Metal Species Research Articles

Exploration on structure-activity relationship over substituted Co-doped spinel AlFe2O4 for enhanced CO2 hydrogenation into C2-C4 hydrocarbons

As the main greenhouse gas, CO2 has caused some serious environmental problems. Hence the abatement of CO2 allows of no delay. Among all strategies for CO2 reduction, CO2 hydrogenation reveals the great potential for industrial application, and becomes the efficient path to achieve target of “Carbon Neutral”. In this work, the Co-doped AlFe2O4 catalysts were firstly reported for CO2 hydrogenation test, and the enhancement of Co doping on activity was explored systematically via a series of conventional characterization methods. The Fischer-Tropsch synthesis-based CO2 hydrogenation was conducted over Co-doped AlFe2O4, thus the dissociation of CO2 and the carbon chain growth were both important. The observation of CoFe2O4 in the composites indicated the strong electronic interaction between Co and Fe species. This could strengthen the electrons transfer to generate more metallic Co and Fe species during H2 reduction, and then increased the Fe3C percentage during CO2 hydrogenation process. Moreover, the generated Co0 species could provide the additional adsorption sites for reactant gas. Therefore, the strategy of Co doping could strengthen the CO2 hydrogenation performance, reflected in the increase of CO2 conversion, the selectivity and space time yield of C2-C4 products. However, the formed “too stable” structure in the condition of the excessive Co doping prohibited the electrons transfer and the generation of Fe3C active species, thus existing an optimum Co doping amount.

Machine learning model with a novel self–adjustment method: A powerful tool for predicting biomass ash fusibility and enhancing its potential applications

Biomass ash has been extensively studied for its potential applications, owing to its high content of alkali and alkaline earth metallic species (AAEMs). These AAEMs can act as catalysts in biomass thermochemical conversion and other industrial processes. However, AAEMs can also cause slagging and agglomeration, which can significantly impact system operations. To better understand these effects, we investigated the relationship between ash melting behavior and the chemical composition of biomass ash using a machine learning (ML) model. To enhance the model's performance, we employed a self-adjustment (SA) method, which significantly improved predictive accuracy. The SA-ETR model achieved an R2 value greater than 0.93, based on a dataset of 268 data points. We provided a detailed explanation of the SA-optimized ML model using Python's Shapley Additive Explanations (SHAP) library, which included global and local feature importance analysis, investigation of simultaneous effects between two features, and individual data point prediction analysis. The contents of K2O, SiO2, CaO, and Al2O3 were considered as the most significant factors affecting biomass ash's initial deformation temperature (IDT). The insights gained from this study can help investors and researchers reduce experimental complexity and improve system operation.

Synergistic mechanisms of humic acid and biomineralization in cadmium remediation using Lysinibacillus fusiformis.

Heavy metal pollution, particularly cadmium, poses severe environmental and health risks due to its high toxicity and mobility, necessitating effective remediation strategies. While both microbially induced carbonate precipitation (MICP) and humic acid adsorption are promising methods for heavy metal mitigation, their combined effects, particularly the influence of humic acid on the MICP process, have not been thoroughly investigated. This study explores the interaction between humic acid and MICP, revealing that humic acid significantly inhibits the MICP process by reducing urease activity, with the 10% humic acid treatment resulting in a 23.8% reduction in urease activity compared to the control. Additionally, while higher concentrations of humic acid did not significantly reduce cadmium ion concentrations, they did result in a slight increase in organically bound cadmium, indicating an interaction that could alter metal speciation in the soil. These findings provide important insights into the mechanisms by which humic acid affects MICP, offering a foundation for optimizing combined remediation approaches. Future research should aim to fine-tune the balance between MICP and humic acid to enhance the overall efficiency of cadmium remediation strategies. This study contributes to the development of more effective and sustainable methods for addressing cadmium contamination.

