Tailoring Second Coordination Sphere for Tunable Solid-Liquid Interfacial Charge Transfer toward Enhanced Photoelectrochemical H2 Production.

The recombination of photogenerated charge carriers severely limits the performance of photoelectrochemical (PEC) H2 production. Here, we demonstrate that this limitation can be overcome by optimizing the charge transfer dynamics at the solid-liquid interface via molecular catalyst design. Specifically, the surface of a p-Si photocathode is modulated using molecular catalysts with different metal atoms and organic ligands to improve H2 production performance. Co(pda-SO3H)2 is identified as an efficient and durable catalyst for H2 production through the rational design of metal centers and first/second coordination spheres. The modulation with Co(pda-SO3H)2, which contains an electron-withdrawing -SO3H group in the second coordination sphere, elevates the flat-band potential of the polished p-Si photocathode and nanoporous p-Si photocathode by 81 mV and 124 mV, respectively, leading to the maximized energy band bending and the minimized interfacial carrier transport resistance. Consequently, both the two photocathodes achieve the Faradaic efficiency of more than 95 % for H2 production, which is well maintained during 18 h and 21 h reaction, respectively. This work highlights that the band-edge engineering by molecular catalysts could be an important design consideration for semiconductor-catalyst hybrids toward PEC H2 production.

Spectroscopic visualization of reversible hydrogen spillover between palladium and metal-organic frameworks toward catalytic semihydrogenation.

Hydrogen spillover widely occurs in a variety of hydrogen-involved chemical and physical processes. Recently, metal-organic frameworks have been extensively explored for their integration with noble metals toward various hydrogen-related applications, however, the hydrogen spillover in metal/MOF composite structures remains largely elusive given the challenges of collecting direct evidence due to system complexity. Here we show an elaborate strategy of modular signal amplification to decouple the behavior of hydrogen spillover in each functional regime, enabling spectroscopic visualization for interfacial dynamic processes. Remarkably, we successfully depict a full picture for dynamic replenishment of surface hydrogen atoms under interfacial hydrogen spillover by quick-scanning extended X-ray absorption fine structure, in situ surface-enhanced Raman spectroscopy and ab initio molecular dynamics calculation. With interfacial hydrogen spillover, Pd/ZIF-8 catalyst shows unique alkyne semihydrogenation activity and selectivity for alkynes molecules. The methodology demonstrated in this study also provides a basis for further exploration of interfacial species migration.

Concentrated Formic Acid from CO2 Electrolysis for Directly Driving Fuel Cell.

The production of formic acid via electrochemical CO2 reduction may serve as a key link for the carbon cycle in the formic acid economy, yet its practical feasibility is largely limited by the quantity and concentration of the product. Here we demonstrate continuous electrochemical CO2 reduction for formic acid production at 2 M at an industrial-level current densities (i.e., 200 mA cm-2 ) for 300 h on membrane electrode assembly using scalable lattice-distorted bismuth catalysts. The optimized catalysts also enable a Faradaic efficiency for formate of 94.2 % and a highest partial formate current density of 1.16 A cm-2 , reaching a production rate of 21.7 mmol cm-2 h-1 . To assess the practicality of this system, we perform a comprehensive techno-economic analysis and life cycle assessment, showing that our approach can potentially substitute conventional methyl formate hydrolysis for industrial formic acid production. Furthermore, the resultant formic acid serves as direct fuel for air-breathing formic acid fuel cells, boasting a power density of 55 mW cm-2 and an exceptional thermal efficiency of 20.1 %.

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.

Highly Efficient Iron-Based Catalyst for Light-Driven Selective Hydrogenation of Nitroarenes.

Light-driven hydrogenation of nitro compounds to functionalized amines is of great importance yet a challenge for practical applications, which calls for the development of high-performance, nonprecious photocatalysts and efficient catalytic systems. Herein, we report a high-efficiency Fe3O4@TiO2 photocatalyst via a sol-gel and subsequent pyrolysis strategy, which exhibits desirable photothermal hydrogenation performance of nitro compounds to functionalized amines with the excellent selectivity of >90% exceeding those of the state-of-the-art heterogeneous photocatalysts. Our experimental results and theoretical calculations for the first time reveal that Fe3O4 is the major active phase, and the strong metal-support interaction between Fe3O4 and reducible TiO2 further leads to performance improvement, taking advantage of the enhanced photothermal effect and the improved adsorption for the reactant and hydrazine hydrate. Notably, a variety of halonitrobenzenes and pharmaceutical intermediates can be completely converted to functionalized amines with high selectivities, even in gram-scale reactions. This work provides a new insight into the rational design of nonprecious photo/thermo-catalysts for other catalytic reactions.

