Ammoxidation Activity Research Articles

Hollow flower-like Cr2V4O13 hierarchical micro-nano architectures: Controlled self-assembly synthesis and the outstanding catalytic performances for ammoxidation of chlorotoluenes

The controlled synthesis of hierarchical micro-nano materials has attracted great interest due to their wide applications in catalysis and many other fields. In this paper, hollow flower-like Cr2V4O13 hierarchical micro-nano structures were successfully synthesized via a facile hydrothermal process and subsequent calcination treatment. The samples were characterized by XRD, TGA, FT-IR, SEM, TEM, XPS, TPR and N2 adsorption-desorption. SEM and TEM micrographs showed that the as-obtained Cr2V4O13 had a three-dimensional (3-D) hollow flower-like superstructure assembled by numerous nanoflakes with widths of 0.2 µm and thickness of about 30 nm. The micro-nano structured Cr2V4O13 exhibited high activity and selectivity in continuous ammoxidation of chlorotoluenes to the corresponding chlorobenzonitriles. To the best of our knowledge, this is the highest activity reported for selective ammoxidation of chlorotoluenes with Cr-V-O binary catalysts. The unique catalytic behavior of Cr2V4O13 was ascribed to the micro-nano hierarchical architecture and the increased active surface sites.

Synthesis of nanoparticle-built FeVO4 microspheres with improved low temperature catalytic activity in ammoxidation

FeVO4 microspheres were successfully fabricated by a hydrothermal approach. Characterization results revealed that the FeVO4 microspheres are composed of numerous nanoparticles. In the ammoxidation of 2,6-dichlorotoluene (DCT) to 2,6-dichlorobenzonitrile (DCBN) catalyzed by FeVO4 microspheres, the conversion of DCT reaches up to 87% at a much lower temperature of 320 °C in comparison to previously reported catalysts (380–420 °C). The reason for this is that irons greatly improve the electron transport, leading to well reduction redox properties of vanadium species which are important to enhance the initial activation efficiency of C-H bond in methyl group.

Understanding the role of Al2O3-ZrO2 mixed oxides as support for vanadium catalysts for the selective ammoxidation of o-chlorotoluene to o-chlorobenzonitrile

o-Chlorotoluene (o-CT) ammoxidation to prepare o-chlorobenzonitrile (o-CBN) was investigated on Al2O3-ZrO2 supported V2O5 catalysts in the temperature range of 360 to 420 °C. A set of vanadium oxide supported on mixed oxides with varying its loadings were prepared by wet impregnation method. The catalysts surface and structural characteristics were derived from BET-surface area, X-ray diffraction, FT-infrared, temperature programmed reduction, temperature programmed desorption of ammonia and UV–Vis diffuse reflectance spectroscopy. The characterization results revealed that vanadium species were well dispersed and strongly interacted with mixed oxide support. The ammoxidation activity was depended on V2O5 content and its nature of surface species existing in the catalyst. The catalyst with 10 wt% of V2O5 on Al2O3-ZrO2 showed high ammoxidation activity with 100% selectivity to o-CBN. Moreover, the catalyst showed consistent activity during time on stream study.

Effect of Organic Matter Promotion on Nitrogen-Cycling Genes and Functional Microorganisms in Acidic Red Soils

The application of exogenous organic matter is considered the main method of increasing the organic matter content of acidic red soils. Nitrogen is an important limiting factor for soil fertility. Changes to the soil ecosystem under organic matter promotion can affect soil nitrogen cycling and related functional microorganisms; however, there have been no studies on this aspect. Acidic upland red soils, with or without long-term organic fertilizer application, were chosen as the research materials in this study. Based on metagenomic sequencing and alignment in the nitrogen-cycling gene database, the present study aimed to investigate the effect of organic matter promotion on nitrogen-cycling genes and functional microorganisms in acidic red soils, which had been amended with exogenous organic matter for 32 years. The results showed that organic matter promotion in acidic soils increased the total organic carbon and total nitrogen content, and alleviated soil acidification. Organic matter promotion increased the soil net nitrification activity and potential for ammoxidation. Organic matter promotion increased the abundance of amoA genes (encoding ammonia monooxygenase) and nar, nap, nir, nor, and nos genes (encoding denitrification reductase); decreased the abundance of hao genes (encoding hydroxylamine oxidase) and nrf genes related to the dissimilatory nitrate reduction to ammonia; increased the abundance of glnA, gdh, glsA, ansB, and nao genes related to organic nitrogen metabolism; altered the abundance of functional genes related to assimilatory nitrate reduction; and changed the community composition of nitrogen-cycling microorganisms. After organic matter promotion, alleviation of soil acidification and enhancement of total organic carbon were the most important factors that affected the abundance of nitrogen-cycling genes and the community composition of functional microorganisms. Our results comprehensively investigated the inorganic and organic nitrogen-cycling genes, and correlated the functional genes, microbial populations, and functional activities in the ammonia oxidizing process, which provided supporting data to understand the nitrogen-cycling characteristics of acidic red soils and provided ideas for acidic soil improvement.

