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The location of aluminum in a zeolite framework structure defines the accessibility and geometry of the catalytically active sites, but determining this location crystallographically is fraught with difficulties. Typical zeolite catalysts contain only a small amount of aluminum, and the X-ray scattering factors for silicon and aluminum are very similar. To address this problem, we have exploited the properties of resonant X-ray powder diffraction across the Al K edge, where the aluminum scattering factor changes dramatically. By combining conventional synchrotron powder diffraction data with those collected at energies near the X-ray absorption edge, aluminum is highlighted. In this way, the different distributions of aluminum in two FER-type zeolites with identical chemical compositions but different catalytic properties could be determined unambiguously. The results are consistent with previous studies, but quantitative. This approach constitutes a major advance in our fundamental understanding of the relationship between zeolite structure and catalytic activity.

Zeolite mordenite (MOR) is one of the most studied zeolites for the stepwise direct conversion of methane to methanol, but it also can exist in two forms: large port and small port. Here we report that the synthesis and selection of the parent mordenite is critical for optimizing productivity, and that large-port mordenite outperforms small-port mordenite for the stepwise conversion of methane to methanol., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

The isothermal, low-temperature stepwise conversion of methane to methanol over copper-exchanged zeolites eliminates the time-consuming heating and cooling steps of the conventional high temperature activation approach. To better understand differences between the two approaches, a series of zeolites were screened, of which omega zeolite (MAZ) showed superior performance in both the isothermal and conventional approaches.

Using heavy-atom labeling in conjunction with electron microscopy, we here visualize the distribution of point defects, i.e. internal silanol groups, in silicalite-1 zeolites at the single crystal level.

The application and quantification of in situ copper K-edge X-ray absorption near-edge structure (XANES), when linked to independently made reactor-based studies of methanol production, result in a majority relation between the production of Cu I and methanol from methane that complies with the expectations of a two-electron mechanism founded upon Cu II /Cu I redox couples.

A family of Al-rich ZSM-5 zeolites with Si/Al = 8 ± 0.5 was prepared according to a biomass-mediated supramolecular approach. A combination of advanced characterisation techniques and periodic density functional theory (DFT) calculations unraveled the purity and stability of un-expected Al-enriched ZSM-5 structures, hence allowing to cross the frontier of Si/Al lower limit. In addition, these Al-rich ZSM-5 zeolites demonstrated high catalytic activity in n -hexane cracking and methanol conversion into hydrocarbons, being in line with the presence of numerous Brønsted acid sites.

Electron-diffraction data on the zeolites Silicalite-1 and ZSM-5 (both MFI framework type) were collected from individual grains of about 150×100×50 nm 3 . Crystals were synthesized with tetrapropylammonium as structure-directing agent. The resolution extended to about 0.8 Å for Silicalite-1 and about 0.9-1.0 Å for ZSM-5 crystals. Analysis of several data sets showed that at the nanometre-scale, these zeolite crystals are single crystals and not intergrown., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The potential of valence to core Al X-ray emission spectroscopy to determine aluminum distribution in ferrierite zeolites was investigated. The recorded emission spectra of four samples prepared with different structure directing agents exhibit slight variations in the position of the main emission peak and the intensity of its low energy shoulder. Theoretical calculations indicate that an increased intensity of the Kβ x shoulder in the Al emission spectra can be linked to a predominant occupation of the T3 site by a single aluminum atom. This study thus suggests that valence to core X-ray emission spectroscopy can be applied to help determine the occupation of aluminum at crystallographic T-sites in zeolites.

Copper-containing zeolites exhibit high activity in the direct partial oxidation of methane into methanol at relatively low temperatures. Di- and tricopper species have been proposed as active catalytic sites, with recent experimental evidence also suggesting the possibility of the formation of larger copper oxide species. Using density functional theory based global geometry optimization, we were able to identify a general trend of the copper oxide cluster stability increasing with size. For instance, the identified ground-state structures of tetra- and pentamer copper clusters of Cu n O n 2+ and Cu n O n-1 2+ stoichiometries embedded in an 8-ring channel of mordenite exhibit higher relative stability compared to smaller clusters. Moreover, the aluminium content and localization in the zeolite pore influence the cluster's stability and its geometrical motif, which offers a perspective of tuning the properties of copper-exchanged zeolites by creating copper oxide clusters of a given structure and size. With the activity of the cluster towards methane being connected to its stability, such tuning will potentially allow the design of catalysts with engineered properties.

The disordered intermediate of the ADORable zeolite UTL has been structurally confirmed using the pair distribution function (PDF) technique. The intermediate, IPC-1P, is a disordered layered compound formed by the hydrolysis of UTL in 0.1 M hydrochloric acid solution. Its structure is unsolvable by traditional X-ray diffraction techniques. The PDF technique was first benchmarked against high-quality synchrotron Rietveld refinements of IPC-2 (OKO) and IPC-4 (PCR) - two end products of IPC-1P condensation that share very similar structural features. An IPC-1P starting model derived from density functional theory was used for the PDF refinement, which yielded a final fit of Rw = 18% and a geometrically reasonable structure. This confirms the layers do stay intact throughout the ADOR process and shows PDF is a viable technique for layered zeolite structure determination.