Enabling direct-growth route for highly efficient ethanol upgrading to long-chain alcohols in aqueous phase.

Upgrading ethanol to long-chain alcohols (LAS, C6+OH) offers an attractive and sustainable approach to carbon neutrality. Yet it remains a grand challenge to achieve efficient carbon chain propagation, particularly with noble metal-free catalysts in aqueous phase, toward LAS production. Here we report an unconventional but effective strategy for designing highly efficient catalysts for ethanol upgrading to LAS, in which Ni catalytic sites are controllably exposed on surface through sulfur modification. The optimal catalyst exhibits the performance well exceeding previous reports, achieving ultrahigh LAS selectivity (15.2% C6OH and 59.0% C8+OH) at nearly complete ethanol conversion (99.1%). Our in situ characterizations, together with theoretical simulation, reveal that the selectively exposed Ni sites which offer strong adsorption for aldehydes but are inert for side reactions can effectively stabilize and enrich aldehyde intermediates, dramatically improving direct-growth probability toward LAS production. This work opens a new paradigm for designing high-performance non-noble metal catalysts for upgrading aqueous EtOH to LAS.

Computational Design and Experimental Validation of Enzyme Mimicking Cu-Based Metal-Organic Frameworks for the Reduction of CO2 into C2 Products: C-C Coupling Promoted by Ligand Modulation and the Optimal Cu-Cu Distance.

While extensive research has been conducted on the conversion of CO2 to C1 products, the synthesis of C2 products still strongly depends on the Cu electrode. One main issue hindering the C2 production on Cu-based catalysts is the lack of an appropriate Cu-Cu distance to provide the ideal platform for the C-C coupling process. Herein, we identify a lab-synthesized artificial enzyme with an optimal Cu-Cu distance, named MIL-53 (Cu) (MIL= Materials of Institute Lavoisier), for CO2 conversion by using a density functional theory method. By substituting the ligands in the porous MIL-53 (Cu) nanozyme with functional groups from electron-donating NH2 to electron-withdrawing NO2, the Cu-Cu distance and charge of Cu can be significantly tuned, thus modulating the adsorption strength of CO2 that impacts the catalytic activity. MIL-53 (Cu) decorated with a COOH-ligand is found to be located at the top of a volcano-shaped plot and exhibits the highest activity and selectivity to reduce CO2 to CH3CH2OH with a limiting potential of only 0.47 eV. In addition, experiments were carried out to successfully synthesize COOH-decorated MIL-53(Cu) to prove its high catalytic performance for C2 production, which resulted in a -55.5% faradic efficiency at -1.19 V vs RHE, which is much higher than the faradic efficiency of the benchmark Cu electrode of 35.7% at -1.05 V vs RHE. Our results demonstrate that the biologically inspired enzyme engineering approach can redefine the structure-activity relationships of nanozyme catalysts and can also provide a new understanding of the catalytic mechanisms in natural enzymes toward the development of highly active and selective artificial nanozymes.

Rational Design of N-Doped Carbon-Coated Cobalt Nanoparticles for Highly Efficient and Durable Photothermal CO2 Conversion.

Photothermal CO2 hydrogenation to high-value-added chemicals and fuels is an appealing approach to alleviate energy and environmental concerns. However, it still relies on the development of earth-abundant, efficient, and durable catalysts. Here, the design of N-doped carbon-coated Co nanoparticles (NPs), as a photothermal catalyst, synthesized through a two-step pyrolysis of Co-based ZIF-67 precursor, is reported. Consequently, the catalyst exhibits remarkable activity and stability for photothermal CO2 hydrogenation to CO with a 0.75 mol gcat -1 h-1 CO production rate under the full spectrum of light illumination. The high activity and durability of these Co NPs are mainly attributed to the synergy of the attuned size of Co NPs, the thickness of carbon layers, and the N doping species. Impressively, the experimental characterizations and theoretical simulations show that such a simple N-doped carbon coating strategy can effectively facilitate the desorption of generated CO and activation of reactants due to the strong photothermal effect. This work provides a simple and efficient route for the preparation of highly active and durable nonprecious metal catalysts for promising photothermal catalytic reactions.

