Electrocatalytic hydrogenation is increasingly studied as an alternative to integrate the use of recycled carbon feedstocks with renewable energy sources. However, the abundant empiric observations available have not been correlated with fundamental properties of substrates and catalysts. In this study, we investigated electrocatalytic hydrogenation of a homologues series of carboxylic acids, ketones, phenolics, and aldehydes on a variety of metals (Pd, Rh, Ru, Cu, Ni, Zn, and Co). We found that the rates of carbonyl reduction in aldehydes correlate with the corresponding binding energies between the aldehydes and the metals according to the Sabatier principle. That is, the highest rates are obtained at intermediate binding energies. The rates of H2 evolution that occur in parallel to hydrogenation also correlate with the H-metal binding energies, following the same volcano-type behavior. Within the boundaries of this model (e.g., compounds reactive at room temperature and without important steric effects over the carbonyl group), the reported correlations help to explain the complex trends derived from the experimental observations, allowing for the correlation of rates with binding energies and the differentiation of mechanistic routes.

We present a perspective on the computational determination of entropy and its effects and consequences on heterogeneous catalysis. Special attention is paid to the role of anharmonicity (a result of collective phenomena) and the deviations from the standard harmonic oscillator approximations, which can fail to provide a reliable assessment of entropy. To address these challenges, advanced methodologies are needed that can explicitly account for these thermodynamic drivers through the appropriate statistical sampling of reactive free-energy surfaces. We discuss where anharmonicity should be expected, where it has been observed from a theoretical perspective, and the methods currently employed to address it. We concentrate on three types of systems where we have observed major, non-negligible anharmonic effects:(1) supported nanoparticles, where the migration of metal atoms, complexes, and entire clusters exhibit anharmonic behavior in their dynamic motion; (2) porous solids, where confinement effects distort potential energy surfaces and hinder molecular motions, resulting in large entropic terms; and (3) solid/liquid interfaces, where interactions between solvent molecules and adsorbed species can result in large solvent organization free energy and unique reactivity.

The high specific activity and cost-effectiveness of single-atom catalysts (SACs) hold great promise for numerous catalytic chemistries. In hydrogenation reactions, the mechanisms of critical steps such as hydrogen activation and spillover are far from understood. Here, we employ a combination of scanning tunneling microscopy and density functional theory to demonstrate that on a model SAC comprised of single Pd atoms on Fe 3 O 4 (001), H 2 dissociates heterolytically between Pd and surface oxygen. The efficient hydrogen spillover allows for continuous hydrogenation to high coverages, which ultimately leads to the lifting of Fe 3 O 4 reconstruction and Pd reduction and destabilization. Water plays an important role in reducing the proton diffusion barrier, thereby facilitating the redistribution of hydroxyls away from Pd. Our study demonstrates a distinct H 2 activation mechanism on single Pd atoms and corroborates the importance of charge transport on reducible support away from the active site.

Using the van der Waals density functional with C09 exchange (vdW-DF-C09), which has been applied to describing a wide range of dispersion-bound systems, we explore the physical properties of prototypical ABO3 bulk ferroelectric oxides. Surprisingly, vdW-DF-C09 provides a superior description of experimental values for lattice constants, polarization and bulk moduli, exhibiting similar accuracy to the modified Perdew-Burke-Erzenhoff functional which was designed specifically for bulk solids (PBEsol). The relative performance of vdW-DF-C09 is strongly linked to the form of the exchange enhancement factor which, like PBEsol, tends to behave like the gradient expansion approximation for small reduced gradients. These results suggest the general-purpose nature of the class of vdW-DF functionals, with particular consequences for predicting material functionality across dense and sparse matter regimes.

Single-atom catalysis has been a topic of increasing interest due to the potential for improved selectivity, reactivity, and catalyst cost. However, single-atom catalysts are still difficult to characterize under realistic reaction conditions, leading to controversy regarding the capabilities of single atoms and a need for model studies. Herein, we examine the reaction of methanol on single Pd atoms supported on Fe 3 O 4 (001) under ultrahigh vacuum conditions. On Pdfree Fe 3 O 4 (001), a small fraction of methanol is converted to formaldehyde through a methoxy intermediate at 516 K. The addition of single Pd atoms lowers the barrier to C−H bond cleavage by a factor of 2, resulting in formaldehyde desorption by 290 K. However, Pd atoms begin to sinter by 300 K in the presence of methanol, and Pd clusters do not exhibit the same chemistry. Single atoms significantly lower the barrier to the oxidation of methanol, although their stability remains an issue.

Single-atom catalysts are often reported to have catalytic properties that surpass those of nanoparticles, while a direct comparison of sites common and different for both is lacking. Here we show that single atoms of Pt-group metals embedded into the surface of Fe 3 O 4 have a greatly enhanced interaction strength with CO 2 compared with the Fe 3 O 4 surface. The strong CO 2 adsorption on single Rh atoms and corresponding low activation energies lead to 2 orders of magnitude higher conversion rates of CO 2 compared to Rh nanoparticles. This high activity of single atoms stems from the partially oxidic state imposed by their coordination to the support. Fe 3 O 4 -supported Rh nanoparticles follow the behavior of single atoms for CO 2 interaction and reduction, which is attributed to the dominating role of partially oxidic sites at the Fe 3 O 4 − Rh interface. Thus, we show a likely common catalytic chemistry for two kinds of materials thought to be different, and we show that single atoms of Pt-group metals on Fe 3 O 4 are especially successful materials for catalyzed reactions that depend primarily upon sites with the metal−O−Fe environment.

The hydrogenation of benzaldehyde to benzyl alcohol on carbon-supported metals in water,e nabled by an external potential, is markedly promoted by polarization of the functional groups.The presence of polar co-adsorbates,such as substituted phenols,e nhances the hydrogenation rate of the aldehyde by two effects,that is,polarizing the carbonyl group and increasing the probability of forming atransition state for Haddition. These two effects enable ahydrogenation route,in which phenol acts as ac onduit for proton addition, with ah igher rate than the direct proton transfer from hydronium ions.The fast hydrogenation enabled by the presence of phenol and applied potential overcompensates for the decrease in coverage of benzaldehyde caused by competitive adsorption. A higher acid strength of the co-adsorbate increases the intensity of interactions and the rates of selective carbonyl reduction.

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