Metal Catalysts Research Articles

Hydrogen Release from Ammonia: Size and Support Effects in Heterogeneous Transition Metal Catalysis

Ammonia can serve as a promising renewable energy carrier based on its high hydrogen content and energy density as well as its full‐fledged transportation infrastructure. Renewable hydrogen can be converted in ammonia synthesis, stored and/or transported bound in ammonia and released on demand by ammonia decomposition. The most active catalysts for this reaction are Ru‐based due to its optimal nitrogen binding energy compared to other transition metals. However, the development of alternative non‐noble transition metal catalysts such as Fe, Ni or Co is attractive. For supported metal catalysts, size and support effects play important roles in many catalytic reactions resulting in a change of geometric and/or electronic properties. In this review, we first discuss existing studies of size and support effects on Ru, Fe, Ni, Co catalysts in ammonia decomposition from an experimental and theoretical viewpoint. Afterwards, we compare the available catalytic data in the form of TOFH2 and reaction rate for each metal catalyst supported on different supports and as a function of particle size, attempting to identify an optimum particle size and a trend for the different supports. Finally, we discuss the challenges and perspectives of future research on the size and support effect in ammonia decomposition.

Multifunctional Heterogeneous Cobalt Catalyst for the One-Pot Synthesis of Benzimidazoles by Reductive Coupling of Dinitroarenes with Aldehydes in Water.

The endeavor of sustainable chemistry has led to significant advancements in green methodologies aimed at minimizing environmental impact while maximizing efficiency. Herein, a straightforward synthesis of benzimidazoles by reductive coupling of o-dinitroarenes with aldehydes is first ever reported in aqueous media using a non-noble metal catalyst. This work demonstrates that the combination of nitrogen and phosphorous ligands in the synthesis of supported heteroatom-incorporated Co nanoparticles is crucial for obtaining the desired benzimidazoles. The process achieves > 99% conversion, > 99% chemoselectivity and stability for the reduction of dinitroarenes using water as the solvent and hydrogen as the reductant under mild reaction conditions. The robustness of the catalyst has been investigated using several advanced techniques such as HRTEM, HAADF-STEM, XEDS, EELS, and NAP-XPS. In fact, we have shown that the introduction of N and P dopants prevents metal leaching and the sintering of the cobalt nanoparticles. Finally, to explore the general catalytic performance, a wide range of substituted dinitroarenes and benzaldehydes were evaluated, yielding benzimidazoles with competitive and scalable results, including MBIB (94% yield), which exhibits favorable biological properties and cytotoxic activity against several types of cancer.

Promoting Alcohols Electrooxidation Coupled with Hydrogen Production via Asymmetric Pulse Potential Strategy.

Electrocatalytic organic oxidation coupled with hydrogen production emerges as a profitable solution to simultaneously reduce overall energy consumption of H2 production and synthetic high-value chemicals. Noble metal catalysts are highly efficient electrocatalysts in oxidation reactions, but they deactivate easily weakening the benefit in actual production. Herein, we report a universal asymmetric pulse potential strategy to achieve long-term stable operationof noble metals for various alcohol oxidation reactions and noble metal catalysts. For example, by pulsed potentials between 0.8 V and 0 V vs. RHE, palladium (Pd)-catalyzed glycerol (GLY) electrooxidation can continuously proceed for more than 2800 h with glyceric acid (GLA) selectivity of >70%. Whereas, Pd electrocatalyst becomes nearly deactivated within 6 h of reaction under conventional potentiostatic strategy. Experimental and theoretical calculation results reveal that the generated electrophilic OH* from H2O/OH- oxidation on Pd (denoted as Pd-OH*) acts as main active species for GLY oxidation. However, Pd-OH* is prone to be oxidized to PdOx resulting in performance decay. When a short reduction potential (e.g., 0 V vs. RHE for 5 s) is powered, PdOx can be reversibly reduced to restore the current. Moreover, we tested the feasibility of this strategy in a flow electrolyzer, verifying the practical application potential.

