind of information is extremely valuable for theorists like Matthew Neurock in chemical engineering.”
“Theory can then be used to examine or screen a wide range of more complex metal alloy nanoparticles for improved catalytic behavior and to help design new catalytic materials,” explains Neurock. “By providing highly precise quantitative kinetic data and by helping to establish the mechanism for elementary bond breaking over well-defined metal surfaces, Ian’s experiments will provide critical information for testing, validating and guiding our theoretical efforts.”
The key to making these measurements is the unique combination of equipment and expertise assembled at U.Va. The Center for Atomic, Molecular, and Optical Science (CAMOS) in the chemistry department houses the Ultrafast Laser Laboratory, which permits femtosecond, picosecond, and nanosecond strobing of materials processes. Kevin Lehmann, who joined the chemistry department from Princeton last year, brought with him additional laser facilities capable of preparing molecules in selected quantum states. And John Polanyi, the 1986 Nobel Laureate in Chemistry, donated a molecular beam scattering chamber to the department, which completes the suite of facilities needed to probe reactivity and energy transfer at the gas-surface interface.
Using these facilities, Harrison and his colleagues can track factors that influence a molecule’s reactivity such as its translational, rotational, and vibrational quantum state as well as the structure, composition, and temperature of the catalytic surface. They have begun by analyzing the reactivity of methane in the presence of common catalysts. This choice has several advantages. Methane makes a good test bed for perfecting their analytical techniques because it is a relatively small molecule. In addition, methane is part of a particularly useful class of hydrocarbons known as alkanes, so the information they discover about its reactivity can be extrapolated to more complex members of this group.
Harrison’s choice of methane is also important because methanol is a candidate for powering fuel cells. Methane is found and produced in abundance around the world, but reactions designed to transform it directly to methanol have proven to be difficult to control. Harrison’s work predicts that given the right circumstances and catalysts, methane might be harnessed at the well-head as a reliable source of easily transportable methanol.
“Ultimately,” Harrison says, “our work is about helping engineers make informed choices. Our goal is to provide people with the quantitative information and qualitative insight they need to optimize catalysis for desirable properties, whether that is increasing yields, improving selectivity for desired products, or minimizing energy use.”