Hydrogenation versus hydrogenolysis during alkaline electrochemical valorization of 5-hydroxymethylfurfural over oxide-derived Cu-bimetallics

Surfactant Directionally Assembled at the Electrode-Electrolyte Interface for Facilitating Electrocatalytic Aldehyde Hydrogenation

Electrocatalytic hydrogenation of unsaturated aldehydes to unsaturated alcohols is a promising alternative to conventional thermal processes. Both the catalyst and electrolyte deeply impact the performance. Designing the electrode-electrolyte interface remains challenging due to its compositional and structural complexity. Here, we employ the electrocatalytic hydrogenation of 5-hydroxymethylfurfural (HMF) as a reaction model. The typical cationic surfactant, cetyltrimethylammonium bromide (CTAB), and its analogs are employed as electrolyte additives to tune the interfacial microenvironment, delivering high-efficiency hydrogenation of HMF and inhibition of the hydrogen evolution reaction (HER). The surfactants experience a conformational transformation from stochastic distribution to directional assembly under applied potential. This oriented arrangement hampers the transfer of water molecules to the interface and promotes the enrichment of reactants. In addition, near 100 % 2,5-bis(hydroxymethyl)furan (BHMF) selectivity is achieved, and the faradaic efficiency (FE) of the BHMF is improved from 61 % to 74 % at -100 mA cm-2. Notably, the microenvironmental modulation strategy applies to a range of electrocatalytic hydrogenation reactions involving aldehyde substrates. This work paves the way for engineering advanced electrode-electrolyte interfaces and boosting unsaturated alcohol electrosynthesis efficiency.

Rational Design of Transition-Metal-Based Catalysts for the Electrochemical 5-Hydroxymethylfurfural Reduction Reaction

The electrochemical reduction reaction (HMFRR) of 5-hydroxymethylfurfural (HMF) has emerged as a promising avenue for the utilization and refinement of the biomass-derived platform molecule HMF into high-value chemicals, addressing energy sustainability challenges. Transition metal electrocatalysts (TMCs) have recently garnered attention as promising candidates for catalyzing HMFRR, capitalizing on the presence of vacant d orbitals and unpaired d electrons. TMCs play a pivotal role in facilitating the generation of intermediates through interactions with HMF, thereby lowering the activation energy of intricate reactions and significantly augmenting the catalytic reaction rate. In the absence of comprehensive and guiding reviews in this domain, this paper aims to comprehensively summarize the key advancements in the design of transition metal catalysts for HMFRR. It elucidates the mechanisms and pH dependency of various products generated during the electrochemical reduction of HMF, with a specific emphasis on the bond-cleavage angle. Additionally, it offers a detailed introduction to typical in-situ characterization techniques. Finally, the review explores engineering strategies and principles to enhance HMFRR activity using TMCs, particularly focusing on multiphase interface control, crystal face control, and defect engineering control. This review introduces novel concepts to guide the design of HMFRR electrocatalysts, especially TMCs, thus promoting advancements in biomass conversion.

Progress and Opportunities in Photocatalytic, Electrocatalytic, and Photoelectrocatalytic Production of Hydrogen Peroxide Coupled with Biomass Valorization

Hydrogen peroxide (H2O2) has been considered an energy carrier (fuel) and oxidizer for various chemical synthesis and environmental remediation processes. Biomass valorization can generate high-value-added products in a green and pollution-free way to solve the energy and environmental crisis. The biomass valorization coupled with H2O2 generation via photo-, electro-, and photoelectrocatalysis plays a positive role in sustainable targets, which can maximize energy utilization and realize the production of value-added products and fuel synthesis. Recently, catalyst design and mechanism studies in H2O2 generation coupled with biomass valorization are in the infancy stage. Herein, this review begins with a background on photo-, electro-, and photoelectrocatalytic techniques for H2O2 generation, biomass valorization, and the H2O2 generation couples with biomass valorization. Meanwhile, the progress and reaction mechanism are reviewed. Finally, the prospects and challenges of a synergistic coupled system of H2O2 synthesis and value-added biomass in achieving high conversion, selectivity, and reaction efficiency are envisioned.

Frontiers in Photoelectrochemical Catalysis: A Focus on Valuable Product Synthesis

Photoelectrochemical (PEC) catalysis provides the most promising avenue for producing value-added chemicals and consumables from renewable precursors. Over the last decades, PEC catalysis, including reduction of renewable feedstock, oxidation of organics, and activation and functionalization of C─C and C─H bonds, are extensively investigated, opening new opportunities for employing the technology in upgrading readily available resources. However, several challenges still remain unsolved, hindering the commercialization of the process. This review offers an overview of PEC catalysis targeted at the synthesis of high-value chemicals from sustainable precursors. First, the fundamentals of evaluating PEC reactions in the context of value-added product synthesis at both anode and cathode are recalled. Then, the common photoelectrode fabrication methods that have been employed to produce thin-film photoelectrodes are highlighted. Next, the advancements are systematically reviewed and discussed in the PEC conversion of various feedstocks to produce highly valued chemicals. Finally, the challenges and prospects in the field are presented. This review aims at facilitating further development of PEC technology for upgrading several renewable precursors to value-added products and other pharmaceuticals.

Recent progress of heterogeneous catalysts for transfer hydrogenation under the background of carbon neutrality

Under the background of carbon neutrality, the direct conversion of greenhouse CO2 to high value added fuels and chemicals is becoming an important and promising technology. Among them, the generation of liquid C1 products (formic acid and methanol) has made great progress; nevertheless, it encounters the problem of how to use it efficiently to solve the overcapacity issue. In this review, we suggest that the catalytic transfer hydrogenation using formic acid and methanol as the hydrogen sources is a critical and potential route for the substitution for the fossil fuel-derived H2 to generate essential bulk and fine chemicals. We mainly focus on summarizing the recent progress of heterogeneous catalysts in such reactions, including thermal- and photo-catalytic processes. Finally, we also propose some challenges and opportunities for this development.