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A layered oxo-vanadium(IV) dihydrogen phosphate, {VO(H2PO 4)2} n has been synthesized hydrothermally and characterized by several physicochemical methods. Single-crystal X-ray analysis (crystal system, tetragonal; space group, P4/ ncc; unit cell dimensions, a = b = 8.9632(4), c = 7.9768(32) A) of {VO(H2PO4) 2} n reveals that the compound has an ext...
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... of {VO(H 2 PO 4 ) 2 } n . The equatorial O atoms of each VO 5 pyramid are shared with four H 2 PO 4 tetrahedra in which the P atoms lie on the crystallographic 2-fold axes, and each H 2 PO 4 tetrahedron in turn connects two adjacent distorted VO 5 pyramids to form a two-dimensional layer parallel to the ab plane ( Figure 2) built with motifs of square V 4 P 4 O 8 having dimensions 6.39 Å × 6.39 Å (Figure 3). Two of the oxygen atoms (O2 and its symmetry related one) of the H 2 PO 4 groups link the neighboring V atoms in the layer, while the remaining two oxygen atoms (O3 and its symmetry related one) of H 2 PO 4 groups are terminal with relatively long P-O bond distances, P1-O3 1.571(3) Å, indicating P-OH groups. ...
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A new iron phosphonate-oxalate [Fe(O3PCH3)(C2O4)0.5(H2O)] (1), has been synthesized under hydrothermal condition. The single-crystal X-ray diffraction studies reveal that 1 consists of layers of vertex-linked FeO6 octahedra and O3PC tetrahedra, which are further connected by bis-chelate oxalate bridges, giving to a 3D structure with 10-membered cha...
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... The diffraction patterns of di-substituted-vanadium cesium salt had more peaks than other salts, according to the literature [41,47]. Previously, we verified that when phosphomolybdic acids were substituted with 1, 2, or 3 vanadium mol per mol of heteropolyanion, their powder XRD patterns were retained [51]. ...
... When the H 3 PMo 12 O 40 acid was converted to Cs 3 PMo 12 O 40 salt, its surface jumped from 3.8 to 104.1 m 2 g −1 , while the pore volume increased from 1.7 to 37.3 cm 3 g −1 (Table S2). It is known that the replacement of H + ions with large-radius cations, such as Cs + , strongly impacts its tertiary structure, creating micro-and/or mesopores and, consequently, increasing its surface area [49][50][51][52][53][54]. ...
In this work, vanadium-substituted cesium phosphomolybdate salts with general formulae Cs3+nPMo12−nVnO40 (n = 0, 1, 2, and 3) were synthesized and evaluated in the acetalization of benzaldehyde with alkyl alcohols. All the catalysts were characterized through Raman, infrared, and ultraviolet–visible spectroscopies, powder X-ray diffraction patterns, isotherms of N2 desorption/adsorption, and measurements of acidity strength. The catalytic activity of cesium phosphomolybdovanadate salts was evaluated in the acetalization reactions of benzaldehyde with alkyl alcohols. Among the salts tested, the Cs4PMo11V1O40 was the most active and selective catalyst in the conversion of benzaldehyde to methyl benzyl acetal and benzoic acid, which was obtained without the use of an oxidant agent. The impact of the main reaction parameters on the conversion and selectivity was evaluated by varying the content of vanadium per heteropolyanion, catalyst load, temperature, and alkyl alcohols. The greatest activity of the Cs4PMo11V1O40 salt was assigned to the highest Brønsted acidity strength, as demonstrated by the acidity measurements and analysis of their surface properties. This solid catalyst has advantages over traditional liquid homogenous catalysts, such as low corrosiveness, a minimum generation of residues and effluents, and easy recovery/reuse. In addition, its synthesis route is easier and quicker than solid-supported catalysts and comprises a potential alternative route to synthesize acetals.
... The Bragg diffraction wide angle reflections at 2h = 8.3°, 9.0°, 27.8°a nd 29.1°are observed and these peaks correspond to the crystalline nature of the Keggin type heteropolyacid [27]. The characteristic diffraction peaks are retained with increasing V/P mole ratios [28]. ...