Promoting Alcohols Electrooxidation Coupled with Hydrogen Production via Asymmetric Pulse Potential Strategy

Electrocatalytic organic oxidation coupled with hydrogen production emerges as a profitable solution to simultaneously reduce overall energy consumption of H2 production and synthetic high‐value chemicals. Noble metal catalysts are highly efficient electrocatalysts in oxidation reactions, but they deactivate easily weakening the benefit in actual production. Herein, we report a universal asymmetric pulse potential strategy to achieve long‐term stable operation of noble metals for various alcohol oxidation reactions and noble metal catalysts. For example, by pulsed potentials between 0.8 V and 0 V vs. RHE, palladium (Pd)‐catalyzed glycerol (GLY) electrooxidation can continuously proceed for more than 2800 h with glyceric acid (GLA) selectivity of >70%. Whereas, Pd electrocatalyst becomes nearly deactivated within 6 h of reaction under conventional potentiostatic strategy. Experimental and theoretical calculation results reveal that the generated electrophilic OH* from H2O/OH− oxidation on Pd (denoted as Pd‐OH*) acts as main active species for GLY oxidation. However, Pd‐OH* is prone to be oxidized to PdOx resulting in performance decay. When a short reduction potential (e.g., 0 V vs. RHE for 5 s) is powered, PdOx can be reversibly reduced to restore the current. Moreover, we tested the feasibility of this strategy in a flow electrolyzer, verifying the practical application potential.

Hydrogenation of biomass‐derived succinic acid to form 1,4‐butanediol over Co/SiO2 catalyst

AbstractBackgroundSuccinic acid is a vital platform chemical derivable from lignocellulosic biomass. Various non‐noble metal catalysts were used to hydrogenate succinic acid and produce 1,4‐butanediol in this study. Among them, Co‐loaded SiO2 with a moderate mean pore size of 10 nm exhibited a superior catalytic performance.ResultsThe high catalytic activity of Co‐loaded SiO2, which was prepared by an impregnation method, was demonstrated in the hydrogenolysis of succinic acid to provide 1,4‐butanediol. The Co/SiO2 catalyst reduced at 400 °C and calcined at 300 °C existed in the form of Co2+ and Co0, exhibiting a high catalytic activity. The production of 1,4‐butanediol from succinic acid was significantly enhanced at a temperature of 200 °C and an H2 pressure exceeding 5 MPa. At 200 °C and 7 MPa H2 pressure, a 1,4‐butanediol selectivity of 67.8% and a full succinic acid conversion were obtained over Co/SiO2.ConclusionThe Co‐loaded SiO2 with a moderate mean pore size of 10 nm was conducive to the efficient generation of 1,4‐butanediol from succinic acid. The Co/SiO2 catalyst reduced at 400 °C existed in the form of Co0 and Co2+. It was suggested that the efficient synthesis of 1,4‐butanediol from succinic acid was facilitated by the cooperative action of Co0 and Co2+. © 2024 Society of Chemical Industry (SCI).

Cascading Water Activation and Interfacial Lattice Oxygen over Nanocluster CuOx‐modified MnO2 for Electrocatalytic Propylene Oxidation

Direct electrooxidation of propylene using water‐oxidation intermediates represents a promising route for propylene glycol production. Unfortunately, this economic and environmentally friendly process suffers from low yield and poor Faradaic efficiency resulting from the mismatched oxidative capacity of reactive oxygen species and pronounced side reactions. Herein, we developed an earth‐abundant metal‐based nanocluster CuOx‐modified MnO2 catalyst for the efficient electrooxidation of propylene into propylene glycol, achieving a remarkable production rate of 63.0 g/m2/h and 95% Faradaic efficiency at 1.3 V vs. Ag/AgCl. Mechanistic studies revealed that the oxygen vacancy‐mediated water activation on CuOx‐MnO2 in synergy with the activated interfacial lattice oxygen drove the propylene oxidation to a novel *OOH pathway rather than the traditional *OH route. Additionally, the interfacial interactions intensified the propylene adsorption and polarization for its activation. This work offers new insights into the mechanism of electrocatalytic propylene oxidation and presents great opportunities for the synthesis of commercial chemicals based on earth‐abundant metal catalysts and renewable electricity‐driven route.