Ni-Co Alloy Nanoparticles Catalyze Selective Electrochemical Coupling of Nitroarenes into Azoxybenzene Compounds in Aqueous Electrolyte.

In theory, electrocatalysts in their metallic forms should be the most stable chemical state under cathodic potentials. It is known that the highly dispersed nanoparticle (NP) types of electrocatalysts often possess higher activity than their bulk counterparts. However, facilely and controllably fabricating well-dispersed nonprecious metal NPs with superior electrocatalytic activity, selectivity, and durability is highly challenging. Here, we report a facile reductive pyrolysis approach to controllably synthesize NiCo alloy NPs confined on the tip of N-doped carbon nanotubes (N-CNTs) from a bimetal-MOF precursor. The electrocatalytic performance of the resultant NiCo@N-CNTs are evaluated by a wide spectrum of nitroarene reductive coupling reactions to produce azoxy-benzenes, a class of precious chemicals for textile, food, cosmetic, and pharmaceutical industries. The superior electrocatalytic stability, full conversion of nitroarenes, >99% selectivities, and >97% faradic efficiencies toward the targeted azoxy-benzene products are readily attainable by NiCo@N-CNTs, attributable to the alloying-induced synergetic effect. The presence of a CNT confinement effect in NiCo@N-CNTs induces high stability. This added to the metallic states of NiCo empowers NiCo@N-CNTs with excellent electrochemical stability under reductive reaction conditions. In an effort to enhance the energy utilization efficiency, we construct a NiCo@N-CNTs||Ni(OH)2/NF two-electrode electrolyzer to simultaneously reduce nitrobenzene at the cathode and 5-hydroxymethylfurfural with >99% yields for both azoxy-benzene and 2,5-furandicarboxylic acid.

Pushing the Performance Limit of Cu/CeO2 Catalyst in CO2 Electroreduction: A Cluster Model Study for Loading Single Atoms.

Pushing the performance limit of catalysts is a major goal of CO2 electroreduction toward practical application. A single-atom catalyst is recognized as a solution for achieving this goal, which is, however, a double-edged sword considering the limited loading amount and stability of single-atom sites. To overcome the limit, the loading of single atoms on supports should be well addressed, requiring a suitable model system. Herein, we report the model system of an ultrasmall CeO2 cluster (2.4 nm) with an atomic precise structure and a high surface-to-volume ratio for loading Cu single atoms. The combination of multiple characterizations and theoretical calculations reveals the loading location and limit of Cu single atoms on CeO2 clusters, determining an optimal configuration for CO2 electroreduction. The optimal catalyst achieves a maximum Faradaic efficiency (FE) of 67% and a maximum partial current density of -364 mA/cm2 for CH4, and can maintain high CH4 FE values over 50% in a wide range of applied current densities (-50 ∼ -600 mA/cm2), exceeding those of the reported catalysts.

Identifying an Interfacial Stabilizer for Regeneration-Free 300 h Electrochemical CO2 Reduction to C2 Products.

The electrochemical CO2 reduction reaction (CO2RR) to produce high value-added hydrocarbons and oxygenates presents a sustainable and compelling approach toward a carbon-neutral society. However, uncontrollable migration of active sites during the electrochemical CO2RR limits its catalytic ability to simultaneously achieve high C2 selectivity and ultradurability. Here, we demonstrate that the generated interfacial CuAlO2 species can efficiently stabilize the highly active sites over the Cu-CuAlO2-Al2O3 catalyst under harsh electrochemical conditions without active sites regeneration for a long-term test. We show that this unique Cu-CuAlO2-Al2O3 catalyst exhibits ultradurable electrochemical CO2RR performance with an 85% C2 Faradaic efficiency for a 300 h test. Such a simple interfacial engineering design approach unveiled in this work would be adaptable to develop various ultradurable catalysts for industrial-scale electrochemical CO2RR.

