Charge-balancing Cations Research Articles

Surface modification of cotton fabric by kaolin-derived zeolite N to enhance efficient removal of particulate matter

Reducing the amount of fine particulate matter (PM) in the atmosphere is essential for preserving a secure and healthy environment. Here, we synthesized zeolite N (potassium ion form, KN) from kaolin clay minerals, coated it on cotton fabric using a simple refluxing method and then removed PM from the air. The following conclusion can be drawn. The average cation exchange capacity (CEC) of KN was 512 meq/100 g, and a CEC value > 400 meq/100 g indicated pure zeolite with a Si/Al ratio of approximately 1.0. The synthesized KN, containing a high proportion of Al, proved highly effective in removing particulates. For instance, KN/cotton (746 GSM (weight of fabric in g/m2) cotton, coated with approximately 1.46 wt% KN) demonstrated an 8-times higher removal efficiency (RE) for PM2.5 and PM1.0 than bare 746 GSM cotton, with only a 7 Pa increase in the pressure drop. PM may have been removed by electrostatic interactions between the charged PM and KN (with charge-balancing cations) owing to the charges and polarity of the outer layer of PM particles. According to the increases in RE and the quality factor, KN/cotton (746 GSM) was the most effective in removing PM from the air compared to other materials. The results suggested that KN, when applied to the surface of cotton fabric, is highly efficient due to its EDI framework structure and high Al content. Finally, biodegradation tests revealed that used filters disintegrated into pieces after being buried for one month in soil, indicating their environmental friendliness.

Formation of Uranyl Peroxide Compounds via Dissolution of Studtite, [(UO2)(O2)(H2O)2](H2O)2, in Ionic Liquids.

Four uranyl peroxide compounds with novel structures were formed following the dissolution of studtite, [(UO2)(O2)(H2O)2](H2O)2, in imidazolium-based ionic liquids. The compounds were characterized using single crystal X-ray diffraction (SCXRD), powder X-ray diffraction (PXRD), Raman and infrared (IR) spectroscopy, and scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDS). The ionic liquids used in the experiments were 1-ethyl-3-methylimidazolium (EMIm) diethyl phosphate, EMIm ethyl sulfate, and EMIm acetate. Each of the four uranyl peroxide compounds contain components from the ionic liquids as terminal ligands on uranyl peroxide molecular units, bridging ligands in uranyl peroxide sheet structures, or charge balancing cations located in the interstitial space. The studtite dissolved in and reacted with the ionic liquids, producing unique crystal structures depending on the anionic component of the ionic liquid, the temperature at which the synthesis was performed, and the introduction of additional ionic species into the solution. This is the first report of studtite dissolving in and reacting with ionic liquids to form uranyl peroxide compounds, which has the potential to vastly increase the number of synthetic routes for the formation of uranyl peroxide clusters and uranyl peroxide cage clusters.

Linear electronic relationship of surface functionalized fly ash and substituted phenols on bactericidal activity with the computational study

AbstractFly ash is a solid waste by‐product obtained from coal‐burning power plants. It is a silico‐aluminate material with an admixture of several metal oxides, which finds an application in geopolymers, zeolites, cement, catalysts, etc. The present article aims to assess the antibacterial activity of fly ash and substituted phenols against Escherichia coli and Staphylococcus in broth and agar cultures, respectively. High‐Temperature Activated Fly Ash (TAFA) shows significant bactericidal activity against gram positive (+) and negative (−) bacteria as compared to Mechanically Activated Fly Ash (MAFA) and Waste Polyethylene Coated Fly Ash (WPCFA), which attribute to the augmentation of mullite phase (lacking charge balancing cation) of fly ash at high temperature. These modified fly ash (TAFA, MAFA, and WPCFA) were characterized by Fourier Transform Infra Red (FT‐IR), Scanning Electron Microscope (SEM), and X‐Ray Diffraction (XRD) techniques. The substituted phenols further explored the significance of charge on the antibacterial properties. The para‐substituted phenols with groups having (+) mesomeric effect M > (−) I Inductive effect and ortho substituents with (+) I effect shows a linear electronic relationship with antibacterial properties with gram (+) bacteria, owing to charge augmentation at oxygen atom of phenoxide ion due to electronic effects. Further, the bactericidal efficacy was less significant on gram (−) bacteria. Small energy gap (Egap) values corroborated the chemical reactivity of phenols and substituted phenols. The antimicrobial potential of phenol/substituted phenols can be correlated with global descriptors. Molecular Electrostatic Potential (MEP) maps obtained through Density Functional Theory (DFT) indicate the nucleophilic centers in the molecular structure.

