Hydrogen Phosphate Hemihydrate Research Articles

Application of vanadyl hydrogen phosphate/KIT-6 composites as a catalyst for dehydration of sucrose

In this research work, the synthesis of well-ordered mesoporous structure KIT-6 silica-supported vanadyl hydrogen phosphate hemihydrate (VHP/KIT-6) catalysts possessing varying surface area was carried out, followed by being utilized in the dehydration of sucrose to 5-hydroxymethylfurfural (5-HMF) as a solid acid catalyst. The fabrication of two different VHP/KIT-6 catalysts was conducted using the impregnation approach through V2O5 reduction in alcoholic media. Then, the catalytic behavior presented by the prepared VHP/KIT-6 samples was compared with unsupported VHP and unsupported vanadyl pyrophosphate (VPP), which was prepared through the calcination of VHP precursor at 400 °C for 24 h. The prepared catalysts were characterized by different analyses, including ICP-OES, BET, XRD, NH3-TPD analysis, FT-IR spectroscopy, as well as SEM and TEM techniques. Furthermore, important parameters, including the catalyst type and weight, sucrose amount, time, temperature, and the type of solvent on sucrose dehydration, were also studied. It was observed that the highest catalytic activity in the dehydration reaction (5-HMF yield: 67%, sucrose conversion: > 94%) could be provided by the catalyst possessing the highest surface area. Moreover, the catalyst reusability was examined for consecutive four times, based on which no considerable change in the catalytic activity was observed.

Ionic Liquid-Assisted Synthesis of Vanadium Phosphate Catalysts from Phosphorous Acid for Selective Oxidation Reactions

Vanadium oxyphosphate (VPO) with a high surface area was synthesized in a mixed solvent of ionic liquid [Bmim]Br and water, using phosphorous acid to reduce V5+ to V4+ and as a partial phosphorus source, and V2O5 as the vanadium source. The effects of ionic liquids on the synthesis process were investigated in detail. Using pure water as the solvent, the product was a vanadium phosphate compound with large flakes. With the increase in the amount of ionic liquid, the size of the large flakes of vanadium phosphate gradually decreased, and the morphology was changed to spherical particles. When the proportion of ionic liquid was 80% or the ionic liquid was solely used as the solvent, the VPO showed completely spherical particle morphology, and the specific surface area was the highest. X-ray diffraction analysis showed that the crystal phase of VPO changed from vanadium (IV) hydrogenphosphate hemihydrate (VOHPO4·0.5H2O) to an amorphous state with an increase in ionic liquid ratio. All of the above results show that ionic liquids play an important role in the synthesis of VPO materials. After being calcined in an n-butane/air atmosphere, the precursors were transformed into the vanadium pyrophosphate phase. The active VPO catalysts were used in the selective oxidation of cyclohexanol, and the yield of cyclohexanone was 57.98% for the VPO-80 catalyst synthesized using the ionothermal method but only 21.41% for the VPO-W catalyst synthesized using a traditional hydrothermal method, which shows the advantage of ionic liquid synthesis for VPO catalysts. Vanadium oxyphosphate material with high surface area was synthesized in the mixed solvent of ionic liquid [Bmim]Br and water. Ionic liquid plays an important role in the morphology and properties of synthesized VPO materials. The active VPO catalysts were used in the selective oxidation of cyclohexanol, and the yield of cyclohexanone was 57.98% for VPO-80 catalyst synthesized by ionothermal method, but only 21.41% for VPO-W catalyst synthesized by traditional hydrothermal method, which exhibited the advantages of ionic liquid synthesis for VPO catalysts.

VOHPO4.5H2O/KIT-6 composites: Preparation and their application in extractive and catalytic oxidation desulfurization of benzothiophene and dibenzothiphene

Abstract The catalytic activity of vanadyl hydrogen phosphate hemihydrate (VPO) for deep desulfurization of a model fuel was explored. For this purpose, a series of composites containing different amounts of vanadyl hydrogen phosphate and well-ordered mesoporous silica (KIT-6) were prepared and their structural and textural characterizations were carried out using SEM, TEM, ICP-AES, FT-IR, N2 adsorption-desorption, XPS and XRD techniques. It was found that the catalyst with maximum vanadium phosphate loading (VPKA) shows the highest catalytic activity in dibenzothiophene (DBT) removal through oxidative desulfurization (ODS) process. Different reaction conditions such as temperature, the mole ratio of H2O2:DBT, and catalyst loading were investigated in the catalytic system.