How Does Mangrove Restoration or Reforestation Change Trace Metal Pollution in Mangrove Ecosystems? A Review of Current Knowledge

In recent years, mangrove restoration has gained significant attention due to its carbon storage capacity, role as a pollution sink, and ecological and economic benefits. Moreover, the United Nations Sustainable Development Goals’ strategies include mangrove restoration. This review investigates the status of mangrove restoration research and the influence of restoration on trace metal accumulation, speciation, and associated risks in mangrove sediments. Our analysis reveals that research on mangrove restoration is increasing globally, with a notable surge in publications after 2017. However, fewer than 25 articles published between 2007 and 2024 address trace metals in restored mangroves, indicating limited focus from researchers on this topic. Research shows that mangrove restoration can quickly alter sediment properties, such as texture, salinity, and pH. As a result, restored sediments tend to accumulate higher organic carbon content than barren areas. Most studies also suggest that trace metal accumulation is higher in restored sites than in non-restored areas. However, metal speciation varies considerably between sites due to local environmental factors. Furthermore, many studies suggest that restoration may increase the risks posed by trace metals to aquatic biota. The challenges of mangrove restoration research include short study timeframes, low success rates, poorly defined targets, small-scale efforts, conflicts with local communities over resources and benefits, insufficient government funding, and a lack of historical data on community health and pollution status.

Physicochemical Rationale of Matrix Effects Involved in the Response of Hydrogel-Embedded Luminescent Metal Biosensors

There is currently a critical need for understanding how the response and activity of whole-cell bacterial reporters positioned in a complex biological or environmental matrix are impacted by the physicochemical properties of their micro-environment. Accordingly, a comprehensive analysis of the bioluminescence response of Cd(II)-inducible PzntA-luxCDABE Escherichia coli biosensors embedded in silica-based hydrogels is reported to decipher how metal bioavailability, cell photoactivity and ensuing light bioproduction are impacted by the hydrogel environment and the associated matrix effects. The analysis includes the account of (i) Cd speciation and accumulation in the host hydrogels, in connection with their reactivity and electrostatic properties, and (ii) the reduced bioavailability of resources for the biosensors confined (deep) inside the hydrogels. The measurements of the bioluminescence response of the Cd(II) inducible-lux biosensors in both hydrogels and free-floating cell suspensions are completed by those of the constitutive rrnB P1-luxCDABE E. coli so as to probe cell metabolic activity in these two situations. The approach contributes to unraveling the connections between the electrostatic hydrogel charge, the nutrient/metal bioavailabilities and the resulting Cd-triggered bioluminescence output. Biosensors are hosted in hydrogels with thickness varying between 0 mm (the free-floating cell situation) and 1.6 mm, and are exposed to total Cd concentrations from 0 to 400 nM. The partitioning of bioavailable metals at the hydrogel/solution interface following intertwined metal speciation, diffusion and Boltzmann electrostatic accumulation is addressed by stripping chronopotentiometry. In turn, we detail how the bioluminescence maxima generated by the Cd-responsive cells under all tested Cd concentration and hydrogel thickness conditions collapse remarkably well on a single plot featuring the dependence of bioluminescence on free Cd concentration at the individual cell level. Overall, the construction of this master curve integrates the contributions of key and often overlooked processes that govern the bioavailability properties of metals in 3D matrices. Accordingly, the work opens perspectives for quantitative and mechanistic monitoring of metals by biosensors in environmental systems like biofilms or sediments.

