Tetrahedral Species Research Articles

Effect of Surface Tungstate W5+ Species on the Metathesis Activity of W-Doped Spherical Silica Catalysts

The high surface area W-doped spherical silica (SSP) catalysts were prepared with different sequences of W and Si addition (W–Si(Alt), Si1–W2, and W1–Si2) by the sol–gel method with CTAB as a structure directing agent and compared with the impregnated one (W/SSP). All the catalysts exhibited high specific surface area (∼ 1100 m2 g−1) with a closely perfect spherical shape. The presence of surface/sub-surface tungstate W5+ species, crystalline bulk WO3, and tetrahedral tungsten oxide species on the prepared catalysts was investigated by means of X-ray photoelectron spectroscopy depth profile analysis, X-ray diffraction, and Raman spectroscopy. Without in situ reduction by the reactants/products, tungstate W5+ species was found on the top surface of the as-prepared W–Si(Alt) whereas for the Si1–W2, W/SSP, and W1–Si2, the W5+ appeared only on the sub-surface of the catalysts after 5 and 15 s Ar+ etching. The abundance of surface W5+ species is suggested to facilitate the establishment of the active tungsten carbenes and was correlated well to the catalytic activity in propene metathesis. The surface W5+-activity relationship of the WO3-based metathesis catalysts is useful especially when the catalyst activity did not depend solely on the amount of active tetrahedral coordinated tungsten oxides.

Choreographing boron-aluminum acidity and hierarchical porosity in *BEA zeolite by in-situ hydrothermal synthesis for a highly selective methanol to propylene catalyst

A successful incorporation of boron into *BEA zeolite framework has been achieved using a in situ hydrothermal synthesis in the presence of aluminum-*BEA seeds. Interestingly, the boron-*BEA crystals exhibited a cubic morphology with a remarkable decrease in the crystal size as compared with Al-*BEA seeds. The effect of boron addition on *BEA zeolite acidity was investigated by NH3-TPD and pyridine FTIR. The type of boron coordination in the framework of *BEA zeolite was observed by 11B MAS NMR. The results confirmed the formation of tetrahedral (BO4) and trigonal (BO3) boron species. The catalyst with highest boron content (Si/B = 6) showed the best catalytic transformation of methanol to olefins and the lowest deactivation rate. Moreover, it showed the highest propylene selectivity of 60% as well as the highest propylene-to-ethylene ratio (P/E) of 7.5.

Deep oxidative desulfurization with simultaneous oxidative denitrogenation of diesel fuel and straight run gas oil

High levels of sulfur organic compounds (SOCs) and nitrogen organic compounds (NOCs), which are contaminants present in diesel fuel and straight run gas oil (SRGO), were removed using tungsten/zirconia catalysts and hydrogen peroxide by oxidative desulfurization and oxidative denitrogenation reactions. Two tungsten sources were used: tungstic acid and ammonium metatungstate. The catalysts obtained by anionic exchange at low pH with tungstic acid showed remarkable homogeneity and high W dispersion attributed to tetrahedral W species and full dibenzothiophene (DBT) oxidation was achieved in 5 min of reaction. On the other hand, the catalysts obtained by impregnation with ammonium metatungstate developed mainly octahedral species with less DBT oxidation. It was also found that tetrahedral species generate more acidity than octahedral species. A density functional theory computational study confirmed the observed DBT oxidation trend shown by tetrahedral and octahedral W species on the peroxide-activated catalysts. Diesel fuel and SRGO were desulfurized and denitrogenated to a high extent: 97% in diesel fuel and 70% in SRGO for sulfur compounds and 96% in diesel fuel and 89% in SRGO for nitrogen compounds, whereas C1–C3 dibenzothiophenes, 4-methyl dibenzothiophene, and 4,6-dimethyl dibenzothiophene were fully removed. The elimination of SOCs and NOCs present in fuels can be effectively carried out in a single process to obtain clean fuels.