Recent Advances in the Hydroxylation of Boronic Acids

Hydroxylated compounds represent a significant and diverse class of substances in the field of chemistry. These compounds play critical roles in various chemical reactions and are essential components in numerous industrial applications. Recent years have witnessed remarkable advancements in the synthesis of hydroxylated compounds, especially those derived from boronic acids. The synthesis of hydroxylated compounds from boronic acids typically involves the utilization of various types of catalysts, which are essential for enhancing reaction rates and selectivity, including metal catalysts such as CuFe₂O₄, Cu@C₃N₄, AgNPs, and Ti0.97Ni0.3O1.97, as well as non‐metal catalysts like polycaprolactone (PCL), TFB‐BMTH COF materials, C70, and graphene oxide (GO). These catalytic reactions often require the addition of oxidants such as hydrogen peroxide (H₂O₂) or molecular oxygen, which serve as critical reagents in the hydroxylation process. In certain cases, organic bases act as electron donors to propel the reaction. Furthermore, some studies have reported oxidative hydroxylation reactions that are catalyst‐free.This review aims to summarize the recent advancements and breakthroughs in the synthesis of hydroxylated compounds from boronic acids, with a particular focus on research conducted from 2014 to 2024.

Upcycling of Polyethylene Wastes to Valuable Chemicals over Group VIII Metal-decorated WO3 Nanosheets.

Catalytic cracking of polyolefin wastes into valuable chemicals at mild conditions using non-noble metal catalysts is highly attractive yet challenging. Herein it is reported that 2D tungsten trioxide (2D WO3) nanosheets, after decorating with group VIII metal promoters (i.e., Fe, Co, or Ni), convert high-density polyethylene (HDPE) into alkylaromatics and olefins at low temperature and ambient pressure without using any solvent or hydrogen: 2D Ni/WO3 with abundant Brønsted acidic sites initiates HDPE cracking at a low temperature of 240°C; 2D Fe/WO3 with low energy barrier of cyclization achieves a high HDPE conversion to 84.2% liquid hydrocarbons with a selectivity of 30.9% to aromatics at 300°C. In-situ spectroscopic investigations and supplementary theoretical calculations illustrate that these aromatics are formed through the cyclization of alkene intermediates. These 2D catalysts also display high efficiency in the low-temperature cracking of single-use commercial polyethylene wastes such as packaging bags and bottles. This work has demonstrated the high potential of 2D non-noble metal catalysts in the efficient upcycling of waste polyolefin at mild conditions.

Modulated Fe Central Spin State in FeCu4 Alloy Nanoparticles for Efficient and Selective Activation of H2O2

AbstractIn advanced oxidation processes, the efficient activation of H2O2 and the selective production of reactive oxygen species are the key steps to achieve the removal of organic pollutants in the water environment. Studies have shown that the precise regulation of catalyst metal active sites can break through the limitation of H2O2 activation and realize the efficient selective conversion of H2O2. Therefore, FeCu bimetallic active sites are developed by constructing FeCu4 alloy nanocluster metal catalyst (FeCu/NC). The introduction of Cu metal sites realized charge redistribution, promoted rapid electron transfer, reduced the spin state of Fe in the catalyst, diminished the interaction between Fe and O, weakened the strong and persistent adsorption between Fe center and *H2O2, lowered the energy barrier of intermediate products in hydroxyl radicals (·OH) generation process, achieved efficient activation of H2O2 and selective generation of ·OH. In addition, a complete electron circulation path is formed between FeCu active sites and the substrate, breaking the contradiction between single metal and H2O2 redox relationship, promoting efficient reduction of Fe3+ to Fe2+. The first‐order kinetic constant (kobs) of FeCu/NC is 0.081 min−1, which is 3.68 and 7.36 times higher than those of single Fe metal species (FeFe/NC) and single Cu metal species (CuCu/NC) catalysts, respectively, and has excellent catalytic performance).

