Single Co3O4 Nanocubes Electrocatalyzing the Oxygen Evolution Reaction: Nano-Impact Insights into Intrinsic Activity and Support Effects

Single-entity electrochemistry allows for assessing electrocatalytic activities of individual material entities such as nanoparticles (NPs). Thus, it becomes possible to consider intrinsic electrochemical properties of nanocatalysts when researching how activity relates to physical and structural material properties. Conversely, conventional electrochemical techniques provide a normalized sum current referring to a huge ensemble of NPs constituting, along with additives (e.g., binders), a complete catalyst-coated electrode. Accordingly, recording electrocatalytic responses of single NPs avoids interferences of ensemble effects and reduces the complexity of electrocatalytic processes, thus enabling detailed description and modelling. Herein, we present insights into the oxygen evolution catalysis at individual cubic Co3O4 NPs impacting microelectrodes of different support materials. Simulating diffusion at supported nanocubes, measured step current signals can be analyzed, providing edge lengths, corresponding size distributions, and interference-free turnover frequencies. The provided nano-impact investigation of (electro-)catalyst-support effects contradicts assumptions on a low number of highly active sites.

Ensemble Effects of Explicit Solvation on Allylic Oxidation

Umbrella-sampling density functional theory molecular dynamics (DFT-MD) has been employed to study the full catalytic cycle of the allylic oxidation of cyclohexene using a Cu(II) 7-amino-6-((2-hydroxybenzylidene)amino)quinoxalin-2-ol complex in acetonitrile to create cyclohexenone and H$_2$O as products. In comparison to gas-phase DFT, the solvent effect is observed as the rate determining allylic H-atom abstraction step has a free energy barrier of 12.1 $\pm$ 0.2 kcal/mol in solution. During the cycle, the explicit solvation and ensemble sampling of solvent configurations reveals important dehydrogenation and re-hydrogenation steps of the -NH$_2$ group bound to the Cu-site that are essential to catalyst recovery. This work illustrates the importance of ensemble solvent configurational sampling to reveal the breadth of processes that underpin the full catalytic cycle.<br>

Ensemble Effects of Explicit Solvation on Allylic Oxidation

<div>Umbrella-sampling density functional theory molecular dynamics (DFT-MD) has been employed to study the full catalytic cycle of the allylic oxidation of cyclohexene</div><div>using a Cu(II) (E)-6-amino-7-((2-hydroxybenzylidene)amino)quinoxalin-2-ol complex in acetonitrile, which creates the desired cyclohexenone and H 2 O as products. In comparison to prior study using gas-phase DFT, a significant solvent effect is observed on the rate determining allylic H-atom abstraction step (which has a free energy barrier of 12.1 ± 0.2 kcal/mol). During the cycle, the explicit solvation and ensemble sampling of solvent configurations reveals an important dehydrogenation and re-hydrogenation step of the -NH 2 ligand that is essential to catalyst recovery. This work illustrates the importance of ensemble solvent configurational sampling to reveal the breadth of processes that underpin the full catalytic cycle.</div>

Ensemble Effects of Explicit Solvation on Allylic Oxidation

<div>Umbrella-sampling density functional theory molecular dynamics (DFT-MD) has been employed to study the full catalytic cycle of the allylic oxidation of cyclohexene</div><div>using a Cu(II) (E)-6-amino-7-((2-hydroxybenzylidene)amino)quinoxalin-2-ol complex in acetonitrile, which creates the desired cyclohexenone and H 2 O as products. In comparison to prior study using gas-phase DFT, a significant solvent effect is observed on the rate determining allylic H-atom abstraction step (which has a free energy barrier of 12.1 ± 0.2 kcal/mol). During the cycle, the explicit solvation and ensemble sampling of solvent configurations reveals an important dehydrogenation and re-hydrogenation step of the -NH 2 ligand that is essential to catalyst recovery. This work illustrates the importance of ensemble solvent configurational sampling to reveal the breadth of processes that underpin the full catalytic cycle.</div>

Ensemble effects in Cu/Au ultrasmall nanoparticles control the branching point for C1 selectivity during CO2 electroreduction

Bimetallic catalysts provide opportunities to overcome scaling laws governing C1 selectivity of CO2 reduction (CO2R).

