Electrodeposition of catalysts for hydrogenation of organic molecules: hydrogenation of benzaldehyde

Electroplated electrodes for continuous and mass-efficient electrochemical hydrogenation

Electrocatalytic hydrogenations (ECH) enable the reduction of organic substrates upon usage of electric current and present a sustainable alternative to conventional processes if green electricity is used. Opposed to most current protocols for electrode preparation, this work presents a one-step binder- and additive-free production of silver- and copper-electroplated electrodes. Controlled adjustment of the preparation parameters allows for the tuning of catalyst morphology and its electrochemical properties. Upon optimization of the deposition protocol and carbon support, high faradaic efficiencies of 93 % for the ECH of the Vitamin A- and E-synthon 2-methyl-3-butyn-2-ol (MBY) are achieved that can be maintained at current densities of 240 mA cm-2 and minimal catalyst loadings of 0.2 mg cm-2 , corresponding to an unmatched production rate of 1.47 kgMBE  gcat -1  h-1 . For a continuous hydrogenation process, the protocol can be directly transferred into a single-pass operation mode giving a production rate of 1.38 kgMBE  gcat -1  h-1 . Subsequently, the substrate spectrum was extended to a total of 17 different C-C-, C-O- and N-O-unsaturated compounds revealing the general applicability of the reported process. Our results lay an important groundwork for the development of electrochemical reactors and electrodes able to directly compete with the palladium-based thermocatalytic state of the art.

Electrocatalytic Hydrogenation of Biomass-Derived Organics: A Review

Sustainable energy generation calls for a shift away from centralized, high-temperature, energy-intensive processes to decentralized, low-temperature conversions that can be powered by electricity produced from renewable sources. Electrocatalytic conversion of biomass-derived feedstocks would allow carbon recycling of distributed, energy-poor resources in the absence of sinks and sources of high-grade heat. Selective, efficient electrocatalysts that operate at low temperatures are needed for electrocatalytic hydrogenation (ECH) to upgrade the feedstocks. For effective generation of energy-dense chemicals and fuels, two design criteria must be met: (i) a high H:C ratio via ECH to allow for high-quality fuels and blends and (ii) a lower O:C ratio in the target molecules via electrochemical decarboxylation/deoxygenation to improve the stability of fuels and chemicals. The goal of this review is to determine whether the following questions have been sufficiently answered in the open literature, and if not, what additional information is required:(1)What organic functionalities are accessible for electrocatalytic hydrogenation under a set of reaction conditions? How do substitutions and functionalities impact the activity and selectivity of ECH?(2)What material properties cause an electrocatalyst to be active for ECH? Can general trends in ECH be formulated based on the type of electrocatalyst?(3)What are the impacts of reaction conditions (electrolyte concentration, pH, operating potential) and reactor types?

An alternative to hydrogenation processes. Electrocatalytic hydrogenation of benzophenone

The electrocatalytic hydrogenation of benzophenone was performed at room temperature and atmospheric pressure using a polymer electrolyte membrane electrochemical reactor (PEMER). Palladium (Pd) nanoparticles were synthesised and supported on a carbonaceous matrix (Pd/C) with a 28 wt % of Pd with respect to carbon material. Pd/C was characterised by transmission electron microscopy (TEM), and thermogravimetric analysis (TGA). Cathodes were prepared using Pd electrocatalytic loadings (L_Pd) of 0.2 and 0.02 mg cm⁻². The anode consisted of hydrogen gas diffusion for the electrooxidation of hydrogen gas, and a 117 Nafion exchange membrane acted as a cationic polymer electrolyte membrane. Benzophenone solution was electrochemically hydrogenated in EtOH/water (90/10 v/v) plus 0.1 M H₂SO₄. Current densities of 10, 15 and 20 mA cm⁻² were analysed for the preparative electrochemical hydrogenation of benzophenone and such results led to the highest fractional conversion (X_R) of around 30% and a selectivity over 90% for the synthesis of diphenylmethanol upon the lowest current density. With regards to an increase by ten times the Pd electrocatalytic loading the electrocatalytic hydrogenation led neither to an increase in fractional conversion nor to a change in selectivity.

One-pot synthesis of Ni nanoparticle/ordered mesoporous carbon composite electrode materials for electrocatalytic reduction of aromatic ketones

A simple one-pot synthesis of Ni nanoparticle/ordered mesoporous carbon composite electrode materials is demonstrated for electrosynthesis for the first time. The obtained nanocomposites have uniform mesopore sizes (3.0-3.7 nm), large specific surface areas (506-633 m² g^-1), high pore volumes (0.28-0.38 cm³ g^-1), well-graphitized carbon frameworks, and uniformly dispersed Ni nanoparticles (7-15 nm) embedded in the carbon pore walls. The prepared materials show very high performance in the selective (∼84%) electrocatalytic reduction of aromatic ketones into alcohols (∼79%).

Formation of Palladium Complex at Carbon Paste Surface in Chloride Solution as Studied by Cyclic Voltammetry

The deposition and dissolution of palladium at non-modified carbon paste electrode (CPE) is studied by cyclic voltammetry in chloride solutions (c ≥ 0.5 M KCl and pH 3 to 6). The Pd0 is deposited from tetrachloropalladate solution by potential cycles from E ≥ 0 V (vs Ag/AgCl) or positive potentials up to -0.5 V or by potentiostatic treatment at E ≤ 0 V. Oxidation peaks appear during potential sweep to positive direction after the preceding deposition of Pd. The appearance of two anodic peaks depends mainly on the amount of Pd0 deposited. The peak at about +0.1 V is caused by the dissolution of a palladium mono- or submonolayer, whereas the oxidation peak at more positive potentials is attributed to the dissolution of Pd from a palladium multilayer. After palladium deposition and potential sweep to positive potentials E > +0.8 V (or potentiostatic treatment at E > +0.8 V), a cathodic peak appears at about 0 V and corresponding anodic peak at +0.1 V. It is concluded that these peaks are caused by reduction and oxidation of the chloropalladate surface complex formed during preceding application of anodic potentials. Reaction schemes of PdII/Pd0 and chloropalladate complex are discussed.