Various V/P mole ratios of vanadium substituted Keggin-type phosphomolybdic acids were synthesized
by the hydrothermal method. These materials were characterized using several physico-chemical techniques
such as X-ray diffraction, FT-IR, N2-sorption, Raman spectroscopy, 31P MAS NMR, SEM and NH3-TPD. FT-IR, Raman spectroscopy and 31P NMR results confirm the formation of the primary structure of the Keggin ion and its crystalline nature is shown clearly by XRD. NH3-TPD results reveal that the acidity of the materials systematically decreases with increasing vanadium content. The Knoevenagel reaction carried out over vanadium substituted phosphomolybdic acid with various V/P mole ratios indicate that the higher V/P mole ratio exhibits better catalytic performance under solvent free conditions. The catalytic properties correlate with the structural properties and the acidity of the materials.
... tert-butyl hydroperoxide (TBHP), to give reactive oxo-peroxovanadium(V) species and have widely been used as effective catalysts for oxidation reactions including epoxidation of olefins. 23 In this regard Sen et al. 24 reported the use of oxo-vanadium(IV) dihydrogen phosphate as a heterogeneous catalyst for olefin epoxidation using TBHP as oxidant. Hsiao et al. 25 reported polymer-supported vanadium complexes as catalysts for the oxidation of alkenes with TBHP in water. ...
Industrial grade cation-exchange resin ‘INDION-130 was modified with vanadyl cations by ion exchange method and then used for the epoxidation of unsaturated fatty materials including acids, esters and vegetable oils by tert-butyl hydroperoxide (TBHP) in decane as oxidant. The effect of oxidant/ double bond ratio, catalyst concentration, recycling of the catalyst, and temperature on the conversion to epoxides was studied. After the epoxidation, the catalyst could easily recover by filtration and successfully reused at least for seven runs without any loss in catalytic activity.
... Keeping such observations in mind we have directed our investigation in synthesizing Schiff base copper(II) complexes and their azido adducts and simultaneous study of their magnetic property and catalytic efficacy. Schiff base copper complexes can now be extensively used as active catalysts in several oxidation reactions both in homogeneous [7][8][9][10][11] and heterogeneous condition [12][13][14][15][16]. So far our knowledge goes, catalytic oxidations involving Schiff base copper azido complexes have been scarcely reported in the literature [17][18]. ...
... However, in the case of trans-stilbene, the epoxidation reaction showed remarkable epoxide selectivity yielding 100% epoxide in 12 h. A layered oxo-vanadium(IV) phosphate catalyst also shows a similar kind of activity towards epoxidation of trans-stilbene in our earlier study [80]. Recently Gelalcha et al. reported asymmetric oxidation catalysis of olefins using FeCl 3 Á6H 2 O and pyridine-2,6-dicarboxylic acid along with appropriately chosen chiral diamine ligands [81]. ...
Nano-sized crystals of maghemite iron oxide (γ-Fe2O3) were synthesized onto the surface of NaY-zeolite crystals by immobilizing a polynuclear iron complex [Fe4O2(O2CCH3)7(bpy)2](ClO4) (bpy=2,2′-bipyridine) and subsequent calcination of the material in oxygen. Superparamagnetic γ-Fe2O3 particles with sizes ∼5nm were formed on the surface of the zeolite matrix. The nano-composite, γ-Fe2O3@NaY has been subsequently subjected for thorough characterization with several spectroscopic techniques as well as magnetic and transmission electron microscopic measurements. This confirms the formation of maghemite nanoparticles on a NaY-zeolite surface. γ-Fe2O3@NaY shows a remarkable catalytic efficiency in epoxidation reactions with various olefins using tert-BuOOH as oxidant. Notably, styrene shows a remarkable high conversion (90%) as well as epoxide selectivity (95%) while trans-stilbene is completely converted to its oxide with tert-BuOOH over a γ-Fe2O3@NaY catalyst.
Novel preferential carbon-dioxide sorption was observed on a cadmium based mixed-linker metal-organic framework (MOF){[Cd(abdc)(azpy)](DMA)}n [where 4,4´-azopyridine = azpy and 2-amino-1,4-benzenedicarboxylic acid = H2abdc]. {[Cd(abdc)(azpy)](DMA)}n features an interpenetrated 3D networked structure consist of pendant Lewis basic −NH2 groups directed towards the pores. PLATON analysis shows that the solvent accessible void space of the MOF is ca. 26.6%. At 298 K, the desolvated MOF showed an uptake of carbon-dioxide of 8.33 wt% or 42.42 cc/g at 1 bar pressure which, upon cooling to 273 K, is increased to about 12.17 wt% or 62 cc/g at 1 bar pressure. In contrast, methane uptake capacities of the desolavated MOF were 0.127 wt% or 1.79 cm³/g and 1.34 wt% or 18.74 cm³/g at the adsorbate pressure of 1 bar at 298 K and 273 K, respectively. On the otherhand, hydrogen uptake capacity of the desolavated MOF reached to 0.31 wt% or 34.87 cm³/g at the adsorbate pressure of 1 bar at 77 K. Selectivity of carbon-dioxide with respect to methane at 273 K is calculated to be 5.4. The heat of adsorption for carbon-dioxide is calculated to be 38 kJmol− 1.