Influence of polyoxometalate structure in ammoxidation of 2-methylpyrazine

Keggin, Wells-Dawson and Preyssler structured polyoxometalates (POMs) were synthesized by different methodologies. The POMs were used as catalysts for ammoxidation of 2-methylpyrazine. The structural properties of POMs were determined by XRD, SEM, DRIFT, DRUV-vis, H2-TPR, NH3-TPD and N2-physisorption. Preyssler POM sample showed highest 2-methylpyrazine conversion (69%) and 2-cyanopyrazine selectivity (98%) at 380°C. Superior performance of Preyssler POM could be attributed to its redox behavior and relatively strong acid sites. Large number of ammonium ions in the secondary structure of Preyssler POM could also enhance the transformation of oxygenated 2-methylpyrazine species into 2-cyanopyrazine. A correlation between the amount of ammonium content of POMs and their catalytic ammoxidation activity was obtained.

Catalytic activity of vanadium-substituted molybdophosphoric acid supported on titania for the vapor-phase synthesis of isophthalonitrile

ABSTRACTDifferent wt% of vanadium-substituted molybdophosphoric acid H4PMo11VO40 loaded on titania (TiO2) are prepared by wet impregnation method. The catalytic activity of PMoV-supported titania catalyst for the vapor-phase ammoxidation of m-xylene at different temperatures is reported here. The synthesized catalysts were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction, N2 adsorption–desorption, thermogravimetric/differential thermal analysis, temperature programmed desorption (TPD), temperature programmed reduction (TPR) scanning electron microscopy, energy-dispersive X-ray spectroscopy (EDX), and transmission electron microscopy (TEM). FTIR studies confirmed that the Keggin structure of PMoV does not change even up to 460°C when loaded on TiO2 surface. Among all the PMoV-supported TiO2 catalysts, 1.7% PMoV/TiO2 showed excellent activity for vapor-phase ammoxidation of m-xylene with 85.4% yield of isophthalonitrile.

The Influence of Phosphorous Precursor on the Structure and Ammoxidation Activity of Molybdenum Phosphate Catalysts

Two series of molybdenum phosphate catalysts were synthesized by reacting ammonium heptamolybdate with (1) diammonium hydrogen phosphate and (2) ammonium dihydrogen phosphate. The structural and textural properties of the catalysts, formed during the calcination between 400 and 550 °C, were determined by physico-chemical methods and their catalytic activity evaluated in the ammoxidation of 2-methylpyrazine (MP). The catalysts formed using diammonium hydrogen phosphate displayed higher activity and selectivity during the ammoxidation reaction as compared to those prepared using ammonium dihydrogen phosphate. Formation of a regenerable Mo(OH)3PO4 appears to be responsible for the higher performance of the catalyst.

Cr–ZSM-5 catalysts for ethylene ammoxidation: Effects of precursor nature and Cr/Al molar ratio on the physicochemical and catalytic properties

Cr–ZSM-5 catalysts prepared by solid-state ion exchange with different Cr/Al molar ratios were characterized and tested in ethylene ammoxidation to acetonitrile in the temperature range 425–500°C. Starting from Cr acetate like precursor and lower Cr load (Cr/Al=0.5), small amount of chromate species, sited inside the zeolite matrix, exhibited lower catalytic activity in ammoxidation (12.5% of CH3CN yield). Increasing the Cr amount (Cr/Al=1) does not significantly improve the catalytic properties since agglomerates of amorphous Cr2O3 inhibited the accessibility of chromate species to the reactants. However, at higher Cr amount (Cr/Al=1.5), crystalline Cr2O3 particles reduced the diffusion of reactants to the internal active sites. Starting from Cr chloride like precursor, the corresponding solids are low-exchanged since CrCl3 evaporates. At Cr/Al molar ratios of 0.5 and 1, chromate species, sited in the exchange sites, exhibited interesting catalytic properties (18.5 and 25% of CH3CN yield at 500°C, respectively). Nevertheless, at higher metal load (Cr/Al=1.5), the excess of Cr transforms into crystalline Cr2O3 which inhibits the diffusion of reactants to the active sites and enhances the hydrocarbon oxidation mainly at low temperatures. As ethylene ammoxidation required ammonia activation over (poly)chromate sites, a possible pathway of such a step has been proposed on the basis of NH3-TPD results.