Corrosion Inhibition Study of Aqueous Vanadate on Mg Alloy AZ31

Corrosion inhibition of AZ31 Mg alloy with aqueous vanadate was studied and has been attributed to the pH dependence of vanadate speciation. Immersion in tetrahedral coordinated vanadate species, present in neutral and alkaline solution, was shown to decrease corrosion current density and increase the breakdown potential, both of which were enhanced with longer immersion times. Exposure to octahedral coordinated vanadate, predominant in acidic solution, only slightly decreased corrosion current density. An acidic solution was adjusted to alkaline conditions and samples were immersed in the adjusted alkaline solution. Inhibition of these samples was weaker than that of samples immersed in initially alkaline solutions. Anodic inhibition was observed on samples treated in solutions containing tetrahedral species. SEM images showed that vanadate formed a film across secondary particles and the Mg matrix, and provided qualitative evidence that inhibition efficiency increased as the pH increased. XPS results indicated that film formation was associated with the reductive adsorption of vanadium oxoions. Exposure at pH 5.0 produced a film predominated by V4+. Exposure at pH values of 7.7 and higher, however, produced a film containing predominantly V3+. Raman analysis confirmed the formation of a vanadate film on the Mg surface after exposure at all pH values.

Template‐Free Synthesis of High‐Content Vanadium‐Doped ZSM‐5 with Enhanced Catalytic Performance

AbstractThe high cost of preparation of transition metal doped ZSM‐5 zeolite is limited to the use of organic template such as tetrapropylammonium hydroxide or tetrapropylammonium bromide. In this work, vanadium atom was successfully incorporated into the framework of ZSM‐5 zeolite without using any organic template. Moreover, the method not only decreases the preparation cost of vanadium doped ZSM‐5, but also greatly enhances the utilization ratio of vanadium atom. Vanadium atom mainly exists as tetrahedral coordination in the framework of ZSM‐5 which was demonstrated by the ultraviolet visible and X‐ray photoelectron spectrum. Furthermore, vanadium doped ZSM‐5 performs high and stability catalytic activity in the oxidation of styrene compared to that of the catalyst prepared by the traditional organic template method ascribe to the greatly increase of tetrahedral vanadium species.

Transitions in Al Coordination during Gibbsite Crystallization Using High-Field 27Al and 23Na MAS NMR Spectroscopy

Mechanisms of nucleation and growth of Al hydroxides such as gibbsite from aqueous solution, particularly in highly alkaline conditions, remain poorly understood. In this work, quantitative 27Al and 23Na MAS NMR experiments were conducted on solid samples extracted from the crystallization of gibbsite from an amorphous aluminum hydroxide gel precursor. The use of a high magnetic field and a moderate sample spinning rate of 20 kHz allowed transitional tetrahedral (AlT) and pentahedral (AlP) aluminum species to be observed along with the octahedral aluminum (AlO) that dominates the gibbsite product. Low-coordinated Al species could be detected at concentrations as low as 0.1% of the total Al sites. The following results have been established: (a) AlT and AlP coexist on the surface of growing gibbsites even with a combined percentage over the total Al sites of less than 1%. (b) Different synthesis methods generate gibbsite with varying amounts of low-coordinated Al. (c) The amorphous gel precursor contains a...

Influence of Levulinic Acid Hydrogenation on Aluminum Coordination in Zeolite-Supported Ruthenium Catalysts: A 27 Al 3QMAS Nuclear Magnetic Resonance Study.

The influence of a highly oxygenated, polar protic reaction medium, that is, levulinic acid in 2‐ethylhexanoic acid, on the dealumination of two zeolite‐supported ruthenium catalysts, namely Ru/H‐β and Ru/H‐ZSM‐5, has been investigated by 27Al triple‐quantum magic‐angle spinning nuclear magnetic resonance spectroscopy (3QMAS NMR). Upon use of these catalysts in the hydrogenation of levulinic acid, the heterogeneity in aluminum speciation is found to increase for both Ru/H‐ZSM‐5 and Ru/H‐β. For Ru/H‐ZSM‐5, the symmetric, tetrahedral framework aluminum species (FAL) were found to be mainly converted into distorted tetrahedral FAL species, with limited loss of aluminum to the solution by leaching. A severe loss of both FAL and extra‐framework aluminum (EFAL) species into the liquid phase was observed for Ru/H‐β instead. The large decrease in tetrahedral FAL species, in particular, results in a significant decrease in strong acid sites, as corroborated by Fourier transform infrared spectroscopy (FT‐IR). This decrease in acidity, evidence of the inferior stability of the strongly acidic sites in Ru/H‐β relative to Ru/H‐ZSM‐5 under the applied conditions, is considered as the main reason for differences seen in catalyst performance.