Spatial Variability in the Speciation of Lead (Pb) and Other Metals Across Urban Lawns Is Linked to Post-Deposition Weathering Reactions

The historical use of lead (Pb) poses ongoing health risks via exposure to contaminated urban soils. However, there is limited information about heterogeneity in Pb speciation and distribution at the house lot scale. This study determined highly spatially resolved Pb and other metal speciation along horizontal transects and vertical soil cores from three homes in the Akron, Ohio (USA) municipal. Solid phase characterization was coupled with a sequential extraction protocol to determine operationally defined speciation (exchangeable (MEX), reducible (MRED), oxidizable (MOX), and residual (MRES)). Lead and Zn were strongly correlated across all fractions (R2 = 0.92). Total extractable Pb and Zn were found in low weight percent concentrations nearest to the homes, and speciation was dominated by MEX and MRED. High Pb in the MEX fraction was correlated with the presence of Pb-bearing paint chips in the soil. Lead in the MEX fraction in soils near the homes decreased with increasing time due to exterior renovations coupled with increases in Pb and Zn in the MRED fraction. These results suggest that homes are the dominant source of Pb and Zn due to the weathering of exterior surfaces and highlight the acute risk of exposure to more labile Pb immediately following exterior renovations and damage to home exteriors in areas of older housing stock.

Stoichiometric Lanthanide Compounds with Diglycolamides: A Synthetic Approach toward Understanding Rare-Earth Speciation in Solution.

A fundamental understanding of coordination chemistry across the lanthanide series is essential for explaining the chemical behavior of rare-earth metals in complex liquid-liquid extraction processes. Probing the exact bonding between the extractant and the metal is sometimes done through the synthesis of solid-state compounds that can serve as models for metal speciation in solution. In the case of diglycolamide (DGA), a commonly used neutral diamide extractant, extensive studies identify the stepwise formation of 1:1 [Ln(DGA)(H2O)6]3+, 1:2 [Ln(DGA)2(H2O)3]3+, and 1:3 [Ln(DGA)3]3+ complexes in solution. The crystallographic reports, however, exclusively show a 1:3 [Ln(DGA)3]3+ moiety in the solid state, while the structures of 1:1 and 1:2 complexes are yet to be isolated and comprehensively studied. In this work, we report the synthesis and characterization of three new families of stoichiometric N,N,N',N'-tetramethyldiglycolamide (TMDGA) compounds: [Ln(TMDGA)(H2O)5Cl]Cl2·2H2O, [Ln(TMDGA)2(H2O)3]Cl3·3H2O, and [Ln(TMDGA)3]Cl3·7H2O, where Ln = Nd, Eu, Gd, with Ln:TMDGA ratios of 1:1, 1:2, and 1:3, respectively. The compounds have been analyzed using vibrational spectroscopy (both Raman and FT-IR), as well as variable temperature fluorescence spectroscopy. A spectrophotometric titration of Eu(III) was performed to confirm the presence of the [Eu(TMDGA)n]3+ (n = 1, 2, and 3) species in solution and to compare the individual solid-state emission spectra to their respective analogues in solution.

Tripartite Detection and Sensing of Toxic Heavy Metals Using a Copper-Based Porphyrin Metal-Organic Framework.

The detection of heavy metals in water sources is a critical concern for environmental preservation and public health. However, current electrochemical heavy metal sensors suffer from high sensing limits, cross-sensitivity, and poor selectivity. In this work, we present the possibility of an electrochemical sensor based on a copper (Cu) metal-organic framework for the detection of lead, cadmium, and mercury by replacing Cu metal nodes. The working electrode consists of a ∼5 μm thin layer of copper- tetracarboxyphenylporphyrin (Cu-TCPP) sheets that are adsorbed on a glassy carbon electrode (GCE). Upon interaction with Pb2+, Cd2+, and Hg2+, these ions are adsorbed on and incorporated into the metal nodes of the MOF. The adsorbed metallic species can be oxidized to the ionic form (Pb → Pb2+) electrochemically, which results in an oxidation response and enables the quantitative detection of these metals. The oxidation peak currents follow a (mostly) bimodal linear regression with a sensing range of up to 30 μM dependent on the deposition time and an ultralow limit of detection (LoD) of up to 5 nM. The system displays robust and selective sensing in saturated solutions of counterions and interfering metal ions (low error margins of <10%). This work represents the first report of a Cu-TCPP-modified GCE anode as an effective electrode for the sensitive detection of multiple heavy metals and an in-depth study into the Cu replacement kinetics of the Cu-MOF.

