Noble Metal Catalysts Research Articles

In-situ constructing ultrafine NiCo alloy confined in LDH nanoflower for efficient selective hydrogenation of furfural

Directional activation of oxygen-containing groups is a crucial challenge in the catalytic conversion of renewable biomass to high-value products. Herein, we fabricated uniform dispersed NiCo alloy nanoparticles by direct reduction flower-like layer double hydroxides (LDHs) precursors. The as-obtained Ni2Co1AlO exhibited outstanding yield (97.6 %) of tetrahydrofurfuryl alcohol (THFOL) in furfural hydrogenation, which is significantly superior to those of monometallic Ni-based (75 %) and Co-based (0 %) LDH catalysts and even higher than the most noble metal catalysts. The Ni2Co1AlO showed robust stability, e.g., the catalyst can be recycled up to 10 times without loss of its conversion and selectivity, which is attributed to the ultra-dispersed metal cations in layers and the confined effect of metal oxides. Characterizations and theoretical calculations demonstrate that alloying Ni with Co can downshift the d-band center of Ni in NiCo alloys, which facilitates the H* desorption to improve hydrogenation activity. The unique electronic interactions between Ni and Co facilitated the parallel adsorption of furfural while reduced the energy barriers of the furan ring hydrogenation, promoting the production of THFOL. This work provides a promising strategy of tailoring d-band center, which can shed light on the design of heterogeneous catalysts.

Surfactant-free synthesis of nanostructured palladium materials under mild conditions and their highly catalytic selective hydrogenation

Nanostructured palladium (Pd) materials are highly efficient noble metal catalysts in various fields, but developing a simple and mild strategy to prepare Pd nanomaterials with high activity and selectivity still remains a big challenge. In this study, uniform-sized Pd popcorn-like nanospheres (PNSs) were successfully synthesized by the slow reduction of Pd(OAc)2 in anhydrous methanol under ambient conditions in the dark without any surfactant, additional reductant and support. The obtained Pd PNSs have rough surface with the average diameter of approximately 140 nm, and are composed of many smaller PNSs with the average size of about 12 nm. Pd PNSs have excellent catalytic performance in the hydrogenation of 4-nitrobenzaldehyde to 4-aminobenzaldehyde under mild conditions. Specifically, using the as-prepared Pd PNSs as catalyst, the 98 % conversion of 4-nitrobenzaldehyde and 98 % selectivity to 4-aminobenzaldehyde can be achieved within 1.5 h at 35°C under atmospheric pressure. After three recycling, the Pd PNSs can still maintain highly catalytic activity and selectivity. The very simple strategy developed here will be a valuable supplement to the methodology for the surfactant-free fabrication of other surface-active metallic nanomaterials for advanced applications.

Toward Developing Superior Cu-Based Metal-Organic Framework-Derived Materials for Electrocatalytic Oxidation of Ethanol.

This project addresses the urgent need for efficient and cost-effective development of electrocatalysts for the ethanol oxidation reaction (EOR). This reaction offers promising renewable energy solutions but faces challenges due to the slow EOR kinetics, typically requiring costly noble metal catalysts. To overcome these limitations, this study focuses on developing CuZn-based EOR catalysts derived from metal-organic frameworks (MOFs), focusing on understanding the structure-performance relationship between pristine MOF-based electrocatalysts and their pyrolyzed counterparts. Herein, bimetallic MOF materials with varying Cu/Zn ratios were synthesized, followed by pyrolysis to produce carbonized counterparts while preserving the fundamental structure but with altered physicochemical properties. Comparative EOR studies revealed the superior performance of pyrolyzed MOFs, demonstrating that optimized Zn-loading is crucial over Cu-based framework for catalyst performance and durability. Overall, this work highlights the potential of MOF-derived Cu-based catalysts for renewable energy applications and provides insights into optimizing their performance through controlled synthesis and post-treatment strategies.

Clarifying Glycerol Electrooxidation Studies on Pd-Based Catalysts: Insights Into Catalytic Performance and Practical Challenges.

