Metal Dispersion Research Articles

Design of Atomically Dispersed CoN4 Sites and Co Clusters for Synergistically Enhanced Oxygen Reduction Electrocatalysis.

Constructing dual-site catalysts consisting of atomically dispersed metal single atoms and metal atomic clusters (MACs) is a promising approach to further boost the catalytic activity for oxygen reduction reaction (ORR). Herein, a porous CoSA-AC@SNC featuring the coexistence of Co single-atom sites (CoN4) and S-coordinated Co atomic clusters (SCo6) in S, N co-doped carbon substrate is successfully synthesized by using porphyrinic metal-organic framework (Co-TPyP MOF) as the precursor. The introduction of the sulfur source creates abundant microstructural defects to anchor Co metal clusters, thus modulating the electronic structure of its surrounding carbon substrate. The synergistic effect between the two types of active sites and structural advantages, in turn, results in high ORR performance of CoSA-AC@SNC with half-wave potential (E1/2) of 0.86V and Tafel slope of 50.17mVdec-1. Density functional theory (DFT) calculations also support the synergistic effect between CoN4 and SCo6 by detailing the catalytic mechanism for the improved ORR performance. The as-fabricated Zn-air battery (ZAB) using CoSA-AC@SNC demonstrates impressive peak power density of 174.1mWcm-2 and charge/discharge durability for 148h. This work provides a facile synthesis route for dual-site catalysts and can be extended to the development of other efficient atomically dispersed metal-based electrocatalysts.

Molecular-level hybridization of single-walled carbon nanotubes and a copper complex with counterbalanced electrostatic interactions

Hybridization and wet processibility are highly desired development strategies for next-generation nanomaterials. In particular, the hybridization of carbon nanotubes (CNTs) and transition metals has been investigated for decades owing to the numerous advantages, such as high mechanical and electrical properties. However, manufacturing nano-hybridized CNTs/transition metals is complicated, and no studies have been reported on the dispersion and hybridization of transition metals with single-walled CNTs (SWCNTs) without any harsh or destructive methods due to the strong van der Waals forces. Herein, we demonstrate a one-step dispersion/hybridization of SWCNTs and a Cu-based complex and provide a mechanism derives from counterbalancing the electrostatic interactions via molecular-level charge transfer. The Cu-based complex-hybridized SWCNTs self-assemble and demonstrate suitable viscoelastic behaviors for various printing or coating processes. Finally, the nanostructured SWCNTs/Cu nanoparticle exhibits multifunctional electrothermal properties, electromagnetic interference shielding performances, and flexibilities. The proposed metal-complex-hybridized SWCNTs dispersions provide a wet process guideline for producing nanostructured electrodes.

Native plant species growing on the abandoned Zaida lead/zinc mine site in Morocco: Phytoremediation potential for biomonitoring perspective.

This study aims to assess the level of metal contamination and the ecological risk index at the abandoned Zaida Pb/Zn mining site in eastern Morocco and identify native plant species found on the site that can be used in site rehabilitation through phytoremediation strategies. Samples from seven native and abundant plant species at the site, along with their rhizospheric soils, were collected and analyzed using Inductively Coupled Plasma Mass Spectrometry (ICP-MS) to determine the concentrations of various metal(loid)s, including As, Cu, Ni, Cd, Sb, Zn, and Pb. Indicators of soil pollution and ecological risks were also assessed, including the enrichment factor (EF), pollution index (PI), and ecological risk index (ERI). The Biological Accumulation Coefficient (BAC), Translocation Factor (TF), and Biological Concentration Factor (BCF) of plant samples were calculated. The results reveal polymetallic soil contamination, with notably higher concentrations of Pb, Cu and Zn, reaching respectively 5568 mg kg-1 DW, 152 mg kg-1 DW, and 148 mg kg-1 DW, indicating a significant potential ecological risk. The enrichment factor (EF) was also assessed for each metal(loid)s, and the results indicated that the metal contamination was of anthropogenic origin and linked to intensive mining activities in Zaida. These findings are supported by the pollution index (PI) ranging from 1.6 to 10.01, which reveals an extremely high metal(loid)s pollution level. None of the plant species exhibited a hyperaccumulation of metal(loid)s. However, Artemisia herba alba demonstrated a strong capacity to accumulate Pb in its aboveground parts, with a concentration of 468 mg kg-1 DW. Stipa tenacissima, Retama spherocarpa, and Astragalus armatus, showed a significant Pb accumulation in their roots reaching 280, 260, and 256 mg kg-1 DW.respectively. Based on BAC, TF, and BCF, Stipa tenacissima exhibited potential for Ni and Cd phytostabilization, as well as the ability for Zn phytoextraction. Additionally, Artemisia herba alba displayed the capability to phytoextract Cd and had a high propensity to translocate all the studied metal(loid)s. Astragalus armatus has the potential to be used in the phytostabilization of Zn and Ni, as well as for the phytoextraction of As and Sb. These native species from the Zaida site, although not hyperaccumulators, have the potential to contribute significantly to the phytoextraction or phytostabilization of potentially toxic elements (PTEs). Moreover, they can serve as vegetative cover to mitigate the erosion and dispersion of metal(loid)s.