Cu and Si co-doping on TiO2 nanosheets to modulate reactive oxygen species for efficient photocatalytic methane conversion.

In this study, we successfully construct Cu and Si co-doped ultrathin TiO2 nanosheets. As confirmed by comprehensive characterizations, Cu and Si co-doping can rationally tailor the electronic structure of TiO2 to maneuver reactive oxygen species for effective photocatalytic methane conversion. In addition, this co-doping greatly enhances the utilization efficiency of photogenerated charges. Furthermore, it is revealed that Cu and Si co-doping can significantly boost the adsorption and activation of methane on TiO2 nanosheets. As a result, the optimized catalyst achieves a C2H6 production rate of 33.8 µmol g-1 h-1 with a selectivity of 88.4%. This work provides insights into nanocatalyst design toward efficient photocatalytic methane conversion into value-added compounds.

Highly efficient electrocatalytic biomass valorization over a perovskite-derived nickel phosphide catalyst.

In this work, we successfully develop a binder-free phosphorus-engineered perovskite-based catalyst grown on nickel foam via a hydrothermal-phosphorization strategy. For the first time, an as-synthesized perovskite-based nickel phosphide catalyst exhibits excellent electrocatalytic oxidation (ECO) performance for biomass valorization to supersede the competitive oxygen evolution reaction (OER).

Synergizing Inter and Intraband Transitions in Defective Tungsten Oxide for Efficient Photocatalytic Alcohol Dehydration to Alkenes.

Photocatalysis under mild conditions is an intriguing avenue for organic chemical manufacturing to confront the serious fossil energy crisis. Herein, we report a direct light-driven alkene production through alcohol dehydration, using nonstoichiometric tungsten oxide of W18O49 nanowires with abundant lattice defects as a photocatalyst. A representative ethylene (C2H4) production rate of 275.5 mmol gcat -1 h-1 is achieved from ethanol (C2H5OH) dehydration, together with excellent selectivity up to 99.9%. The universality of our approach is further demonstrated with other alcohol dehydration. Combining ultrafast transient absorption spectroscopy with in situ X-ray photoelectron spectroscopy, we underline that the inter- and intraband transitions synergistically contribute to such excellent activity. In particular, the intraband transition excites the electrons in defect bands into an energetically "hot" state, largely alleviating the charge recombination. As a result, the C-OH bond of chemisorbed C2H5OH molecules can be effectively dissociated to furnish the formation of C=C bonds. Our work offers a fresh insight into sustainable alkene production with renewable energy input under mild conditions.

Sunlight-Driven Highly Selective Catalytic Oxidation of 5-Hydroxymethylfurfural Towards Tunable Products.

Owing to the easy over-oxidation, it is a promising yet challenging task to explore renewable carbon resources to control the sunlight-driven selective catalytic oxidation of biomass-derived 5-hydroxymethylfurfural (HMF), producing important chemical feedstocks, namely, less-oxidized 2,5-diformylfuran (DFF) and 5-hydroxymethyl-2-furancarboxylic acid (HMFCA). Herein, we have developed a photocatalyst by anchoring a Ru complex on CdS quantum dots, which achieves selective oxidation of HMF toward DFF or HMFCA with high conversion (>81 %) and selectivity (>90 %), based on the controllable generation of two oxygen radicals under different atmospheres. Such selective conversion can also work well outside the laboratory by using natural sunlight. In particular, the selective production of HMFCA through photocatalytic HMF oxidation is achieved for the first time. More importantly, our photocatalyst is applicable for the selective oxidation of other compounds with hydroxyl and aldehyde groups.

In situ growth of MOFs on Ni(OH)2 for efficient electrocatalytic oxidation of 5-hydroxymethylfurfural.

A Ni-based MOF is in situ grown onto Ni(OH)2 nanosheets to effectively suppress the oxygen evolution reaction for the efficient electrocatalytic oxidation of biomass-derived 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid with 100% yield and faradaic efficiency at 1.4 V (vs. RHE).

