Noble Metal Catalysts Research Articles

Boosting hydrogenation properties of supported Cu-based catalysts by replacing Cu0 active sites

Balancing the Cu+/Cu0 ratio is a common strategy to improve catalytic activity of Cu-based catalysts but is still constrained by low atomic utilization and the inherent nature of charge distribution. Herein, we reported a strategy of replacing the Cu0 active sites in Cu-based catalysts by constructing bimetallic sites on ceria, which consist of spatially separated trace amounts of palladium metal and plate-shaped Cu+ clusters with one-atom layers. The catalytic activity of the prepared Cu100Pd1/CeO2-FA catalyst (using formic acid) was 4 times that of conventional Cu100Pd1/CeO2-H catalyst in selective hydrogenation of 5-hydroxymethylfurfural to 2,5-bis(hydroxymethyl)furan, even outperforming some existing noble metal catalysts. Multiple characterizations and theoretical calculations demonstrated that the Pd atom is the heterolytic activation site for H2 molecules while plate-shaped Cu+ metal clusters act as effective hydrogenation places. This directional control involving both spatial relationship and electronic structure of the active site provides a new strategy for designing hydrogenated catalysts.

Copper restructured transition metal/metal oxide heterostructure with a hierarchical nanostructure for accelerated water dissociation kinetics and alkaline hydrogen evolution

The slow kinetics of water dissociation on electrocatalysts lacking platinum hinders the advancement of cost-effective hydrogen production via alkaline water electrolysis. Herein, a hierarchically peach-flower-shaped electrocatalyst consisting of copper-restructured cobalt–nickel/cobalt–nickel oxide heterostructure anchored on copper nanowires (Cu-CoNiO/CoNi@Cu NWs) is developed for efficient hydrogen evolution reaction (HER). Benefiting from the optimized electronic configuration and geometric structure, this Cu-CoNiO/CoNi@Cu NWs catalyst performs an outstanding alkaline HER activity of 29 mV at 10 mA cm−2 and 98 mV at 100 mA cm−2, which is comparable with the state-of-the-art Pt/C catalyst (26 mV at 10 mA cm−2 and 117 mV at 100 mA cm−2). Our findings rank among the topmost catalytic efficiencies when compared to all previously reported non-noble metal catalysts and numerous noble metal catalysts. The combined experimental exploration and theoretical studies reveal that the incorporation of Cu dopant into CoNiO/CoNi heterostructure enhances electron transfer from metal atoms to O atom, leading to the formation of the polarized electric field to accelerate water dissociation and H evolution, eventually facilitating the overall alkaline HER process. The boosted electron exchange and mass transportation deriving from the introduction of Cu NWs and hierarchically peach-flower-shaped nanostructure further reinforce the HER activity of the Cu-CoNiO/CoNi catalyst.

Nickel-catalyzed, silyl-directed, ortho-borylation of arenes via an unusual Ni(II)/Ni(IV) catalytic cycle

Nickel-catalyzed C–H bond functionalization reactions provide an impressive alternative to those with noble metal catalysts due to their unique reactivity and low cost. However, the regioselective C(sp2)–H borylation reaction of arenes accomplished by nickel catalyst remains limited. We herein disclose a silyl-directed ortho C(sp2)–H borylation of substituted arenes with a Ni(cod)2/PMe3/KHMDS catalyst system. Using readily available starting materials, this protocol provides easy access to ortho-borylated benzylic hydrosilanes bearing flexible substitution patterns. These products can serve as versatile building blocks for the synthesis of sila or sila/borine heterocycles under mild conditions. Control experiments and DFT calculations suggest that a catalytic amount of base prompts the formation of Ni(II)-Bpin-ate complex, likely related to the C(sp2)–H bond activation. This borylation reaction might follow an unusual Ni(II)/Ni(IV) catalytic cycle.

Hydrolysis of Chitin with Acid and Noble Metal Catalyst

Hydrolysis of Chitin with Acid and Noble Metal Catalyst

Polyolefin waste to light olefins with ethylene and base-metal heterogeneous catalysts.