Revealing the structure of the active sites for the electrocatalytic CO2 reduction to CO over Co single atom catalysts using operando XANES and machine learning.

Transition-metal nitrogen-doped carbons (TM-N-C) are emerging as a highly promising catalyst class for several important electrocatalytic processes, including the electrocatalytic CO2 reduction reaction (CO2RR). The unique local environment around the singly dispersed metal site in TM-N-C catalysts is likely to be responsible for their catalytic properties, which differ significantly from those of bulk or nanostructured catalysts. However, the identification of the actual working structure of the main active units in TM-N-C remains a challenging task due to the fluctional, dynamic nature of these catalysts, and scarcity of experimental techniques that could probe the structure of these materials under realistic working conditions. This issue is addressed in this work and the local atomistic and electronic structure of the metal site in a Co-N-C catalyst for CO2RR is investigated by employing time-resolved operando X-ray absorption spectroscopy (XAS) combined with advanced data analysis techniques. This multi-step approach, based on principal component analysis, spectral decomposition and supervised machine learning methods, allows the contributions of several co-existing species in the working Co-N-C catalysts to be decoupled, and their XAS spectra deciphered, paving the way for understanding the CO2RR mechanisms in the Co-N-C catalysts, and further optimization of this class of electrocatalytic systems.

An unexpected case of instability of metal nanoclusters

It is known that Pt clusters on the surface of chlorinated alumina are highly stable against sintering in reducing or inert environments and easily disintegrate into single atoms upon heat treatments under O2. However, this study reveals that partially oxidized nanoclusters tend to grow in size and reconstruct upon further annealing in an inert gas (conventionally prepared 0.25 ÷ 1 %Pt/γ-Al2O3-Cl samples). Even more surprisingly, the sintering takes place at rather mild conditions (He/Ar, 400–500 °C) but stops soon after it commences (within minutes). The lower the temperature of O2-pretreatment (500 → 20 °C), the sharper the further drop in metal dispersion, and one to a few cycles of the consecutive treatments could be sufficient for the unique properties of Pt clusters to be lost. Possible reasons, contributing factors, and implications of the results for different catalytic systems are discussed.

Precursor-Driven Catalytic Performances of Al2O3-Supported Earth-Abundant Ni Catalysts in the Hydrogenation of Levulinic Acid and Hydroxymethylfurfural into Added-Value Chemicals.

It has been shown that the nature of the metal precursor and the thermal effects during calcination determine the physicochemical properties of the catalysts and their catalytic activity in the levulinic acid (LA) and 5-hydroxymethylfurfural (HMF) hydrogenation reactions. The endothermic effect during calcination of the inorganic nickel precursor promoted higher metal dispersion and stronger interaction with the alumina surface. In contrast, the exothermic effects during the calcination of organic nickel precursors resulted in smaller metal dispersion and lower interaction with the support surface. A clear relationship was found between the size of the metal crystallites and the yield of LA hydrogenation reaction. The smaller crystallites were more active in the LA hydrogenation reaction. In turn, the size of the metal particles and their nature of interaction with the surface of the alumina influence the hydrogenation pathways of the HMF.

