Conventional water electrolyzers produce H2 and O2 simultaneously, such that additional gas separation steps are needed to prevent H2/O2 mixing. The sluggish anodic O2 evolution reaction (OER) always results in low overall energy conversion efficiency and the product of OER, O2, is not of significant value. In addition, the potential formation of reactive oxygen species (ROS) may lead to degradation of cell membranes and thus premature device failure. Herein we report a general concept of integrating oxidative biomass upgrading reactions with decoupled H2 generation from water splitting. Five representative biomass substrates, ethanol, benzyl alcohol, furfural, furfuryl alcohol, and 5-hydroxymethylfurfural (HMF), were selected for oxidative upgrading catalyzed by a hierarchically porous Ni3S2/Ni foam bifunctional electrocatalyst (Ni3S2/NF). All the five organics can be oxidized to value-added liquid products at much lower overpotentials than that of OER. In particular, the electrocatalytic oxidation of HM...

A General Strategy for Decoupled Hydrogen Production from Water Splitting by Integrating Oxidative Biomass Valorization

Heterogeneous catalysis is a promising technology for the valorization of renewable biomass to sustainable advanced fuels and fine chemicals. Porosity and nanostructure are the most versatile features of heterogeneous solid catalysts, which can greatly determine the accessibility of specific active sites, reaction mechanisms, and the selectivity of desirable products. Hence, the precise tuning of porosity and nanostructure has been a potential strategy towards developing novel solid catalysts with indispensable characteristics for efficient biomass valorization. Herein, we present a timely and comprehensive review of the recent advances in catalytic biomass conversions over microporous zeolites, mesoporous silicas, and nanostructured metals/metal oxides. This review covers the catalytic processing of both edible (lipids and starch) and non-edible (lignocellulose) biomass as well as their derived compounds, along with a systematic evaluation of catalyst reusability/kinetic/mechanistic aspects in the relevant processes. The key parameters essential for tailoring particle size, morphology, porosity, acid–base, and redox properties of solid catalysts are emphasized, while discussing the ensuing catalytic effects towards the selective conversion of biomass into desirable chemicals. Special attention has been drawn to understand the role of water in liquid phase biomass conversions as well as the hydrothermal stability and the deactivation of nanoporous catalysts. We believe this comprehensive review will provide new insights towards developing state-of-the-art solid catalysts with well-defined porosity and nanoscale properties for viable biomass conversion.

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Advances in porous and nanoscale catalysts for viable biomass conversion.

A wide variety of commodity chemicals can be produced from the catalytic oxidation of carbohydrates or carbohydrate derived molecules including formic acid, acetic acid, glycolic acid, gluconic acid, glucaric acid, malonic acid, oxalic acid, 2,5-diformylfuran (DFF), 5-hydroxymethyl-2-furancarboxylic acid (HFCA), 5-formyl-2-furancarboxylic acid (FFCA), and 2,5-furandicarboxylic acid (FDCA). This review will highlight the recent research progress in the development of new routes for the production of organic acids and furan compounds via catalytic oxidation reactions. Particular attention will be paid to these one-pot reactions with the requirements of an acidic site and a metal site. For the one-pot transformation of cellobiose or lignocellulose into gluconic acid, these reactions were performed via a one-step strategy using a single catalyst containing an acidic site and a metal site. However, a two-step strategy was adopted for the oxidative transformation of carbohydrates into DFF or FDCA in order to avoid the oxidation of the carbohydrates. The first step was performed for the dehydration of carbohydrates into 5-hydroxylmethylfuran (HMF) in the presence of an acid catalyst, and the second step was performed for the oxidation of HMF into DFF or FDCA with a metal catalyst.

Catalytic oxidation of carbohydrates into organic acids and furan chemicals

Since the discovery of catalysis by Au nanoparticles (NPs), unique catalytic features of Au have appeared that are greatly different from those of Pd and Pt. In this Review, we aimed to disclose how the unique catalytic abilities of Au are generated with respect to (a) the contact structures between Au and its supports and (b) the size of the Au particles. For CO oxidation, the catalytic activity of Au on reducible metal oxides (MOx) is strongly correlated with the amount of oxygen vacancies of the MOx surface, which play a key role in O2 activation. Single atoms, bilayers of Au, sub-nm clusters, clusters (1-2 nm), and NPs (2-5 nm) have been proposed as the active sizes of the Au species, which may depend on the type of support. For propylene epoxidation, the presence of isolated TiO4 units in SiO2 supports is important for the production of propylene oxide (PO). Au NPs facilitate the formation of Ti-OOH species, which leads to PO in the presence of H2 and O2, whereas Au clusters facilitate propylene hydrogenation. However, Au clusters can produce PO by using only O2 and water, whereas Au NPs cannot. For alcohol oxidation, the reducibility of the MOx supports greatly influences the catalytic activity of Au, and single Au atoms more effectively activate the lattice oxygen of CeO2. The basic and acidic sites of the MOx surface also play an important role in the deprotonation of alcohols and the activation of aldehydes, respectively. For selective hydrogenation, heterolytic dissociation of H2 takes place at the interface between Au and MOx, and the basic sites of MOx contribute to H2 activation. Recent research into the reaction mechanisms and the development of well-designed Au catalysts has provided new insights into the preparation of high-performance Au catalysts.