Ceramic cements are good candidates for the stabilization of fractured bone due to their potential ease of application and biological advantages. New formulations of ceramic cements have been tested for their mechanical properties, including strength, stiffness, toughness and durability. The changes in the mechanical properties of a soluble cement (calcium sulfate) upon water-saturation (saturation) was reported in our previous study, highlighting the need to test ceramic cements using saturated samples. It is not clear if the changes in the mechanical properties of ceramic cements are exclusive to soluble cements. Therefore the aim of the present study was to observe the changes in the mechanical properties of soluble and insoluble ceramic cements upon saturation. A cement with high solubility (calcium sulfate dihydrate, CSD) and a cement with low solubility (dicalcium phosphate dihydrate, DCPD) were tested. Three-point bending tests were performed on four different groups of: saturated CSD, non-saturated CSD, saturated DCPD, and non-saturated DCPD samples. X-ray diffraction analysis and scanning electron microscopy were also performed on a sample from each group. Flexural strength, effective flexural modulus and flexural strain at maximum stress, lattice volume, and crystal sizes and shape were compared, independently, between saturated and non-saturated groups of CSD and DCPD. Although material dissolution did not occur in all cases, all calculated mechanical properties decreased significantly in both CSD and DCPD upon saturation. The results indicate that the reductions in the mechanical properties of saturated ceramic cements are not dependent on the solubility of a ceramic cement. The outcome raised the importance of testing any implantable ceramic cements in saturated condition to estimate its in vivo mechanical properties., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Advances in materials synthesis bring about many opportunities for technological applications, but are often accompanied by unprecedented complexity. This is clearly illustrated by the case of hierarchically organized zeolite catalysts, a class of crystalline microporous solids that has been revolutionized by the engineering of multilevel pore architectures, which combine unique chemical functionality with efficient molecular transport. Three key attributes, the crystal, the pore and the active site structure, can be expected to dominate the design process. This review examines the adequacy of the palette of techniques applied to characterize these distinguishing features and their catalytic impact.

A literature survey reveals a prominent reduction in the concentration of Brønsted acid sites in hierarchically organized zeolites with increasing mesoporous or external surface area independent of the framework type or synthesis route; this suggests a common fundamental explanation. To determine the cause, nature, and impact of the underlying changes in aluminum speciation, this study combines a multitechnique analysis that integrates basic characterization, a detailed synchrotron XRD and multiple-quantum NMR spectroscopy assessment, and catalytic tests to correlate evolution of the properties with performance during successive steps in the preparation of hierarchical MFI-type zeolites by desilication. The findings, subsequently generalized to FAU- and BEA-type materials, identify the crucial impact of calcination on the protonic form, which is an integral step in the synthesis and regeneration of zeolite catalysts; on aluminum coordination; and the associated acidity trends., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The germanosilicate ITQ-24 (IWR framework type) was synthesized in fluoride medium using 1,3,5-tris(1,2-dimethylimidazolium) benzene as the structure directing agent (SDA). A structure analysis of the as-synthesized ITQ-24 material using synchrotron powder diffraction data and difference electron density calculations have allowed the fluoride ions and the germanium atoms to be located and the conformation of the SDA to be determined. The benzyl ring is perpendicular to the b axis with the three imidazolium moieties forming a "T-shaped" arrangement. Ge atoms replace some of the Si in the double-4-ring (d4r) and in one of the single-4-rings (s4r). The other s4r contains only Si. Fluoride ions are in the d4r units. Initially, the space group Cmmm (highest possible symmetry) was assumed, but the framework geometry was strained. An independent evaluation of the symmetry using the powder charge flipping algorithm in Superflip led to a successful refinement with reasonable geometry and a refined composition of |[(C6H3)(C7H10N2)3]2F2|[Si(40.2)Ge(15.8)O112] in the space group Pban.

Zeolites are important materials whose utility in industry depends on the nature of their porous structure. Control over microporosity is therefore a vitally important target. Unfortunately, traditional methods for controlling porosity, in particular the use of organic structure-directing agents, are relatively coarse and provide almost no opportunity to tune the porosity as required. Here we show how zeolites with a continuously tuneable surface area and micropore volume over a wide range can be prepared. This means that a particular surface area or micropore volume can be precisely tuned. The range of porosity we can target covers the whole range of useful zeolite porosity: from small pores consisting of 8-rings all the way to extra-large pores consisting of 14-rings., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Hydrolysis of germanosilicate zeolites with the IWW structure shows two different outcomes depending on the composition of the starting materials. Ge-rich IWW (Si/Ge=3.1) is disassembled into a layered material (IPC-5P), which can be reassembled into an almost pure silica IWW on treatment with diethoxydimethylsilane. Ge-poor IWW (Si/Ge=6.4) is not completely disassembled on hydrolysis, but retains some 3D connectivity. This structure can be reassembled into IWW by incorporation of Al to fill the defects left when the Ge is removed., (© 2014 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.)

Herein, the first comparison of the mechanisms of glucose-to-fructose isomerization in aqueous media enabled by homogeneous (CrCl3 and AlCl3 ) and heterogeneous catalysts (Sn-beta) by using isotopic-labeling studies is reported. A pronounced kinetic isotope effect (KIE) was observed if the deuterium label was at the C2 position, thus suggesting that a hydrogen shift from the C2 to C1 positions was the rate-limiting step with the three catalysts. (13) C and (1) H NMR spectroscopic investigations confirmed that an intra-hydride-transfer reaction pathway was the predominant reaction channel for all three catalysts in aqueous media. Furthermore, the deuterium atom in the labeled glucose could be mapped onto hydroxymethylfurfural and formic acid through reactions that followed the isomerization step in the presence of Brønsted acids. In all three catalysts, the active site appeared to be a bifunctional Lewis-acidic/Brønsted-basic site, based on a speciation model and first-principles calculations. For the first time, a mechanistic similarities between the homogeneous and heterogeneous catalysis of aldose-to-ketose isomerization is established and it is suggested that learning from homogeneous catalysis could assist in the development of improved heterogeneous catalysts., (Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Proper combination of template and optimized reaction conditions provides zeolite FER with homogeneous distribution of Al in the framework; this results in a new zeolite adsorbent exhibiting a constant heat of CO(2) adsorption.