Ruthenium and gold-doped M1 phase MoVNbTeO catalysts for propane ammoxidation to acrylonitrile

Abstract Ammoxidation of propane to acrylonitrile was investigated over the M1 phase MoVNbTeO catalysts doped with 5 wt.% Ru and Au, respectively. The MoVNbTeO mixed metal oxide catalyst was synthesized by a hydrothermal method, whereas ruthenium and gold were introduced by incipient wetness impregnation. The structures of the MoVNbTeO mixed metal oxide and ruthenium- and gold-doped catalysts were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The XRD patterns of the original MoVNbTeO catalyst confirmed the formation of the orthorhombic M1 phase, while the XRD patterns of ruthenium- and gold-doped catalysts demonstrated that the presence of ruthenium and gold significantly affected the crystal structure of the MoVNbTeO M1 phase. The catalytic activity was studied in a tubular fixed-bed micro-reactor at atmospheric pressure and 360–445 °C. Ru- and Au-doped MoVNbTeO M1 catalysts showed lower ammoxidation activity than the original MoVNbTeO M1 catalyst. However, both doped catalysts were much more active in the oxidative dehydrogenation (ODH) of propane at relatively low temperature (

Dual-templating of macroporous multicomponent MoVTeNbO x catalysts for propane ammoxidation to acrylonitrile

Thermally stable ordered porous MoVTeNbO x phases displaying both macroporous and mesoporous structures were prepared for the first time by a dual-templating approach employing colloidal arrays of polystyrene spheres and non-ionic surfactants. The MoVTeNbO x phases possessing such dual porosity were obtained after polystyrene spheres and non-ionic surfactants were removed in a low temperature calcination step. These hierarchical MoVTeNbO x phases displaying bimodal pore structure transformed into macroporous rutile phase possessing nanocrystalline inorganic walls at high temperature. These MoVTeNbO x rutile phases possessed high surface areas (70 m2/g), desirable pore architectures, robust nanocrystalline inorganic walls, and enhanced thermal stability (up to 600 °C). Although these macroporous MoVTeNbO x rutile catalysts displayed lower activity in propane ammoxidation and lower acrylonitrile selectivity in propane ammoxidation as compared to the active and selective M1 phase, the novel synthesis method reported in these studies represents a promising general approach to design novel complex mixed metal oxides for a wide range of applications in selective oxidation catalysis.

Ammoxidation activity of in situ synthesized ammonium salt of molybdophosphoric acid on VOPO 4 catalysts

Two isomorphous VOPO 4 samples were synthesized by means of well-known aqueous and organic preparation methods. These materials are further used for the in situ generation of ammonium salt of 12-molybdophosphoric acid (AMPA) from their solid phase phosphate components. Formation of AMPA was confirmed by XRD, FTIR, Raman and XPS analyses. The activity of the catalysts was tested in a fixed bed tubular glass reactor at atmospheric pressure for the selective ammoxidation of 2-methylpyrazine (MP) to 2-cyanopyrazine (CP). The reaction was carried out in the temperature range of 360–420 °C. Between the two mono-phosphates tested, the α-VOPO 4 is observed to show somewhat better activity compared to β-VOPO 4. Interestingly, in situ synthesized AMPA catalysts displayed significantly better performance compared to their corresponding parent VOPO 4 solids. Among all catalysts tested, AMPA-α-VOPO 4 exhibited the best performance (conversion (MP) = ca. 90%, selectivity (CP) = 65% at T = 420 °C). The differences in catalytic performance of the tested catalysts are ascribed to the structural differences of the used VOPO 4 solids.

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.

The synthesis of rutile-type V/Sb mixed oxides, catalysts for the ammoxidation of propane to acrylonitrile: A comparison of high-energy milling and co-precipitation methods

This paper describes the preparation of rutile-type V/Sb mixed oxide (vanadium antimonate) with the ball-milling (mechano-chemical) method starting from single metal oxides, as well as the comparison with a similar system prepared by the co-precipitation method. Samples were tested as catalysts for the gas-phase ammoxidation of propane to acrylonitrile. The mechano-chemical method allowed the preparation of the rutile-type mixed oxide characterized by smaller crystallite size than the catalyst prepared by co-precipitation and calcined at 450 °C. The calcination at 700 °C of the sample prepared by the mechano-chemical method led to a crystalline vanadium antimonate characterized by a higher concentration of cationic defects than the corresponding calcined sample prepared by co-precipitation. This led to a considerably higher activity in propane ammoxidation, but to a lower selectivity to acrylonitrile.

