12-molybdophosphoric Acid Catalysts Research Articles

Ultralow sulfur diesel production with defective 12-molybdophosphoric acid polyoxometalate

Highly dispersed 12-molybdophosphoric acid catalysts with oxygen defects and strong acidity were synthesized and applied in the oxidation removal of dibenzothiophene for ultraclean diesel production.

Ammoxidation of 2-methyl pyrazine on supported ammonium salt of 12-molybdophosphoric acid catalysts: The influence of nature of support

Influence of the nature of support on the formation of catalytically active species was investigated to clarify the key factor for the synthesis of supported ammonium salt of 12-molybdophosphoric acid (AMPA) catalyst which maintains the activity of ammoxidation during 2-methylpyrazine reaction. With this aim, different loadings of niobia-, silica- and alumina-, supported AMPA catalysts were prepared. The AMPA loading was varied in the range of 5–25 wt%. The synthesized solids were characterized by nitrogen adsorption for BET surface area, XRD and 31P MAS NMR techniques. All the AMPA-supported samples are poorly crystalline even after 25 wt% AMPA loading. Investigations using 31P MAS NMR spectroscopy of samples revealed that Keggin ion existed as at least five different species on the supports. The investigated properties were acidity of the support and amount of AMPA loading on the support. Active sites for the ammoxidation of MP on supported AMPA catalysts seem to be the interacted and/or the lacunary species. Maximum catalytic activity could be obtained at lower loadings with AMPA deposited on acidic supports whereas the less acidic supports require higher loading. It was found that in order to efficiently generate the active interactive species, the support must have an acidity which promotes the formation of support-AMPA interactive species. It is possible to enhance the catalytic activity of the supported AMPA catalyst for ammoxidation of 2-methylpyrazine by controlling the acidity of the support and AMPA loading on the support. Ammonium salt of 12-molybdophosphoric acid (AMPA) supported on niobia, silica and alumina was studied for the ammoxidation of 2-methylpyrazine to 2-cyanopyrazine. The Keggin ion existed as five different species on the supports. The interacted and/or the lacunary species were proposed to be the active sites for the ammoxidation.

Effect of Ti Incorporation on Structure and Oxidation Activity of Ammonium Salt of 12-Molybdophosphoric Acid Catalysts

Effect of Ti Incorporation on Structure and Oxidation Activity of Ammonium Salt of 12-Molybdophosphoric Acid Catalysts

Single-step esterification of crude karanj (Pongamia pinnata) oil to fatty acid methyl esters over mesostructured SBA-16 supported 12-molybdophosphoric acid catalyst

Fatty acid methyl esters (FAME) are synthesized via the single step esterification of non-edible feedstock, crude karanj oil (CKO), of high level of free fatty acids (FFAs about 20%) with methanol over series of solid acid catalysts prepared by anchoring molybdophosphoric acid (MP, 5 to 25wt.%) onto SBA-16 support. The prepared catalysts were intensively characterized for their intrinsic physicochemical and textural properties using BET surface area, NH3-TPD, XRD, SAXS, FT-IR, SEM and EDX. Characterization results revealed that the intact MP Keggin structure was preserved in the final catalyst after the thermal treatment at 220°C. The catalyst with 15wt.% MP (MP-S-16(15)) exhibited a peerless catalytic activity achieving 82% of FAME yield using a molar ratio of methanol to CKO of 1:8 at 140°C and after 5h. The effect of different operational parameters such as MP concentration in the final catalysts, reaction temperature, molar ratio of methanol to CKO, catalyst wt.% and reaction time were investigated over the MP-S-16(15) catalyst toward the maximum FAME yield. The stability of the catalytic activity was examined through leaching and reusability tests. As such, the MP-S-16(15) catalyst was recycled through four consecutive batch runs to understand its stability.

Hydrotreating of coker light gas oil on Ti-modified HMS supports using Ni/HPMo catalysts

In the present investigation, Ti–HMS materials with variable Si/Ti molar ratios of 20, 40, and 80 were synthesized and employed as supports for Ni-promoted 12-molybdophosphoric acid (NiPMo) catalysts. The effect of the Ti ions and the immobilization of 12-molybdophosphoric acids on mesoporous materials were studied. Supports and catalysts were thoroughly characterized by using XRD, N2 adsorption analysis, FT-IR, Raman, TPR, DRIFT, SEM and TEM techniques. Results from XRD and IR measurements confirm the hexagonally ordered mesoporous structure and incorporation of Ti into the HMS support, respectively. It was found that incorporation of Ti and presence of HPA into the HMS structure increased the reducibility of the catalysts. Hydrotreating experiments were conducted using coker light gas oil under industrial conditions of temperature, pressure, LHSV, and gas to oil ratio of 330–370°C, 8.8MPa, 1h−1, and 600mL/mL, respectively. It was found that NiPMo catalysts prepared from heteropolyacids showed better performance in HDS and HDN of coker light gas oil (CLGO) than the NiMo catalysts prepared by conventional method using ammonium hepta molybdate (AHM) as Mo source.