Ultrasmall Fe3O4 Nanoparticles on ZrO2 as Catalysts for CO2 Hydrogenation to Lower Olefins

AbstractOrganic synthesis presents significant opportunities for converting the abundant and hazardous carbon dioxide (CO2) in the atmosphere into a more sustainable carbon source. To reduce the carbon footprint, we explored the direct hydrogenation of CO2 to lower (C2‐4=) olefins using various catalysts composed of ZrO2‐supported alkali‐metal‐promoted superparamagnetic iron oxide nanoparticles (SPIONs; Fe3O4). These catalysts are notable for their straightforward preparation; we employed a cost‐effective dry‐mixing method to create a range of alkali metal‐doped SPIONs supported on ZrO2. Results showed that the strong interactions between Fe3O4 and the ZrO2 support enhanced CO2 hydrogenation performance compared to other forms.. Under optimal conditions – using a gas hourly space velocity (GHSV) of 4500 mL/h/gcat. and a feed ratio of H2:CO2=3 : 1 – this catalyst achieved over 22 % CO2 conversion and high selectivity for light (C2–4=) olefins at 30 bar and 375 °C, with 30 wt% Fe3O4 loading on ZrO2 and 2 wt% K promoter. We also investigated several variables, including alkali metal concentration, iron content, reaction conditions, and catalyst stability over 96 hours.

Transition-Metal-Catalyzed C(sp3)–H Alkylation of Methyl Heteroarenes with Alcohols

Transition-metal-catalyzed C(sp3)-H bond functionalization is a useful transformation for the construction of C–C bonds. A versatile and easy-to-perform protocol in this respect is the C-alkylation of methyl heteroarenes with alcohols using auto-transfer hydrogenative (ATH) reactions. Various transition metal catalysts based on Ir, Pt, Ru, Ni, Co, Fe and Mn have been employed for the construction of chain-elongated alkyl-substituted heterocyclic compounds using this chemistry. Water is the only byproduct and the starting alcohols are less toxic, readily available, more easily handled and more atom-economical substrates than their halogen counterparts. This review details recent advances in this synthetic methodology, describing the scope, reaction mechanism, chemo-selectivity and applications.

Methanol Activation: Strategies for Utilization of Methanol as C1 Building Block in Sustainable Organic Synthesis.

The development of efficient and sustainable chemical processes which use greener reagents and solvents, currently play an important role in current research. Methanol, a cheap and readily available resource from chemical industry, could be activated by transition metal catalysts. This review focuses in covering the recent five-years literature and provides a systematic summary of strategies for methanol activation and the use in organic chemistry. Based on these strategies, many new synthetic methods have been developed for methanol utilization as the C1 building block in methylation, hydromethylation, aminomethylation, formylation reactions, as well as the syntheses of urea derivatives and heterocycles. The achievements, synthetic applications, limitations, some advanced approaches, and future perspectives of the methanol activation methodologies have been described in this review.

Computational Insights into the Effect of Ligands and Transition-Metal Centers on the Mechanism and Regioselectivity of Hydrosilylation of Alkenes.

Development of sustainable synthetic methods for the hydrosilylation of alkenes, catalyzed by 3d transition metals, offers a promising alternative to traditional noble metal catalysts. This study presents a computational mechanistic investigation into the hydrosilylation of alkenes, focusing on the role of ligands and metal centers in modulating the reaction's mechanism and regioselectivity. The ligand's electronic and steric properties were found to modulate the regioselectivity for cobalt catalysts, with phosphine ligand (xantphos) promoting higher linear selectivity compared to nitrogen-based ligand (mesPDI). The energy decomposition analysis reveals that the xantphos ligand favors linear products due to stronger electrostatic and orbital interactions despite increased steric repulsion. The metal center also plays a crucial role, with cobalt catalysts favoring the modified Chalk-Harrod mechanism for branched product formation in the presence of PNN ligand (iPrPCNNMe), due to lower activation barriers in alkene insertion. Beneficial electrostatic and orbital interactions predominate, rendering the alkene insertion transition state for cobalt more favorable compared to that for iron. This work provides a comprehensive understanding of how ligand and metal center effects can be harnessed to control regioselectivity in hydrosilylation reactions.