Dual-atom Pt heterogeneous catalyst with excellent catalytic performances for the selective hydrogenation and epoxidation.

Atomically monodispersed heterogeneous catalysts with uniform active sites and high atom utilization efficiency are ideal heterogeneous catalytic materials. Designing such type of catalysts, however, remains a formidable challenge. Herein, using a wet-chemical method, we successfully achieved a mesoporous graphitic carbon nitride (mpg-C3N4) supported dual-atom Pt2 catalyst, which exhibited excellent catalytic performance for the highly selective hydrogenation of nitrobenzene to aniline. The conversion of ˃99% is significantly superior to the corresponding values of mpg-C3N4-supported single Pt atoms and ultra-small Pt nanoparticles (~2 nm). First-principles calculations revealed that the excellent and unique catalytic performance of the Pt2 species originates from the facile H2 dissociation induced by the diatomic characteristics of Pt and the easy desorption of the aniline product. The produced Pt2/mpg-C3N4 samples are versatile and can be applied in catalyzing other important reactions, such as the selective hydrogenation of benzaldehyde and the epoxidation of styrene.

In Situ Growth of Ultrathin Ni(OH)2 Nanosheets as Catalyst for Electrocatalytic Oxidation Reactions.

Development of electrocatalysts that are capable of efficiently oxidizing biomass-derived 5-hydroxymethylfurfural (HMF) into 2,5-furandicarboxylic acid (FDCA) is critically important for production of degradable plastics via non-fossil routes. In this study, a facile and scalable immersion synthetic approach has been developed to grow ultrathin nickel hydroxide nanosheets in situ on commercial nickel foam (Ni(OH)2 /NF) as an anode for the electrocatalytic oxidation of HMF to FDCA with complete HMF conversion, 100 % FDCA yield, and >99 % faradaic efficiency at 1.39 V (vs. RHE) within 90 min. Mechanistic studies reveal that the initial oxidation of HMF takes place at the carbonyl group and FDCA is generated through two further oxidation steps. Impressively, the synthesized Ni(OH)2 /NF can also be used to electrocatalytically oxidize other alcohol/aldehyde-containing compounds to the targeted products in alkaline medium with 100 % yield and >94 % faradaic efficiency under a low oxidation potential of 1.39 V (vs. RHE) within short reaction times.

Fe-Co Alloyed Nanoparticles Catalyzing Efficient Hydrogenation of Cinnamaldehyde to Cinnamyl Alcohol in Water.

Selective hydrogenation of C=O against the conjugated C=C in cinnamaldehyde (CAL) is indispensable to produce cinnamyl alcohol (COL). Nonetheless, it is challenged by the low selectivity and the need to use organic solvents. Herein, for the first time, we report the use of Fe-Co alloy nanoparticles (NPs) on N-doped carbon support as a selective hydrogenation catalyst to efficiently convert CAL to COL. The resultant catalyst with the optimized Fe/Co ratio of 0.5 can achieve an exceptional COL selectivity of 91.7 % at a CAL conversion of 95.1 % in pure water medium under mild reaction conditions, ranking it the best performed catalyst reported to date. The experimental results confirm that the COL selectivity and CAL conversion efficiency are, respectively promoted by the presence of Fe and Co, while the synergism of the alloyed Fe-Co is the key to concurrently achieve high COL selectivity and CAL conversion efficiency.

Liberating N-CNTs Confined Highly Dispersed CoNx Sites for Selective Hydrogenation of Quinolines.

Selective hydrogenation of quinoline and its derivatives is an important means to produce corresponding 1,2,3,4-tetrahydroquinolines for a wide spectrum of applications. A facile and efficient "laser irradiation in liquid" technique to liberate the inaccessible highly dispersed CoNx active sites confined inside N-doped carbon nanotubes is demonstrated. The liberated CoNx sites possess generic catalytic activities toward selective hydrogenation of quinoline and its hydroxyl, methyl, and halogen substituted derivatives into corresponding 1,2,3,4-tetrahydroquinolines with almost 100% conversion efficiency and selectivity. This laser irradiation treatment approach should be widely applicable to unlock the catalytic powers of inaccessible catalytic active sites confined by other materials.