Development of VPO catalysts supported on mesoporous modified material based on an aerosil gel

Supports modified with different organic substances and vanadium-phosphorus oxide catalysts on their basis were developed with the use of the barothermal treatment of aerosil. It was found that the anchoring of a modifier to the surface of a support occurred with the participation of OH groups. The modifier content found from differential thermal analysis data depended on the pore structure of the support and the nature of the modifier. It was demonstrated that, with the use of a modified support in the catalysts, a vanadyl hydrogen phosphate hemihydrate phase—the precursor of a catalyst for the selective oxidation of hydrocarbons—was formed; under reaction conditions, this precursor was converted into vanadyl pyrophosphate. On supporting, the phase grew from the micropore bulk and covered only part of the support surface. The synthesized catalysts exhibited high activity and selectivity in the reaction of n-butane oxidation under hydrocarbon-rich conditions and also in the oxidative dehydrogenation of ethane.

Innovative process for the synthesis of vanadyl pyrophosphate as a highly selective catalyst for n-butane oxidation

Vanadyl pyrophosphate (VPO) catalysts are used for the selective oxidation of light alkanes, which are based on vanadyl hydrogen phosphate hemihydrate (VOHPO 4·0.5H 2O) as the precursor. Catalyst precursor with well-defined crystal size has been successfully synthesized for the first time, using a simple one-step high-pressure autoclave that was surfactant-free and water-free method with significantly lower temperature and shorter reaction time. VOHPO 4·0.5H 2O was prepared from V 2O 5 using an isobutanol, 1-pentanol, 1-heptanol and 1-dectanol as both solvent and reducing agent at elevated temperatures (100, 120, and 150 °C). This new method significantly reduced the preparation time and lowered production temperature (50%) of catalyst precursor (VOHPO 4·0.5H 2O) when compared to conventional hydrothermal synthesis methods. VOHPO 4·0.5H 2O can be obtained at temperature far below 150 °C. It was found that the presence of 1-heptanol and 1-decanol in the reaction mixtures is crucial for obtaining a well-defined crystal size of precursor phase and solely generated impurity [VO(H 2PO 4) 2]. Our findings show that both the phase composition and morphology of vanadium phosphate can be influenced by the use of different reducing agents and temperatures during the preparation process. This new methodology produces catalysts with a much higher surface area ( ca. 23 m 2 g −1) compared with those materials prepared by slow hydrothermal synthesis ( ca. 9.5 m 2 g −1). Finally, the yield of maleic anhydride was significantly increased from 21.3% for conventional catalyst to 37.9% for the new solvothermal catalyst.

Novel Synthesis Techniques for Preparation of Ultrahigh-Crystalline Vanadyl Pyrophosphate as a Highly Selective Catalyst for n-Butane Oxidation

