A Coverage Self-Consistent Microkinetic Model for Vapor-Phase Formic Acid Decomposition over Pd/C Catalysts

Journal Article · Tue Feb 28 00:00:00 EST 2023 · ACS Catalysis

DOI:https://doi.org/10.1021/acscatal.2c06078· OSTI ID:2007846

Bhandari, Saurabh ^[1]; Rangarajan, Srinivas ^[2]; Li, Sha ^[3]; Scaranto, Jessica ^[4]; Singh, Suyash ^[4]; Maravelias, Christos T. ^[5]; Dumesic, James A. ^[4]; Mavrikakis, Manos ^[4]

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1. University of Wisconsin-Madison, WI (United States); University of Wisconsin-Madison Department of Chemical and Biological Engineering
2. University of Wisconsin-Madison, WI (United States); Lehigh University, Bethlehem, PA (United States)
3. University of Wisconsin-Madison, WI (United States); Guangdong Laboratory (China)
4. University of Wisconsin-Madison, WI (United States)
5. University of Wisconsin-Madison, WI (United States); Princeton University, NJ (United States)

An iterative approach utilizing density functional theory (DFT, PW91-GGA)-informed mean-field microkinetic models and reaction kinetics experiments is used to determine the reaction mechanism and the active site for formic acid (HCOOH, FA) decomposition over a Pd/C catalyst. Models parametrized using DFT energetics on clean Pd(100) and Pd(111) required large corrections to the DFT energetics for capturing our experimental data. Further, both Pd(111) and Pd(100) models predicted a high coverage of adsorbed CO (CO*), inconsistent with the assumption of a clean surface at which the rate parameters for these models were calculated. To better represent the active site under reaction conditions and explicitly account for the presence of CO*, subsequent microkinetic models were formulated using DFT energetics that were calculated on partially (5/9 ML) CO*-covered Pd (111) and (100) facets. Upon parameter adjustment, the resultant 5/9 ML CO*-covered Pd(100) model, although consistent in terms of CO* coverage, was unable to capture the dehydration path measured in the experiments and was, therefore, deemed not to offer an accurate representation of the active site for FA decomposition over Pd/C. In contrast, a partially CO*-covered Pd(111) model was better at representing the catalytic active site, as in addition to being consistent in terms of CO* coverages, it required small adjustments of the DFT parameters to accurately capture the experimental data set (both dehydrogenation and dehydration). Our results suggest that the reaction occurs via the spectroscopically elusive carboxyl (COOH*) intermediate and that spectator CO*-assisted decomposition pathways play an important role under typical experimental conditions. In addition, our study highlights the importance of striving for coverage self-consistent microkinetic models and for including spectator-assisted mechanisms in order to develop an improved picture of the active site under reaction conditions.

• Research Organization: University of Wisconsin-Madison, WI (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES)
• Contributing Organization: Center for Nanoscale Materials at Argonne National Laboratory; National Energy Research Scientific Computing Center
• Grant/Contract Number: AC02-05CH11231; AC02-06CH11357; FG02-05ER15731
• OSTI ID: 2007846
• Journal Information: ACS Catalysis, Journal Name: ACS Catalysis Journal Issue: 6 Vol. 13; ISSN 2155-5435
• Publisher: American Chemical Society (ACS)
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
CO poisoning
binding energy
chemical reactions
coverage effects
dehydration
formic acid decomposition
kinetic modeling
microkinetic modeling
organic reactions
vapor phase dehydrogenation