Relationship between the catalytic activity and Mo–V surface species in bimetallic catalysts for the oxidative desulfurization of dibenzothiophenic compounds

This work shows the performance of MoOx–VOx based bimetallic catalysts tested on the oxidative desulfurization (ODS) process of refractory dibenzothiophenic compounds using H2O2 as an oxidant. The catalytic activity was related with the oxidation state of molybdenum and vanadium surface species and with the interaction of both metals. The prepared molybdenum–vanadium oxides supported on alumina were subjected to reduction treatments at different temperature to obtain molybdenum and vanadium species with different oxidation state. Catalysts were characterized by their textural properties, scanning electron microscopy–energy dispersive X-ray, X-ray diffraction, temperature programed reduction and X-ray photoelectron spectroscopy. The characterization results showed that metal interactions promote the generation of highly active tetrahedral molybdenum species and isolated vanadium species, which increase the ODS performance of Mo–V based catalysts compared with their respective monometallic catalysts. Also, it was observed that combination of Mo6+, Mo4+ and V4+ superficial species promoted the ODS catalytic activity.

Characterizations and HDS performances of sulfided NiMoW catalysts supported on mesoporous titania-modified SBA-15

This work studies the effect of the support modifications (SBA-15) with Ti by using a ternary system as an active phase (Ni, Mo, W). Calcined and sulfided catalysts were characterized by a variety of techniques such as XRD, SBET, TPR, TPD-NH3, DRS-UV–vis, micro-Raman spectroscopy and HRTEM. Sulfided catalysts were tested in the hydrodesulphurization (HDS) of dibenzothiophene (DBT) performed in a batch reactor at 320°C and total hydrogen pressure of 800psi. This reaction was selected for the catalyst screening because DBT is a typical sulfur-containing hydrocarbon present in high-boiling petroleum fractions and coal derived liquids and the absence of any diffusion limitation for DBT molecule to entry into the porous structure of the SBA-15 supported catalysts. We observed that the incorporation of Ti did not decrease the catalytic activity in the HDS of DBT reaction except for Si/Ti=40 catalyst. UV–vis analyses show a higher amount of tetrahedral species for CAT/40TiS15 in counterpart with CAT/60TiS15 that showed a lower amount of those species however, the lower amount of Ti in the catalyst (CAT/60TiS15) showed the highest hydrogenation capability among the catalysts studied (HYD/DDS=0.81) despite the main route in the HDS of DBT reaction was the direct desulfurization (DDS) pathway (selectivity).

Pure rotation spectrum of CF4 in the v3 = 1 state using THz synchrotron radiation

Spherical-top tetrahedral species like CH4, SiH4, CF4, …possess no permanent dipole moment. Therefore, probing their pure rotation spectrum is very challenging since only a very weak dipole moment can be induced by centrifugal distortion and/or rovibrational interaction. If some Q branch lines have been recorded thanks to microwave techniques, R branch lines in the THz region have been poorly explored until recently. In previous studies, we have reported the pure rotation THz spectrum of cold and hot band lines of methane recorded at the SOLEIL Synchrotron facility. Here, we present the first recorded THz spectrum of the R branch of CF4, a powerful greenhouse gas, in its v3=1 state. This Fourier transform spectrum covers the R(20) to R(37) line clusters, in the 20–37cm−1 spectral range. It was recorded thanks to a 150m multiple path cell at room temperature. We could estimate the vibration-induced dipole moment value and also include the recorded line positions in a global fit of many CF4 transitions.

Zn Speciation and Stable Isotope Fractionation in a Contaminated Urban Wetland Soil-Typha latifolia System.

Wetlands play a key role in the immobilization of metallic contaminants. In this context the mechanisms of Zn sequestration and Zn transfer and storage in Typha latifolia L. colonizing a frequently flooded contaminated soil were studied. A combination of EXAFS spectroscopy, micro X-ray fluorescence (μXRF) and Zn isotope measurements was applied to soil, plant organs and decaying biomass. Zn was present in the soil as Zn-layered double hydroxide, as tetrahedral and octahedral sorbed Zn species, and as ZnS. Octahedral and tetrahedral Zn (attributed to symplastic Zn-organic acid and apoplasmic Zn-cell wall complexes, respectively) and Zn-thiol species were observed in the roots, rhizomes and stems. Iron plaque was present on the rhizomes and roots. Enrichment in light isotopes for Zn sorbed on the plaque relative to the soil (Δ66Znplaque-soil = -0.3 to -0.1‰) suggested the dissolution of ZnS (enriched in light isotopes) in the rhizosphere with subsequent Zn2+ sorption on the root plaque. Furthermore, enrichment in light isotopes of stems relative to leaves (Δ66Znstem-leaves = -0.2‰) suggested the remobilization of Zn via the phloem, from leaves back to the stems. Overall these data highlight the role of thiols in controlling Zn speciation during its transfer and storage in T. latifolia.