Escalating biodiesel production led to a surplus of glycerol, prompting its exploration as a valuable resource in industrial applications. Electrochemical systems have been studied, specifically employing noble metal catalysts like palladium for glycerol electrooxidation. Despite numerous studies on Pd-based catalysts for glycerol electrooxidation, a comprehensive analysis addressing critical questions related to the economic feasibility, global sourcing of Pd, and the thematic cohesion of publications in this field is lacking. Moreover, a standardized framework for comparing the results of various studies is absent, hindering progress on glycerol technologies. This critical overview navigates the evolution of Pd-based catalysts for glycerol electrooxidation, examining catalytic activity, stability, and potential applications. It critically addresses the geographical sources of Pd, the motivation behind glycerol technology exploration, thematic coherence in existing publications, and the meaningful comparison of results. It correlates the use of Pd-based catalysts with the natural source of Pd and the origin of glycerol derived from biodiesel. The proposed standardized approach for comparing electrochemical parameters and establishing experimental protocols provides a foundation for meaningful study comparisons. This critical overview underscores the need to address fundamental questions to accelerate the transition of glycerol technologies from laboratories to practical applications.

Pt-Embedded Metal–Organic Frameworks Deriving Pt/ZnO-In2O3 Electrospun Hollow Nanofibers for Enhanced Formaldehyde Gas Sensing

Functionalization by noble metal catalysts and the construction of heterojunctions are two effective methods to enhance the gas sensing performance of metal oxide-based sensors. In this work, we adopt the porous ZIF-8 as a catalyst substrate to encapsulate the ultra-small Pt nanoparticles. The Pt/ZnO-In2O3 hollow nanofibers derived from Pt/ZIF-8 were prepared by a facile electrospinning method. The 25PtZI HNFs sensor possessed a response value of 48.3 to 100 ppm HCHO, 2.7 times higher than the pristine In2O3, along with rapid response/recovery time (5/22 s), and lower theoretical detection limit (74.6 ppb). The improved sensing properties can be attributed to the synergistic effects of electron sensitization effects and catalytic effects of Pt nanoparticles, and the high surface O− absorbing capability of heterojunctions. The present study paves a new way to design high performance formaldehyde gas sensors in practical application.

Bridging Atom Engineering for Low-Temperature Oxygen Activation in a Robust Metal-Organic Framework.

Achieving active site engineering at the atomic level poses a significant challenge in the design and optimization of catalysts for energy-efficient catalytic processes, especially for a reaction with two reactants competitively absorbed on catalytic active sites. Herein, we show an example that tailoring the local environment of cobalt sites in a robust metal-organic framework through substituting the bridging atom from -Cl to -OH group leads to a highly active catalyst for oxygen activation in an oxidation reaction. Comprehensive characterizations reveal that this variation imparts drastic changes on the electronic structure of metal centers, the competitive reactant adsorption behavior, and the intermediate formation. As a result, exceptional low-temperature CO oxidation performance was achieved with T25(Temperature for 25 % conversion)=35 °C and T100 (Temperature for 100 % conversion)=150 °C, which stands out from existing MOF-based catalysts and even rivals many noble metal catalysts. This work provides a guidance for the rational design of catalysts for efficient oxygen activation for an oxidation reaction.

Bridging Atom Engineering for Low‐Temperature Oxygen Activation in a Robust Metal–Organic Framework

AbstractAchieving active site engineering at the atomic level poses a significant challenge in the design and optimization of catalysts for energy‐efficient catalytic processes, especially for a reaction with two reactants competitively absorbed on catalytic active sites. Herein, we show an example that tailoring the local environment of cobalt sites in a robust metal–organic framework through substituting the bridging atom from −Cl to −OH group leads to a highly active catalyst for oxygen activation in an oxidation reaction. Comprehensive characterizations reveal that this variation imparts drastic changes on the electronic structure of metal centers, the competitive reactant adsorption behavior, and the intermediate formation. As a result, exceptional low‐temperature CO oxidation performance was achieved with T25(Temperature for 25 % conversion)=35 °C and T100 (Temperature for 100 % conversion)=150 °C, which stands out from existing MOF‐based catalysts and even rivals many noble metal catalysts. This work provides a guidance for the rational design of catalysts for efficient oxygen activation for an oxidation reaction.