Molecular complex inspired design of an efficient copper(II)-containing robust porous polymers for electrochemical water oxidation

Homogeneous copper-bipyridine complexes have been reported as effective catalysts for water oxidation, demonstrating significant potential as alternatives to precious metal-based complexes. However, these complexes face long-term stability and product separation challenges similar to many homogeneous catalysts. Meanwhile, recent studies have underscored the potential of metalated polymer networks, which integrate the structural advantages of polymers with the functional benefits of metal species, making them highly attractive for various applications. Herein, we integrated copper-bipyridine units into porous polymer networks to overcome the limitations of copper-bipyridine complexes. We prepared a series of copper-incorporated polymers (TpBpy-Cux) for electrochemical water oxidation. The electrochemical properties of these polymers were tuned by varying the copper content, with TpBpy-Cu3 presenting the best performance among the samples studied. TpBpy-Cu3 demonstrated a low Tafel slope of 69 mV/decade, achieved a high Faradaic efficiency (FE) of 94 %, and exhibited exceptional stability over 1000 cyclic scans. This study offers insights into the design and optimization of metal-incorporated porous polymer networks building on the foundational understanding of their molecular counterparts for advanced catalytic applications.

A new strategy toward synthesis of novel bifunctional N- and S-bearing sorbent for platinum(IV) removal from aqueous solutions and acidic leaching residue of Pt/Al2O3 catalyst

Strong incentive politics have been elaborated for promoting the recovery of precious metals from secondary resources. Solid leaching generates acidic effluents that can be pre-treated using precipitation steps for partial separation before applying sorption for metal recovery from mild acidic solutions. For this purpose, a new sorbent was designed bearing numerous N- and S-bearing reactive groups with good affinity for platinum (as chloroanionic species). Thiazole precursors were first reacted before being grafted (by free radical reaction) with triallyl cyanurate (to form CTTR sorbent). The material was characterized by a series of analytical tools (SEM, BET, FTIR, XPS, TGA, elemental analysis, and titration). The effect of pH combined with FTIR and XPS spectroscopy analyses allowed identifying the mechanisms involved in metal binding: (a) electrostatic attraction of chloroplatinate anions with protonated amine groups (especially in acidic conditions), (b) while at moderate acidic pH metal sorption proceeds through ligand exchange and chelation onto N-based and S-based groups. Optimum sorption was found at pH close to 4 (near pHpzc value). Under selected experimental conditions, the equilibrium was reached in 25–35 min. The pseudo-first order rate equation fitted well experimental profile (though the resistance to intraparticle diffusion contributes to the kinetic control). The maximum sorption capacity at room temperature reached up to 1.58 mmol Pt g−1 (at pH 4). The sorption isotherm was successfully fitted by the Temkin equation. The sorption is spontaneous and exothermic (with reduction in maximum sorption capacity reaching up to 25 %, when temperature increases to 50 °C). Optimum platinum desorption was obtained with 0.3 M HCl solution (with solid/liquid ratio 1.67 g L−1) for complete desorption and enrichment factor close to 4.6. Complete desorption was maintained over 5 cycles, while the sorption efficiency decreased by less than 3.5 % at the fifth cycle. The sorbent showed remarkable stability for PGMs (Pd(II) in addition to Pt(IV)) against alkali-earth elements or base metals (from equimolar synthetic solutions); the selectivity is driven by the preference of the reactive groups (soft base and intermediary base) for soft PGM metals against hard and borderline metal ions; this selectivity is also affected by metal speciation (formation of chloro-anionic species). The valorization of platinum from non-compliant Pt/Al2O3 catalyst was investigated after leaching with aqua regia. Platinum was precipitated from the leachate with ammonium chloride. In a second step, aluminum was removed by precipitation at pH 5. The residual solution was then treated by adsorption on CTTR: optimum separation between Pt and Al was achieved at pH ≈ 3.