A strategical approach for morphological transformation and heterojunction formation was utilized to suppress the shortcomings of uni-metal oxide electrocatalysts and enhance their bifunctionality. In situ generation of copper oxide (CuO) over the surface of manganese oxide (Mn2O3) resulted in a morphological transformation from solid spheres to hollow spherical structures due to the ion-exchange diffusion (Kirkendall effect) of Cu ions into Mn2O3 particles. This hollowness resulted in the advancement of the bifunctional electrocatalytic behavior of Mn2O3/CuO (overpotential (η10) of 280 mV for an OER and 310 mV for an HER at a current density of 10 mA/cm2) by virtue of increased exposed surface active sites aiding the adsorption of water molecules on the surface. The increased electrochemical active surface area (ECSA/Cdl = 34 mF/cm2) and reduced charge transfer resistance resulted in the formation of Mn2O3/CuO hollow spheres to achieve an approximately threefold enhancement in the turnover frequency (TOF) compared to the bare Mn2O3. The electrocatalytic efficiency of Mn2O3/CuO was further enhanced by virtue of the faster charge transfer coefficient of two-dimensional (2D) vanadyl phosphate hexahydrate (VOP) sheets deposited over its surface. This boosted the overall water splitting with attained overpotential (η10) values of 190 and 220 mV with Tafel slopes of 60 and 105 mV/decade for an OER and HER, respectively. The morphological transformation and formation of an n-p heterojunction between Mn2O3 and CuO based on their work function (φ) values evaluated from the density functional theory (DFT) calculation and the effect of the VOP overlayer for faster reaction kinetics at the electrolyte interface resulted in an ∼10-fold increment in TOF values compared to the bare counterpart.
A dimeric copper(II) complex, bis{(2-[1-(aminoethylimino)ethyl]-phenoxo}-di-μ1,1-azido-dicopper(II), [Cu2(L)2(μ2-1,1-N3)2] (1) [L = 2-[1-(aminoethylimino)ethyl]-phenoxo ion], has been isolated using a self-assembly reaction using a 1:1:1 molar ratio of Cu(NO3)2·3H2O, HL and NaN3 in methanol at room temperature and characterized through X-ray diffraction analysis and spectroscopic studies. X-ray structural analysis reveals that 1 consists of two distinct dinuclear molecular units, where each copper(II) center in the individual dinuclear unit adopts a distorted square pyramidal geometry with a CuN4O chromophore ligated through a tridentate (NNO) Schiff base and two N atoms of two different bridging azides in µ1,1-mode. Two Cu(II) centers are linked through double µ2-1,1-N3 bridges to form the dinuclear unit [Cu2(L)2(μ2-1,1-N3)2]. In the crystalline state, the dinuclear units in 1 are associated through weak intermolecular N-H⋯O hydrogen bonds to afford a 2-D sheet structure viewed along the crystallographic a-axis. The small magnitude of the antiferromagnetic interaction (J = –0.45 cm⁻¹) is a result of the long Cu···Cu separation (3.205(2) Å). The catalytic efficacy of 1 was studied in a series of solvents for the epoxidation of alkenes using tert-butyl-hydroperoxide (TBHP) as an efficient oxidant under mild conditions.
Composite materials have revealed remarkable activities in various catalytic applications. However, choosing an appropriate material to enhance the catalytic activity and stability is a major challenge in the field of catalysis. In this article, we reported vanadium phosphorus oxide (VPO)/β-SiC as a stable composite material with good catalytic activity. VPO/β-SiC composite materials with different compositions were fabricated by the impregnation technique to investigate the catalytic activity and stability of these materials in liquid-phase reactions. The physiochemical characteristics of the prepared catalysts were analyzed by several spectroscopic methods. The catalytic activities of VPO/β-SiC composites were studied in a solvent-free oxidation of methanol using tert-butyl hydroperoxide (TBHP) as an oxidant. The reaction conditions were optimized by changing various reaction parameters. Under optimized reaction conditions, the 10 wt % VPO/β-SiC composite showed 100% conversion with 89.8% selectivity to formaldehyde.