Liquid phase nitration of benzene over supported ammonium salt of 12-molybdophosphoric acid catalysts prepared by sol–gel method

A mild and clean liquid nitration of benzene with 65% nitric acid as nitrating agent over silica supported ammonium salt of 12-molybdophosphoric acid catalysts has been investigated. These catalysts with different loadings were prepared by sol–gel method and characterized by X-ray diffraction (XRD) and FTIR spectra. The acidity of these catalysts was measured by the potentiometric titration method. The XRD and IR analysis revealed that supported catalysts possess the Keggin structure which is similar to 12-molybdophosphoric acid. And it can be found that the supported catalysts had high nitration reaction catalytic activity and selectivity over nitrobenzene. The effects of various parameters such as nitric acid/benzene volume ratio, temperature and time of reaction have also been systematically studied.

Host (nanocavity of dealuminated zeolite Y)–guest (12-molybdophosphoric acid) nanocomposite material: An efficient and reusable catalyst for oximation of aldehydes

12-Molybdophosphoric acid (MPA) encapsulated in the supercage of dealuminated zeolite Y (DAZY) was prepared and characterized by infrared spectroscopy (FT-IR), X-ray diffraction (XRD), differential thermal gravimetry (DTG) and atomic absorption spectroscopy (AAS) techniques. The amount of MPA in the supercage of zeolite was 0.0875 g/g of supported catalyst. This catalyst was used for efficient oximation of aldehydes under mechanical stirring, ultrasonic irradiation and solvent-free conditions and the corresponding products were obtained in 65–100% yields. The reaction times were 25–250 min for system under agitation with magnetic stirring, while under ultrasonic irradiation or solvent-free conditions, the oxime yields were increased and the reaction times decreased. The zeolite Y encapsulated 12-molybdophosphoric acid (MPA-DAZY) catalyst was reused several times without loss of its catalytic activity. The amount of Mo leached was less than 2.9%.

Studies on Ceria Supported Vanadium Incorporated Ammonium Salt of 12-Molybdophosphoric Acid Catalysts

A series of ceria supported vanadium incorporated ammonium salt of 12-molybdophosphoric acid (AMPV) catalysts were synthesized in a single-step by generating Keggin structure in situ. These catalysts were characterized by X-ray diffraction, FT-infrared, BET surface area, thermal analysis (TG/DTA) temperature programed reaction and acidity by potentiometric titration. The catalytic activities of these catalysts were tested for the vapor phase ammoxidation of 2-methylpyrazine to 2-cyanopyrazine. The CeO2 supported AMPV catalysts are more active and selective compared to other supports. The high activity and selectivity of these catalysts are related to the presence of both redox vanadium and oxygen storage release function of ceria.

Synthesis, Characterization and Ammoxidation Functionality of Silica Supported Vanadium Incorporated Ammonium Salt of 12-Molybdophosphoric Acid Catalyst

A series of silica supported vanadium incorporated ammonium salts of 12-molybdophosphoric acid (AMPV) catalysts, with 5–25 wt% of active component were prepared. These catalysts were characterized by XRD, FTIR, BET-Surface Area, TGA/DTA and acidity by potentiometry techniques. The characterization data derived from XRD, FT-IR techniques reveal that the AMPV on silica support exists in the form of Keggin structure. These catalysts are studied for the vapor phase ammoxidation of 2-methyl pyrazine (MP) to cyanopyrazine (CP). The conversion of methyl pyrazine increased with increase in loading on silica showing a maximum value of conversion at 20 wt% AMPV loading. The ammoxidation activity of these catalysts with and without vanadium is studied and the vanadium incorporation led to substantial improvement in the cynopyrazine selectivity.

Synthesis and Characterization of Zirconia Supported Vanadium Incorporated Ammonium Salt of 12-molybdophosphoric Acid Catalyst for Aerobic Oxidation of Benzyl alcohol

A series of zirconia supported ammonium salt of molybdophosphoric acid (AMPV) catalysts with and with out vanadium incorporation are prepared in a single step adopting wet impregnation method. These catalysts are characterized by BET surface area, XRD, FT-IR and potentiometric titration. XRD and FT-IR techniques suggest the formation of Keggin ion on zirconia support. The high resolution FT-IR analysis reveals the incorporation of vanadium into the primary structure of Keggin ion. The catalytic functionalities of these catalysts are tested for the aerobic oxidation of benzyl alcohol. The vanadium containing AMPV results in higher selectivity towards the oxidation product compared to the catalyst without vanadium incorporation.