Zn atoms have been incorporated into the STA-1 microporous framework (SAO framework type) for the first time. Pure Zn-containing STA-1 aluminophosphate has been obtained in the presence of either (S)-(-)-N-benzylpyrrolidine-2-methanol (BPM) or benzylpyrrolidine (BP) as structure-directing agent. Characterisation results have demonstrated that the organic molecules remain intact within the microporous framework after the hydrothermal treatment. The X-ray diffraction pattern has been indexed in the tetragonal space group I ̅4m2 (a = 13.7828(1) Å and c = 21.9444(4) Å). Chemical analysis and (31)P MAS NMR spectroscopy confirm the incorporation of ca. 4.5 Zn atoms per unit cell by isomorphous substitution of Al. This large-pore aluminophosphate has one of the lowest framework densities among the known zeolite structures, and is therefore of potential interest for applications in adsorption or catalytic processes involving bulky molecules., (This journal is © The Royal Society of Chemistry 2011)

A computational study is performed to rationalize the effect of the organic template molecules used in the synthesis of zeolites on their catalytic behaviour. Apart from being structure-directing, these molecules influence the location of heteroatoms. Molecules bearing acidic protons susceptible to forming H-bonds with framework oxygens show the strongest dopant-siting direction.

Fluorescence spectroscopy and a range of computer simulation techniques are used to study the structure directing effect of benzylpyrrolidine (BP) and (S)-(-)-N-benzylpyrrolidine-2-methanol (BPM) in the synthesis of nanoporous aluminophosphate frameworks with AFI (one-dimensional channels) and SAO (three-dimensional interconnected channels) topologies. We study the supramolecular chemistry of BP and BPM molecules in aqueous solution and compare it with the aggregation state of the molecules found when they are inside the AlPO nanopores after crystallization. The aggregation of the molecules within the structures can be explained by a combination of thermodynamic and kinetic effects. The former are given by the stability of the molecular species interacting with the oxide networks relative to their stability in solution; the latter depend on the aggregation behavior of the molecules in the synthesis gels prior to crystallization. Whereas BPM only forms one type of aggregate in solution, which has the appropriate conformation to match the empty channels of the forming nanoporous frameworks, BP forms aggregates with different molecular orientations, of which only one matches the framework interstices. This different supramolecular chemistry, together with the higher interaction of BPM with the oxide networks, makes BPM a better structure directing agent (SDA); it is also responsible for the higher incorporation of BPM as dimers in the frameworks, especially in the AFI structure, observed experimentally. The concentration of the SDA molecules in the gels, and so the density per volume of the SDAs, determines the exclusion zone from which the pores and/or cavities of the framework will arise, and so the porous network of the formed material. A clear relationship between the SDA density in solution and in the framework is observed, thus enabling an eventual control of the material density by adjusting the SDA concentration in the gels. The topological instability intrinsic to these open framework structures is compensated by a high host-guest interaction energy; the SAO topology is further stabilized by doping with Zn. Our computational results account for and rationalize all the effects observed experimentally, providing a complete picture of the mode of structure direction of these aromatic molecules in the synthesis of nanoporous aluminophosphates.

Zeolites synthesis using a combination of tetraethylammonium hydroxide (TEAOH) and 1,6-diaminohexane (DAH) as organic structure-directing agents (OSDAs) has been studied in order to understand how they acted during the synthesis. This combination can crystallize four zeolites: beta, ZSM-12, ZSM-48, and silicalite-1. TEAOH is found to direct the synthesis of beta, and ZSM-12 zeolites, whereas DAH directs the synthesis of ZSM-48 zeolite. On the other hand, the two organic components are found to have a cooperative role in the crystallization process of silicalite-1, with greater templating ability for TEAOH compared to DAH. The use of a supplementary organic component does not affect the degree of filling of the primary OSDA in the structure or the morphology of the obtained zeolites. The carbon dioxide (CO2) adsorption capacity of the zeolites obtained was evaluated at a temperature of 293 K in a pressure range of 0 to 1 atm. The relationship between the surface properties of the zeolites and their adsorption behavior was studied. Beta zeolite had the highest adsorption capacity with 2.9 mmol/g, while ZSM-48 zeolite had the lowest adsorption capacity with only 0.7 mmol/g. [ABSTRACT FROM AUTHOR]

The introduction of an oxime group into indirubin (INR) derivatives, including INROx, MINROx, and 6-BrINROx, and its impact on the spectral and photophysical properties of INR was investigated using a combination of fast-transient absorption (fs-TA/fs-UC) and steady-state fluorescence techniques. The oxime group introduces structural modifications that promote a rapid keto–enol tautomeric equilibrium and enhance the excited-state proton transfer (ESPT) process compared to its analogue, INR. In the oxime–indirubin derivatives investigated, the ESPT process is notably more efficient than what is observed in INR and indigo, occurring extremely fast (<1 ps) in all solvents, except for the viscous solvent glycerol. The more rapid deactivation mechanism precludes the formation of an intermediate species (syn-rotamer), as observed with INR. These findings are corroborated by time-dependent density functional theory (TDDFT) calculations. The work demonstrates that introducing an oxime group to INR, whether in nature or in the laboratory, results in an enhancement of its photostability. [ABSTRACT FROM AUTHOR]

