SusChEM: Single Molecule Studies of Aldol Condensation on Heterogeneous Catalysts

Kansas State University, Manhattan KS

Investigators

Abstract

Converting renewable biomass resources to fuels provides a way to meet society's growing energy demands sustainably without reliance on fossil fuels. However, the compounds most easily extracted from biomass are quite different from conventional hydrocarbons obtained from processing petroleum or shale. One major difference is that most biomass-derived compounds are smaller than hydrocarbon fuels, necessitating catalytic reactions to build larger molecules from the original compounds. In these reactions, the catalyst is a solid film comprising chemicals that aid the efficiency of the reaction, but are not themselves consumed in the reaction. Drs. Hohn and Higgins are studying one such reaction, aldol condensation, to understand what catalytic properties are best suited to this task. To accomplish this, they follow a light-emitting reaction occurring on a catalyst film that they create with a gradient of catalytic properties along the film surface. Observing which parts of the film emit the brightest light provides information on the types of catalytic sites that are most active and allows the team to design improved catalysts. Research results are being disseminated in several ways, including through presentations at scientific conferences and peer reviewed publications. Dr. Hohn is also incorporating research results into outreach activities for K-12 students, while Dr. Higgins is introducing research results into a textbook on microscopy and into a graduate-level chemistry class. With funding from the Chemical Catalysis Program of the Chemistry Division, Drs. Hohn and Higgins of Kansas State University are developing a fundamental understanding of the catalytic properties responsible for activity in aldol condensation. They are applying single molecule methods to simultaneously measure acid/base properties and aldol condensation activity on thin films incorporating gradients in acid/base site densities. With these measurements, they are correlating catalytic activity in aldol condensation with the strengths and densities of the acid/base sites. The team applies surface characterization methods, including x-ray photoelectron spectroscopy (XPS) and Raman mapping studies, to augment the single molecule characterization studies. In addition, Drs. Hohn and Higgins correlate catalytic activity in aldol condensation with acid/base site proximity by preparing films with acid and base sites mixed at the molecular level and films where acid and base sites are separated by macroscopic distances. Along with regular publication of the results in the peer reviewed literature and presentation at conferences, Dr. Hohn is incorporates aspects of the research into activities for outreach programs at Kansas State University to enhance the recruitment of students from under-represented groups into science and engineering, while Dr. Higgins is introducing selected results into a graduate-level course and a textbook on chemical microscopy.