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.

Electrocatalytic hydrogenation is a particularly attractive approach for converting the most unstable compounds in biogenic feedstocks at ambient conditions without external H2. Here, we synthesized a variety of carbon-supported transition metal catalysts and characterized their activity for the electrocatalytic hydrogenation of a series of model compounds and pyrolysis bio-oil. Carbonyl compounds, especially aromatic aldehydes, such as furfural and benzaldehyde, are particularly inclined to hydrogenation driven by an applied current. This was verified with pure solutions of the model compounds and with pyrolysis bio-oil, where we achieved stable and steady continuous operation on Pd. When optimal catalyst composition was chosen, the conversion of benzaldehyde shifted from alcohol production (e.g., on Pd and Cu) to dimerization (e.g., on Co, Ni, and Zn). Pd and Cu were shown to offer the best compromise between reaction rates and efficiency although, in general, base metals offer similar conversions but better efficiencies than noble metals. Thus, the present work offers foundational results and guidelines for choosing the optimal metal catalyst and the applied potential for processing organic feedstocks as a function of its composition.

The reversible reactions involving formate and bicarbonate can be used to store and release hydrogen (H 2), allowing H 2 to serve as an effective energy carrier in energy systems such as fuel cells. However, to feasibly utilize these reactions for renewable energy applications, efficient catalysts that can reversibly promote both reactions are required. Herein we report the synthesis of novel polyaniline (PANI)derived mesoporous carbon-supported Pd nanoparticles, or materials that can efficiently catalyze these reversible reactions. The synthesis involves pyrolysis of PANI/colloidal silica composite materials at temperatures above 500 °C and then removal of the colloidal silica from the carbonized products with an alkaline solution. The resulting nanomaterials efficiently catalyze the reversible reactions, i.e., the dehydrogenation of formate (HCO 2 ‾ + H 2 O  H 2 + HCO 3 ‾) and the hydrogenation of bicarbonate (H 2 + HCO 3 ‾ H 2 O + HCO 2 ‾). The porosity and the catalytic property of the materials can be tailored, or improved, by changing the synthetic conditions (in particular, the pyrolysis temperature and the amount of colloidal silica used for making the materials). The study further reveals that having an optimum density of N dopant species in the catalysts makes Pd to exhibit high catalytic activity toward both reactions. Among the different materials studied here, the one synthesized at 800 °C with relatively high amount of colloidal silica templates gives the best catalytic activity, with a turnover frequency (TOF) of 2,562 h-1 for the dehydrogenation reaction and a turnover number (TON) of 1,625 for the hydrogenation reaction. These TOF and TON values are currently among the highest values reported for heterogeneous catalysts for these reversible reactions.

Molecular interactions with both oxides and metals are essential for heterogenous catalysis, leading to remarkable synergistic impacts on activity and selectivity. Here, we show that the direct link between the two phases (and not merely being together) is required to selectively hydrogenate CO2 to methanol on catalysts containing Cu and ZrO2. Materials consisting of isolated Cu particles or atomically dispersed Cu–O–Zr sites only catalyze the reverse water-gas shift reaction. In contrast, a metal organic framework structure (UiO-66) with Cu nanoparticles occupying missing-linker defects maximizes the fraction of metallic Cu interfaced to ZrO2 nodes leading to a material with high adsorption capacity for CO2 and high activity and selectivity for low-temperature methanol synthesis.

Amine-functionalized mesoporous silica-supported ultrasmall Pd nanoparticles catalyze hydrogen evolution from formic acid at ambient temperature.

A series of Pd/SBA-15-amine materials (where “Amine” is primary amine, secondary amine and tertiary amine) containing Pd nanoparticles are synthesized and their catalytic properties for formic acid dehydrogenation are investigated.

Acid functionalization of a carbon support allows to enhance the electrocatalytic activity of Pd to hydrogenate benzaldehyde to benzyl alcohol proportional to the concentration of Brønsted‐acid sites. In contrast, the hydrogenation rate is not affected when H2 is used as a reduction equivalent. The different responses to the catalyst properties are shown to be caused by differences in the hydrogenation mechanism between the electrochemical and the H2‐induced hydrogenation pathways. The enhancement of electrocatalytic reduction is realized by the participation of support‐generated hydronium ions in the proximity of the metal particles.

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.