Mesoporous amorphous non-noble metals as versatile substrates for high loading and uniform dispersion of Pt-group single atoms.

Atomically dispersed Pt-group metals are promising as nanocatalysts because of their unique geometric structures and ultrahigh atomic utilization. However, loading isolated Pt-group metals in single-atom alloys (SAAs) with distinctive bimetallic sites is challenging. In this study, we present amorphous mesoporous Ni boride (Ni-B) as an ideal substrate to uniformly disperse Pt atoms with tunable loadings (1.7 to 12.2 wt %). The effect of the morphology, composition, and crystal phase of the Ni-B host on the growth and dispersion of Pt atoms is discussed. The resulting amorphous Pt-Ni-B mesoporous nanospheres exhibit superior electrocatalytic H2 evolution performance in acidic media. This strategy holds the potential to synthesize a diverse library of mesoporous amorphous Pt-group SAAs, by leveraging functional amorphous nanostructured 3d transition-metal borides as substrates, thereby proposing a comprehensive strategy to control atomically dispersed Pt-group metals.

Highly dispersed Cu loaded on HNO3-treated activated carbon for enhanced NH3 adsorption performance

Activated carbon (AC) is highly desirable as an adsorbent for NH3 due to its low cost. Metal chlorides, such as CuCl2, are also known as efficient components for NH3 adsorption. However, once loaded onto AC, CuCl2 tends to aggregate easily, thereby reducing its utilization efficiency. In this work, a facile approach involving HNO3 treatment followed by Cu loading was employed to prepare a high-performance AC adsorbent for NH3 adsorption at room temperature. The AC with a defect-rich surface and a well-developed pore structure was obtained by 30% HNO3 treatment. The subsequently loaded 5 wt% Cu exhibited a highly dispersed state. Consequently, compared to AC directly loaded with Cu without HNO3 treatment, the NH3 adsorption capacity was increased more than 5-fold. Meanwhile, the acidic functional groups introduced by HNO3 treatment also played a significant role in this enhancement. Furthermore, the structure-performance relationship of the prepared adsorbent and the mechanism of NH3 adsorption were elucidated according to characterization results. This work provides a facile strategy for enhancing metal dispersion on activated carbon and its adsorption performance.

Non-noble metal–carbon-based electrocatalyst derived from porphyrin-doped UiO-66-NH2 for hydrogen evolution

This study adopts non-noble metal porphyrin-doped UiO-66-NH2 as a precursor to form highly dispersed metal active species embedded into graphite-like carbon-based materials (metal = Co, Cu, Ni, and Zn) through high-temperature pyrolysis for electrocatalytic hydrogen evolution (HER). The metalloporphyrin provides anchoring sites to facilitate the stabilization of metal species, while the graphite-like carbon-based materials formed derived from metal-organic framework (MOFs) precursor pyrolysis could enhance the transport of electrons. Electrochemical studies indicate that Co-NC has the best performance among the four non-noble metal carbon materials. When the current density is 10 mA·cm−1, the overpotentials of Co-NC in acidic and alkaline media are 256 mv and 325 mv, respectively, and the Tafel slopes are 162.46 mV·dec−1 and 143.05 mV·dec−1, respectively. Therefore, the pyrolysis of MOFs precursor incorporated with a certain amount of metalloporphyrin to form graphite-like carbon-based materials is an effective strategy to obtain low-cost, stable HER catalysts.

Coordination Microenvironment Regulation in Carbon−Based Atomically Dispersed Metal Catalysts for Clean Energy−Conversion

AbstractEmerging atomically dispersed metal catalysts (ADCs), especially carbon−based ADCs have arguably received enormous attention in diverse electrochemical energy conversion processes. Such catalysts have well−defined active centers, and their geometric and electronic structures depend greatly on their coordination microenvironments, which, in turn, govern the performances in the realm of electrocatalysis. In this review, it is focused on the state−of−the−art synthesis strategies for carbon−based ADCs, with particular emphasis on their microenvironment modulations. The advances in characterizing the microenvironment alongside understanding the synthetic pathway are outlined, and exemplified in electrochemical applications, including electrocatalytic H2 evolution, O2 evolution/reduction, CO2 reduction, and Li polysulfides conversion reactions. Rather than focusing on the catalysis metrics, this review delved deeply into the underly science and the associated reaction mechanisms of these catalysts in diverse electrochemical systems. The fundamental impacts of the microenvironments of the catalysts on electrocatalytic activities, selectivities, and stabilities are discussed. In the end, it is concluded by highlighting the current issues of the microenvironment engineering of these carbon−based ADCs and propose the prospects for future opportunities and challenges.