The vanadyl hydrogen phosphate hemihydrate (VOHPO 4 ·0.5H 2 O), with well-defined crystal size, has been successfully synthesized for the first time, using a simple one-step solvothermal process that was free of surfactants and water and had a short reaction time and low temperature. The synthesis was performed via the reaction of V 2 O 5 and H 3 PO 4 with an aliphatic alcohol (1-propanol or 1-butanol) at high temperatures (373. 393, and 423 K) in a high-pressure autoclave. The mixture of reactions directly gave the VOHPO 4 ·0.5H 2 O, which is a valuable commercial catalyst precursor for the selective oxidation of n-butane to maleic anhydride. The catalyst precursors were dried by microwave irradiation. The reaction conditions (by varying the reducing agent and reaction temperature) were used further for optimization of the crystallite size, surface area, morphology, and activity of the nanostructure of vanadium phosphate oxide [(VO) 2 P 2 O 7 ] catalyst. This new method significantly reduced the preparation time and lowered the production temperature (50%) of catalyst precursor (VOHP0 4 ·0.5H 2 O), when compared to conventional hydrothermal synthesis methods. The as-prepared (VO) 2 P 2 O 7 catalyst under various conditions exhibited remarkably different physical and chemical properties, indicating the potential of the suggested method in tuning the crystalline structure and surface area of (VO) 2 P 2 O 7 to improve its catalytic performance. It was found that the length of the carbon chain in an alcohol and reaction temperature in the solvothermal condition had a great impact on the chemical and physical properties of resulting catalysts. Interestingly, there was no trace of YO(H 2 PO 4 ) 2 , which is an impurity noted to be readily formed under solvothermal preparation conditions. The precursors and catalysts were characterized using a combination of powder X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) surface area measurement, scanning electron microscopy (SEM), and temperature-programmed reduction in hydrogen (H 2 - TPR). A correlation between the surface area of the catalyst and the activity was observed. Finally, the yield of maleic anhydride was significantly increased from 21% for conventional catalyst to 38% for the new solvothermal catalyst.

Solvothermal synthesis of vanadium phosphate catalysts for n-butane oxidation

In this paper, we have developed a simple, low-cost, template-free and surfactant-free solvothermal process for synthesis of vanadyl hydrogen phosphate hemihydrate (VOHPO 4·0.5H 2O) with well defined crystal size. The synthesis was performed by reaction of VPO 4·2H 2O with an aliphatic alcohol (isobutyl alcohol, 1-pentanol, 1-hexanol, 1-heptanol or 1-decanol). This afforded well crystallized VOHPO 4·0.5H 2O by solvothermal methods at 120 °C temperature. This new method significantly reduced the preparation time and lowered production temperature (50%) of catalyst precursor (VOHPO 4·0.5H 2O) when compared to conventional hydrothermal synthesis methods. By varying the reducing agent, the solvothermal evolution process from layered tetragonal phase VOPO 4·2H 2O to orthorhombic phase VOHPO 4·0.5H 2O was observed. It was found that the length of carbon chain in an alcohol in the solvothermal condition had a great impact on chemical and physical properties of resulting catalysts. Interestingly, there was no trace of VO(H 2PO 4) 2 an impurity noted to be readily formed under solvothermal preparation condition. Therefore, this study introduces a more facile synthetic pathway to V(III) compounds. In addition, the microwave-synthesized catalysts exhibited some properties superior to those of conventionally synthesized catalyst such as better stability, crystallinity, and catalytic activity in the production of maleic anhydride. The characterization of both precursors and calcined catalysts was carried out using X-ray diffraction (XRD), inductively coupled plasma-atomic emission spectrometer (ICP-AES), N 2 physisorption, temperature programmed reduction (H 2-TPR) and scanning electron microscopy (SEM). The XRD pattern of the active catalyst prepared by this solvothermal method confirmed the presence of smaller crystal size (between 6 and 13 nm along 0 2 0 planes) of vanadium phosphate catalyst with higher specific surface area. Finally, the yield of maleic anhydride was significantly increased from 29% for conventional catalyst to 44% for the new solvothermal catalyst.

Influence of Rare-Earth and Bimetallic Promoters on Various VPO Catalysts for Partial Oxidation of n-Butane

Vanadium phosphorous oxide (VPO) catalyst was prepared using dihydrate method and tested for the potential use in selective oxidation of n-butane to maleic anhydride. The catalysts were doped by La, Ce and combined components Ce + Co and Ce + Bi through impregnation. The effect of promoters on catalyst morphology and the development of acid and redox sites were studied through XRD, BET, SEM, H2-TPR and TPRn reaction of n-butane/He. Addition of rare-earth element to VPO formulation and drying of catalyst precursor by microwave irradiation increased the fall width at half maximum (FWHM) and reduced the crystallite size of the Vanadyl hydrogen phosphate hemihydrate (VOHPO4 · 1/2 H2O, VHP) precursor phase and thus led to the production of final catalysts with larger surface area. The Ce doped VPO catalyst which, assisted by the microwave heating method, exhibited the highest surface area. Moreover, the addition of promoters significantly increased catalyst activity and selectivity as compared to undoped VPO catalyst in the oxidation reaction of n-butane. The H2-TPR and TPRn reaction profiles showed that the highest amount of active oxygen species, i.e., the V4+–O− pair, was removed from the bimetallic (Ce + Bi) promoted catalyst. This pair is responsible for n-butane activation. Furthermore, based on catalytic test results, it was demonstrated that the catalyst promoted with Ce and Bi (VPOD1) was the most active and selective catalyst among the produced catalysts with 52% reaction yield. This suggests that the rare earth metal promoted vanadium phosphate catalyst is a promising method to improve the catalytic properties of VPO for the partial oxidation of n-butane to maleic anhydride.