Spectral reconstruction for radiation hydrodynamic simulations of galaxy evolution

Radiation from stars and active galactic nuclei (AGN) plays an important role in galaxy formation and evolution, and profoundly transforms the intergalactic, circumgalactic, and interstellar medium (IGM, CGM, and ISM). On-the-fly radiative transfer (RT) has started being incorporated in cosmological simulations, but the complex evolving radiation spectra are often crudely approximated with a small number of broad bands with piece-wise constant intensity and a fixed photo-ionisation cross-section. Such a treatment is unable to capture the changes to the spectrum as light is absorbed while it propagates through a medium with non-zero opacity. This can lead to large errors in photo-ionisation and heating rates. In this work we present a novel approach of discretising the radiation field at discrete photon energies, at the edges of the typically used photo-ionising bands, in order to capture the power-law slope of the radiation field. In combination with power-law approximations for the photo-ionisation cross-sections, this model allows us to self-consistently combine radiation from sources with different spectra and accurately follow the ionisation states of primordial and metal species through time. The method is implemented in GASOLINE2 in connection with TREVR2, a fast reverse ray tracing algorithm with 𝒪(Nactive log2 N) scaling. We compare our new piece-wise power-law reconstruction to the piece-wise constant method in calculating the primordial chemistry photo-ionisation and heating rates under an evolving UV background (UVB) and stellar spectrum, and find that our method reduces errors significantly, by up to two orders of magnitude in the case of HeII ionisation. We apply our new spectral reconstruction method in RT post-processing of a cosmological zoom-in simulation, MUGS2 g1536, including radiation from stars and a live UVB, and find a significant increase in total neutral hydrogen (HI) mass in the ISM and the CGM due to shielding of the UVB and a low escape fraction of the stellar radiation. This demonstrates the importance of RT and an accurate spectral approximation in simulating the CGM-galaxy ecosystem.

Mass flow and ecological risk of heavy metals in anaerobic digestion of food waste

Conversion of food waste (FW) to bioenergy via anaerobic digestion (AD) has become a topic of worldwide research interest. However, the content, distribution, and speciation of heavy metals (HMs) in feedstock and digestate samples throughout the AD process are currently unknown. Especially, the potential ecological risk (PER) of solid digestate with potential of land application was vague. Mass flow of HMs (Cr, Cu, Mn, Ni, Zn, As, Cd, Hg, and Pb) were estimated in a two-stage wet AD of FW plant in Shenzhen, China. Furthermore, the PER of the HMs in solid digestate (SD) was studied. The findings revealed that the variation in the HM contents of the intermediates, as well as the comparatively high HM contents of the SD, were mostly influenced by the total solid contents of the samples, since HMs tend to adhere to the solid matrix. As per mass balance, the Cr and Ni contents of the digestate samples were 4.7 and 5.5 times higher than in the feedstock samples, respectively. The remaining metals were within the range of 82.2126.1%. Furthermore, the enrichment of HMs in SD must be resolved before reclamation. Moreover, the PER of the HMs in SD was 279.6, considered as a considerable risk level, of which Hg and Cd contributed 46.3% and 33.6%, respectively. This research presents a case study for quantitatively assessing the distribution of typical pollutants throughout the AD process, and it offers preliminary data for potential environmental issues caused by digestion product recycling.

Experimental and molecular insights into ionic liquid-based recovery of valuable metals from spent lithium-ion batteries

A new type of collaborative extractants consisting of the ionic liquid (IL) 1-aminoprooyl-3-methylimidazolium bis((trifluoromethyl)sulfonyl)imide, ([APMIM][Tf2N]) and Cyanex 923 (C923) is first applied for selective extraction of valuable metals from spent lithium-ion batteries (LIBs). The one-stage extraction efficiencies of Co2+, Ni2+ and Mn2+ are up to 99.87 %, 97.74 %, 99.98 %, respectively, at the optimal conditions, and the high-purity Li+ was enriched at the raffinate. It is found that the extraction process follows the so-called “cation exchange mechanism”, and the molecular-level mechanism is revealed via quantum chemical (QC) calculations. The findings show that C923 plays the role of coordinating with metal ions, the cation of IL exchanges metal ions from the aqueous to organic phases, and the anion [Tf2N]- of IL can stabilize the complex species of metal ion-[Tf2N]--C923 in organic phase. This work provides new insights for the design of novel IL-based extractants for the recycling of spent LIBs.