Morphology-controlled mesoporous core–shell carbon nanospheres decorated with Cu nanoparticles as highly efficient and reusable catalyst

Environmental pollution caused by industrial waste has recently become a serious issue. Therefore, effective pollutant removal using nanotechnology is required, in which catalysts based on precious metals, such as Pt, Ag, Au, and Pd, are widely utilized. However, the manufacturing costs of precious metal catalysts are high. In this study, copper, a promising metal for catalysis, is evaluated as an alternative to precious metal catalysts because of its low cost, high efficiency, and abundant natural reserves. However, nanoparticle agglomeration is problematic when evaluating the catalytic performance of isolated metal nanoparticles. To solve this problem and maintain a high catalytic activity of Cu, in this study, Cu was loaded on a mesoporous carbon support derived from a carbon precursor with a core–shell structure. The core–shell-structured carbon precursor was obtained by coating resorcinol-formaldehyde polymer spheres as the core with a 50 nm thick polydopamine shell with 10 nm mesopores through π–π stacking interactions. A copper precursor was used to form Cu(OH)2 on the surface of the support, and then the nanocomposite was synthesized at 500 °C for 2 h. The synthesized copper-carbon nanocomposite exhibits high catalytic activity owing to its high specific surface area, porosity, and accessible internal space. It exhibits excellent catalytic activity and stability, along with excellent reusability, in the reduction of 4-nitrophenol to 4-aminophenol using NaBH4. Moreover, excellent catalytic activity, exceeding 99 %, was achieved in the reduction of another organic dye, methylene blue.

Enhanced H2O2 Production by Two-Electron Oxygen Reduction on Co3O4/MXene Catalyst

The two-electron oxygen reduction reaction (ORR) using an electrochemical method is considered a viable green technology for generating H2O2. Platinum group metals demonstrate excellent H2O2 generation performance due to their superior ORR activity and stability. However, the high cost of these electrocatalysts is a significant barrier to the widespread adoption of this technology, prompting research into non-precious metal catalysts as alternatives. In this work, Co3O4 nanoparticles with sized from 5 to 10 nm were synthesized on MXene sheets. Compared with Co3O4/C and MXene, the results indicated that Co3O4/MXene exhibited the best electrochemical performances, with an electron transfer number of ∼3.1 during oxygen reduction and an H2O2 selectivity of ∼47%. Co3O4/MXene also demonstrated great stability. After 5000 cycles, the H2O2 selectivity and electron transfer number remained at 50% and 3.0, respectively. After 12 h of continuous testing, Co3O4/MXene exhibited a high Faraday efficiency of 50% and H2O2 yield of 0.14 mol h−1 g−1, with H2O2 selectivity increasing to 68.7% and an electron transfer number of 2.6. The excellent electrochemistry is attributed to the synergistic effect between MXene and Co3O4. This study provides valuable insights into non-precious metal electrocatalysts for H2O2 generation.

MnO2 Nanowire Thin Mesh With Enhanced Mass Transfer as Hydroxide Exchange Membrane Fuel Cell Cathode

AbstractHydroxide exchange membrane fuel cells (HEMFCs) are promising due to the potential use of nonprecious metal catalysts. However, the performance of HEMFCs based on nonprecious catalysts is still unsatisfactory, and one reason for this is hindered mass transfer in the catalyst layer. In this study, we employ a hydrothermal method to grow in situ a MnO2 nanowire thin mesh (NTM) catalytic layer on the gas diffusion electrode. The HEMFC prepared with MnO2 NTM cathode achieves a peak power density of 425 mW cm−2, surpassing the performance of the HEMFC prepared using the traditional powder catalyst spraying method by four times. High‐frequency resistance and limiting current tests indicate that the MnO2 NTM reduces ohmic resistance and improves mass transfer, thereby enhancing the HEMFC performance. Furthermore, the peak power density of the HEMFC is increased to 626 mW cm−2 by depositing additional active Co3O4 nanoparticles on the MnO2 NTM. These findings demonstrate that an interconnected and porous catalyst layer structure is beneficial for improving mass transfer properties, which in turn enhances HEMFC performance.