Asymmetric hydrogenation of ketimines with minimally different alkyl groups.

Asymmetric catalysis enables the synthesis of optically active compounds, often requiring the differentiation between two substituents on prochiral substrates1. Despite decades of development of mainly noble metal catalysts, achieving differentiation between substituents with similar steric and electronic properties remains a notable challenge2,3. Here we introduce a class of Earth-abundant manganese catalysts for the asymmetric hydrogenation of dialkyl ketimines to give a range of chiral amine products. These catalysts distinguish between pairs of minimally differentiated alkyl groups bound to the ketimine, such as methyl and ethyl, and even subtler distinctions, such as ethyl and n-propyl. The degree of enantioselectivity can be adjusted by modifying the components of the chiral manganese catalyst. This reaction demonstrates a wide substrate scope and achieves a turnover number of up to 107,800. Our mechanistic studies indicate that exceptional stereoselectivity arises from the modular assembly of confined chiral catalysts and cooperative non-covalent interactions between the catalyst and the substrate.

Magnetic Order Transition of a Two-Dimensional Square-Lattice Electrocatalyst Assembled by Fe-N4 Units: Crucial Role on Oxygen Reduction.

Herein, we theoretically investigate the effect of magnetic orders on electrocatalytic oxygen reduction reaction (ORR) properties on the Fe-N4 site-embedded two-dimensional (2D) covalent organic framework (Fe-N4@COF-C3N2) under realistic environments. The Fe-N4@COF-C3N2 shows a 2D square-lattice (sql) topology with three magnetic order states: one ferromagnetic state (FM) and two antiferromagnetic states (AFM1 and AFM2). Specially, the electrocatalyst in the AFM2 state shows a remarkable onset potential of 0.80 V/reversible hydrogen electrode (RHE) at pH 1, superior to the existing most excellent noble-metal catalysts. Thermodynamically, the onset potential for the 4e- ORR is 0.64 V/RHE at pH 1, with a magnetic state transition process of FM → AFM1 → FM → FM → FM, while at pH 13, the onset potential for the 4e- ORR is 0.54 V/RHE, with the magnetic transition process of FM → FM → AFM1 → FM → FM. Generally, this finding will provide new avenues to rationally design the Fe-N4 electrocatalyst.

Cobalt-catalyzed cross-electrophile coupling of alkynyl sulfides with unactivated chlorosilanes.

Herein, we disclose a highly efficient cobalt-catalyzed cross-electrophile alkynylation of a broad range of unactivated chlorosilanes with alkynyl sulfides as a stable and practical alkynyl electrophiles. Strategically, employing easily synthesized alkynyl sulfides as alkynyl precursors allows access to various alkynylsilanes in good to excellent yields. Notably, this method avoids the utilization of strong bases, noble metal catalysts, high temperature and forcing reaction conditions, thus presenting apparent advantages, such as broad substrate scope (72 examples, up to 97% yield), high Csp-S chemo-selectivity and excellent functional group compatibility (Ar-X, X = Cl, Br, I, OTf, OTs). Moreover, the utilities of this method are also illustrated by downstream transformations and late-stage modification of structurally complex natural products and pharmaceuticals. Mechanistic studies elucidated that the cobalt catalyst initially reacted with alkynyl sulfides, and the activation of chlorosilanes occurred via an SN2 process instead of a radical pathway.

Whole-cell selective oxidation of 5-HMF by sugarcane bagasse isolated Bacillus nitratireducens