Ensemble Effects on Allylic Oxidation within Explicit Solvation Environments

Umbrella-sampling density functional theory molecular dynamics (DFT-MD) has been employed to study the full catalytic cycle of the allylic oxidation of cyclohexene using a Cu(II) 7-amino-6-((2-hydroxybenzylidene)amino)quinoxalin-2-ol complex in acetonitrile to...

Oxygenate Reactions over PdCu and PdAg Catalysts: Distinguishing Electronic and Geometric Effects on Reactivity and Selectivity

We investigate PdCu and PdAg catalysts in the context of oxygenate upgrading for biofuels. To this end, we measure the rates of decarbonylation and hydrogenation of butyraldehyde, the reactive intermediate for the industrially relevant Guerbet condensation, and correlate the selectivity and reactivity with the properties of the catalysts via a range of characterization efforts. Data obtained from EXAFS and XANES show that the bulk of the catalyst metallic nanoparticles is enriched in Pd, while the surface is enriched in Cu and Ag. The data for PdCu show clear dominance of geometric (ensemble) effects on the selectivity. Conversely, the electronic (ligand) effects of alloying dominate over the reaction rate of the catalysts, as electron donation from Cu to Pd promotes the Cu and increases the desired (de)hydrogenation reactions. In contrast, in PdAg catalysts, the weaker electronic exchange, as indicated by Pd L edge XANES and theoretical calculations, is not sufficient to promote Ag, resulting in monotonic loss of activity with increasing Ag content and without selectivity improvement. We use the implications of these findings to provide valuable design principles for oxygenate catalysis and to discover a highly selective bifunctional catalyst system, comprised of a PdCu alloy catalyst and titanium dioxide for the upgrading of ethanol to longer-chain oxygenates.<br>

Oxygenate Reactions over PdCu and PdAg Catalysts: Distinguishing Electronic and Geometric Effects on Reactivity and Selectivity

We investigate PdCu and PdAg catalysts in the context of oxygenate upgrading for biofuels. To this end, we measure the rates of decarbonylation and hydrogenation of butyraldehyde, the reactive intermediate for the industrially relevant Guerbet condensation, and correlate the selectivity and reactivity with the properties of the catalysts via a range of characterization efforts. Data obtained from EXAFS and XANES show that the bulk of the catalyst metallic nanoparticles is enriched in Pd, while the surface is enriched in Cu and Ag. The data for PdCu show clear dominance of geometric (ensemble) effects on the selectivity. Conversely, the electronic (ligand) effects of alloying dominate over the reaction rate of the catalysts, as electron donation from Cu to Pd promotes the Cu and increases the desired (de)hydrogenation reactions. In contrast, in PdAg catalysts, the weaker electronic exchange, as indicated by Pd L edge XANES and theoretical calculations, is not sufficient to promote Ag, resulting in monotonic loss of activity with increasing Ag content and without selectivity improvement. We use the implications of these findings to provide valuable design principles for oxygenate catalysis and to discover a highly selective bifunctional catalyst system, comprised of a PdCu alloy catalyst and titanium dioxide for the upgrading of ethanol to longer-chain oxygenates.<br>

Oxygenate Reactions over PdCu and PdAg Catalysts: Distinguishing Electronic and Geometric Effects on Reactivity and Selectivity

We investigate PdCu and PdAg catalysts in the context of oxygenate upgrading for biofuels. To this end, we measure the rates of decarbonylation and hydrogenation of butyraldehyde, the reactive intermediate for the industrially relevant Guerbet condensation, and correlate the selectivity and reactivity with the properties of the catalysts via a range of characterization efforts. Data obtained from EXAFS and XANES show that the bulk of the catalyst metallic nanoparticles is enriched in Pd, while the surface is enriched in Cu and Ag. The data for PdCu show clear dominance of geometric (ensemble) effects on the selectivity. Conversely, the electronic (ligand) effects of alloying dominate over the reaction rate of the catalysts, as electron donation from Cu to Pd promotes the Cu and increases the desired (de)hydrogenation reactions. In contrast, in PdAg catalysts, the weaker electronic exchange, as indicated by Pd L edge XANES and theoretical calculations, is not sufficient to promote Ag, resulting in monotonic loss of activity with increasing Ag content and without selectivity improvement. We use the implications of these findings to provide valuable design principles for oxygenate catalysis and to discover a highly selective bifunctional catalyst system, comprised of a PdCu alloy catalyst and titanium dioxide for the upgrading of ethanol to longer-chain oxygenates.<br>