Nanocomposites are emerging as a new generation of materials that can be used to combat water pollution. Zeolite-based nanocomposites consisting of combinations of metals, metal oxides, carbon materials, and polymers are particularly effective for separating and adsorbing multiple contaminants from water. This review presents the potential of zeolite-based nanocomposites for eliminating a range of toxic organic and inorganic substances, dyes, heavy metals, microplastics, and ammonia from water. The review emphasizes that nanocomposites offer enhanced mechanical, catalytic, adsorptive, and porosity properties necessary for sustainable water purification techniques compared to individual composite materials. The adsorption potential of several zeolite-metal/metal oxide/polymer-based composites for heavy metals, anionic/cationic dyes, microplastics, ammonia, and other organic contaminants ranges between approximately 81 and over 99%. However, zeolite substrates or zeolite-amended soil have limited benefits for hyperaccumulators, which have been utilized for phytoremediation. Further research is needed to evaluate the potential of zeolite-based composites for phytoremediation. Additionally, the development of nanocomposites with enhanced adsorption capacity would be necessary for more effective removal of pollutants. [ABSTRACT FROM AUTHOR]

Although expensive, rare-earth oxides are well known for being powerful defluoridation agents. Being costlier, cerium is used as a hybrid adsorbent in conjunction with a prudent and environmentally benign substance like biochar. The novel CeO2/BC (surface area 260.05 m2/g) composite was shaped using the facile chemical precipitation technique without any cross-linkers. Surface properties of synthesised CeO2/BC were investigated using powder XRD, FTIR, BET, pH point of zero charge and SEM. According to XRD analysis, immobilized Ce is primarily in form of CeO2, while pristine biochar is in an amorphous state. Batch mode adsorption tests were carried out with different solution pH, F− initial concentration, adsorbent dosage and contact time and counter anions. CeO2/BC can be used in a varied pH range (2–10) but shows maximum removal at pH 4. The Langmuir adsorption isotherm and a pseudo-second-order kinetic model are best fitted to support the adsorption process with a maximum Langmuir adsorption capacity of 16.14 mg/g (F− concentration 5 to 40 mg/L). The removal phenomenon is non-spontaneous in nature. The plausible mechanism of fluoride uptake was explained using XPS and pHPZC, and it was demonstrated that the fluoride was mainly removed by ion exchange and electrostatic attraction. The adsorbent could be successfully used up to fourth cycle after regenerating. [ABSTRACT FROM AUTHOR]

Apple pomace is a waste stream produced by fruit processing industry millions of tons annually. It is rich in carbohydrates making it a potential feedstock for the production of 5-hydroxymethylfurfural (HMF), one of the most valuable platform chemicals. In this work, the conversion of apple pomace carbohydrates to HMF was studied in a choline chloride:glycolic acid (1:3) deep eutectic solvent. To prevent undesired side reactions of HMF methyl isobutyl ketone was added to the reaction system as an extractive phase. The effect of reaction conditions, i.e., the amount of water added to the reaction system, the presence of Lewis acid co-catalyst, as well as the reaction temperature and time, on HMF yield were studied. The highest total HMF yield (44.5%) was achieved at 110 °C in 10 min with 15 wt% H2O, and 0.01 g CrCl3 as co-catalyst. Without the co-catalyst, the highest achieved HMF yield was 37.3% (120 °C, 20 min, 15 m% H2O). The results indicated that apple pomace can be used as the feedstock for HMF production but the reaction procedure, especially the extraction process of HMF from deep eutectic solvent needs to be studied further. [ABSTRACT FROM AUTHOR]

Owing to the intrinsic signal noise in the characterization of chemical structures through Fourier transform infrared (FT-IR) spectroscopy, the determination of the signal-to-noise ratio (SNR) depends on the level of the concentration of the chemical structures. In situations characterized by limited concentrations of chemical structures, the traditional approach involves mitigating the resulting low SNR by superimposing repetitive measurements. In this study, we achieved comparable high-quality results to data scanned 64 times and superimposed by employing machine learning algorithms such as the principal component analysis and non-negative matrix factorization, which perform the dimensionality reduction, on FT-IR spectral image data that was only scanned once. Furthermore, the spatial resolution of the mapping images correlated to each chemical structure was enhanced by applying both the machine learning algorithms and the Gaussian fitting simultaneously. Significantly, our investigation demonstrated that the spatial resolution of the mapping images acquired through relative intensity is further improved by employing dimensionality reduction techniques. Collectively, our findings imply that by optimizing research data through noise reduction enhancing spatial resolution using the machine learning algorithms, research processes can be more efficient, for instance by reducing redundant physical measurements. [ABSTRACT FROM AUTHOR]

Compared with the conventional microporous FER zeolite, FER nano-sheets could reduce the diffusional path lengths, increase the active catalytic sites and prolong the catalytic life. Hierarchically porous FER nano-sheets were prepared by using piperidine and cetyltrimethylammonium bromide (CTABr) as the dual-templates, aided with crystalline seeds. The addition of seeds to the synthesis system effectively reduced the amount the templates and shortened the crystallization time. The prepared FER zeolite exhibited nano-sheet morphology, with the thickness of the nano-sheets less than 20 nm. The FER nano-sheets possessed aggregated meso/macropore volume of larger than 0.5 cm3·g− 1 and external surface area higher than 100 cm2·g− 1, giving excellent catalytic LDPE cracking performance by greatly reducing the cracking temperature. This method is fast, facile and cost-effective, and can be easily scale-up, possessing wide potentials in the industrial processes. [ABSTRACT FROM AUTHOR]

In this work, we present the results of the ortho-positronium (o-Ps) annihilation lifetimes and nitrogen adsorption measurements for different porous materials and an approach for describing the annihilation of o-Ps in a pore, which results in a surface-volume formula (SVF) for calculating the pore-related o-Ps lifetime. This proposed formula gives the relationship between the o-Ps annihilation rate and the effective pore radius, bulk composition, and pore structure, including pore geometry and topology. The pore-related o-Ps lifetimes of different materials calculated by the SVF are consistent with experimental results for both micro- and mesopores (and macropores) with different geometries and topologies. The SVF is convenient for calculations of pore dimensions for many cases of metal organic frameworks and zeolites. This approach enables us to fully explain the temperature dependence of the o-Ps annihilation lifetime over a wide temperature range, 20–700 K. [ABSTRACT FROM AUTHOR]