Efficient activation of peroxyacetic acid by cobalt-iron alloy/oxide heterojunctions anchored in defect-rich biochar for pesticide degradation in water: Unravelling the radical-unradical mechanism

The activation processes of peracetic acid (PAA-AOPs) have garnered significant attention in wastewater treatment. In this study, an amorphous carbon-modified bimetallic CoFe alloy/oxide catalyst (CoFe@DBCx-y, where x represents biomass mass and y represents pyrolysis temperature) was developed to activate PAA for the degradation of organochlorine pesticides (OCPs). Due to the size effect, biochar dynamically regulates the particle size of metal species, which is influenced by the pyrolysis temperature. Among these systems, the CoFeDBC2.0–700/PAA oxidation system effectively removed 95.7 % of 2,4-dichlorophenoxyacetic acid (2,4-D), exhibiting a kinetic constant 1.7 times higher than that of the Nano/PAA system. Furthermore, quenching experiments and electron paramagnetic resonance (EPR) analysis revealed that high-valent metal oxides (MIV = O) and singlet oxygen (1O2) are the primary active species responsible for the removal of 2,4-D, whereas organic radicals (RO·) and hydroxyl radicals (·OH) play a secondary role. Electrochemical and Raman spectroscopy tests revealed the formation of a metastable surface complex (≡Co(III)–OO(O)CCH3) between PAA and the catalyst, which acted as an intermediate oxidant to generate reactive oxygen species (ROS) through a chain reaction. Carbon defects in the biochar functioned as an electron source, continuously replenishing the electrons consumed in the reaction and facilitating the valence cycling between Co and Fe. This study provides new insights into the remediation of pesticide-contaminated wastewater using PAA-AOPs with heterogeneous bimetallic carbon-based catalysts.

Recovering Volatilized Salts from MSWI Fly Ash into Different Metal Species with High Purifies

Recovering Volatilized Salts from MSWI Fly Ash into Different Metal Species with High Purifies

Evaluation of Anti-Alzheimer's Potential of Azo-Stilbene-Thioflavin-T derived Multifunctional Molecules: Synthesis, Metal and Aβ Species Binding and Cholinesterase Activity.

Inhibition of amyloid β (Aβ) aggregation and cholinesterase activity are two major therapeutic targets for Alzheimer's disease (AD). Multifunctional Molecules (MFMs) specifically designed to address other contributing factors, such as metal ion induced abnormalities, oxidative stress, toxic Ab aggregates etc. are very much required. Several multifunctional molecules have been developed using different molecular scaffolds. Reported herein is a new series of four MFMs based on ThT, Azo-stilbene and metal ion chelating pockets. The synthesis, characterization, and metal chelation ability for [Cu(II) and Zn(II)] are presented herein. Furthermore, we explored their multifunctionality w.r.t. to their (i) recognition of Aβ aggregates and monomeric form, (ii) utility in modulating the aggregation pathways of both metal-free and metal-bound amyloid-β, (iii) ex-vivo staining of amyloid plaques in 5xFAD mice brain sections, (iv) ability to scavenge free radicals and (v) ability to inhibit cholinesterase activity. Molecular docking studies were also performed with Aβ peptides and acetylcholinesterase enzyme to understand the observed inhibitory effect on activity. Overall, the studies presented here establish the multifunctional nature of these molecules and qualify them as promising candidates for furthermore investigation in the quest for finding Alzheimer's disease treatment.