The selective conversion of polyethylene, polypropylene, and mixtures of the two polymers to form products with high volume demand is urgently needed because current methods suffer from low selectivity, produce large quantities of greenhouse gases, or rely on expensive, single-use catalysts. The isomerizing ethenolysis of unsaturated polyolefins could be an energetically and environmentally viable route to propylene and isobutylene, but noble-metal homogeneous catalysts and an unsaturated polyolefin are currently required, and the process has been limited to polyethylene. We show that the simple combination of tungsten oxide on silica and sodium on gamma-alumina transforms polyethylene, polypropylene, or a mixture of the two, including post-consumer forms of these materials, to propylene or a mixture of propylene and isobutylene in greater than 90% yield at 320°C without the need for dehydrogenation of the starting polyolefins.

Catalytic depolymerization of Camellia oleifera shell lignin to phenolic monomers: Insights into the effects of solvent, catalyst and atmosphere

Camellia oleifera shell (COS) is a renewable biomass resource abundant in lignin with significant potential for producing phenolic monomers. However, the dearth of research has led to considerable resource wastage and environmental pollution. Herein, reductive catalytic fractionation (RCF) of COS was performed using noble metal catalysts in different solvents. An 11.1 wt% yield of phenolic monomers was achieved with 91% selectivity toward propylene-substituted monomers in H2O/EtOH (3:7, v/v) cosolvent under N2 atmosphere. Notably, the highest phenolic monomer yield of 17.0 wt% was obtained with impressive selectivity (86.9%) toward propanol-substituted monomers in the presence of H2. The GPC analysis and 2D HSQC NMR spectra indicated the effective depolymerization of lignin oligomers with catalysts. Phenolic monomers with ethyl, propyl, or propanol side chain could be produced from lignin-derived oligomers through hydrogenolysis, hydrogenation, and decarboxylation reactions. Overall, this study has paved the way for the valorization of COS lignin through the RCF strategy.

Revealing the Effect of Anion Regulation in NiCo2X4 (X = O, S, Se, Te) on Photoassisted Methanol Electrocatalytic Oxidation.

Designing nonprecious metal anode catalysts for photoassisted direct methanol fuel cells (PDMFCs) remains a challenge. As a semiconductor catalyst with a spinel structure, NiCo2O4 has good methanol catalytic oxidation activity and photocatalytic activity, making it a highly promising anode non-noble metal catalyst for PDMFCs. However, compared with the noble metal catalyst, the photoelectrocatalytic activity remained to be improved. In this report, an anion regulation strategy was adopted to improve the photoassisted methanol electrocatalytic activity. Using a CoNi-Aspartic (CoNi-Asp) nanorod as the precursor, the anion-regulated NiCo2X4 (X = O, S, Se, Te) was prepared by oxidation, sulfuration, selenization, and telluridation reactions. The regulation of anions and their effects on the electronic structure, intermediate product, and photoelectric catalytic performance of NiCo2X4 (X= O, S, Se, Te) was systematically discussed. Photoelectrochemical characterization and adsorption energy of •OH revealing the volcano-like correlation between the anion in NiCo2X4 (X = O, S, Se, Te) and their photoelectrocatalytic performance. The narrowest band gap (2.239 eV), the highest •OH adsorption energy (-3.32 eV), and the highest ratio of Co3+/Co2+ (2.19) ensure the best photoelectric catalytic performance of NiCo2S4, under the visible light irradiation, the photoresponse current density was 1.9 A g-1, the current density at 0.6 V was up to 21.9 A g-1. After 9 h of stability testing, the current retention rate was 80%. This report sheds an idea for the rational design of non-noble anode catalysts for PDMFCs.

