Fundamental Mechanistic Studies of Formic Acid Decomposition on Pd: Structure Sensitivity and Surface Coverage Effects
Sha Li, Srinivas Rangarajan, Jessica Scaranto, Suyash Singh, Brandon O’ Neill, James A. Dumesic, Manos Mavrikakis
Department of Chemical & Biological Engineering
University of Wisconsin-Madison
The catalytic decomposition of formic acid is of great importance not only because formic acid is a by-product derived with high concentrations in biomass reforming1, but also because it can be used effectively as a fuel in fuel cells2-3 or as a hydrogen donor in catalytic transfer hydrogenation reactions4. Pd represents one of the most active catalysts for formic acid decomposition and it is widely employed as anode in direct formic acid fuel cells. In this work, we studied the gas-phase decomposition of formic acid on Pd(111) and Pd(100) surfaces using first-principles density functional theory (DFT) calculations. Minimum energy paths for HCOOH decomposition into CO2 and H2 (dehydrogenation products) or CO and H2O (dehydration products) were analyzed and compared on the two Pd facets. As there is clear experimental evidence that CO is accumulated on Pd surfaces during the reaction, we also studied this reaction on CO covered Pd(111) and Pd(100) surfaces. The presence of CO not only changed the reaction energetics but also changed the minimum energy pathways for formic acid decomposition on both facets. Compared with clean surfaces, formic acid decomposition is more difficult in the presence of CO on both facets. The DFT obtained results were then compared with the experimental results in a microkinetic model, shedding light on the reaction pathway and the active site for formic acid decomposition reaction on Pd catalysts.
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