2019 AIChE Annual Meeting

(224a) Active Sites and Mechanisms for Vapor-Phase Decomposition of Formic Acid on Pt Catalysts

Authors

Rangarajan, S., University of Wisconsin-Madison
Maravelias, C. T., University of Wisconsin-Madison
Dumesic, J. A., University of Wisconsin-Madison
Mavrikakis, M., University of Wisconsin - Madison
Formic acid (FA) has gained widespread attention as a promising hydrogen storage material for on-demand production in fuel cells or catalytic hydrogenation.1,2 Obtained as a by-product in biomass reforming, FA has a high volumetric capacity (53.4 g-H2/l), is liquid at ambient conditions, and exhibits low toxicity and flammability, thus making it a favorable hydrogen storage option for transportation applications. Formic acid conversion can occur through the desired dehydrogenation pathway to form CO2 and H2, or through the undesired dehydration pathway to produce CO and H2O, the two routes coupled together through the water gas shift reaction (WGSR).3 Experimentally, Pt has been reported to be one of the most active and selective monometallic catalysts for vapor-phase decomposition of FA.4

Despite numerous studies in the literature, the reaction mechanism and the nature of the reactive intermediate are still under debate. In this study, we present a combined approach utilizing density functional theory (DFT) calculationson Pt(100) and Pt(111)5 facets, reaction kinetics experiments using carbon supported Pt catalysts, and mean field microkinetic modeling6. This approach allows us to identify a coverage self-consistent description for the active site and gain deeper understanding of the reaction mechanism. The results also give insight into the nature of the reactive intermediate, rate-determining steps, and surface environment under reaction conditions. Our coverage self-consistent model predicts the (111) facet to be the active site with the reaction flux passing through the carboxyl mechanism.

Fundamental understanding of the reaction mechanism derived from this work, will advance the consideration of FA as a hydrogen storage option and can serve as the basis for design of improved catalysts for its decomposition to H2.

References

  1. Alonso, D. M., Bond, J. Q. & Dumesic, J. A. Catalytic conversion of biomass to biofuels. Green Chem. 12, 1493 (2010).
  2. Grasemann, M. & Laurenczy, G. Formic acid as a hydrogen source – recent developments and future trends. Energy Environ. Sci. 5, 8171 (2012).
  3. Gokhale, A. A., Dumesic, J. A. & Mavrikakis, M. Article On the Mechanism of Low-Temperature Water Gas Shift Reaction on Copper On the Mechanism of Low-Temperature Water Gas Shift Reaction on Copper. J. Am. Chem. Soc. 130, 1402–1414 (2008).
  4. Solymosi, F., Koós, Á., Liliom, N. & Ugrai, I. Production of CO-free H2 from formic acid. A comparative study of the catalytic behavior of Pt metals on a carbon support. J. Catal. 279, 213–219 (2011).
  5. Scaranto, J. & Mavrikakis, M. HCOOH decomposition on Pt(111): A DFT study. Surf. Sci. 648, 201 (2016).
  6. Rangarajan, S., Maravelias, C.T., & Mavrikakis, M. Sequential-Optimization-Based Framework for Robust Modeling and Design of Heterogeneous Catalytic Systems. J. Phys. Chem. C. 46, 121 (2017)