Mesoporous silica beads containing active and stable tin species for the Baeyer-Villiger oxidations of cyclic ketones

Porous anion-exchange resin was introduced as hard template to hydrothermally synthesize tin-containing mesoporous silica beads (Sn-MesoSB) with the diameter in the range of 0.3–0.9 mm. The characterization results showed the existence of continuous large-mesopore channels and tetrahedral tin species in the bead samples. Sn-MesoSB proved to exhibit high catalytic performances in the Baeyer-Villiger oxidation of adamantanone by using H2O2 as green oxidant, mainly attributed to the enhancement of the access to the catalytic tin sites through the continuous large-mesopore channels. Under the optimized experimental conditions, the conversion of adamantanone approached ca.100% in dioxane for 3 h at 90 °C. Notably, the bead format of such material could be remained during the catalysis procedure, which favors to the straightforward separation from the reaction system without any means of filtration or centrifugation. Working as a liquid-phase heterogeneous catalyst, this is pretty appealing to potential industrial applications. The catalyst was robust and can be reused up to 5 times without significant loss of activity and selectivity, pointing out that the tin species incorporated in the framework possessed high stability. Moreover, the bead material exhibits activity and selectivity in the Baeyer-Villiger oxidations with a broad range of substrates.

Structural properties of liquid aluminosilicate with varying Al2O3/SiO2 ratios: Insight from analysis and visualization of molecular dynamics data

Molecular dynamics (MD) simulations and visualizations were explored to investigate the changes in structure of liquid aluminosilicates. The models were constructed for four compositions with varying Al2O3/SiO2 ratio. The local structure and network topology was analyzed through the pair of radial distribution functions, bond angle, bond length and coordination number distributions. The results showed that the structure of aluminosilicates mainly consists of the basic structural units TO[Formula: see text] (T is Al or Si; y = 3, 4, 5). Two adjacent units TO[Formula: see text] are linked to each other through common oxygen atoms and form continuous random network of basic structural units TO[Formula: see text]. The bond statistics (corner-, edge- and face- sharing) between two adjacent TO[Formula: see text] units are investigated in detail. The self-diffusion coefficients for three atomic types are affected by the degree of polymerization (DOP) of network characterized by the proportions of nonbridging oxygen (NBO) and Q[Formula: see text] species in the system. It was found that Q4 and Q3 tetrahedral species (tetrahedron with four and three bridging oxygens, respectively) decreases, while Q0 (with four nonbridging oxygen) increase with increasing Al2O3/SiO2 molar ratio, suggesting that a less polymerized network was formed. The structural and dynamical heterogeneities, micro-phase separation and liquid–liquid phase transition are also discussed in this work.

Synthesis of iron substituted zeolite with Na-P1 framework

Zeolites with substitution by transition metals are expected to have unique catalytic properties in addition to common cation exchange abilities, but studies on the synthesis of iron-substituted zeolites with a greater cation exchange capacity (CEC) are very few. We hydrothermally synthesized iron-substituted Na-P1 type zeolites having CEC values of >300 cmolc kg−1 with iron content of up to 90 cmolc kg−1 with changing the addition of iron. Most of the iron in the products was concluded to be incorporated into the structure of Na-P1 by substituting aluminum, because measured CEC value and the content of sodium (exchangeable cation) nearly coincided with the sum of aluminum and iron contents in each product. In addition, UV–Visible diffuse reflectance spectra of the products revealed characteristic bands of isolated tetrahedral iron species and Fourier Transform Infrared spectroscopy (FT-IR) results indicated the existence of Si-O-Fe bonds in the products. These results confirmed the substitution of iron in the framework of Na-P1 by a hydrothermal synthesis in a short time.