Transformation of nano-sized vanadyl hydrogen phosphate hemihydrate crystallites to vanadyl pyrophosphate during activation in the presence of n-butane and oxygen

The transformation of nano-sized VOHPO 4⋅0.5H 2O crystallites (340 nm × 40 nm) to (VO) 2P 2O 7 was examined. The crystalline structure of VOHPO 4⋅0.5H 2O quickly collapsed to form an oxidized amorphous phase within 1 h (reaction conditions: 1.5% n-butane, 17% O 2, and 81.5% He at 663 K), followed by gradual crystallization to (VO) 2P 2O 7, accompanied by the formation of sharply angular nano-sized crystallites (about 50 nm). No crystalline phases other than (VO) 2P 2O 7 were formed during this transformation. This is quite different from the transformation of large and thick VOHPO 4⋅0.5H 2O crystallites, in which α II-VOPO 4 and δ-VOPO 4 have been detected in the resulting catalyst. The selectivity to maleic anhydride increases during the transformation as a result of the formation of (VO) 2P 2O 7. The activity increases in the early stages of the transformation, then decreases with time. The decrease in activity is caused by gradual reduction of the catalyst surface during the transformation.

Pressure Calcination of VPO Catalyst

Calcination and activation are critical steps in the transformation of vanadyl hydrogen phosphate hemihydrate (VPO precursorVOHPO4·0.5H2O) to vanadyl pyrophosphate (VPO catalyst(VO)2P2O7). Whereas many published kinetics studies for butane oxidation over VPO demonstrate the relationship between catalytic activity and reaction conditions, the relationship between calcination conditions and activity has only received superficial attention in the open literature. This study delineates the operating boundaries in which to optimize catalytic performance. The control variables included temperature, pressure, time, and gas-phase composition (principally, oxygen and water vapor partial pressures), and their effects on surface area, oxidation state, and catalytic activity were measured. The experimental plan included several hundred calcination experiments. The commercial-design operating conditions were chosen as the base-case conditions: temperatures from 330 to 460 °C, pressures up to 6 atm, and oxygen and water concentrations between 0 and 20% and 0−3%, respectively. The optimal temperature was found to be about 390 °C. Catalyst performance declines with increasing pressure, but the pressure−time relationship allows a range of conditions: optimal catalytic performance was achieved within 20 h of calcination at atmospheric pressure, but it took less than 4 h to achieve this high level of performance when precursor was calcined at 3.5 atm (at longer times, the catalytic performance deteriorated). Co-feeding steam (in the presence of oxygen) generally had a deleterious affect on catalyst performance and, in particular, maleic anhydride yield. Moreover, oxidation states higher than 4.5 were achieved with steam/oxygen mixtures in as little as 20 h. Catalyst performance declined linearly with oxidation state for precursor calcined to vanadium oxidation states exceeding 4.5.

Novel Method for Synthesis of Well-Crystallized Vanadyl(2+) Hydrogen Phosphate Hemihydrate: Crystallization in Organic Media Containing a Small Amount of Water

Vanadyl(2+) hydrogen phosphate hemihydrate (VOHPO 4 .0.5H 2 O, VHP) that had high crystallinity and showed a strong (001) peak in its X-ray diffractometry (XRD) pattern was synthesized via thermal treatment of a mixture of vanadyl(2+) acetylacetonate and triethyl phosphate at 200°C in organic solvents that contained a small amount of water. Scanning electron microscopy observations revealed that the product consisted of thin plates (2-4 μm wide and 20 μm. The present VHP sample was topotactically transformed to divanadyl(2+) pyrophosphate, which showed a strong (020) XRD peak, via thermal treatment in a nitrogen atmosphere at 500°C.