BACKGROUND: Grand efforts have been recently devoted to the development of catalysts based on the excellent performance of Cu‐ and Fe‐dependent enzymes in methanotrophic bacteria for the partial oxidation of methane to methanol under ambient conditions. As a continuation of the study on the stepwise manner for this conversion over zeolite‐based catalysts, in this work, the effects of zeolite topology and activation temperature on the catalytic performance of Cu‐ and Fe‐containing zeolites were investigated. RESULTS: Cu species exchanged in the medium‐pore zeolites (mordenite, ZSM‐5, and ferrierite) afforded better methanol production, while large‐pore zeolites (zeolite β and zeolite γ) were inappropriate to accommodate active Cu sites. Notably, Cu/silicalite‐1 containing CuO species was also reactive to methane after the activation in O2, yielding a minor methanol amount. Furthermore, the activity of Fe/mordenite towards the methanol in the O2‐assisted procedure was reported for the first time but with a much lower yield as compared to that of Cu/mordenite. The methanol yield over Cu/mordenite increased with the activation temperature because increasing the activation temperature favored the Cu‐exchange degree with a higher priority at the side pockets as compared to the main channels of mordenite, as evidenced from infrared analysis. CONCLUSION: The selective oxidation of methane to methanol by O2 via a stepwise manner can be obtained over both ion‐exchanged Cu species and well‐dispersed CuO nanoparticles with better activity being recorded for the former. The activity of Cu‐exchanged zeolites was considerably dependent on the zeolite topology and the charge‐balancing position of the Cu2+ cations. © 2023 Society of Chemical Industry (SCI). [ABSTRACT FROM AUTHOR]

The dynamics of H2O molecules confined in mesopores of about 3.4 nm in size, formed by amorphous SiO2 pillars separating 2D mordenite nanolayers, was probed by 1H nuclear magnetic relaxation. 1H nuclear magnetic resonance (NMR) spectra evidence the presence of water with different local surroundings and mobility. The temperature dependence of 1H spin–lattice relaxation T1 and relaxation in rotating frame T1ρ indicate the complex behavior of nanoconfined water that can be characterized by different activation energies: freezing (29 kJ/mol), fast rotation (12 kJ/mol), and translational motion (23.6 kJ/mol). [ABSTRACT FROM AUTHOR]

As a well‐known porous inorganic material formed of aluminosilicate structures, Zeolit Socony Mobil Number 5 (ZSM‐5) zeolite has been widely used for various applications, especially oil‐chemical conversion processes and environmental pollution treatment. This study provides an overview of the natural sources as well as the role and categorization of structural compounds used for the synthesis of ZSM‐5. Overall, clay, natural minerals, or leftovers from agricultural and industrial activities (all of which offer several advantages, such as low cost, availability, and environmental friendliness) have been used to manufacture ZSM‐5. Moreover, green structural directing agents (known as soft templates) have been increasingly employed to replace pure chemicals in the production of ZSM‐5, aiming to decrease unexpected effects on the environment. This research orientates the production of ZSM‐5 zeolite on a low‐cost and environmentally friendly industrial scale. © 2023 Society of Chemical Industry (SCI). [ABSTRACT FROM AUTHOR]

The fluidized catalytic cracking (FCC) process converts heavy petroleum fractions into lighter hydrocarbons for use as fuels and petrochemicals. Even though it is a mature process, several improvements have been achieved by FCC catalyst development. Here, we study the cracking of n-butyl-cyclohexane (nC4CyC6) to establish a model catalytic test for fresh and deactivated catalysts. We propose a test to be carried out in a fixed-bed reactor at 500 °C with online analysis of products. Simple parameters are defined to classify products of side-chain cracking, ring-opening, and hydrogen-transfer (HT) reactions. Fresh zeolites (H-ZSM-5, H-Beta and H-USY) were tested. Their performances were consistent with their characteristics: the H-ZSM-5 showed the lowest activity and gave mainly cracked products from side-chain cracking. H-Beta and H-USY gave products from both side-chain cracking and ring-opening. H-USY was more active to HT, yielding more aromatics compared to H-Beta. The advantage of the model testing was demonstrated using deactivated USY and also equilibrium FCC catalysts (E-Cats). The nC4CyC6 test was sensitive to deactivated USY and showed 20-fold higher activity than n-hexane cracking. The results of the activity and hydrogen transfer capacity of 2 E-Cats revealed by the model nC4CyC6 test showed the same tendency obtained from the micro-activity test with real feed. Hence, this new model test has good potential for practical screening of FCC catalysts. [ABSTRACT FROM AUTHOR]

Diffusion is an extremely critical step in zeolite catalysis that determines the catalytic performance, in particular for the conversion of bulky molecules. Introducing interconnected mesopores and macropores into a single microporous zeolite with the rationalized pore size at each level is an effective strategy to suppress the diffusion limitations, but remains highly challenging due to the lack of rational design principles. Herein, we demonstrate the first example of boosting molecular diffusion by constructing hierarchical Murray zeolites with a highly ordered and fully interconnected macro–meso–microporous structure on the basis of the generalized Murray's Law. Such a hierarchical Murray zeolite with a refined quantitative relationship between the pore size at each length scale exhibited 9 and 5 times higher effective diffusion rates, leading to 2.5 and 1.5 times higher catalytic performance in the bulky 1,3,5-triisopropylbenzene cracking reaction than those of microporous ZSM-5 and ZSM-5 nanocrystals, respectively. The concept of hierarchical Murray zeolites with optimized structural features and their design principles could be applied to other catalytic reactions for maximized performance. [ABSTRACT FROM AUTHOR]