Highly dispersed MgInCe-mixed metal oxides catalyzed direct carbonylation of glycerol and CO2 into glycerol carbonate

Glycerol carbonate, an important glycerol value-added product, has been widely used as the active intermediates and inert solvents in the synthesis of cosmetics, detergents, chemical intermediates, polymers, and so on. The direct carbonylation from glycerol with CO2 is considered as a promising route, but still a tough work due to the thermodynamic stability and the kinetic inertness of CO2. In this work, highly-selective direct carbonylation of glycerol and CO2 into glycerol carbonate has been achieved over highly dispersed MgInCe-mixed metal oxides (MgInCe-MMO), which were prepared through the topological transformation derived from the MgInCe-layered double hydroxides (MgInCe-LDHs). By precisely modulating the surface basic-acidic properties and the oxygen vacancies, an efficient carbonylation of glycerol with CO2 has been achieved with a selectivity of up to > 99% to glycerol carbonate. Deep investigation on the synergistic catalysis of base-acid sites and oxygen vacancies has been clarified.

Ensemble density functional perturbation theory: Spatial dispersion in metals

Ensemble density functional perturbation theory: Spatial dispersion in metals

Single‐Site Heterogenized Molecular Catalysts towards CO2 Hydrogenation to Formates, Formamides and Methanol

AbstractHarnessing CO2 in conjunction with inexpensive reusable H2 for catalytic hydrogenation is a viable method for lowering the environmental impact of industrial operations while producing useful chemicals and fuels. To make the process more sustainable, particular emphasis was paid to the heterogeneous catalyst system in this regard. Intending to profit from both homogeneous and heterogeneous catalysis in real‐world circumstances for the CO2 hydrogenation reaction, heterogenized molecular catalysts are receiving a lot of attention among heterogeneous catalysts. This review is devoted to significant developments in single‐site heterogenized molecular catalysts for CO2 hydrogenation reactions. Attempting to illustrate the state‐of‐the‐art developments in this domain, the present work meticulously summarizes several recently reported heterogenized molecular catalysts for the CO2 hydrogenation process producing formic acid/formate, N‐formamide, and methanol. The fundamental structure–activity relationships and mechanistic understanding are given particular attention since they offer solid foundations for sensible catalyst architectural design. Important variables that influence catalytic activity are also emphasized, such as electron density, metal dispersion, porous nature, surface area, a robust backbone, and coordination environment of metal sites. Finally, a short assessment is given as potential directions for further research.

Photothermal dry reforming of ethanol over rod-like Ni/ZrO2 catalysts

Photo-assisted ethanol dry reforming (EDR) for syngas production was deeply studied over nanorod-like Ni/ZrO2 catalyst synthesized by precipitation and impregnation technique, respectively. The effect of light irradiation as well as catalyst preparation method on EDR reaction was investigated in detail with the stoichiometric feed ratios, over a temperature region of 350 to 550 °C. Photo-enhancement factor of ethanol conversion greatly increased from 10% (dark) to 40% (light) together with less formation of byproducts. Moreover, the experimental results depicted the better performance of P-Ni/ZrO2 catalyst due to its abundant oxygen vacancies and strong Ni-Zr interaction. Enriched interfacial oxygen defects and more light-excited electrons facilitated the activation/dissociation of ethanol and CO2, thereby enhancing the catalytic activity. In addition, the mean particle size of NiO in P-Ni/ZrO2 was (10.3 nm) which was smaller than that of the I-Ni/ZrO2 (16.5 nm), suggesting its higher dispersion of active metal. The calculated apparent activation energy of P-Ni/ZrO2 was 20.6 eV which was much less than the value of I-Ni/ZrO2 (37.7 eV). This work might provide the valuable insight for the development of highly-efficient photothermal catalyst to enhance the value-added utilization of greenhouse gas CO2.