Negative Temperature Coefficient Properties of Natural Clinoptilolite

Negative temperature coefficient (NTC) materials are usually based on ceramic semiconductors, and electrons are involved in their transport mechanism. A new type of NTC material, adequate for alternating current (AC) applications, is represented by zeolites. Indeed, zeolites are single charge carrier ionic conductors with a temperature-dependent electrical conductivity. In particular, electrical transport in zeolites is due to the monovalent charge-balancing cations, like K+, capable of hopping between negatively charged sites in the aluminosilicate framework. Owing to the highly non-linear electrical behavior of the traditional electronic NTC materials, the possibility to have alternative types of materials, showing linearity in their electrical behavior, is very desirable. Among different zeolites, natural clinoptilolite has been selected for investigating NTC behavior since it is characterized by high zeolite content, a convenient Si/Al atomic ratio, good mechanical strength due to its compact microstructure, and low toxicity. Clinoptilolite has shown a rapid and quite reversible impedance change under heating, characterized by a linear dependence on temperature. X-ray diffraction (XRD) has been used to identify the natural zeolite, to establish all types of crystalline phases present in the mineral, and to investigate the thermal stability of these phases up to 150 °C. X-ray photoelectron spectroscopy (XPS) analysis was used for the chemical characterization of this natural clinoptilolite sample, providing important information on the cationic content and framework composition. In addition, since electrical transport takes place in the zeolite free-volume, a Brunauer–Emmett–Teller (BET) analysis of the mineral has also been performed.

Yttrium-based metal-organic frameworks built on hexanuclear clusters.

Yttrium-based metal-organic frameworks built on hexanuclear clusters (Y6-MOFs) represent an important subgroup of MOFs that are assembled from Y6 clusters and diverse organic linkers, featuring a variety of topologies. Due to the robust Y-O bonds and high connectivity of hexanuclear SBUs, Y6-MOFs are generally thermally stable and resistant to water. Additionally, their pore structures are highly tunable through the practice of the reticular chemistry strategy, resulting in excellent performance in gas adsorption and separation related applications. Y6-MOFs are structurally analogous to Zr6-MOFs; however, the existence of charge-balancing cations in Y6-MOFs serves as an additional pore structure regulator, enhancing their tailorability with respect to pore shape and dimensions. In this Frontier article, we summarize the main advances in the design and synthesis of Y6-MOFs, with a particular focus on the precise engineering of their pore structure for gas separation. Future directions of research efforts in this field are also discussed.

Photoinduced electron-hole recombination in zeolites: Marcus theory applied to DCB@MFI systems

The adsorption of DCB in MZSM-5 (M = H+, Na+) and silicalite-1 channel zeolites takes place without chemical or structural modification of the zeolite. Upon UV photoexcitation, a radical anion - hole pair is stabilized as demonstrated by time resolved diffuse reflectance UV–visible spectroscopy. The photogeneration of the radical anion DCB- is assigned to the dual (ambivalent) role of the zeolite framework as electron donor and hole stabilizator. The observation of such electron transfer only in the aluminated zeolite highlights the key role of the aluminum and of charge balancing cations. By studying the recombination of the radical anion – hole pairs at different temperature, the activation energy has been determined as a function of the nature of the charge-balancing cation. The values of the free enthalpy have been calculated using the Marcus theory from which the local redox potential of the zeolite has been estimated.