Hierarchical H/ZnZSM-5 was synthesised and tested to study the effect of modifying the catalyst with Zn in the aromatisation of propane using a fixed bed microreactor. Characterisation of the samples was done with FTIR, Raman spectroscopy, XRF, XRD, BET, N2 adsorption study and TEM. Based on the XRD and BET results, synthesised hierarchical H/ZnZSM-5 with 2 % zinc loading was the best, with a percentage crystallinity of 85.4 % and surface area of 405.97 m2/g, and hierarchy factor of 0.14. TEM results showed the mesoporous nature of the synthesised catalyst, and the peak at the Raman shift of 1645 cm− 1 confirmed the modification with Zn. Propane aromatisation performance evaluation of the synthesised catalyst samples was done in a fixed bed reactor, and the products were analysed with the aid of online gas chromatography (GC). The results showed that conversion was not significantly altered with increasing zinc loading. In contrast, selectivity of aromatics increased with an increase in zinc loading, reaching a maximum of about 62.7 % for 2 % zinc loading and dropping to 42.4 % for 3 % loading of zinc. The characterisation and performance test results indicated that 2 % zinc loading is the best catalyst. [ABSTRACT FROM AUTHOR]

Silicoaluminophosphate (SAPO) zeolites are well-known catalytic materials because of the mild acidity originating from the isolated SiO4 tetrahedra in their frameworks. Regulating the distribution of isolated SiO4 tetrahedra in SAPO zeolites is formidably challenging because SiO4 tetrahedra tend to agglomerate to form Si islands and the isolated SiO4 tetrahedra are difficult to determine using conventional characterization techniques. Here we synthesized Si-island-free SAPO-35 zeolites by using N -methylpiperidine as a new template, which exhibited excellent thermal stability compared to conventional SAPO-35 zeolites and a substantially improved methanol-to-olefins catalytic lifetime even comparable to that of commercial SAPO-34 zeolites. More strikingly, with the aid of high-throughput computations on 44   697 structure models combined with various state-of-the-art characterization techniques, for the first time, we reveal that the host–guest interactions between template molecules and SAPO frameworks determine the specific distributions of isolated SiO4 tetrahedra, which are responsible for the improvement in the chemical properties of zeolites. Our work provides an insight into the template-based regulation of isolated SiO4 tetrahedra in SAPO zeolites, which opens a new avenue in the discovery of promising zeolite catalysts with optimal SiO4 distribution. [ABSTRACT FROM AUTHOR]

The rational design synthesis of zeolite catalysts with effective, environmentally benign and atom-economic routes is a major topic in the field of microporous materials, as it would avoid the high labor cost and inefficiency of traditional trial-and-error methods in developing new structures and dispel environmental concerns regarding the industrial mass production of zeolites. Catalytic applications of zeolite materials have expanded from conventional single functionalities, such as solid acids or selective oxidation catalysts to bi/multifunctionalities through combination with metals or metal oxides. This is a response to new requirements from petrochemical and fine chemical industries, such as precise control of product distribution, conversion of low-carbon resources for chemical production, and solutions to increasingly severe environmental problems related to CO2 and NOx. Thus, based on the systematic knowledge of zeolite chemistry and science that researchers have acquired in the past half-century and the development requirements, remarkable progress has been made in zeolite synthesis and catalysis in the past 10 years. This includes the manipulation of zeolitic monolayers derived from layered zeolites and germanosilicates to construct novel zeolite materials and effective and green zeolite syntheses as well as the synergistic interaction of zeolites and metal/metal oxides with different space distributions in the conversion of low-carbon resources. With many zeolite catalysts and catalytic processes being developed, our understanding of the close relationship between zeolite synthesis, structure and catalytic properties has deepened. Researchers are gradually approaching the goal of rationally designing zeolite catalysts with precisely controlled activity and selectivity for particular applications. [ABSTRACT FROM AUTHOR]

In this work, a novel adsorbent of aluminium/lanthanum loaded wheat straw biochar (Al-La-WSB), was prepared by using a facile approach and used for fluoride removal. The Al-La-WSB and its pristine wheat straw biochar (WSB) were characterized by scanning electronic microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), and X-ray powder diffraction (XRD) methods. Batch adsorption experiments were carried out to investigate adsorbent performance, the highest removal rate was observed at pH 9, contact time of 7 h and Al-La-WSB dose of 1 g L−1. Lagergren pseudo-second-order kinetics and Langmuir isotherm model fitted the experimental data well. The maximum fluoride adsorption capacity of Al-La-WSB at different experiment temperature of 298, 308 and 318 K, was 51.28 mg g–1, 46.73 mg g–1 and 50.25 mg g–1, respectively, which was better than most reported adsorbents. The Al-La-WSB performed well over a considerable wide pH range of 3–10 and carried positive charge at pH < 4.8. The presence co-existing ions of SO42−, HCO3−, Cl− and NO3− had a minor impact on fluoride adsorption besides PO43−. Regeneration experiment results showed that the Al-La-WSB had an excellent reusability. According to the adsorbent characterization and batch adsorption experiment, the adsorption of fluoride on the Al-La-WSB was primarily a chemisorption, involving electrostatic interactions and ion exchange, which nitrate ion and hydroxyl played a major role. The results suggested that the Al-La-WSB could be a great adsorbent for removing fluoride from drinking water. [ABSTRACT FROM AUTHOR]