Transforming cyclopropanes to enamides via σ-C–C bond eliminative borylation

Recent strides in C–H borylation have significantly expanded our toolkit for the preparation of organoboronates. Nevertheless, avenues alternative to obtain these compounds via σ-C–C cleavage, thereby facilitating molecular scaffold editing, remain scarce. Several methodologies have been proposed for hydroboration of cyclopropanes by activating C–C bonds, conventionally relying on noble and hazardous metal catalysts to control reaction outcomes. Here, we present a strategy for crafting stereochemically precise γ-borylenamides through ring-opening of cyclopropanes avoiding any metallic entities. Boryl species, generated through a ternary reaction with BCl3, cyclopropanes, and a tertiary amine, selectively undergo C–C bond eliminative borylation under the directing of N-acyl group, thereby ensuring enhanced selectivity and efficiency along the reaction pathway. Such inherently stereoconvergent approach accommodates precursors of diverse geometries, including cis/trans isomeric blends.

Unveiling the mechanistic synergy in Mn-doped NiO catalysts with atomic-burry structure: Enhanced CO oxidation via Ni-OH and Mn bifunctionality

The development of non-noble metal catalysts for low-temperature CO oxidation is a pivotal subject in various disciplines. In this study, an optimized Mn-doped NiO catalyst (Mn-NiO-0.5), prepared via aerosol pyrolysis with an equal molar ratio of Ni to Mn, demonstrates remarkable performance. It achieves an 82 % CO conversion at -20 °C and a 100 % conversion between 10 °C and 800 °C. The catalyst’s turnover frequency (TOF) for CO oxidation significantly surpasses that of previously reported noble-metal-based catalysts, underscoring its superior efficiency. Dynamic analyses suggest that the enhanced catalytic activity is a result of the unique atom burr structure, which presents an extensive surface area replete with abundant active sites. This structural feature is instrumental in maximizing the catalyst’s interaction with CO molecules. Experimental findings, corroborated by density functional theory (DFT) calculations, elucidate the mechanism of CO oxidation on the Mn-NiO-0.5 catalyst. The process is facilitated by the synergistic action of bimetallic sites, where the Ni–OH site acts as the primary adsorption point for CO. Subsequently, the CO is oxidized to bicarbonate through the interaction with the oxygen (O or O2) at adjacent Mn sites. This pioneering study introduces a paradigm-shifting insight: the effectiveness of non-noble metal oxide catalysts can now compete with, and in some cases, outperform their noble metal counterparts. This breakthrough is set to transform the industry, presenting a compelling alternative to conventional noble metal catalysts and propelling the evolution of state-of-the-art environmental conservation technologies.

Strong interaction between promoter and metal in Pd-Ba/TiO2 catalysts for formaldehyde oxidation

As our previous works found, alkali metals have a common promotion effect on supported noble metals catalysts for formaldehyde (HCHO) oxidation. As second-group elements, alkaline earth metals (AEMs) are neighbors to the first-group elements and share some properties in common. However, detailed investigations into the specific mechanisms underlying AEMs’ effects on HCHO oxidation remain limited. In this study, we found that Ba addition showed a similar promotion effect on HCHO oxidation for Pd/TiO2. Ba species stabilized Pd groups, improved the dispersion, and even caused a large number of monatomic-like Pd sites to appear, which may be attributed to the electronic interaction between promoter and metal (EIPM) between Ba and Pd. Besides, AEM loading had the important effect of increasing the electron density of metallic Pd nanoparticles, which further improved the ability for O2 activation and so enhanced the mobility of chemisorbed oxygen on the catalyst surface. For Pd/TiO2, the HCHO oxidation path is mainly HCHO→HCOOH→HCOO→H2O+CO2. By contrast, for Pd-Ba/TiO2, with more surface-active species, the formate intermediate was more likely to be directly oxidized into H2O and CO2, which is a more effective reaction pathway. The details of the EIPM between Pd and Ba were investigated by GPAW (DFT calculation module) in ASE (Atomic Simulation Environment). The AEM Ba acted as an electron donor and could interact with Pd d orbital electrons through BaO sp orbital electrons. Ba species were highly dispersed on the carrier due to the Ba-Ti interaction. Ba species dispersed over large areas stabilized the Pd particles and donated electrons to Pd. Therefore, adding an AEM is an efficacious strategy to improve the performance of the catalytic oxidation of HCHO.