Boosting methylene blue adsorption capacity of an industrial waste-based geopolymer by depositing graphitic carbon nitride onto its surface: Towards sustainable materials for wastewater treatment

Surface characteristics of a geopolymer (GP) from an industrial waste, red mud (RM), and metakaolin (MK), were tuned by depositing urea-derived graphitic carbon nitride (g-C3N4) onto its surface. Methylene blue (MB) adsorption measurements demonstrated that the resulting g-C3N4/RM-MK-GP offers an excellent MB uptake capacity of 170.9 mg g−1, much higher than those of either the GP or the g-C3N4. Kinetics measurements revealed that chemisorption has an important effect on adsorption. The regenerability of g-C3N4/RM-MK-GP was studied for up to four consecutive cycles. Differences between the adsorption capacities of g-C3N4 and g-C3N4/RM-MK-GP were investigated by combining the power of various characterization tools. Results pointed out that surface functional groups associated with g-C3N4, surface hydroxyl and silanol groups of RM-MK-GP, together with exchangeable charge balancing cations of geopolymeric framework provide a unique structure for g-C3N4/RM-MK-GP. This study presents a versatile route to produce a sustainable, efficient, and cheap adsorbent for wastewater treatment.

Nanoscale calcium uranyl carbonate clusters in water

Aqueous calcium uranyl carbonate complexes are the predominant form of U(VI) in neutral to alkaline water in the environment, including seawater. We report a robust and repeatable synthesis of a nanoscale [(UO2)24O4(OH)12(CO3)36]44− cage cluster that we co-crystallized with Ca and Na countercations and determine its structure using single-crystal X-ray diffraction. Crystals were harvested and dissolved in water, followed by collection of electrospray ionization-mass spectra (ESI-MS). Introduction of a pH 8.1 solution containing 1.19 ± 0.04 mmol·L−1 U into the spectrometer produced broad m/z peak envelopes with −7 and 6 charge states at 1375, 1430, 1530, 1600, and 1675 m/z corresponding to mass 9625, 10,010, 10,710, 9600 and 10,080 amu, respectively. The spectra are consistent with [(UO2)24O4(OH)12(CO3)36]44− in solution (8909.07 amu), together with charge-balancing cations and H2O. Intentional fragmentation of the clusters yielded uranyl hydroxide and uranyl carbonate species containing Na. The [(UO2)24O4(OH)12(CO3)36]44− cluster is similar to that found in the mineral ewingite, which has been found to form in mine waters of an abandoned uranium mine. Demonstration of persistence of a nanoscale Ca uranyl carbonate cage cluster in aqueous solution reveals the need to re-examine aspects of environmental metal speciation to evaluate the extent to which nanoscale clusters may be important. SynopsisThis study demonstrates the existence of a nanoscale aqueous uranyl carbonate macroion at environmentally relevant pH conditions using mass spectrometry.

Molecular Network Approach to Anisotropic Ising Lattices: Parsing Magnetization Dynamics in Er3+ Systems with 0-3-Dimensional Spin Interactivity.

We present a wide-ranging interrogation of the border between single-molecule and solid-state magnetism through a study of erbium-based Ising-type magnetic compounds with a fixed magnetic unit, using three different charge-balancing cations as the means to modulate the crystal packing environment. Properties rooted in the isolated spin Hamiltonian remain fixed, yet careful observation of the dynamics reveals the breakdown of this approximation in a number of interesting ways. First, differences in crystal packing lead to a striking 3 orders of magnitude suppression in magnetic relaxation rates, indicating a rich interplay between intermolecular interactions governed by the anisotropic Ising lattice stabilization and localized slow magnetic relaxation driven by the spin-forbidden nature of quantum tunneling of the f-electron-based magnetization. By means of diverse and rigorous physical methods, including temperature-dependent X-ray crystallography, field, temperature, and time-dependent magnetometry, and the application of a new magnetization fitting technique to quantify the magnetic susceptibility peakshape, we are able to construct a more nuanced view of the role nonzero-dimensional interactions can play in what are predominantly considered zero-dimensional magnetic materials. Specifically, we use low field susceptibility and virgin-curve analysis to isolate metamagnetic spin-flip transitions in each system with a field strength corresponding to the expected strength of the internal dipole-dipole lattice. This behavior is vital to a complete interpretation of the dynamics and is likely common for systems with such high anisotropy. This collective interactivity opens a new realm of possibility for molecular magnetic materials, where their unprecedented localized anisotropy is the determining factor in building higher dimensionality.

