Aqueous phase reforming (APR) of sugar alcohol molecules derived from biomass, e.g. , C x H (2x+2) O x (aq) + x H 2 O → x CO 2 (g) + (2 x + 1)H 2 (g), creates hydrogen gas sustainably, making it an important component of future bio-refineries; however, problems with the cost, activity, and selectivity of present precious metal based catalysts impede its broader adoption. Ideally, new catalysts would be designed to optimize activity and selectivity; however, a comprehensive understanding of the APR mechanism is lacking. This is complicated by the fact that the primary biomass-derived sugar alcohols are large molecules (meaning that their reaction networks are large) and because of the presence of liquid water. Water influences catalytic phenomena in multiple ways, including altering the thermodynamics of catalytic surface species and participating in catalytic reactions. Understanding the mechanism of APR requires understanding these various effects; however, computational strategies based solely on density functional theory (DFT) are computationally prohibitive for such large and complicated reaction networks. In this work, we investigate the mechanism of APR reactions in the context of glycerol reforming. To calculate the reaction network, we combine DFT calculations, force-field molecular dynamics (MD) simulations, linear scaling relations (LSRs), transition state scaling (TSS) relationships, and data from the literature into a microkinetic model. The microkinetic model is run under vacuum and aqueous phases in order to learn about the roles of water molecules on the mechanism of glycerol APR. We identify four such roles: providing surface hydroxyl groups, which promote oxidation of surface CO formed in glycerol decomposition; promoting C–H scissions; promoting O–H scissions; and inhibiting the thermodynamics of decarbonylation of C3 intermediates.
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Insights into how the aqueous environment influences the kinetics and mechanisms of heterogeneously-catalyzed COH* and CH 3 OH* dehydrogenation reactions on Pt(111)
Water influences catalytic reactions in multiple ways, including energetic and mechanistic effects. While simulations have provided significant insight into the roles that H 2 O molecules play in aqueous-phase heterogeneous catalysis, questions still remain as to the extent to which H 2 O structures influence catalytic mechanisms. Specifically, influences of the configurational variability in the water structures at the catalyst interface are yet to be understood. Configurational variability is challenging to capture, as it requires multiscale approaches. Herein, we apply a multiscale sampling approach to calculate reaction thermodynamics and kinetics for COH* dehydrogenation to CO* and CH 3 OH* dehydrogenation to CH 2 OH* on Pt(111) catalysts under liquid H 2 O. We explore various pathways for these dehydrogenation reactions that could influence the overall mechanism of methanol decomposition by including participation of H 2 O structures both energetically and mechanistically. We find that the liquid H 2 O environment significantly influences the mechanism of COH* dehydrogenation to CO* but leaves the mechanism of CH 3 OH* dehydrogenation to CH 2 OH* largely unaltered.
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- Award ID(s):
- 1725573
- NSF-PAR ID:
- 10111158
- Date Published:
- Journal Name:
- Physical Chemistry Chemical Physics
- Volume:
- 21
- Issue:
- 19
- ISSN:
- 1463-9076
- Page Range / eLocation ID:
- 9895 to 9904
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/C9CP00824A
