Collaborative Research: Combining Operando Spectroscopy and Multi-Scale Modeling to Elucidate the Mechanism of Aqueous Phase Reforming of Oxygenates

Clemson University, Clemson SC

Investigators

Abstract

One of the greatest challenges facing society is supplying energy to an ever-increasing population in the face of declining petroleum reserves and an increasingly need for sustainability. One promising strategy is to derive energy from biomass. Specifically, it is estimated that by 2030, the U.S. can produce more than 1 billion metric tons of dry biomass per year, which would have an energy content equivalent to 46% of the current oil consumption, if properly converted into usable fuels. However, many processes for converting biomass into fuels and chemicals require the addition of hydrogen gas. Unfortunately, present methods for supplying hydrogen gas from renewable resources are inefficient and costly, impeding the expansion of the biomass economy. The aqueous phase reforming (APR) of biomass is a promising strategy for producing hydrogen gas. Specifically, in APR, a part of the biomass is converted into H2 over a catalyst, which is a material that enables a chemical reaction without being consumed itself. Although promising, hydrogen yields from APR have thus far been disappointing, indicating a need to improve the efficiencies of APR catalysts. The first step in designing new catalysts entails understanding the function of the existing catalysts. Here, Dr. Rachel Getman of Clemson University and Dr. Carsten Sievers of the Georgia Institute of Technology are combining state-of-the-art modeling and spectroscopy to study the three key steps of the APR reaction: i) the removal of hydrogen; ii) generation of carbon monoxide; and iii) reaction of water and carbon monoxide to form hydrogen and carbon dioxide. Since the carbon dioxide produced in APR will be used to grow new biomass, APR is a "carbon-neutral" process. Broader impacts involve the inclusion of undergraduates, especially women and underrepresented minorities, into meaningful explorations of fundamental and applied chemistry. Research results are also being presented at the Robert C. Williams Paper Museum of Papermaking in Atlanta, GA. With funding from the Chemical Catalysis Program of the Chemistry Division, Dr. Rachel Getman from Clemson University and Dr. Carsten Sievers from the Georgia Institute of Technology are combining multiscale modeling and operando spectroscopy to provide fundamental insight regarding the active sites and mechanism of the Aqueous Phase Reforming (APR) of biomass-derived oxygenates to hydrogen and carbon dioxide over supported Pt catalysts. Specifically, the project is focused on how selective and non-selective dehydrogenation, decarbonylation, and Water Gas Shift (WGS) are affected by water as a solvent, co-adsorbed water and spectator species, and the nature of support. The new insight will enable researchers to design improved catalysts and optimize process conditions. Modeling studies involve combining methods in density functional theory with classical molecular dynamics, in order to simultaneously incorporate the breaking and forming of chemical bonds and the thermal motions of the liquid water molecules in the solvent. The main experimental technique is attenuated total reflection IR spectroscopy, which allows for probing surface species on catalysts that are immersed in a solution of the reactant. Experimental and theoretical efforts are highly integrated. For example, calculated and measured vibrational frequencies of surface species and rate constants for their formation and conversion are compared, enabling the development of models that are consistent with experimental observations. The PIs are strongly supporting the participation of female and underrepresented minority students. Further, the results from this project are presented to a broader audience through a display at the Robert C. Williams Paper Museum of Papermaking in Atlanta, GA as well as through a biorefining elective. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.