Modification of zeolite Na-X, sodalite and cancrinite in salt melts

The possibility of occlusion in melts of useful components of some of the most economically advantageous materials, obtained during zeolitization of fly ash – Na-X, sodalite and cancrinite, was investigated. A very high degree of occlusion of ZnCl2 in zeolite Na-X was achieved along with complete exchange of Na extra framework cations with Zn2+. By elution, it was proved that, in the interaction of zeolite Na-X with ZnCl2 melt, occlusion takes place without destroying the zeolite aluminum-silicate framework. In a KNO3 melt, in the narrowest pore structure – the sodalite structure, occlusion does not proceed, only ion exchange occurs. Through computer modeling, the ion exchange of both the charge-balancing cations and the synthetically incorporated cation-anion pairs has been proven. The interaction of cancrinite-SO4 with a KNO3 melt results in the formation of a material with an altered cationic composition and occluded KNO3, which gradually comes out of the structure upon elution. The results obtained in the work can be a basis for the development of future applications of the modified minerals as materials with antibacterial properties (occluded ZnCl2 in the structure of zeolite Na-X) and as slow-acting fertilizers or micro-fertilizers (occluded with KNО3 cancrinite and sodalite forms).

A mechanistic study on the CO2 activation over Pd-containing MCM-22 zeolite based on DRIFT analysis: Impact of counter cations in the zeolite framework

Zeolites have been playing an important role in the field of so-called “Carbon dioxide Capture, Utilization, and Storage (CCUS)”. Catalytic activation of CO2 over zeolite-based catalysts has been extensively investigated, while many issues remain unsolved. In this study, the MWW-type zeolites impregnated with the Pd nanoparticles were used as the catalysts for CO2 activation. Furthermore, various amounts of charge balance cations (Na+ and H+) were added to the Pd-MWW with the intention of improving CO2 adsorption capacity. A fixed-bed reactor equipped with the Mass Spectrometer for effluent gas analysis was used to evaluate the steady-state conversion of the CO2 activation on these as-prepared catalysts from 50 to 650 °C. The compositions of the effluent gases and their associated quantities were monitored for each test. Finally, two infrared techniques (steady-state and dynamic measurements) were applied to identify the spectroscopic evidence of the heterogeneous catalysis reaction. In the first technique, the amount of chemisorbed CO2 was quantified by the infrared transmitted intensity across the samples from the vacuum to various levels of CO2 pressure at ambient temperature. The second technique investigates the hydrogenation mechanisms of adsorbates by the time-resolved FTIR with an in-situ diffusive reflectance airtight chamber. Both methods facilitated the infrared spectra of surface-adsorbed species during the hydrogenation. In combination with the temperature-programmed CO2 activation tests, this research prompted to reveal the kinetic mechanisms of CO2 activation.

Titelbild: Guiding Principles for the Rational Design of Hybrid Materials: Use of DFT Methodology for Evaluating Non‐Covalent Interactions in a Uranyl Tetrahalide Model System (Angew. Chem. 33/2023)

Uranyl tetrahalide ions assemble into hybrid material through Non-Covalent Interactions (NCIs) in the presence of organic charge balancing cations. NCIs such as hydrogen bonding serve to stabilize these supramolecular hybrid complexes and act as the fundamental driving force for crystallization. In their Research Article (e202305073), Sara E. Mason, Tori Z. Forbes et al. employed these hybrid complexes as a model system to assess the effect of NCIs on the vibrational properties and formation enthalpies of metal–organic hybrid materials.

