Solvothermal synthesis and characterization of nanocrystalline vanadium-chromium composite oxides and catalytic ammoxidation of 2,6-dichlorotoluene

Vanadium‐chromium oxides(VCrO)were usually prepared by high‐temperature solid‐state reactions;however,mixed phases were frequently produced and the morphology of the products was not well controlled.In this work,we prepared amorphous VCrO precursors by using V2O5 and CrO3 and alcohols or mixtures of alcohol and water via solvothermal reaction at 180°C.The precursors were then calcined under nitrogen at various temperatures.The products were characterized by powder X‐ray diffraction,transmission electron microscopy,and X‐ray photoelectron spectroscopy.It was revealed that pure‐phase nanocrystalline orthorhombic CrVO4 was obtained when methanol or methanol/water was used as the solvothermal medium and the precursor was calcined at 700°C.The size of the CrVO4 crystals was around 500 nm when methanol was used,whereas it reduced significantly to less than 50 nm when a mixture of methanol and water was used.The sizes could be effectively tuned from 10 to 50 nm by varying the methanol/water volume ratio.To the best of our knowledge,this is the first report on the synthesis of pure‐phase CrVO4 nanocrystals.The nano‐CrVO4 showed almost the highest catalytic activity for the ammoxidation of 2,6‐dichlorotoluene to 2,6‐dichlorobenzonitrile among the reported bi‐component composite oxides,owing to its smaller particle size,larger specific surface area,and more exposed active centers.

Monte Carlo Simulation of Kinetics of Ammonia Oxidative Decomposition over the Commercial Propylene Ammoxidation Catalyst (Mo-Bi)

Monte Carlo method is applied to investigate the kinetics of ammonia oxidative decomposition over the commercial propylene ammoxidation catalyst(Mo-Bi). The simulation is quite in agreement with experimental results. Monte Carlo simulation proves that the process of ammonia oxidation decomposition is a two-step reaction.

Product selectivity controlled by manganese oxide crystals in catalytic ammoxidation

The performances of heterogeneous catalysts can be effectively tuned by changing the catalyst structures.Here we report a controllable nitrile synthesis from alcohol ammoxidation,where the nitrile hydration side reaction could be efficiently prevented by changing the manganese oxide catalysts.α-Mn_(2)O_(3)based catalysts are highly selective for nitrile synthesis,but MnO_(2)-based catalysts includingα,β,γ,andδphases favour the amide production from tandem ammoxidation and hydration steps.Multiple structural,kinetic,and spectroscopic investigations reveal that water decomposition is hindered onα-Mn2O3,thus to switch off the nitrile hydration.In addition,the selectivity-control feature of manganese oxide catalysts is mainly related to their crystalline nature rather than oxide morphology,although the morphological issue is usually regarded as a crucial factor in many reactions.

3,4-Dichlorotoluene Ammoxidation to 3,4-Dichlorobenzonitrile over VPO/SiO_2 Catalyst

Ammoxidation of 3,4\|dichlorotoluene(DCT) to prepare 3,4\|dichlorobenzonitrile (DCBN) over silica supported vanadium phosphorus oxide catalysts has been studied. On the VPO/SiO 2 catalyst, the influence of the reaction temperature, the molar ratio of air/DCT, the molar ratio of NH 3 /DCT in the feed gas and the space velocity ( v s) on the conversion, yield and selectivity was observed. The most appropriate reaction condition is: reaction T =673 K, n (DCT)∶ n (NH 3 )∶ n (air)=1∶7∶30 and v s=250 h -1 . At this optimum reaction condition, the conversion of DCT is 97.8%; the molar yield of DCBN is 67.4%. It was found that the addition of element phosphorus can improve the yield of DCBN compared with VO/SiO 2 catalyst.

Ammoxidation of Substituted Toluenes on Silica-Supported VPO Catalysts

The ammoxidation of substituted toluenes to their corresponding nitriles over silica-supported vanadium phosphorus oxide (VPO/SiO2) catalysts has been studied. the effects of carrier silica, the addition of phosphorus, the substituents and the loadings have been discussed. Compared with unsupported VPO, the VPO/SiO2 catalysts have higher catalytic activity for ammoxidation of substituted toluenes and much lower reaction temperature. XRD shows that vanadium phosphorus oxides exist as amorphous phase and disperse to a high degree on the silica surface in 10%loading catalyst. When the loadings are over 10%, the crystalline α-VOPO4 would emerge, which would decrease the yield and selectivity. Additional phosphorus can form composite oxides with vanadia and play concerted catalytic function, which increase the selectivity of nitriles remarkably. Different substituents or same substituents on different positions have different influences because of the variant electronic stability of intermediates, the hindered accessibility of methyl group or the chemisorption state of the substrate molecule on the electrophilic catalyst surface.