Water-vapor-induced transformation of two-dimensional vanadyl hydrogen phosphate hemihydrate, VOHPO4·0.5H2O, to one-dimensional tetrahydrate, VOHPO4·4H2O

The catalytically important, two-dimensional vanadyl hydrogen phosphate hemihydrate, VOHPO4·0.5H2O phase was transformed to the one-dimensional vanadyl hydrogen phosphate tetrahydrate, VOHPO4·4H2O for the first time by mild treatment with water vapor. It was also observed that for three samples of VOHPO4·0.5H2O prepared under different conditions, the rate of transformation to the tetrahydrate was markedly affected by morphology and crystallinity. The tetrahydrate phase could also be re-transformed to the hemihydrate by applying high vacuum or by heating at 120 °C, but this was accompanied by significant loss in crystallinity.

In situ X-ray diffraction studies of the crystallization of VOHPO4·0.5H2O

Time resolved in situ X-ray diffraction was used to study the formation of vanadyl hydrogen phosphate hemihydrate (VOHPO4·0.5H2O) in organic media. This technique has identified a new phase at early synthesis times (less than 300s) at a d-spacing of 7.5 and 3.1Å. The feature at 7.5Å shifted to 6.7Å during the first 20min of synthesis and this phase collapsed as VOHPO4·0.5H2O formed. Thin symmetrical platelets of 10μm×10μm dimensions were observed when samples were recovered after short synthesis times. Energy dispersive X-ray analysis indicated that these platelets contained vanadium and phosphorus. The platelets appeared to delaminate possibly associated with the strain generated when the d-spacing shifted from 7.5 to 6.7Å, from which growth of the VOHPO4·0.5H2O into the familiar rosette morphology occurs.

Surfactant assisted organization of an exfoliated vanadyl ortho phosphate to a mesostructured lamellar vanadium phosphate phase

The catalytically important vanadyl hydrogen phosphate hemihydrate, VOHPO 4 · 0.5H 2O phase with strong interlayer bonding has been exfoliated for the first time in DMF-water mixture and the exfoliated hemihydrate phase has been reorganized into a novel mesostructured lamellar VPO phase having the same V–P–O connectivity as in VOHPO 4 · 0.5H 2O, using octadecyl amine as the structure directing template.

Crystallisation of VOHPO 4·0.5H 2O in the presence of a surfactant

The formation of vanadyl hydrogen phosphate hemihydrate (VOHPO 4·0.5H 2O) by progressive attachment of phosphorous to a vanadium oxide lamellar phase in the presence of cetyltrimethylammonium bromide (CTAB) is described. Evidence from nuclear magnetic resonance (NMR), XPS, X-ray diffraction (XRD) and scanning electron microscopy (SEM) is presented for the initial formation of a vanadium oxide lamellar structure with no long-range order to which phosphate is then progressively attached. Phosphate attachment leads to lamellar collapse with the resultant formation of the hemihydrate phase, VOHPO 4·0.5H 2O.

The effect of varying the duration of the butane/air pretreatment on the morphology and reactivity of (VO) 2P 2O 7 catalysts