Cover Picture: Guiding Principles for the Rational Design of Hybrid Materials: Use of DFT Methodology for Evaluating Non‐Covalent Interactions in a Uranyl Tetrahalide Model System (Angew. Chem. Int. Ed. 33/2023)

Uranyl tetrahalide ions assemble into hybrid material through Non-Covalent Interactions (NCIs) in the presence of organic charge balancing cations. NCIs such as hydrogen bonding serve to stabilize these supramolecular hybrid complexes and act as the fundamental driving force for crystallization. In their Research Article (e202305073), Sara E. Mason, Tori Z. Forbes et al. employed these hybrid complexes as a model system to assess the effect of NCIs on the vibrational properties and formation enthalpies of metal–organic hybrid materials.

Chemistry and Dynamics of Supercritical Carbon Dioxide and Methane in the Slit Pores of Layered Silicates.

ConspectusIn the mid 2010s, high-pressure diffraction and spectroscopic tools opened a window into the molecular-scale behavior of fluids under the conditions of many CO2 sequestration and shale/tight gas reservoirs, conditions where CO2 and CH4 are present as variably wet supercritical fluids. Integrating high-pressure spectroscopy and diffraction with molecular modeling has revealed much about the ways that supercritical CO2 and CH4 behave in reservoir components, particularly in the slit-shaped micro- and mesopores of layered silicates (phyllosilicates) abundant in caprocks and shales. This Account summarizes how supercritical CO2 and CH4 behave in the slit pores of swelling phyllosilicates as functions of the H2O activity, framework structural features, and charge-balancing cation properties at 90 bar and 323 K, conditions similar to a reservoir at ∼1 km depth. Slit pores containing cations with large radii, low hydration energy, and large polarizability readily interact with CO2, allowing CO2 and H2O to adsorb and coexist in these interlayer pores over a wide range of fluid humidities. In contrast, cations with small radii, high hydration energy, and low polarizability weakly interact with CO2, leading to reduced CO2 uptake and a tendency to exclude CO2 from interlayers when H2O is abundant. The reorientation dynamics of confined CO2 depends on the interlayer pore height, which is strongly influenced by the cation properties, framework properties, and fluid humidity. The silicate structural framework also influences CO2 uptake and behavior; for example, smectites with increasing F-for-OH substitution in the framework take up greater quantities of CO2. Reactions that trap CO2 in carbonate phases have been observed in thin H2O films near smectite surfaces, including a dissolution-reprecipitation mechanism when the edge surface area is large and an ion exchange-precipitation mechanism when the interlayer cation can form a highly insoluble carbonate. In contrast, supercritical CH4 does not readily associate with cations, does not react with smectites, and is only incorporated into interlayer slit mesopores when (i) the pore has a z-dimension large enough to accommodate CH4, (ii) the smectite has low charge, and (iii) the H2O activity is low. The adsorption and displacement of CH4 by CO2 and vice versa have been studied on the molecular scale in one shale, but opportunities remain to examine behavioral details in this more complicated, slit-pore inclusive system.

Periodic Density Functional Theory Calculations of Uranyl Tetrachloride Compounds Engaged in Uranyl-Cation and Uranyl-Hydrogen Interactions: Electronic Structure, Vibrational, and Thermodynamic Analyses.