Assessment of heavy metal pollution in soils of Jebba Area, Nigeria: Concentrations, source analysis and implications for ecological and human health risks

This comprehensive research investigates heavy metal contamination in the rapidly developing town of Jebba in north-central Nigeria, which is essential to the nation's economy due to its agro-allied and non-agro-allied businesses. The research focuses on soil samples, collecting and analyzing 137 surface soil samples to assess the presence of 25 distinct metals. After statistical analysis and simple mathematical models are applied to the data, the amounts of harmful metals and their probable causes are revealed. The study identifies geogenic and anthropogenic origins of toxic metals, with some elements exceeding average crustal concentrations. Non-homogeneous metal dispersion is shown in the region by spatial distribution maps. The geo-accumulation index reflects various amounts of contamination, with particular metals posing significant threats to the ecosystem. Additionally, the study compares results with worldwide studies, revealing distinct pollution patterns in Jebba. The research delves into weathering processes, employing chemical indices to quantify the level of soil weathering and uncovering a prominent role of geogenic activities in metal release. Bivariate correlation and principal component analysis indicate links and possibly common sources among heavy metals, emphasizing anthropogenic contributions. In addition, assessments of ecological and medical risks are conducted, indicating possible threats to human wellness and the ecosystem. Children, in particular, are regarded as especially vulnerable to non-carcinogenic health concerns, with various heavy metals posing potential threats through diverse exposure routes. The study emphasizes the need to implement remediation procedures to address the risks to public health and the environment related to metal pollution.

Single atoms/metal nanoparticles-decorated hollow carbon spheres as oxygen reduction catalyst for zinc-air batteries

Non-platinum electrocatalyst development for improving the oxygen reduction reaction (ORR) is critical in electrochemical energy conversion applications such as zinc-air batteries (ZABs). Herein, we developed dual Fe-Co single atoms and Co nanoparticles embedded N-doped hollow carbon (Fe-Co/N-HCS-x) catalysts via the carbonization of polypyrrole (PPy)@zeolitic imidazolate framework (ZIF) core–shell particles, with various PPy concentrations. PPy serves as a secondary nitrogen source that enhances nitrogen amount and promotes metal dispersion to increase active sites density. The Fe-Co/N-HCS-x catalysts with optimized PPy concentration control demonstrated improved ORR performance in alkaline media, with a half-wave potential (E1/2) of 0.921 V and an onset potential (Eonset) of 1.019 V. Fe-Co/N-HCS-x also exhibited high ZABs performance, with a power density of 244.6 mW cm−2 and an operating time of more than 100 h. Our research contributes to the development of optimized active sites for ORR, which can be applied to new electrochemical storage and conversion systems.

Atomically Dispersed Metal Catalysts for the Conversion of CO2 into High-Value C2+ Chemicals.

The conversion of carbon dioxide (CO2) into value-added chemicals with two or more carbons (C2+) is a promising strategy that cannot only mitigate anthropogenic CO2 emissions but also reduce the excessive dependence on fossil feedstocks. In recent years, atomically dispersed metal catalysts (ADCs), including single-atom catalysts (SACs), dual-atom catalysts (DACs), and single-cluster catalysts (SCCs), emerged as attractive candidates for CO2 fixation reactions due to their unique properties, such as the maximum utilization of active sites, tunable electronic structure, the efficient elucidation of catalytic mechanism, etc. This review provides an overview of significant progress in the synthesis and characterization of ADCs utilized in photocatalytic, electrocatalytic, and thermocatalytic conversion of CO2 toward high-value C2+ compounds. To provide insights for designing efficient ADCs toward the C2+ chemical synthesis originating from CO2, the key factors that influence the catalytic activity and selectivity are highlighted. Finally, the relevant challenges and opportunities are discussed to inspire new ideas for the generation of CO2-based C2+ products over ADCs.