This study delves into the biocatalytic oxidation of 5-hydroxymethylfurfural (5-HMF) by the newly isolated Bacillus nitratireducens, from sugar cane bagasse. This reaction remains unexplored within the existing scientific literature concerning this microbial strain. Initially, to comprehensively characterize the strain and classify it taxonomically, genotypic and phenotypic analysis were conducted, including whole genome sequencing and ANI analysis. Subsequently, the study proceeded to evaluate for the first time with B. nitratireducens the efficiency of 5-HMF oxidation under aerobic conditions. The process resulted in the formation of 5-hydroxymethyl-2-furancarboxylic acid (HMFCA) as the principal product, a valuable molecule that demonstrates promising potential as a precursor for polyesters. Additionally, the compound exhibits medical applications, including its role as an anti-tumor agent and interleukin inhibitor. Employing Response Surface Methodology (RSM), the conditions conducive to optimizing HMFCA production were assessed. These conditions, including a 3 mM 5-HMF concentration, a pH level of 5.6, and a temperature of 30 °C maintained over a period of 24 h, were found to yield optimal results. Model validation further underscored the effectiveness of these conditions, demonstrating a 91% HMFCA yield, which slightly exceeded the predicted 88%. In conclusion, the study highlights the potential of the biomass-derived Bacillus strain in achieving a high conversion rate through the selective oxidation of the aldehyde group present in the 5-HMF molecule. This whole-cell catalytic process eliminates the need for noble metal catalysts, commonly employed in similar chemical reactions, thereby underscoring its potential for enhancing environmental sustainability and reducing reliance on costly and potentially harmful catalysts.

Integration of a Bismuth-Based Tris-Mononuclear Complex with 2D Functional Materials for Highly Efficient and Durable Aqueous Electrocatalytic Hydrogen Evolution.

The eminence of transitioning from traditional fossil fuel-based energy resources to renewable and sustainable energy sources is most evidently crucial. The potential of hydrogen as an alternative energy source has specifically focuses the electrocatalytic water splitting (EWS) as a promising technique for generating hydrogen. Development of efficient electrocatalysts to facilitate the EWS process while rationalizing the limitations of noble metal catalysts like platinum has become one of the daunting tasks. Consequently, porous functional materials such as metal complexes (MCs) and graphene oxide (GO) can act as potential catalysts for EWS. Therefore, a composite of GO and a mononuclear bismuth metal complex is synthesized through in situ facile synthesis, which is further utilized as an efficient electrocatalyst for the hydrogen evolution reaction (HER). Several potential electrocatalytic MC@GO composite (BMGO-3,5,7) materials were prepared with compositional variation of GO (3, 5, and 7 wt %). The experimental results demonstrate that the BMGO5 composite exhibits excellent HER activity with a low overpotential value of 105 mV at 10 mA cm-2 and a low Tafel slope of 44 mV dec-1 in 1 M KOH solution. Furthermore, a comprehensive investigation on the potentiality of the BMC-GO composite for hydrogen evolution from river water splitting was performed in order to address the issue of freshwater depletion. Inclusion of a mononuclear MC for facile synthesis of functional GO-based efficient electrocatalyst material is very scanty in the literature. This unique approach could assist future research endeavors toward designing efficient electrocatalysts for sustainable renewable energy generation. This is one of the first of its kind, where mononuclear MCs were utilized to develop GO-based functional composite materials for efficient electrocatalysis toward sustainable renewable energy generation.

Highly efficient conversion of biomass-derived furanic compounds into alkyl diols by selective hydrogenolysis using non-noble metal catalysts with tunable surface oxygen vacancies

Production of alkyl diols from biomass-derived furanic compounds by hydrogenolysis is a promising route to the fabrication of bio-based polyesters and polyurethanes. However, it faces many challenges such as the use of noble metal catalysts, or low hydrogenolysis activity of the furan rings and poor product selectivity with non-noble metal catalysts. In this work, non-noble metal catalysts Cu-Co3O4 (CuCox) catalysts were modified by magnesium, obtaining CuCoxMgy catalysts with tunable surface oxygen vacancies (OV). The CuCoxMgy catalysts demonstrated greatly improved activity and selectivity (approx. 50 %), comparable to those of noble metal catalysts, in the hydrogenolysis of furfuryl alcohol into 1,5-pentanediol (1,5-PeD). The obtained CuCoxMgy catalysts are even superior to the noble metal catalysts in terms of production rate or productivity. Extensive characterizations including XAS, EPR and XPS revealed that magnesium significantly promotes the formation of Co2+-OV pair sites on the catalyst surface, which simultaneously activate furan ring and hydroxyl group in furfuryl alcohol, leading to the efficient and selective cleavage of the C2-O1 bond to form 1,5-PeD. The CuCoxMgy catalysts also exhibited high activity and selectivity in hydrogenolysis of various other biomass-derived furanic compounds towards ring-opening products.