Solid-state uranyl hybrid structures are often formed through unique intermolecular interactions occurring between a molecular uranyl anion and a charge-balancing cation. In this work, solid-state structures of the uranyl tetrachloride anion engaged in uranyl-cation and uranyl-hydrogen interactions were studied using density functional theory (DFT). As most first-principles methods used for systems of this type focus primarily on the molecular structure, we present an extensive benchmarking study to understand the methods needed to accurately model the geometric properties of these systems. From there, the electronic and vibrational structures of the compounds were investigated through projected density of states and phonon analysis and compared to the experiment. Lastly, we present a DFT + thermodynamics approach to calculate the formation enthalpies (ΔHf) of these systems to directly relate to experimental values. Through this methodology, we were able to accurately capture trends observed in experimental results and saw good quantitative agreement in predicted ΔHf compared to the value calculated through referencing each structure to its standard state. Overall, results from this work will be used for future combined experimental and computational studies on both uranyl and neptunyl hybrid structures to delineate how varying intermolecular interaction strengths relates to the overall values of ΔHf.

Interlayer Cation Polarizability Affects Supercritical Carbon Dioxide Adsorption by Swelling Clays.

Several strategies for mitigating the build-up of atmospheric carbon dioxide (CO2) bring wet supercritical CO2 (scCO2) in contact with phyllosilicates such as illites and smectites. While some work has examined the role of the charge-balancing cation and smectite framework features on CO2/smectite interactions, to our knowledge no one has examined how the polarizability of the charge-balancing cation influences these behaviors. In this paper, the scCO2 adsorption properties of Pb2+, Rb+, and NH4+ saturated smectite clays at variable relative humidity are studied by integrating in situ high-pressure X-ray diffraction (XRD), infrared spectroscopic titrations, and magic angle spinning nuclear magnetic resonance (MAS NMR) methods. The results are combined with previously published data for Na+, Cs+, and Ca2+ saturated versions of the same smectites to isolate the roles of the charge-balancing cations and perform two independent tests of the role of charge-balancing cation polarizability in determining the interlayer fluid properties and smectite expansion. Independent correlations developed for (i) San Bernardino hectorite (SHCa-1) and (ii) Wyoming montmorillonite (SWy-2) both show that cation polarizability is important in predicting the interlayer composition (mol% CO2 in the interlayer fluid and CO2/cation ratio in interlayer) and the expansion behavior for smectites in contact with wet and dry scCO2. In particular, this study shows that the charge-balancing cation polarizability is the most important cation-associated parameter in determining the expansion of the trioctahedral smectite, hectorite, when in contact with dry scCO2. While both independent tests show that cation polarizability is an important factor in smectite-scCO2 systems, the correlations for hectorite are different from those determined for montmorillonite. The root of these differences is likely associated with the roles of the smectite framework on adsorption, warranting follow-up studies with a larger number of unique smectite frameworks. Overall, the results show that the polarizability of the charge-balancing cation should be considered when preparing smectite clays (or industrial processes involving smectites) to capture CO2 and in predicting the behavior of caprocks over time.

Polyoxometalates as chemically and structurally versatile components in self-assembled materials.

Polyoxometalates (POMs) are anionic molecular metal oxides with expansive diversity in terms of their composition, structure, nuclearity and charge. Within this vast collection of compounds are dominant structural motifs (POM platforms), that are amenable to significant chemical tuning with minimal perturbation of the inorganic oxide molecular structure. Consequently, this enables the systematic investigation of these compounds as inorganic additives within materials whereby structure and charge can be tuned independently i.e. [PW12O40]3−vs. [SiW12O40]4− while also investigating the impact of varying the charge balancing cations on self-assembly. The rich surface chemistry of POMs also supports their functionalisation by organic components to yield so-called inorganic–organic hybrids which will be the key focus of this perspective. We will introduce the modifications possible for each POM platform, as well as discussing the range of nanoparticles, microparticles and surfaces that have been developed using both surfactant and polymer building blocks. We will also illustrate important examples of POM-hybrids alongside their potential utility in applications such as imaging, therapeutic delivery and energy storage.