Sabatier principle based design of high performance FeCoNiMnMoP high entropy electrocatalysis for alkaline water splitting

FeCoNi-based high entropy intermetallic compounds are promising substitutes for noble metal catalysts for hydrogen evolution reaction (HER) and oxygen evolution (OER), while their activity is restricted by the synergistic effect between the elements. In this paper, the theoretical model of FeCoNiMnMoP bifunctional catalyst has been reasonably designed given the volcanic curve of M−H bond energy as a valuable guide for candidate metal elements. Theoretical calculations show that the synergistic effect between multiple sites not only accelerates the electron transfer but also reduces the rate-determining step (RDS) barrier. At the same time, the introduction of Mo also enhances the total density of states and reduces the d-band center, thus optimizing the adsorption and dissociation of intermediates. The experimental results confirm that the theoretical model has excellent catalytic performance. In the alkaline solution, FeCoNiMnMoP‖FeCoNiMnMoP requires only an ultra-low cell voltage of 1.49 V for overall water splitting when the current density is 10 mA cm−2. In general, novel insights on the effects of intermetallic synergies on water decomposition are provided, which is helpful for the design of bifunctional catalysts based on volcanic diagrams.

High Temperature Solid Oxide Electrolysis for Green Hydrogen Production.

Global warming and energy crises have motivated the development of renewable energy and its energy carriers. Green hydrogen is the most promising renewable energy carrier and will be fundamental to future energy conversion and storage systems. Solid Oxide Electrolysis Cells (SOECs) are a promising green hydrogen production technology featuring high electrical efficiency, no noble metal catalyst usage, and reversible operation. This review provides a timely summary of the latest SOEC progress, covering developments at various levels, from cells to stacks to systems. Cell/stack components, configurations, advanced electrode material/fabrication, and novel characterization methods are discussed. Electrochemical and durable performance for each cell/stack configuration is reviewed, focusing on degradation mechanisms and associated mitigation strategies. SOEC system integration with renewable energy and downstream users is outlined, showing flexibility, robustness, scalability, viability, and energy efficiency. Challenges of cost and durability are expected to be overcome by innovation in material, fabrication, production, integration, and operation. Overall, this comprehensive review identifies the SOEC commercialization bottleneck, encourages further technology development, and envisions a future green hydrogen society with net-zero carbon emissions.

Self-assembled formation of platinum single atoms and nanoclusters stabilized on MXene as an efficient catalyst for boosting electrocatalytic hydrogen evolution

Atomic isolated and dispersed single atom catalyst is ideal for high-performance industrial catalyst. However, the contribution from small amounts of nanoclusters coexisting with single atoms to the catalytic reaction activity is often neglected. In this work, a MXene-supported uniformly dispersed Pt single atoms and nanoclusters (Pt1+Ptn/MXene) were obtained by self-assembly through an impregnation method. The catalyst exhibits high electrochemical performance in the hydrogen evolution reaction with an overpotential of only 61.3 mV and a Tafel slope of 32.5 mV dec−1 at a current density of 10 mA cm−2 in an acidic environment. The XAFS analysis and further DFT calculation indicate that the synergistic effect between single atoms and nanoclusters can facilitate adsorption of H* and promote the HER reaction. This work provides an efficient method for integrating multiple active sites in noble metal catalysts.

High-temperature planar asymmetric ceramic membranes: Effect of the Pt amount and dispersion on the H2 separation performance