Benzothiophene hydrodesulfurization over NiMo/alumina catalysts modified by citric acid. Effect of addition stage of organic modifier

NiMo/Al2O3 catalysts were obtained by one-pot simultaneous impregnation of Mo, Ni and P (at 12, 3 and 1.6 wt%, respectively) over alumina. Citric acid (CA) was added (Ni/CA=1 mol ratio) to determine its influence over molybdenum species, as nickel precursor used was complexated Ni acetate. Three different preparation methodologies were used: (a) modification of calcined (400 °C) NiMo/Al2O3 by CA impregnation, (b) CA deposition directly onto Al2O3 carrier, prior to Ni-Mo-P impregnation, (c) simultaneous Ni-Mo-P-CA deposition on alumina support. Materials were characterized by N2 physisorption, infrared and UV-vis spectroscopies, temperature-programmed reduction and thermal analysis (TG-DTG), and tested in liquid-phase benzothiophene (BT) conversion in batch reactor. CA deposition over calcined NiMo/Al2O3 resulted in diminished proportion of refractory Mo6+(t) tetrahedral species but also in octahedral Mo6+(o) reducible at higher temperature, as to those over non-modified NiMo/alumina. That was reflected in lower hydrodesulfurizating (HDS) ability. The highest BT HDS activity (70% increase, as to the conventional calcined formulation with no organic additive) was found when CA was impregnated over bare alumina prior to Ni-Mo-P deposition. In that case, decreased interaction between deposited molybdenum and nickel species and the support was evidenced, that due to surface “passivation” from citric adsorption/decomposition on alumina surface. On the other hand, simultaneous Ni-Mo-P-CA deposition, where low pH of impregnating solution (pH~1.4) devoided citric acid ionization, (then, no Mo-citrate complex formation) was ineffective in providing catalyst of enhanced HDS activity.

The Effect of the Second Coordination Sphere on Vanadium Speciation in Molten Chlorides

Molten salts have a wide range of unique properties that make them particularly useful in many areas of modern technology. From the fundamental point of view, analysis of speciation of vanadium in chloride melts leads to deeper understanding the nature of complex ion formation in ionic media. In the present work formation of vanadium complex ions in 3LiCl-2KCl, NaCl-KCl and NaCl-2CsCl mixtures at 450-750 oC was studied employing high temperature electronic absorption spectroscopy. The electronic absorption spectra (EAS) were recorded in the course of dissolution of vanadium(II) and vanadium(III) chlorides, anodic dissolution of metallic vanadium, and chlorination of various vanadium oxides (V2O3, V2O4, V2O5). Dissolution of VCl3 in fused alkali chlorides leads to the formation of V(III) species. Average oxidation state of vanadium in the quenched melt samples was 2.9-3.1. Spectral curves were resolved into two individual bands attributed to the 3T1g→3T1g(P) and 3T1g→3T2g electronic transitions in the octahedral VCl6 3-complex. The positions of the band maxima shift towards longer wavelengths with increasing average radius of alkali metal cation, in agreement with the expected decrease of the polarizing effect of the second coordination sphere. Vanadium dichloride added to the alkali chloride melts partly disproportionated forming V(III) species and vanadium metal. The resulting spectrum represented a superposition of the absorption bands of V2+ and V3+ions. The average oxidation state of vanadium in the quenched melts was higher than two and the concentration of vanadium was noticeably lower than expected. The best method for preparing vanadium(II) containing melts is the anodic dissolution of the metal. Position of the maximum in the EAS of V(II) in 3LiCl-2KCl at 450 oC (18770 cm-1) is very close to that of V(III), being shifted to higher energies only by about 900 cm-1 (Figure). This band corresponds to 4A2g→4T1g (P) electronic transition in the octahedral VCl6 4- complex (d3-configuration). Second band, with the maximum at 11890 cm-1 is attributed to 4A2g→4T1g electron transition in the same ion. Increasing temperature and the mean radius of the alkali metal cation on the solvent melt resulted in certain changes of EAS of vanadium(II)-containing melts, i.e., the intensity of the second peak decreased and a new, third, band appeared around 13300 cm-1 (Figure). The position of this third peak did not change with temperature and was the same in different melts. This band is attributed to 4T1→4T1 (P) electronic transition in the tetrahedral VCl4 2- ion. Therefore, increasing temperature and the mean radius of the salt-solvent cation shifts the VCl6 4-–VCl4 2-equilibrium towards the tetrahedral species. The results of in situ spectroscopy measurements conducted during the reactions of various vanadium oxides with hydrogen chloride in alkali chloride melts showed that the nature of the products formed does not depend on the type oxide and the flow rate of HCl. Oxidation state of vanadium in all the resulting melts was close to four. The EAS corresponded to the absorption of vanadyl-ions. Oxygen-containing vanadium(IV) species exhibited somewhat anomalous behavior in NaCl-2CsCl melt as the temperature was varied. Increasing temperature resulted in decreasing intensity of the band at 13000-14000 сm-1. This is explained by the coordination environment of vanadyl species in NaCl-2CsCl melts, different from the melts containing smaller cations. This conclusion was confirmed by XRD and Raman spectroscopy analysis of the quenched melts. Figure. Resolution into Gaussian bands of EAS recorded after anodic dissolution of vanadium metal in 3LiCl-2KCl (a) and NaCl-2CsCl (b) eutectic melts at 450 and 750 oC, respectively. Figure 1