Structure and reactivity of zirconium oxide-supported ammonium salt of 12-molybdophosphoric acid catalysts

A series of catalysts with varying quantities of ammonium salt of 12-molybdophosphoric acid supported on zirconium dioxide was synthesized. The catalysts were characterized by nitrogen adsorption for BET surface area, X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and 31P MAS NMR techniques to study the nature of the interactions of the active component with the support as a function of salt loading. The nature of the Keggin ion species (intact, fragmented or decomposed) formed on the support varies with the extent of loading of the heteropolyacid salt. A good correlation was obtained between the extent of formation of lacunary Keggin ion species and the activity of the catalysts during the ammoxidation of 2-methylpyrazine at different reaction temperatures.

Synthesis of linear alkyl benzenes over zirconia-supported 12-molybdophosphoric acid catalysts

The liquid-phase alkylation of benzene with 1-octene and 1-dodecene was investigated using zirconia-supported 12-molybdophosphoric acid (MPA) as catalyst. The catalysts with different MPA loading (5–25 wt.% calcined at 700 °C) and calcination temperature (15 wt.% calcined from 500 to 750 °C) were prepared by suspending zirconium oxyhydroxide in methanol solution of MPA followed by drying and calcination. These catalysts were characterized by X-ray diffraction, and 31P MAS NMR spectroscopy measurements. The XRD results indicated that MPA stabilizes the tetragonal phase of zirconia. 31P MAS NMR spectra show that the nature of phosphorous species depend on MPA loading and calcination temperature, and it show the existence of three types of phosphorous species, one is the Keggin unit and the other is the decomposition product of MPA and third one an unidentified species. FT-IR pyridine adsorption on 15% MPA catalyst calcined at 700 °C showed the presence both Brönsted and Lewis acidity. Under the reaction conditions of 83 °C, benzene/1-olefin molar ratio of 10 (time, 1 h), the most active catalyst, 15% MPA calcined at 700 °C gave more than 90% olefin conversion with selectivity to 2-phenyl octane, 55% and 2-phenyl dodecane, 45%.

Interaction-induced enhancement in the activity and selectivity of a titania-supported ammonium salt of a 12-molybdophosphoric acid catalyst during ammoxidation of 2-methylpyrazine.

A titania-supported ammonium salt of 12-molybdophosphoric acid has been synthesized, and the salt-support interaction, which enhanced the reaction rate, has been correlated with the activity of the catalyst in the ammoxidation of 2-methylpyrazine.

Surface Behavior of Supported 12-Heteropoly Acid As Revealed by Nuclear Magnetic Resonance, X-ray Photoelectron Spectroscopy, and Fourier Transform Infrared Techniques

Bulk, silica-, and zirconia−silica-supported 12-molybdophosphoric acid (HPMo) catalysts have been characterized by 31P and 1H-magic angle spinning NMR spectroscopy, X-ray photoelectron spectroscopy and Fourier transform infrared (FTIR) spectroscopy of pyridine adsorption. Two species, bound to the support surface and acid-free components, were found in both types of supported catalysts. The relative amount of these species varied depending on the type of the support and on the degree of hydration of the samples. Thermally stable molybdophosphate species up to higher temperature (723 K) were formed on silica support compared to bulk. The mixed zirconia−silica support causes the destruction of HPMo at significantly lower temperature, due to a stronger interaction of the zirconia with supported molybdophosphates. The FTIR of pyridine adsorption showed two types of acidity on the supported samples: Lewis and Brönsted. A correlation between the change in the intensities of the Brönsted acidity band and 1H NMR signal of acidic protons with temperature was found for supported HPMo: high intenstity of 1H NMR signal for HPMo on the mixed zirconia−silica support corresponds to high Brönsted acidity band caused from the residual protons involved in bridging OH groups.