CVO/TiO2 Heterojunction Photocatalyst for the Synthesis of Arylamines via Oxidative Aromatization of Amines and Cyclohexenones

A novel CVO/TiO2 heterojunction material has been prepared and used to catalyze the oxidative aromatization of amines and cyclohexenones under visible light irradiation, avoiding the use of noble metal catalysts and providing an environmentally friendly alternative for the synthesis of aromatic amines. The catalytic reaction uses oxygen as the final oxidant and provides good yields over a wide range of substrates. Notably, the recyclable heterogeneous semiconductor photocatalyst can be readily recovered and reused for at least four cycles. In addition, several biologically active molecules were successfully synthesized using the photocatalytic method.

Superior Oxygen Evolution Electrocatalyst based on Ni‐Ellagic Acid Coordination Polymer

AbstractThe oxygen evolution reaction (OER) is central to energy conversion technologies, but the high cost and scarcity of commercial noble metal catalysts limit their widespread application. Natural products exhibit great potential in preparing high‐performance electrocatalysts due to their cost‐effectiveness and sustainability. Here, a kind of 1D polymers [M‐EA (M═Co, Cu, Ni)] for oxygen evolution reaction via the complexation of ellagic acid (EA) with metal ions are reported. It is found that Ni‐EA displays a low overpotential (190 mV at 10 mA cm−2) and an ultralow Tafel slope (28 mV dec−1), with a production cost of only 3.6 × 10−2% of IrO2. Density functional theory investigations reveal the electrocatalytic mechanism of the OER. A rechargeable Zn‐Air battery using Ni‐EA+Pt/C as the air electrode shows a lower charging potential and better cycling stability than the IrO2+Pt/C‐based battery. This work provides a train for the development of state‐of‐the‐art OER catalysts.

Superlative Porous Organic Polymers for Photochemical and Electrochemical CO2 Reduction Applications: From Synthesis to Functionality.

To mimic the carbon cycle at a kinetically rapid pace, the sustainable conversion of omnipresent CO2 to value-added chemical feedstock and hydrocarbon fuels implies a remarkable prototype for utilizing released CO2. Porous organic polymers (POPs) have been recognized as remarkable catalytic systems for achieving large-scale applicability in energy-driven processes. POPs offer mesoporous characteristics, higher surface area, and superior optoelectronic properties that lead to their relatively advanced activity and selectivity for CO2 conversion. In comparison to the metal organic frameworks, POPs exhibit an enhanced tendency toward membrane formation, which governs their excellent stability with regard to remarkable ultrathinness and tailored pore channels. The structural ascendancy of POPs can be effectively utilized to develop cost-effective catalytic supports for energy conversion processes to leapfrog over conventional noble metal catalysts that have nonlinear techno-economic equilibrium. Herein, we precisely surveyed the functionality of POPs from scratch, classified it, and provided a critical commentary of its current methodological advancements and photo/electrochemical achievements in the CO2 reduction reaction.

Promoting effect of potassium over Pd/SiO2 catalyst for ambient formaldehyde oxidation

Highly dispersed noble metals are acknowledged for its pivotal role in influencing the efficiency of catalysts during the HCHO oxidation process. Interestingly, in this work, an innovative approach was employed to augmenting the stabilization of noble metals on irreducible carriers supported noble metal catalyst (Pd/SiO2) by adding alkali metal potassium (K). A formidable promotion effect was observed when the K doping to Pd/SiO2 catalysts. It achieves a conversion rate of 93% for 270 ppmV of HCHO to harmless CO2 and H2O at a weight hourly space velocity (WHSV) of 300,000 mL/(g·hr) at 25°C. Multiple characterization results illustrated that a strong interaction between added K and Pd species was formed after K addition, which not only stabilized Pd species on the carrier surface but also markedly enhanced its dispersal on the SiO2 carrier. The increasing Pd dispersion induced more oxygen vacancies on the surfaces of the Pd/SiO2 catalysts. The formation of these oxygen vacancies can be attributed to the phenomenon of hydrogen spillover, which also contributed to elevating the electron density on the Pd sites. Meanwhile, the oxygen vacancies favored the O2 activation to form more reactive oxygen species participating in the HCHO oxidation reaction, thus improving the performance of Pd/SiO2 catalysts displayed for HCHO oxidation. This study provides a simple strategy to design high-performance irreducible carriers supported noble metal catalysts for HCHO catalytic oxidation.