Non-Oxidative Coupling of Methane Catalyzed by Heterogeneous Catalysts Containing Singly Dispersed Metal Sites

Direct upgrading of methane into value-added products is one of the most significant technologies for the effective transformation of hydrocarbon feedstocks in the chemical industry. Both oxidative and non-oxidative methane conversion are broadly useful approaches, though the two reaction pathways are quite distinguished. Oxidative coupling of methane (OCM) has been widely studied, but suffers from the low selectivity to C2 hydrocarbons because of the overoxidation leading to undesired byproducts. Therefore, non-oxidative coupling of methane is a worthy alternative approach to be developed for the efficient, direct utilization of methane. Recently, heterogeneous catalysts comprising singly dispersed metal sites, such as single-atom catalysts (SAC) and surface organometallic catalysts (SOMCat), have been proven to be effectively active for direct coupling of methane to product hydrogen and C2 products. In this context, this review summarizes recent discoveries of these novel catalysts and provides a perspective on promising catalytic processes for methane transformation via non-oxidative coupling.

Synthesis, characterization, and catalytic performance of Ni supported on sustainable POFA-derived SBA-15 for hydrogen-rich syngas from CO2 reforming of methane

Palm Oil Fuel Ash (POFA) is massively produced by numerous palm oil mills worldwide, creating an environmental waste disposal problem. Notably, POFA serves as a cost-effective alternative silica source instead of the expensive tetraethyl orthosilicate (TEOS). This research focused on synthesizing SBA-15 from POFA waste and examining the effect of promoters on POFA-derived SBA-15-supported Ni-based catalysts. The 10 wt% Ni/SBA-15-POFA catalyst was sequentially impregnated with promoters having 1 wt% loading of Zr, Ce, La, and Cr. The catalysts were tested for CO2 methane reforming (CMR) at 800 °C for 8 hours while maintaining a stoichiometric feed ratio. Various characterization techniques, including XRD, FESEM, XPS, H2-TPR, CO2-TPD, and BET analysis were employed to assess the catalyst physicochemical properties. The addition of promoter changed the properties of catalyst. Except for Cr-promoted catalyst, the addition of promoters positively impacted catalytic performance, activity, and stability. XRD analysis showed that Cr addition had detrimental effects on the crystallite structure of the Ni/SBA-15-POFA catalyst. In contrast, Zr, Ce, and La additions significantly reduced the crystallite size and improved active metal dispersion. Overall, the Zr-promoted catalyst exhibited the best performance in terms of activity and stability, with a CH4 conversion of 90 % and CO2 conversion of 94.4 %. The spent catalyst characterization, including XRD, FESEM, O2-TPO, and RAMAN, showed that promoter addition significantly reduced carbon deposition. The stable and superior perfromance of Zr-promoted catalyst was attributed to the production of MWCNTs. Conversely, the rapid deactivation of the unpromoted catalyst may be due to the formation of amorphous carbon, which tends to quickly block active sites and reduce the catalytic activity.

Impact of the support material on the phosphorus poisoning on Co-based catalysts for Fischer-Tropsch synthesis

The role of the support on the poisoning by phosphorus of cobalt-based catalysts for the Fischer-Tropsch synthesis was investigated. Four different supports were used in this study, γ-alumina, titania and two silica gels with different pore sizes and surface areas. The deactivation varies in intensity depending on the type of support. The trend follows the strength of the metal-support interactions, γ-alumina being the least affected, while SiO2 (2 samples with different pore structures) was most affected. These results suggest that in the first case, P interacts mainly with the support while with less interacting supports, P will interact more with the cobalt particles. The addition of different loadings of P was done after the preparation of the catalysts simulating the possible behaviour of a Biomass to Liquids process. The P loading resulted in a decrease in site-time yield and a higher hydrogenation activity leading to a reduced production of value products. Conventional characterization of the catalysts showed two different deactivation mechanisms, including site blocking and electronic effects. The addition of phosphorus decreased the metallic dispersion and reducibility of the catalysts, inhibited the hydrogen desorption and reduced the CO adsorption. Phosphorus species might be altering the catalyst surface, yielding a higher H2/CO ratio adsorbed on the catalyst through the modification of the bonding strength between the cobalt and CO, and preventing the desorption of H2.