Structural and spectroscopic characterization of epiisopiloturine-metal complexes, and anthelmintic activity vs. S. mansoni

Epiisopiloturine (EPI), extracted from leaves of Pilocarpus microphyllus, a plant originally from the Amazon and Savanna regions in Brazil, was described as a potential drug against Schistosomiasis, a neglected severe disease. Herein, EPI was complexed with copper(II) or zinc(II) salts and the isolated species, [Cu(epi)4](ClO4)2 (1) and [Zn(epi)2Cl2] (2), were structurally and spectroscopically characterized. By using X-ray diffraction, the crystal structures of both metal complexes were determined, indicating a square pyramidal geometry for copper for 1 and a tetrahedral environment around zinc for 2. EPR spectra of 1 show a typical tetragonal environment around the central metal ion with some tetrahedral distortion, both in the solid state and in frozen acetonitrile solution, in accordance with crystallographic data. For 2, NMR spectra have bands consistent with a tetrahedral species in solid state or in DMSO-d6 solution. These spectroscopic characterization data were further supported by Density Functional Theory calculations, showing that these metal complexes are also stable in solution. Those metal complexes were tested against adult worms of Schistosoma mansoni, in comparison to the free alkaloid as anthelmintic agent. Coordination with copper(II) improved the alkaloid schistosomicidal properties, while binding to zinc(II) decreased its activity.

Mesoporous silica-anchored organotin as heterogeneous catalyst for the transesterification of dimethyl carbonate with phenol

A simple scheme for a mesoporous silica-anchored organotin catalyst was developed for the transesterification of dimethyl carbonate with phenol to diphenyl carbonate. N2-sorption, TEM, UV–Vis, and elemental analysis combined with 29Si and 13C NMR measurements evidenced the formation of mesoporous organic–inorganic hybrid silica with a highly dispersed tetrahedral Sn species. The catalyst exhibited excellent activity and reusability in the transesterification. With a catalyst of 1.0 g, a reaction temperature of 150–180 °C, and a reaction time of 9 h, the phenol conversion and transesterification selectivity reached 51.1 and 99.9 %, respectively. The phenol conversion just decreased from 41.2 to 35.0 % after five runs with 0.5 g of catalyst. The improved stability was attributed to the strong covalent bonding between the organotin and mesoporous silica.

Enhancing the selectivity of Pare-dihydroxybenzene in hollow titanium silicalite zeolite catalyzed phenol hydroxylation by introducing acid–base sites

A facile and effective method for enhancing the selectivity of Pare-dihydroxybenzene in phenol hydroxylation has been developed by introducing acid–base sites (MgO–Al2O3 binary oxide) to the micropores of hollow titanium silicalite (HTS, Ti/Si=25) zeolite. For MgO–Al2O3 modified HTS zeolites, the biggest ratio of para- to ortho-dihydroxybenzene is over 2, while that is close to 1 for conventional HTS zeolite. The high pare-dihydroxybenzene selectivity is ascribed to the steric hindrance and the synergistic effect between acid–base sites of mixed oxide and tetrahedral framework Ti species in HTS zeolite.

Preparation of Fe-BEA zeolites by isomorphous substitution for oxidehydration of glycerol to acrylic acid

The preparation by post-synthesis isomorphous substitution of FeX-BEA-Y in one step was investigated for the oxidehydration of pure glycerol. TPR and DR UV–vis highlighted the presence of Fe(+III) species in the framework of zeolites. Iron allows the activation of the catalyst by the reduction by glycerol of part of Fe(+III) into Fe(+II) species, which stabilizes the glycerol conversion. Total glycerol conversion is obtained with 4wt% of iron and acrylic acid yield reaches 23% over this catalyst. The Fe(+III) tetrahedral species are thought to be the main active redox sites for the formation of acrylic acid.