In situ surface etching strategy for bimetallic MOFs-derived oxides and their catalytic properties

MOFs and their derivatives are excellent carriers with large specific surface area. Here, we propose a new strategy to engineer a supported-Pt core shell MOF-derived metal oxide catalyst. In this work, ZnCo-glycol microspheres were used as sacrificial templates, and the pre-prepared Pt nanoparticles were modified in MOFs during the in situ surface etching strategy. Compared to the ZnCo-2MI-330 and ZnCo–Pt-330, ZnCo–Pt-2MI-330 presents good catalytic activity (T10 = 110 °C,T90 = 123 °C) and excellent stability on CO oxidation reaction. By detailed characterization, ZnCo–Pt-2MI-330 remains the original pore structure of MOFs and provides a larger specific surface area, while the addition of Pt NPs changes the content of active species (the high ratio of Co3+ and active oxygen species) in the metal oxides. More importantly, the strategy effectively improves the noble metal catalysts are apt to lose their activities during the thermal catalytic caused by the serious working environment.

Constructing Co@C nanoparticles with chainmail-structure for highly efficient hydroformylation of 1-hexene

Constructing highly active noble-metal-free heterogeneous catalysts is the crux for the hydroformylation of long-chain α-olefins. Herein, novel chainmail-structured cobalt oxide nanoparticles (CoO@C|SBA-15) are fabricated by the channel confinement strategy, which display excellent activity for the 1-hexene hydroformylation. Specifically, the obtained catalyst shows 100% 1-hexene conversion and 94% heptanal selectivity, as well as up to 2.0 linear to branch (l/b) ratio, outperforming most of heterogeneous noble metal catalysts. Remarkably, in-situ DRIFT spectra combined with density functional theory calculations disclosed the metallic Co derived from in-situ reconstruction of CoO is the key active site for 1-hexene hydroformylation. Specifically, the reconstructed Co site is responsible for the adsorption of 1-hexene, and the graphite carbon layer promotes the adsorption of H2 and CO by interacting with the reconstructed Co. Moreover, the graphite carbon layer provides a strong protective effect on the internal cobalt active sites and thus enhances the catalytic stability during the harsh condition. This work provides a new method for designing the low-cost heterogeneous catalyst and emphasizes the intrinsic active sites for 1-hexene hydroformylation reaction.

Dehydrogenative synthesis of N-functionalized 2-aminophenols from cyclohexanones and amines: Molecular complexities via one-shot assembly.

Polyfunctionalized arenes are privileged structural motifs in both academic and industrial chemistry. Conventional methods for accessing this class of chemicals usually involve stepwise modification of phenyl rings, often necessitating expensive noble metal catalysts and suffering from low reactivity and selectivity when introducing multiple functionalities. We herein report dehydrogenative synthesis of N-functionalized 2-aminophenols from cyclohexanones and amines. The developed reaction system enables incorporating amino and hydroxyl groups into aromatic rings in a one-shot fashion, which simplifies polyfunctionalized 2-aminophenol synthesis by circumventing issues associated with traditional arene modifications. The wide substrate scope and excellent functional group tolerance are exemplified by late-stage modification of complex natural products and pharmaceuticals that are unattainable by existing methods. This dehydrogenative protocol benefits from using 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO) as oxidant that offers interesting chemo- and regio-selective oxidation processes. More notably, the essential role of in situ generated water is disclosed, which protects aliphatic amine moieties from overoxidation via hydrogen bond-enabled interaction.