Silica-supported 12-molybdophosphoric acid catalysts: Influence of the thermal treatments and of the Mo contents on their behavior, from IR, Raman, X-ray diffraction studies, and catalytic reactivity in the methanol oxidation

The thermal behavior of silica-supported 12-molybdophosphoric acid catalysts (PMoH- x series, x = Mo wt%, varying from 16.2 to 0.9) was investigated by using different techniques (IR and Raman spectroscopies, X-ray diffraction, and catalytic reactivity in methanol oxidation). The silica support used in the study (surface area 376 m 2 g −1) induces destabilization of 12-molybdophosphoric acid. The transformation into β-MoO 3 begins from 250°C, and is achieved at 350°C. β-MoO 3 is the main species on silica support in a wide range of temperatures, and seems to be stabilized by the support. The role of this molybdenum oxide is discussed in terms of active species in the catalytic reaction, and the capability to rebuild the Keggin unit under exposure to water vapor.

Modification of 12-molybdophosphoric acid catalyst by blending with polysulfone and its catalytic activity for 2-propanol conversion reaction

H 3PMo 12O 40 embedded in a polysulfone film was prepared by blending H 3PMo 12O 40 with polysulfone using dimethylformamide as a common solvent and its catalytic activity for 2-propanol conversion reaction was examined. The prepared film catalyst showed a higher yield for acetone but a lower yield for propylene than H 3PMo 12O 40 itself. The decrease of acidic function of the film catalyst was mainly due to dimethylformamide strongly adsorbed on the acid sites of H 3PMo 12O 40, while the increase of oxidation function was due to uniformly and finely distributed H 3PMo 12O 40 in the film. When the film catalyst was used as a membrane, it showed higher ratio of acetone to propylene than H 3PMo 12O 40 itself.

Evidence of β-MoO3formation during thermal treatment of silica-supported 12-molybdophosphoric acid catalysts

Unsupported and silica-supported H3PMo12O40 catalysts show a wide temperature range for decomposition on thermal treatment allowing the formation of monoclinic β-MoO3(characterized by Raman spectroscopy and X-ray powder diffraction); this new supported phase leads specifically to dimethoxymethane in the methanol oxidation reaction.

In situ laser Raman study of the effect of water on undoped and caesium-doped silica-supported 12-molybdophosphoric acid catalysts

The surface chemistry of silica-supported 12-molybdophosphoric acid (HPMo) catalysts and the caesium salts, in dehydrated and hydrated form, has been investigated by laser Raman spectroscopy (LRS). The Raman spectra were observed to be dependent on both the pretreatment temperature and the environment of the sample during heating. A sample containing 23 wt.% HPMo, equivalent to 0.12 of the molybdophosphate anions (Keggin unit, KU) per nm2, a loading only marginally greater than the monolayer loading found from X-ray photoelectron spectroscopy (XPS), produced an unidentified species and/or MoO3 on heating to temperatures higher than 300 °C. Upon exposure to water vapour, the unknown species is reconverted to the KU. With loadings of HPMo less than the monolayer equivalent no decomposition into MoO3 is observed at temperatures up to 550 °C. The stable species found on the silica surface after heating is believed to be the dehydrated or defect KU formed on removal of an oxygen ion in the process of the desorption of water.

The interaction of cesium ions with silica-supported 12-molybdophosphoric acid

The characterization by X-ray photoelectron spectroscopy (XPS), laser Raman spectroscopy (LRS), 31P NMR spectroscopy, and ion scattering spectroscopy (ISS) of cesium-doped silica-supported 12-molybdophosphoric acid (HPMo) is reported. The addition of cesium to a silica-supported 12-molybdophosphoric acid catalyst has been shown in previous work to poison the catalytic properties for partial oxidation of methane of the original HPMo catalyst. In this work it is shown that the HPMo anions, Keggin Units (KU) are not decomposed upon addition of Cs up to 3 Cs per KU although modification of the surface dispersion of the HPMo seems to occur. Evidence of a direct interaction between the KU and the cesium ions has been obtained from Raman, XPS, and ISS spectroscopies, resulting from an ion exchange between the proton of the acid and the Cs ions. XPS studies show that the Cs ions are well dispersed up to a loading corresponding to the exchange of the three H + by 3 Cs +. In addition an electronic perturbation of Cs and Mo is detected by XPS as well as a shift of the main Raman band corresponding to a weakening of the MoO t , bond in accordance with the electronic effect of Cs deduced from the catalytic results.

Ion-exchange properties of microporous monovalent salts of 12-tungstophosphoric acid and 12-molybdophosphoric acid catalysts

Ion exchange of the ammonium, potassium, and cesium salts of 12-tungstophosphoric and 12-molybdophosphoric acids has been studied at 298 K. Residual protons contained in the nonstoichiometric salts are exchanged as well as the original cations. The completeness of the ion-exchange process varied from approximately 5 to 70%, depending on both the solid phase and liquid phase cations. The maximum exchange capacities are shown to decrease significantly as the size of the cation leaving the solid becomes larger than that of the cation entering the solid.