Glycerol, a major byproduct of biodiesel processing, could be leveraged as a platform to higher‐value products if the selectivity of its transformations could be improved. Herein, density functional theory (DFT) calculations are used to identify reactivity trends for the initial glycerol dehydrogenation steps involving C−H and O−H bond cleavage on a variety of transition metals including Ag, Au, Cu, Pd, Pt, and Rh considering both (111) and (100) surface facets. Additional activation energies calculated on Pt(111), Pt(100), Au(111), and Au(100) surfaces indicate that the most energetically favorable pathway is highly sensitive to the local surface structure and depends on the adsorption strength of reactive intermediates to the metal surface. Finally, adsorbate‐based and structure‐based energy scaling approaches for glycerol are identified, suggesting the ability to screen candidate materials using both structure‐ and composition‐based reactivity descriptors.
Reaction pathways for HCN on transition metal surfaces
The adsorption and decomposition of HCN on the Pd(111) and Ru(001) surfaces have been studied with reflection absorption infrared spectroscopy and density functional theory calculations. The results are compared to earlier studies of HCN adsorption on the Pt(111) and Cu(100) surfaces. In all cases the initial adsorption at low temperatures gives rise to a ν (C–H) stretch peak at ∼3300 cm −1 , which is very close to the gas phase value indicating that the triple CN bond is retained for the adsorbed molecule. When the Pd(111) surface is heated to room temperature, the HCN is converted to the aminocarbyne species, CNH 2 , which was also observed on the Pt(111) surface. DFT calculations confirm the high stability of CNH 2 on Pd(111), and suggest a bi-molecular mechanism for its formation. When HCN on Cu(100) is heated, it desorbs without reaction. In contrast, no stable intermediates are detected on Ru(001) as the surface is heated, indicating that HCN decomposes completely to atomic species.
more »
« less
- Award ID(s):
- 1800236
- NSF-PAR ID:
- 10098470
- Date Published:
- Journal Name:
- Physical Chemistry Chemical Physics
- Volume:
- 21
- Issue:
- 9
- ISSN:
- 1463-9076
- Page Range / eLocation ID:
- 5274 to 5284
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
more » « less
Abstract -
Metal phosphides are promising catalysts for hydrocarbon transformations, but computational screening is complicated by their diverse structures and compositions. To disentangle structural from compositional contributions, here we explore the metal-rich M 2 P (M = Fe, Co, Ni, Cu, Mo, Ru, Rh, Pd, Ag, Pt) series in hexagonal and orthorhombic structures that are common to a subset of these materials, using supercell density functional theory (DFT). To understand the contribution of metal choice to utility for catalytic ethane dehydrogenation (EDH), we compute and compare the adsorption of key EDH intermediates across low-index surface terminations. These materials expose both metal and phosphide sites. Calculations show that binding energies at metal sites correlate with the bulk metals, with P incorporation either enhancing or suppressing binding. Phosphide sites compete with metal sites for adsorbates and tend to suppress overactivation by destabilizing highly dehydrogenated species engaging in C–H bond breaking. Results are generally insensitive to bulk structure and surface facet. Results suggest metal-rich Pd phosphides to have favorable adsorption characteristics for catalytic dehydrogenation, consistent with recent observations.more » « less
-
Periodic Density Functional Theory calculations reveal the potential application of 10 imidazole based N-heterocyclic carbenes to behave as “molecular corks” for hydrogen storage on single atom alloys, comprised of Pd/Cu(111) or Pt/Cu(111). Calculations show that functionalizing the NHC with different electron withdrawing/donating functional groups results in different binding energies of the NHC with the alloy surfaces. The results are compared to DFT calculations of carbon monoxide bound to these alloys. The Huynh electronic parameter (is calculated for several simple imidazole NHCs to gauge σ-donor ability, while Se-NMR of and P-NMR calculations of selenourea derivatives and carbene-phosphinidene adducts, respectively, have been utilized to gauge π-acidity of the NHCs. It is demonstrated that consideration of both σ and π donating/accepting ability must be considered when predicting the surface-adsorbate binding energy. It was found that electron withdrawing groups tend to weaken the NHC-surface interaction while electron withdrawing substituents tend to strengthen the interaction.more » « less
-
Periodic Density Functional Theory calculations reveal the potential application of 10 imidazole based N-heterocyclic carbenes (NHCs) to behave as “molecular corks” for hydrogen storage on single atom alloys, comprised of Pd/Cu(111) or Pt/Cu(111). Calculations show that functionalizing the NHC with different electron withdrawing/donating functional groups results in different binding energies of the NHC with the alloy surfaces. The results are compared to DFT calculations of carbon monoxide bound to these alloys. The Huynh electronic parameter (HEP) is calculated for several simple imidazole NHCs to gauge σ-donor ability, while Se-NMR and P-NMR calculations of selenourea derivatives and carbene-phosphinidene adducts, respectively, have been utilized to gauge π-acidity of the NHCs. It is demonstrated that consideration of both σ and π donating/accepting ability must be considered when predicting the surface-adsorbate binding energy. It was found that electron withdrawing groups tend to weaken the NHC-surface interaction while electron donating substituents tend to strengthen the interaction.more » « less
-
The adsorption of crotonaldehyde on Cu-Pt alloy surfaces was characterized by density functional theory (DFT). Two surfaces were considered: Cu2Pt/Cu(111) and Cu3Pt/Cu(111). It was determined that the presence of Pt on the surface, even when isolated as single atoms fully surrounded by Cu, provides additional stability for the adsorbates, increasing the magnitude of the adsorption energy by as much as 40 kJ/mol. The preferred bonding on both surfaces is via multiple coordination, with the most stable configuration being a cis arrangement with di-σ bonding of the C=O bond across a Cu–Cu bridge and an additional π bonding to a Pt atom. The fact that Pt significantly affects the adsorption of unsaturated aldehydes such as crotonaldehyde explains why the kinetics of their hydrogenation using single-atom alloy (SAA) catalysts vary with alloy composition, as we previously reported, and brings into question the simple model in which the role of Pt is only to promote the dissociation of H2.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/C8CP07548D