Microwave‐Assisted Hydrothermal Synthesis of Monophasic Mo‐V‐Te‐Nb‐O Mixed Oxide Catalyst for the Selective Ammoxidation of Propane

Rapid and green: Crystalline, multimetallic oxide with orthorhombic M1 phase structure can be synthesized rapidly and reproducibly by microwave heating. The material exhibits very high catalytic activity for direct ammoxidation of propane to acrylonitrile (see picture).

Effect of P/Fe ratio on the structure and ammoxidation functionality of Fe-P-O catalysts

Abstract Bulk FePO 4 catalysts, with varying P/Fe atomic ratio in the range of 1–1.6, were prepared and characterized by XRD, FT-IR, TPR, Potentiometric titration, Laser Raman, TEM, XPS and TG/DTA techniques in order to study the influence of P/Fe atomic ratio on the nature and extent of the active phase formation. The data obtained from XRD and Laser Raman techniques suggested predominant formation of the quartz type iron phosphate at close to stoichiometric P/Fe ratio, but as the ratio increased beyond 1.4 a progressive transformation of monomeric phosphate into its polymeric form was observed. XPS spectra reflected the presence of iron in its 3+ state when P/Fe ≤ 1.2 and exists as Fe 2+ and Fe 3+ when P/Fe ≥ 1.4. The catalytic properties of these iron phosphates were studied in the vapor phase ammoxidation, taking 2-methylpyrazine (MP) to 2-cyanopyrazine (CP) as an example. The ammoxidation activity of the catalysts was found to be proportional to the extent of quartz phase formed which in turn was proportional to the redox property, as observed by the oxidation functionality of the catalysts in benzyl alcohol transformation. However, the selectivity to nitrile was found to be dependent on the acid strength of the catalysts.

Characterization and reactivity of Al 2O 3–ZrO 2 supported vanadium oxide catalysts

Vanadium oxide catalysts with V 2O 5 loadings ranging from 2.5 to 20 wt.% supported on Al 2O 3–ZrO 2 (1:1 wt.%) mixed oxide have been prepared by wet impregnation method. The calcined samples were characterized by X-ray diffraction (XRD), BET surface area, pulse oxygen chemisorption, electron spin resonance (ESR), temperature-programmed reduction (TPR) of H 2, X-ray photoelectron spectroscopy (XPS), and UV–vis diffuse reflectance spectroscopy (UVDRS). The catalytic properties have been evaluated for vapor phase ammoxidation of toluene to benzonitrile. Dispersion of vanadia was determined by the pulse oxygen chemisorption method at 643 K. Vanadia is found to be present in a highly dispersed state at lower loadings and dispersion decreases steadily with increase of vanadia loading. The ESR spectra obtained under ambient conditions shows the presence of V 4+ in tetrahedral symmetry. The TPR results show a single reduction peak corresponding to V 5+→V 3+. XPS results reveal that vanadium is present in a fully oxidized state (+5) in all the samples. The intensity ratio V 2p 3/2/Al 2p 3/2 and V 2p 3/2/Zr 3d 5/2 is found to increase with increase in vanadia loading up to 12.5 wt.% and levels off at higher vanadia loadings. The UV–vis diffuse reflectance spectra indicate the existence of isolated and clusterized tetrahedral (Td) V 5+ species in all catalysts. Ammoxidation activity increases with vanadia loading up to 12.5 wt.%, which corresponds to monolayer coverage and remains constant at higher vanadia loadings. The catalytic activity in ammoxidation of toluene to benzonitrile has been correlated to the oxygen chemisorption sites.