Hydrogen bond network and bond valence analysis on uranyl sulfate compounds with organic-based interstitial cations

Seven new uranyl sulfate compounds with organic charge-balancing cations have been synthesized and structurally characterized. The structural unit topologies of the two chains and five sheets have been previously reported in uranyl sulfate crystal chemistry, although they were synthesized using different organic molecules. With the inclusion of six of these structures to the 48 previously published uranyl sulfate compounds, a total of 54 known uranyl sulfate compounds with organic charge-balancing cations were compiled and analyzed. A graphical approach was used to compare the structural unit topologies, and a bond valence approach was used to quantify the hydrogen bond networks that exist between the interstitial cationic and solvent species to the uranyl sulfate anionic structural units. This analysis helped elucidate which oxygen atoms in the structural unit receive hydrogen bonds and how the organic cations stabilize the overall crystal structures in this subclass of U(VI) materials.

Strain Development of Selective Adsorption of Hydrocarbons in a Cu-ZSM-5 Crystal.

Zeolites are 3D aluminosilicate materials having subnanometer pore channels. The Lewis basic pores have charge-balancing cations, easily tuned to metallic ions as more chemically active sites. Among the ion-exchanged zeolites, Cu2+ ion-exchanged ZSM-5 (Cu-ZSM-5) is one of the most active zeolites with chemical interactions of Lewis basic compounds. Even though the chemical interactions of hydrocarbons with Cu2+ sites in Cu-ZSM-5 have been tremendously studied in the category of zeolite catalysts, it is not yet thoroughly investigated how such interactions affect the structural lattice of the zeolite. Hydrocarbons with different chemical properties and their relative size can induce lattice strain by different chemical adsorption effects on the Cu2+ sites. In this work, we investigate the internal deformation of the Cu-ZSM-5 crystal using Bragg coherent X-ray diffraction imaging during the adsorption of four hydrocarbons depending on the alkyl chain length, the existence of a double bond in the molecule, linear structure versus benzene ring structure, and so forth. In the three-carbon system (propane and propene), relatively weak chemical adsorption occurred at room temperature and 100 °C, whereas strong adsorption was observed over 150 °C. For the six-carbon system (n-hexane and benzene), strong strains evolved in the crystal by active chemical adsorption from 150 °C. The observations suggest that propene and propane adsorb at the Cu2+ sites from the outer shell to the center with increasing temperature. In comparison, n-hexane and benzene adsorb at both parts at the same temperature. The results provide the internal structural information for the lattice with the chemical interactions of hydrocarbons in the Cu-ZSM-5 zeolite and help to understand zeolite-based chemisorption or catalysis research.

Highly selective reduction of biomass-derived furfural by tailoring the microenvironment of Rh@BEA catalysts

Furfural is a renewable lignocellulose-derived platform molecule, which can be transformed into biofuels and value-added chemicals (e.g., furfuryl alcohol and 2-methylfuran over metal-supported catalysts). Despite a number of approaches proposed for designing hydrogenation catalysts, highly selective furfural hydrogenation towards furfuryl alcohol (FA) or 2-methylfuran (2-MF) is still challenging. Here, we report on selective transformation of furfural either to FA or 2-MF achieved over zeolite BEA-supported Rh catalysts by optimizing Si/Al ratio and charge-balancing cations of the support. Among studied H- and Na-exchanged aluminosilicate BEA zeolite supports (Si/Al = 12.5; 25; 68; 150), Rh@Na-BEA catalysts lacking Brønsted and strong Lewis acidity showed enhanced selectivity towards FA (75 – 94% depending on the Si/Al ratio) at 74 – 84% conversion of furfural. In turn, selective formation of 2-MF (98% selectivity at 87% conversion) was observed over Al-rich Rh@H-BEA catalyst (Si/Al=12.5) with the highest concentration of Brønsted acid sites. Weaker adsorption of FA on Na- vs. H-form of Rh@BEA-12.5 catalyst was verified by FTIR spectroscopy and is assumed a key factor governing selective hydrogenation of furfural to FA over Rh@Na-BEA catalysts.