This work investigates for the first time the effect of Pt catalyst amount and dispersion on hydrogen permeation performances of BaCe0.65Zr0.20Y0.15O3−δ–Gd0.2Ce0.8O2−δ (BCZY–GDC) composite planar Cer-Cer membranes with asymmetrical architecture, aiming to maximize the ratio between the permeated hydrogen and the metal content. To boost the hydrogen separation reactions, Pt must be deposited on both the dense and porous sides of the membrane. Moreover, the complex architecture of the porous layer can be used to disperse Pt particles providing a good interaction with the membrane. To fulfil this aim BCZY-GDC membranes composed of a 20 μm thick active dense layer and a 600 μm thick, porous support were produced by tape casting and impregnated with different amounts of platinum. Hydrogen permeation properties were thoroughly investigated examining the composition of the feed and the sweep gasses, temperature, stream humidification, catalyst amount and nature of the dispersion media. The effect of Pt-catalysed hydrogen permeation and water splitting reaction at the permeate side was investigated and discussed. It was found that using an optimal amount of Pt solution to activate the porous side of the membranes is paramount to increase hydrogen permeation in the whole operating temperature range while keeping low the amount of noble metal catalyst. Moreover, the selection of a proper solvent with good interaction with the membrane allows the obtainment of smaller Pt nanoparticles resulting in higher permeation. The best performances in terms of hydrogen permeation (0.74 and 1.29 mL min−1 cm−2 at 750 °C using a feed stream with respectively 50 % and 80 % of H2 in He) were obtained using an acetone-based solution for depositing 1.5 mg cm−2 of Pt at the porous side. This work suggests that the metal deposition plays a non-trivial role in the hydrogen separation process and should be fully evaluated to increase the final performance while cutting down the cost of the Pt catalyst and therefore, of the final device.

Aqueous Phase Hydrogenation of 4-(2-Furyl)-3-buten-2-one over Different Re Phases.

4-(2-furyl)-3-buten-2-one (FAc) is obtained by aldol condensation of furfural and acetone and has been used in hydrodeoxygenation reactions to obtain fuel products using noble metal catalysts. The hydrogenation of FAc in the aqueous phase using metallic- and Re oxide-supported catalysts on graphite was studied, within a temperature range of 200-240 °C, in a batch reactor over a 6 h reaction period. The catalysts were characterized using N2 adsorption-desorption, TPR-H2, TPD-NH3, XRD, and XPS analyses. Catalytic reactions revealed that metallic rhenium and rhenium oxide-supported catalysts are active for the hydrogenation and Piancatelli rearrangement of FAc. Notably, metallic rhenium exhibited a fourfold higher initial rate than rhenium oxide, which was attributed to the higher dispersion of Re in the Re/G catalyst over graphite. Re/G and ReOx/G catalysts tended to rearrange and hydrogenate FAc to 2-(2-oxopropyl)cyclopenta-1-one in water.

Copper-catalyzed intermolecular formal [4 + 1] annulation of 1,5-diynes with benzocyclobutenones

The one-carbon ring expansion of benzocyclobutenones is an efficient methodology for the assembly of cyclic ketones. However, hazardous reagents or noble metal catalysts are frequently required. Herein, we disclose a copper-catalyzed intermolecular formal [4 + 1] annulation of 1,5-diynes with benzocyclobutenones, allowing the practical and atom-economical construction of diverse pyrryl 1-indanones in generally good yields under mild reaction conditions. This reaction represents an important advancement in the ring expansion of benzocyclobutenones via vinyl cation pathway.

Electroreductive Cross-Coupling between Aromatic Aldehydes and Chlorosilanes Enabling the Synthesis of α-Silyl Alcohols.

α-Silyl alcohols are powerful structural motifs for pharmaceutical chemistry, materials chemistry, and organic synthesis. The limitations of current synthetic techniques encompass a requirement for difficult-to-obtain silyl precursors, noble-metal catalysts, and narrow substrate scopes. Here, we developed a general synthetic method for α-silyl alcohols through electroreductive cross-coupling of aldehydes and chlorosilane. This method features easily available reagents, mild conditions, and a wide substrate scope. The establishment of this protocol will provide an alternative for access to α-silyl alcohols.

