(750b) Determining How Support pH and Hydrophilicity and Metal Particle Size Influence Activity and Product Distributions in Aqueous Phase Reforming of Glycerol

Authors: 
Sewell, T., Clemson University
Getman, R., Clemson University
Bruce, D. A., Clemson University
The catalytic conversion of biomass derivatives, such as glycerol, to platform chemicals or energy products could lessen dependence on fossil fuels, thus providing a sustainable source of energy for the world’s growing demand. One method for performing these conversions is aqueous phase reforming (APR), which is of interest because it utilizes low operating temperatures. Presently, catalysts synthesized to carry out APR are comprised of noble metals catalysts supported on metal oxides or other minerals. One of our goals is to learn how these materials function so that we can design less expensive catalysts for APR and other similar reactions. One of the challenges in understanding how APR catalysts function is the aqueous environment itself: H2O molecules not only influence catalytic chemistry and physics in numerous ways, they also impede our ability to observe these influences. Our group and others have recently reported several ways in which H2O influences the catalytic chemistry of glycerol APR and related reactions over transition metal catalysts. However, how the support participates, and especially how the catalytic chemistry is influenced by the H2O/catalyst/support interface is still largely unknown. In this research, we identify how multiple support properties influence catalytic activity and product distributions in glycerol APR. Specifically, we examine the effects of acidity/basicity, hydrophobicity/hydrophilicity, and catalyst particle size on Pt-catalyzed glycerol APR. These properties are expected to have the following influences on catalytic activity and performance. Acidity/basicity of the support is caused by the presence of Brønsted and Lewis acid/base sites on the support surface, which promote some of the reaction steps in APR. Additionally, they influence the pH of the catalyst due to the presence of H+ and OH- ions, which also alter the hydrophobicity/hydrophilicity of the catalyst. These effects also influence the structure of liquid H2O at the interface, which in turn influences the thermodynamics and kinetics of catalytic reactions. Catalyst particle sizes are dictated by metal/support interactions and influence catalytic activity and selectivity. Our goal is to identify the support properties that lead to optimal performance but also that have the least influence on performance, as these materials can be best compared with simulation work from our group. Synthesized catalysts undergo various characterization methods, including scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive X-ray (EDX), nuclear magnetic resonance (NMR), thermogravimetric analysis (TGA), temperature-programmed-desorption (TPD), and various infrared (IR) spectroscopy methods. Results from these characterization methods as well as product distributions from catalytic experiments will be presented, and comparisons with simulations will be made where possible.