Searching for the optimum Pt loading in bimetallic PtXNi/SBA-15 catalysts for hydrodeoxygenation

AbstractBimetallic PtXNi5/SBA-15 catalysts with 5 wt% Ni and X = 0.1–2.0 wt% Pt were synthesized and characterized. The XPS characterization of bimetallic catalysts showed the presence of oxide Ni2+, Pt2+ and reduced Pt0 species in the calcined catalysts. After the reduction, metallic Ni0 appeared in addition to the above-mentioned species. The proportions of the reduced Ni and Pt increased with increasing Pt content in the catalysts. The presence of metal species of different oxidation states at the Ni–Pt interface was crucial for their catalytic performance in the hydrodeoxygenation of anisole. The Pt0.5Ni5/SBA-15 catalyst was the most active and selective. Graphical abstract

Spectroscopic Signature of Metal-hydroxo and Peroxo Species in K-edge X-ray Absorption Spectra.

Metal-dioxygen species are important intermediates formed during dioxygen activations by metalloenzymes in various biological processes, by catalysts in fuel cells, and prior to O2 evolution by photosystem II. In this work, we focus on manganese-porphyrin complexes using tetramesitylporphyrin ligand (TMP) to explore changes in Mn K-edge X-ray absorption spectroscopy (XAS) associated with the formation of Mn-hydroxide and Mn-O2 peroxide species. With limited spectroscopic characterization of these compounds, Mn Kβ X-ray emission spectroscopy (XES), XAS, density functional theory (DFT), and time-dependent DFT (TD-DFT) analysis will enhance our understanding of their complex electronic structure. We show that the shape of the pre-edge in the K-edge Mn X-ray absorption near-edge structure (XANES) can serve as a spectroscopic signature of the MnIII-peroxo formation and thus can be used to track the presence of the side-on peroxide as an intermediate in time-resolved or in situ experiments. Our results will help to further summarize the spectroscopic fingerprints for peroxo and hydroxo species, addressing the challenge of identifying the reactive metal species in catalytic reactions.

Structure, Electronic Properties and Nonlinear Optical Properties of Silagraphdiyne (SiGDY): The Role of Alkali Metal Species

Structure, Electronic Properties and Nonlinear Optical Properties of Silagraphdiyne (SiGDY): The Role of Alkali Metal Species

Catalytic Conversion of Levulinic Acid over Sn-BTC and Sn-H3-5-SIP Heterogeneous Acid Catalysts

This work presents the synthesis and characterization of materials that contain Sn metal clusters formed by ligands of trimesic acid (Sn-BTC) or 5-sulfobenzene-1,3-dicarboxylic acid (Sn-H3-5-SIP). These catalysts were used to convert levulinic acid with ethanol to produce ethyl levulinate under mild reaction conditions. The characterization results confirmed that Sn is mainly present in the cassiterite crystalline phase with a tetragonal rutile structure in octahedral and tetrahedral coordination in the materials. The assembly of trimesic acid (a hard base) with metal species (Sn) results in the formation of acid and thermally stable metal–organic frameworks. The use of 5-sulfobenzene-1,3-dicarboxylic acid instead of trimesic acid in the synthesis incorporates sulfonic groups in the material, enhancing the total acidity of the Sn-H3-5-SIP catalyst compared to the Sn-BTC material. The Sn-H3-5-SIP catalyst exhibited the highest catalytic activity when converting levulinic acid with ethanol, resulting in a turnover frequency (TOF) of 0.0495 s−1, which is a 50% increase compared to the TOF of the Sn-BTC catalyst (0.0329 s−1). This result can be attributed to its higher concentration of acid sites (2.23 ± 0.05 mmol H+/gcat) and specific area (139 m2/g). Thus, materials containing tin metal clusters and sulfonic groups are promising materials that could be used as catalysts for synthesizing ethyl levulinate under mild reaction conditions.