Alkali Metal Amide-Catalyzed α-Deuteration of Sulfides.

The catalytic α-deuteration of sulfides was developed under mild conditions by using alkali metal amides [KN(SiMe3)2 and CsN(SiMe3)2] as the catalyst. This approach successfully achieves a selective and efficient H/D exchange reaction of sulfides with D2 without using transition metal catalysts. A series of deuterium-labeled thioanisoles and alkyl methyl sulfides were obtained in good to high levels of deuterium incorporation.

Enhanced electrochemical oxygen reduction reaction on “C–O–Si” bonds in Si-doped graphene-like carbon

The use of heteroatom-doped carbon materials as non-precious metal catalysts for oxygen reduction reactions has attracted much attention from researchers. This paper presents the synthesis of two-dimensional Si-doped graphene-like materials (Si-GLC) featuring “C–O–Si” bonds through an in-situ doping method. Since the electronegativity of the Si (1.90) is much smaller than that of C (2.55) and O (3.44), the formation of the “C–O–Si” bond causes Si to lose a large number of electrons and become positively charged. This increases the adsorption of electronegative oxygen, thereby improving the activity of oxygen reduction reactions. The adsorption energy of oxygen molecules on Si-GLC was calculated to be −3.57 eV using density functional theory, much lower than on GLC (−2.18 eV). This suggests that Si doping enhances the adsorption of oxygen molecules by graphene-like materials, which is crucial for improving the performance of oxygen reduction reaction. Si-GLC displayed a half-wave potential of 0.80 V (vs. RHE) and a diffusion-limited current density of 5.81 mA cm−2 in 0.1 M KOH solution, demonstrating excellent catalytic activity for oxygen reduction reaction. It also exhibits good stability and tolerance to methanol crossover effect. In-situ doping creates “C–O–Si” bonds, modulating charge density and providing a strategy for high-performance oxygen reduction catalysts.

Electrocatalytic performance on methanol oxidation reaction of highly stabilized Pt–Pd–Co ternary alloys by organometallic approach in alkaline medium

CoPtPd/C ternary alloys were prepared in situ as catalysts in different compositions by tuning the architecture and composition of cobalt in the reduction and displacement of ligands method to improve the efficiency of renewable energy, specifically in the methanol oxidation reaction (MOR) in alkaline medium. Chemical analyses shown that the theoretical and experimental compositions were well matched to obtain Pt70Pd10Co20/C, Pd70Pt10Co20/C, Co70Pt20Pd10/C and Co70Pt10Pd20/C ternary alloys, indicating that the method allowed precise control of components loading. Electrochemical investigations confirmed that the proposed method promoted a better synergistic effect between the components when Co is added in large amounts (70 wt%) regardless of the noble metal ratio, accelerating the oxidation of the adsorbed CO to CO2, inhibiting the poisoning during MOR. The Co70Pd20Pt10/C electrode materials displayed the highest electroactivity on MOR. This method is a promising alternative to reduce the amount of noble metal in catalysts used in direct alcohol fuel cells.

Effect of synthesis route of graphene on the hydrogen storage in Mg-Ni-rGO ternary system

The H uptake/release performance of Mg is studied by combining transition metal (Ni) and lightweight C-based (rGO) catalysts. Further, the effect of the synthesis route on the morphology and catalytic ability of rGO is understood by synthesizing it via electrochemical (erGO), chemical (crGO) and thermal (trGO) exfoliation. These rGOs (10 wt%) and 3 atom% of Ni were ball-milled with Mg and subjected to isothermal H uptake at 15 bar and 320 °C. The Mg97-Ni03-erGO nanocomposite shows the lowest incubation period of 2–3 h, whereas it is 8–9 h for Mg97-Ni03-trGO. Moreover, the Mg97-Ni03-erGO nanocomposite shows the lowest onset temperature of H release at 275 °C, which is 300 °C in the case of Mg97-Ni03-trGO. From the spectroscopic analysis, it is inferred that the presence of lower defects in erGO and higher C–C sp2 domains facilitate enhanced Mg–C interaction during the H uptake/release.