In the current period, there is a high demand for the production of liquid fuel which is used for transport purposes all over the world. Therefore, the conversion of methane to methanol fuel is reported as an alternative option for natural gas. Some approaches such as the two-step syngas process, direct single step, and bacterial agent catalyzed reaction use steam reform of methane, methane oxidation processes (via methane selectivity), and methane gaseous form (via methane monooxygenase enzymes) respectively to produce methanol fuel from methane. Also, chemical routes have applied high temperature/pressure catalytic conversion of syngas to methanol. Most conventional approaches discussed are gas to liquid technologies that exploit and monetize nontraditional methanol sources. The utility of methanol as liquid fuel is discussed and now researchers have invented the greatest potential of methanol as a robust product that is produced or synthesized by using a commercial scale conversion process from methane. Normal conversion for methane to methanol via chemical routes is exploited by high temperature and pressure as an energy-intensive process. However, the biological modes of conversion of methane to methanol occur by using methanotrophic bacteria, exhibiting desired transformation capacity at ambient conditions via methane monooxygenase enzyme. Biotechnological modes of conversion have shown the potentiality for their application in an industrially relevant process in eco-friendly ways. Some approaches of biotechnological modes of conversion of methane to methanol by whole-cell, wild-type, and methanotroph cultures are discussed along with many chemical route approaches. In this paper, the authors emphasize the different chemical and biological approaches for methane to methanol conversion with their limitations and applications. [ABSTRACT FROM AUTHOR]

Cu-containing Beta zeolites (Cu-Beta) are straightforwardly synthesized in a one-pot method without template, where the crucial step is the co-hydrolysis/condensation of silica source and copper salt at the moderate acidic condition. In the solvent-free oxidation of cyclohexane with molecular oxygen (O2), the best cyclohexane conversion result (9.7%) with a KA-oil (cyclohexanone and cyclohexanol) selectivity of 94.1% is obtained over Cu-Beta(100). Structure—activity relationship analysis indicates that the isolated tetrahedral framework Cu2+ species and chemisorption oxygen species in high concentration on the catalyst surface enhannce the catalic performance. In addition, the catalyst can be easily separated and still remain stable after recycling five times, providing new insights into catalysts design for the catalytic oxidation of cyclohexane to KA-oil. [ABSTRACT FROM AUTHOR]

A simple and efficient biphasic system comprising H2O, tetrahydrofuran (THF), cyclohexane (CHX) and Al2(SO4)3 was employed to convert cellulose into 5-hydroxymethylfurfural (HMF). The volume ratio of the organic phase to the aqueous phase (Vorg/Vaque), concentration of Al2(SO4)3 in the aqueous phase (C[Al2(SO4)3]aque) and concentration of Al2(SO4)3 in the organic phase (C[Al2(SO4)3]org) of the biphasic system played critical roles in the conversion of cellulose into HMF. In the biphasic systems with H2O/THF/Al2(SO4)3 of 4/18/0.4 and H2O/THF/CHX/Al2(SO4)3 of 3/16/3/0.4, > 80% of the added H2O was dissolved in the organic phase, whereas most of the added Al2(SO4)3 remained in the aqueous phase under the reaction temperature, jointly leading to high Vorg/Vaque, high C[Al2(SO4)3]aque and low C[Al2(SO4)3]org in the biphasic system. All of these results yield the excellent performance of these biphasic systems in the conversion of cellulose into HMF. The addition of CHX into the biphasic system can decrease the solubility of Al2(SO4)3 in the organic phase, thus improving the stability of HMF in the reaction system. The influences of catalyst usage, reaction temperature and time, and cellulose/solvent ratio were all explored, and a high HMF yield of 71.2% was obtained in the H2O–THF–CHX biphasic system with an H2O/THF/CHX volume ratio of 3/16/3 under optimized conditions. [ABSTRACT FROM AUTHOR]

Heterogeneous tin-based sulfonated graphite (Sn-GP) catalyst was prepared with graphite as carrier. The physicochemical properties of Sn-GP were captured by FT-IR, XRD, SEM and BET. Organic acids with different pKa values were used to assist Sn-GP for transforming corncob (CC), and a linear equation (Furfural yield = − 7.563 × pKa + 64.383) (R2 = 0.9348) was fitted in acidic condition. Using sugarcane bagasse, reed leaf, chestnut shell, sunflower stalk and CC as feedstocks, co-catalysis of CC (75.0 g/L) with maleic acid (pKa = 1.92) (0.5 wt%) and Sn-GP (3.6 wt%) yielded the highest furfural yield (47.3%) for 0.5 h at 170 °C. An effective furfural synthesis was conducted via co-catalysis with Sn-GP and maleic acid. Subsequently, E. coli CG-19 and TS completely catalyzed the conversion of corncob-derived FAL to furfurylalcohol and furoic acid, respectively. Valorisation of available renewable biomass to furans was successfully developed in tandem chemoenzymatic reaction. [ABSTRACT FROM AUTHOR]

Synthetic fragrance has dominated the perfumery industry in recent decades due to the ability to produce perfumery ingredients on a large scale at a low cost. Extensive research in the field of synthetic perfumery chemical involved the utilization of catalysts to improve the productivity. This review will discuss recent advances of heterogeneous catalysts for the synthesis of perfumery chemicals as fragrance ingredients. Transition from homogeneous to heterogeneous catalysts will be included in order to provide insight into the benefits of heterogeneous catalysts to overcome the limitation of homogeneous reaction. Isomerization, acetalization and hydrogenation were identified as three main reactions for the synthesis of perfumery chemicals based on the number of reported work since 2000. This review will focus on α‐pinene and α‐pinene oxide as the main molecular substrates, however, different molecules, for example, linalool, citronellal and cinnamaldehyde will also be included. The synthesis, modification and possible mechanisms for the reactions involving zeolite, aluminosilicate, metal oxides, metal organic framework, monometallic and bimetallic nanoparticles as heterogeneous catalysts will be discussed. Discussion on isomerization and acetalization reactions will focus on the acidity and the porosity of the catalysts as the two main factors that determine the conversion and selectivity. For perfumery chemicals produced via hydrogenation reaction, the role of monometallic and bimetallic nanoparticles catalysts will be discussed in the chemoselective reduction of cinnamaldehyde and citronellal. [ABSTRACT FROM AUTHOR]