A Bi2Te3 topological insulator/carbon nanotubes hybrid composites as a new counter electrode material for DSSC and NIR photodetector application

Two-dimensional layered bismuth telluride (Bi2Te3), a prominent topological insulator, has garnered global scientific attention for its unique properties and potential applications in optoelectronics and electrochemical devices. Notably, there is a growing emphasis on improving photon-to-electron conversion efficiency in dye-sensitized solar cells (DSSCs), prompting the exploration of alternatives to noble metal catalysts like platinum (Pt). This study presents the synthesis of Bi2Te3 and its hybrid nanostructure with single-wall carbon nanotubes (SWCNT) via a straightforward hydrothermal process. The research unveils a novel application for the Bi2Te3-SWCNT hybrid structure, serving as a counter electrode in platinum-free DSSCs, facilitating the conversion of triiodide (I3−) to iodide (I−) and functioning as an active electrode material in a photodetector (n-Bi2Te3-SWCNT/p-Si). The resulting DSSC employing the Bi2Te3-SWCNT hybrid counter electrode achieves a power conversion efficiency (PCE) of 4.2 %, a photocurrent density of 10.5 mA/cm2, a fill factor (FF) of 62 %, and superior charge transfer kinetics compared to pristine Bi2Te3 based counter electrode (PCE 2.1 %, FF 34 %). Additionally, a spin coating technique enhances the performance of the n-Bi2Te3-SWCNT/p-Si photodetector, yielding a responsivity of 2.2 AW−1, detectivity of 1.2 × 10−3 and enhanced external quantum efficiency. These findings demonstrate that the newly developed Bi2Te3-SWCNT heterostructure enhances interfacial charge transport, electrocatalytic performance in DSSCs, and overall photodetector performance.

Recycling Spent Ternary Cathodes to Oxygen Evolution Catalysts for Pure Water Anion-Exchange Membrane Electrolysis.

Recycling spent lithium-ion batteries (LIBs) to efficient water-splitting electrocatalysts is a promising and sustainable technology route for green hydrogen production by renewables. In this work, a fluorinated ternary metal oxide (F-TMO) derived from spent LIBs was successfully converted to a robust water oxidation catalyst for pure water electrolysis by utilizing an anion-exchange membrane. The optimized catalyst delivered a high current density of 3.0 A cm-2 at only 2.56 V and a durability of >300 h at 0.5 A cm-2, surpassing the noble-metal IrO2 catalyst. Such excellent performance benefits from an artificially endowed interface layer on the F-TMO, which renders the exposure of active metal (oxy)hydroxide sites with a stabilized configuration during pure water operation. Compared to other metal oxides (i.e., NiO, Co3O4, MnO2), F-TMO possesses a higher stability number of 2.4 × 106, indicating its strong potential for industrial applications. This work provides a feasible way of recycling waste LIBs to valuable electrocatalysts.

Activated Migration of Hydroxide Ion in Anolyte for Enhancing Performance of Scaled-up Non-Noble Catalysts in Pure Water-Fed Anion Exchange Membrane Water Electrolysis

The continuous advancement in water electrolysis technologies has illuminated the potential of sustainable energy sources, particularly in the realm of green hydrogen production. Anion exchange membrane water electrolysis (AEMWE) stands out as a promising technology capable of theoretically yielding high-purity hydrogen. However, the commercialization of AEMWE faces challenges arising from the inherent discord between high performance and the elevated costs associated with noble metal catalysts, such as platinum and iridium. Moreover, prevalent studies often focus on a limited electrode area of less than 4 cm2, thereby restricting the exploitation of the high purity hydrogen production capabilities inherent in AEMWE. This research prioritizes the enhancement of performance through a meticulously crafted membrane-electrode assembly (MEA) employing a 25 cm2 Ni-frame caged NiMoO4 catalyst for cathode synthesis. The observed performance improvement is attributed to the augmented active site of the catalyst, consisting of NiMoO4 entrapped in the Ni substrate during the compression process of the electrode. Additionally, the increase in local pH at the interfacial between electrode and bulk electrolyte is facilitated by the capillary phenomenon resulting from the space between the Ni substrate and the NiMoO4 catalyst layer, leading to enhanced migration of the electrolyte containing hydroxide ions. Acknowledgements This research was supported by the Korea Institute of Energy Technology Evaluation and Planning (KETEP) granted financial resources from the Ministry of Trade, Industry & Energy, Republic of Korea (No. 20213030040590).