The influence of support on ammoxidation of 3-picoline over vanadia catalyst

The influence of high content of MoO 3 (32 mol%) in V 2 O 5 –MoO 3 –P 2 O 5 catalyst system supported on alumina, silica, HZSM-5 and modified clay was investigated for ammoxidation of 3-picoline. Unsupported VMPO catalyst and supported catalysts were prepared by incipient wet impregnation method keeping the mole ratio of V 2 O 5 –MoO 3 –P 2 O 5 (1.00:3.27:0.14) constant. FT-IR spectra and X-ray diffractograms showed interaction among the active oxides and the support. The major phases identified were Mo 4 V 6 O 25 , Mo 6 V 9 O 40 and MoV 2 O 8 . TG–DTA also showed the exothermic peaks indicating the formation of new compounds above 400 ° C. The physico-chemical properties of the catalysts were correlated with their activity and selectivity for ammoxidation of 3-picoline. The unsupported catalyst showed 96.0% selectivity whereas VMPO/HZSM-5 showed the highest selectivity (91.3%) amongst the supported catalysts. The influence of high content of MoO 3 (32 mole%) in V 2 O 5 -MoO 3 -P 2 O 5 catalyst system supported on alumina, silica, HZSM-5 and modified clay was investigated for ammoxidation of 3-picoline. Major intermediate phases identified are Mo 4 V 6 O 25 , Mo 6 V 9 O 40 , MoV 2 O 8 . FT-IR spectra and X-ray diffractograms showed interaction among the active oxides and the support. The physico-chemical properties of the catalysts were correlated with their activity and selectivity for ammoxidation of 3-picoline.

Cerium fluoride supported V2O5 catalysts: physico-chemical characterization and 3-picoline ammoxidation activity

Abstract V2O5/CeF3 catalysts with 2.4–15.2 wt.% of V2O5 were prepared by wet impregnation method. The catalysts were characterized by BET surface area and pore size distribution, powder X-ray diffraction and FT-IR. It was found that the formation of Cerium Vanadate (CeVO4) occurs during the stages of the catalyst preparation. The X-ray diffraction studies of the catalysts revealed the presence of crystalline CeVO4 phase. The lines due to CeVO4 phase were found to increase in intensity with the increase in amount (wt.%) of V2O5 in the catalysts. The FT-IR investigation also showed the formation of CeVO4 phase with increasing loadings of V2O5. The shift of pore-size distribution to lower pore range and increased pore volume confirmed the formation of CeVO4 structure in the catalysts. The catalytic activity for the ammoxidation of 3-picoline to nicotinonitrile on V2O5/CeF3 catalysts as a function of V2O5 loading on CeF3 has been studied. The continuous increase of CeVO4 with V2O5 loadings is responsible for the higher ammoxidation activity of the V2O5/CeF3 catalysts.

Synthesis, characterization and evaluation as catalysts for propane ammoxidation of VMoSbO systems with rutile-type structure

Monophasic, rutile-type Mo/V/Sb mixed oxides were synthesized with the co-precipitation procedure; Mo6+ replaced for V4+ in the lattice of V antimonate, and the (Mo+V)/Sb ratio remained approximately constant. The addition of Mo increased the catalytic activity in propane ammoxidation, but the catalysts became less selective to acrylonitrile, due to the increased contribution of combustion, and more active in ammonia oxidation to molecular nitrogen. This was attributed to an enhanced Lewis acidity, which increased the interaction of the catalyst with ammonia and favored its unselective transformation.

Studies on catalytic functionality of V2O5/Nb2O5 catalysts

Abstract A series of V 2 O 5 /Nb 2 O 5 catalysts with V 2 O 5 loadings ranging from 2 to 12 wt.% of V 2 O 5 were prepared by wet impregnation method. These catalyst samples were characterized by X-ray diffraction (XRD), oxygen chemisorption, electron spin resonance (EPR), temperature-programmed desorption (TPD) of ammonia, and scanning electron microscopy (SEM). The catalytic properties of these catalysts were tested for vapor phase ammoxidation of toluene to benzonitrile and compared with more traditional supports, such as Al 2 O 3 , SiO 2 and TiO 2 . Dispersion of vanadia was determined by the static oxygen chemisorption method at 640 K on the samples prereduced at the same temperature. At low vanadia loadings ( 2 O 5 phase at higher loadings of V 2 O 5 . The EPR spectra obtained under ambient conditions for the catalysts show the presence of V 4+ ions in a distorted tetrahedral symmetry. SEM results suggest that at low vanadia loadings vanadia is well dispersed and at higher loadings dense clusters are formed. The results of temperature programmed desorption of ammonia indicate that the acidity increases with vanadia loading up to 6 wt.% V 2 O 5 and decreases at higher vanadia loadings. The ammoxidation activity also increases with vanadia loading up to 6 wt.%, which corresponds to monolayer coverage and remains constant at higher vanadia loadings. The catalytic properties during ammoxidation of toluene are correlated to the oxygen chemisorption sites and acidic sites.