Background: Over the last few years, valorization of lignocellulosic biomass has been expanded beyond the production of second-generation biofuels to the synthesis of numerous platform chemicals to be used instead of their fossil-based counterparts. One such well-researched example is 5-hydroxymethylfurfural (HMF), which is preferably produced by the dehydration of fructose. Fructose is obtained by the isomerization of glucose, which in turn is derived by the hydrolysis of cellulose. However, to avoid harsh reaction conditions with high environmental impact, an isomerization step towards fructose is necessary, as fructose can be directly dehydrated to HMF under mild conditions. This work presents an optimized process to produce fructose from beechwood biomass hydrolysate and subsequently convert it to HMF by employing homogeneous catalysis. Results: The optimal saccharification conditions were identified at 10% wt. solids loading and 15 mg enzyme/gsolids, as determined from preliminary trials on pure cellulose (Avicel® PH-101). Furthermore, since high rate glucose isomerization to fructose requires the addition of sodium tetraborate, the optimum borate to glucose molar ratio was determined to 0.28 and was used in all experiments. Among 20 beechwood solid pulps obtained from different organosolv pretreatment conditions tested, the highest fructose production was obtained with acetone (160 °C, 120 min), reaching 56.8 g/100 g pretreated biomass. A scale-up hydrolysis in high solids (25% wt.) was then conducted. The hydrolysate was subjected to isomerization eventually leading to a high-fructose solution (104.5 g/L). Dehydration of fructose to HMF was tested with 5 different catalysts (HCl, H3PO4, formic acid, maleic acid and H-mordenite). Formic acid was found to be the best one displaying 79.9% sugars conversion with an HMF yield and selectivity of 44.6% and 55.8%, respectively. Conclusions: Overall, this work shows the feasibility of coupling bio- and chemo-catalytic processes to produce HMF from lignocellulose in an environmentally friendly manner. Further work for the deployment of biocatalysts for the oxidation of HMF to its derivatives could pave the way for the emergence of an integrated process to effectively produce biobased monomers from lignocellulose. [ABSTRACT FROM AUTHOR]

Furfural from biomass such as corncob is an important chemical with wide applications. The current industrial production of furfural uses H2SO4 as catalyst which is highly toxic and corrosive. It was demonstrated that the acidic salt KHSO4 was an effective and safer catalyst for furfural production. The optimum conditions for furfural production from corncob were investigated. The XRD and TG analyses of raw corncob and typical reaction residue were conducted and discussed. Finally, an outlook to the future work was put forward. [ABSTRACT FROM AUTHOR]

The two-region ("Kärger") model of diffusion in complex pore spaces is exploited for quantitating mass transfer in hierarchically organized nanoporous materials, consisting of a continuous microporous bulk phase permeated by a network of transport pores. With the implications that the diffusivity in the transport pores significantly exceeds the diffusivity in the micropores and that the relative population of the transport pores is far below that of the micropores, overall transport depends on only three independent parameters. Depending on their interrelation, enhancement of the overall mass transfer is found to be ensured by two fundamentally different mechanisms. They are referred to as the limiting cases of fast and slow exchange, with the respective time constants of molecular uptake being controlled by different parameters. Complemented with reaction terms, the two-region model may equally successfully be applied to the quantitation of the combined effect of diffusion and reaction in terms of the effectiveness factor. Generalization of the classical Thiele concept is shown to provide an excellent estimate of the effectiveness factor of a chemical reaction in hierarchically porous materials, solely based on the intrinsic reaction rate and the time constant of molecular uptake relevant to the given conditions. [ABSTRACT FROM AUTHOR]

A strategy has been developed for the synthesis of ferrierite (FER) zeolites possessing strong acid sites (SAS) with different strength by using silica sol modified by different amounts of hydrochloric acid (HCl) as silicon source. The effect of HCl-modified silica sol on FER zeolite was investigated by XRD, ICP-AES, SEM, N2 adsorption–desorption, NH3-TPD and Py-IR. Moreover, some typical samples were evaluated in the reaction of 1-butene skeletal isomerization and the coke properties of the deactivated samples were analyzed by TG-MS and Raman spectroscopy. The results revealed that FER zeolite possessing weak SAS has excellent catalytic performance in the reaction of skeletal isomerization of 1-butene. Whereas FER zeolite with moderate SAS exhibits poor stability. By contrast, FER zeolite exhibiting SAS with high strength is easy to promote oligomerization-cracking reaction and reduce isobutene selectivity. Conversely, these findings also confirmed the effectiveness of the strategy for controlling the strength of SAS of FER zeolite. [ABSTRACT FROM AUTHOR]

Carbon dioxide and methane emissions are major greenhouse gases contributing to global warming, thus calling for rapid techniques of sequestration. For instance, dry reforming of methane transforms CO2 and CH4 into syngas, a mixture of H2 and CO, yet the reaction catalyst becomes inactivated by carbon formation and metal sintering. Here, we review catalytic systems used for dry reforming of methane. Improved catalysts of high catalytic performance and stability are obtained by selecting the active metal, supporting materials, promoters and preparation techniques. We found a strong correlation between the support morphology, physicochemical properties and catalytic performances. In particular, fibrous structures show optimal metal–support interaction, distribution, particle size, basicity, storage of oxygen space, surface area and porosity, resulting in high performance of anti-coking and anti-sintering. [ABSTRACT FROM AUTHOR]