Three vanadium pyrophosphate catalysts have been prepared by calcining vanadium hydrogen phosphate hemihydrate (VOHPO 4·0.5H 2O), prepared in an organic medium, for different lengths of time (40, 100 and 132 h) in a n-butane (0.75%)/air mixture at 673 K. The catalysts were designated VPO40, VPO100 and VPO132. Increasing the duration of reaction with n-butane/air mixture led to an increase in the total surface area from 21.3 (VPO40) to 24.9 m 2 g −1 (VPO100) and 27 m 2 g −1 (VPO132). It also led to the complete removal of the VOPO 4 phase from catalysts VPO100 and VPO132, this VOPO 4 phase having been seen as a minor component of catalyst VPO40. Scanning electron microscopy showed that longer periods of pretreatment in the n-butane/air mixture produced catalysts with increasing amounts of a characteristic rosette-type of agglomerate. Increasing the duration of the butane/air pretreatment at 673 K resulted in a lowering in the amount of oxygen desorbed on temperature programming, indicating that the butane/air pretreatment was effectively reducing. However, and apparently paradoxically, increasing the duration of the butane/air pretreatment resulted in an increase in the amount of oxygen removed from the catalysts by temperature programmed reduction in H 2, rising from 11 monolayers for VPO40 to 14 monolayers for VPO100 and to 15 monolayers for VPO132. All three catalysts showed a reduction peak with a maximum temperature of ∼1000 K for the removal of 11 monolayers of oxygen, while catalysts VPO100 and VPO132 showed a second reduction peak at ∼1100 K for the removal of an additional three (VPO100) and four monolayers (VPO132) of oxygen.

Characterization and catalytic activity of novel palladium-incorporated vanadium phosphates

Palladium has been introduced into the layered vanadyl hydrogen phosphate hemihydrate VOHPO 4·0.5H 2O in different ways depending upon the medium of preparation. In aqueous medium, the introduction of palladium leads to the formation of a new phase containing mixed valent vanadium whereas in the preparation in organic medium, the palladium appears to substitute into the lattice of the parent compound. The palladium-incorporated compounds have been found to be catalytically active, both for oxidative coupling as well as for hydrogenation reactions, with the activity and selectivity varying quite markedly with the mode of incorporation.

The effect of the duration of n-butane/air pretreatment on the morphology and reactivity of (VO)2P2O7 catalysts

Three vanadium pyrophosphate catalysts have been prepared by calcining vanadium hydrogen phosphate hemihydrate (VOHPO4⋅0.5H2O, prepared in an organic medium) for different lengths of time (40, 100 and 132 h) in a n-butane (0.75%)/air mixture at 473 K. The catalysts were designated VPO40, VPO100 and VPO132. Increasing the duration of reaction with n-butane/air mixture led to an increase in the total surface area from 21.3 m2 g−1 (VPO40) to 24.9 m2 g−1(VPO100) and to 27.0 m2 g−1(VPO132). It also led to the complete removal of the VOPO4 phase from catalysts VPO100 and VPO132, this VOPO4 phase having seen as a minor component of catalyst VPO40. Scanning electron microscopy showed that longer periods of pretreatment in the n-butane/air mixture produced catalysts with increasing amounts of a characteristic rosette-type of agglomerate. Temperature-programmed reduction with H2 resulted in the removal of ∼11 monolayers equivalent of oxygen from all three of these catalysts at a peak maximum temperature of ∼1000 K with the development of a second reduction peak at ∼1100 K which increases with increasing time of n-butane/air pretreatment. The morphology produced by extended pretreatment in the n-butane/air mixture at 673 K is therefore predisposed to reaction with H2 (and probably with n-butane). Apparently paradoxically, increasing the duration of n-butane/air pretreatment results in catalysts which on temperature-programmed desorption desorb less oxygen.

Tribomechanical pretreatment of vanadium phosphates: structural and catalytic effects

The influence of the tribomechanical pretreatment of the precursor vanadyl hydrogenphosphate hemihydrate, VOHPO4·0.5H2O, prepared in aqueous medium and of the catalyst vanadyl pyrophosphate, (VO)2P2O7, on the structural and catalytic properties of (VO)2P2O7 in the oxidation of n-butane to maleic anhydride was investigated. Due to the pretreatment the activity and selectivity of the catalyst were markedly increased. The increase in catalytic performance is explained as an effect of the particle size in connection with lattice imperfections.

On the rehydration of vanadyl pyrophosphate to vanadyl hydrogenphosphate hemihydrate

Vanadyl pyrophosphate-based VPO catalysts for butane oxidation to maleic anhydride can be completely rehydrated in the solid phase into their vanadyl hydrogenphosphate hemihydrate precursors which again can be transformed into vanadyl pyrophosphate thus enabling a reuse of spent catalysts.