Importance of Size and Contact Structure of Gold Nanoparticles for the Genesis of Unique Catalytic Processes.

Due to the growing demand for energy and impending environmental issues, fuel cells have attracted significant attention as an alternative to conventional energy technologies. As cost is the main inhibitor of this technology, low cost catalysts with high activity and stable catalytic performance are the key to large scale application of fuel cells. The development and recent advancements of Pt and Pt-based electrocatalysts are discussed in this review. Discussion is mainly focused on the structure and composition of Pt and Pt-based electrocatalysts, which significantly affect the catalytic activities and durability of fuel cell catalysts. The electrocatalysts including Pt single metal, Pt-based alloys (including noble alloys, non-noble alloys, metal oxide alloys, and non-metal alloys), and structure-controlled alloys (nanopolyhedra, nanodendrites, and hollow and core–shell structures) were discussed. The activity, stability, and efficiency of Pt and Pt-based catalysts for both the oxygen reduction reaction (ORR) and methanol oxidation reaction (MOR) as well as the correlation between the catalytic performance, structure optimization, and composition modulation of catalysts are also discussed.

Current progress of Pt and Pt-based electrocatalysts used for fuel cells

Exceptional performance of bimetallic Pt1Cu3/TiO2 nanocatalysts for oxidation of gluconic acid and glucose with O2 to glucaric acid

We report for the first time the performance of hybridized Cu/CaO-Al2O3 catalysts for aqueous-phase hydrogenolysis of sorbitol to ethylene glycol (EG), 1,2-propanediol (1,2-PDO), and 1,2-butanediol (1,2-BDO) with linear alcohols as coproducts in a base-free liquid phase. These supported Cu catalysts with solid bases as promoters show significant activity for C–C cleavage and high selectivity (∼84%) to glycols and linear alcohols. The effects of Cu loading, catalyst pretreatment conditions, H2 pressure, and temperature on activity and selectivity of Cu/CaO-Al2O3 catalysts were investigated. The strong interaction between Cu and Ca2+ cations in the solid support is found to facilitate C–C and C–O cleavage of sorbitol, as evidenced from TEM, SEM, and TPR studies of the catalysts. Surface characterization and activity tests further suggest that CaxCuyAlzOp (Phase I) promotes dehydrogenation and isomerization reactions, whereas spinal CuAl2O4 (Phase II) species facilitates hydrogenation reactions. In addition,...

Sorbitol Hydrogenolysis over Hybrid Cu/CaO-Al2O3 Catalysts: Tunable Activity and Selectivity with Solid Base Incorporation

Direct oxidation of glucose with enhanced selectivity to glucaric acid with tartronic and oxalic acids as coproducts is reported using bimetallic PtPd/TiO2 catalysts under mild conditions. Bimetallic PtPd catalysts display significantly enhanced catalytic activity (turnover frequency (TOF) 2404 h–1) and improved selectivity to glucaric acid (S 44%) in glucose oxidation compared to monometallic catalysts (TOF 248 h–1, S 4%). Oxidation of glucose follows a consecutive reaction with gluconic acid as an intermediate with inhibition of the second step (to glucaric acid and C–C cleavage reactions) by the presence of glucose. Surface characterization using TEM, SEM, chemisorption, UV–vis spectroscopy, and XRD distinguished the particle morphologies and provided insights into structure–activity relations. A reaction pathway for glucose oxidation is proposed based on the product distribution. These results provide new insights into the design of bimetallic catalysts for the oxidation of glucose to glucaric acid.

Synergistic Effects of Bimetallic PtPd/TiO2 Nanocatalysts in Oxidation of Glucose to Glucaric Acid: Structure Dependent Activity and Selectivity

In this paper, the performance of cobalt-based catalysts was reported for oxidation of glycerol to dicarboxylic acids such as tartronic and oxalic acids. Cobalt catalysts supported on Mg3Al(OH)y(CO3)z structures prepared by a two-step modified sol–gel method showed 100% glycerol conversion with 64% and 24% selectivity toward tartronic and oxalic acids under mild conditions (55–70 °C and 0.1 MPa O2). Surface and bulk characterization by N2 adsorption/desorption, X-ray diffraction, and temperature-programmed reduction reveals that the cobalt sites interacting with surface hydroxides are catalytically more active than those incorporated into a framework leading to selective glycerol oxidation to dicarboxylic acids in one pot. On the basis of the experiments at different cobalt contents, temperatures, and concentration–time profiles, possible reaction pathways are discussed to explain the selectivity profile. Deactivation of the catalyst under certain conditions has been discussed as a result of loss of surfa...

Wenjuan Yan

Papers

Exceptional performance of bimetallic Pt1Cu3/TiO2 nanocatalysts for oxidation of gluconic acid and glucose with O2 to glucaric acid

Sorbitol Hydrogenolysis over Hybrid Cu/CaO-Al2O3 Catalysts: Tunable Activity and Selectivity with Solid Base Incorporation

Synergistic Effects of Bimetallic PtPd/TiO2 Nanocatalysts in Oxidation of Glucose to Glucaric Acid: Structure Dependent Activity and Selectivity

Oxidation of Glycerol to Dicarboxylic Acids Using Cobalt Catalysts

Towards highly selective ethylene epoxidation catalysts using hydrogen peroxide and tungsten- or niobium-incorporated mesoporous silicate (KIT-6)