Electrocatalytic Hydrogenation of Biomass-Derived Organics: A Review

Abstract

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: 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? What material properties cause an electrocatalyst to be active for ECH? Can general trends in ECH be formulated based on the type of electrocatalyst? What are the impacts of reaction conditions (electrolyte concentration, pH, operating potential) and reactor types?

Electrocatalysts for Using Renewably-Sourced, Organic Electrolytes for Redox Flow Batteries

“…Cathode catalysts are usually chosen from platinum group metals, as these elements are all active as hydrogenation catalysts [6,[13][14][15]21,[40][41][42][43][44][45][46][47]. Their utility is limited when the supporting electrolyte is aqueous because they are also active for reducing water (to make H 2 ).…”

“…Beyond those rules of thumb, there is little guidance available for the choice of either the cathode or anode. There are structure/activity correlations in electrochemistry, for example, volcano plots [40,56,57], but they are more interpolative than predictive towards the detailed aspect of the metal (alloy composition, particle size, particle shape, etc.) or towards the substrate.…”

“…For example, volcano curves have been compiled for the reductions of three organic oxygenates, benzaldehyde, furfural, and heptanal [40,57]. The original correlations plotted the adsorption energies of the substrates on the indicated metals on the x axis.…”

“…Superposed volcano graphs for the electrochemical hydrogenation of benzaldehyde (•), furfural ( ) and heptanal ( ). Data from[40,57].…”

Recent Advances in the Value Addition of Biomass‐Derived Levulinic Acid: A Review Focusing on its Chemical Reactivity Patterns

“…Electrocatalysis has also been used for the value addition of biomass‐derived chemical intermediates, where electrons are directly employed to bring about chemical changes in the place of reagents [25] . For example, biomass‐derived organic compounds (e. g., phenol) and aliphatic compounds (e. g., cyclohexanone) have been hydrogenated into fuels under energy‐efficient conditions using electrocatalysis [26] . A classic example of the chemocatalytic conversion of biomass is the acid‐catalyzed depolymerization, hydrolysis, and dehydration of biomass‐derived carbohydrates into furanics and levulinates such as 5‐(hydroxymethyl)furfural (HMF), furfural (FUR), and levulinic acid (LA) (Scheme 1).…”