Synthesis of 4-Phenylphthalonitrile by Vapor-Phase Catalytic Ammoxidation of Intermediate 4-Phenyl-<i>o</i>-Tolunitrile: Reaction Kinetics

Kinetic regularities of 4-phenyl-o-tolunitrile ammoxidation on V-Sb-Bi-Zr/γ-Al2O3 oxide catalyst in the temperature interval 633 - 673 K have been studied. It has been established that rates of conversion of 4-phenyl-o-tolu- nitrile into the aimed 4-phenylphthalonitrile and CO2 are described by half-order equation on concentration of substratum and to be independent of the oxygen and ammonia partial pressures. It has been revealed that formation of 4-phenylphthalimide from byproducts is due to hydrolysis of 4-phenylphthalonitrile;carbon dioxide is produced by oxidation of 4-phenyl-o-tolunitrile and decarboxylation of 4-phenylphthalimide, and 4-phenylben- zonitrile is produced from 4-phenyl-o-tolunitrile and 4-phenylphthalimide.

Effect of reduction-oxidation treatment on the properties of VSb_3W-Al_2O_3 catalyst for propane ammoxidation

VSb3W-Al2O3 catalysts for propane ammoxidation were prepared by the conventional slurry method and new slurry method,namely,the reduction-oxidation slurry method.The effect of preparation methods on the physicochemical properties of VSb3W-Al2O3 catalysts were studied by N2 adsorption,XRD,XPS and Raman spectroscopy,and their catalytic performance for the ammoxidation of propane to acrylonitrile were tested.Compared with the VSb3W-Al2O3 catalyst prepared by the conventional slurry method,the VSb3W-Al2O3 catalyst prepared by the reduction-oxidation slurry method exhibited better propane conversion and acrylonitrile selectivity.This is due to that the reduction-oxidation treatment was advantageous for obtaining low valence state vanadium and high valence state antimony to form more rutile SbVO4,which is a vital active phase for propane ammoxidation.

Monte Carlo Simulation of Propylene Selective Oxidation and Ammoxidation overβ-Bi2Mo2O9 Catalyst under Anaerobic Condition

A random walk Monte Carlo （RWMC） simulation model of catalytic particle was established on the basis of the structures of bismuth molybdate catalysts and mechanisms of catalytic reactions with propylene selective oxidation and ammoxidation. The simulation results show that rationality of the RWMC model is proved on the basis of pulse experimental data. One of the most remarkable factors affecting catalytic behavior is the transfer of bulk lattice oxygen, which decides the rate of ammonia-consuming and propylene-consuming. The selectivity of main products reaches the maximum after the reduction of catalysts to a certain degree. It is inferred that catalytic performance improves greatly if the ratio of capacity for dehydrogenation from adsorbed propylene molecule on catalytically active site of molybdenum metal-imido group （Mo=NH） to that on catalytically active site of molybdenum metal-oxo group （Mo=O） becomes much higher.

2-Cyanopyrazine Prepared from 2-Methylpyrazine by Catalytic Ammoxidation on MoVPO Catalyst

The mechanism of 2-cyanopyrazine prepared from 2-methylpyrazine （2-MP） by catalytic ammoxidation has been explained by the theory of appropriate structure of group. A new catalyst of MoVPO was developed. The effects of catalyst promoter phosphorus and supports were investigated. The catalyst containing P, V and Mo in molar ratio of 1.4 ： 1 ： 0.02 and supported on activated alumina and prepared by impregnation method exhibits good activity and selectivity. Reaction factors such as reaction temperature, space velocity, feed composition and service life of catalyst were investigated. Optimum reaction conditions （the volume space velocity of 0.2h-1, the reaction temperature of 380 ~C and molar ratio of 1 ： 7.8 ： 8 ： 8 for 2-MP, water, oxygen and ammonia） were obtained. Selectivity of 93% and yield of 86% could be achieved under these conditions.

Sepiolite supported catalyst multicomponent metal oxide for ammoxidation of propane

Natural sepiolite was treated with HCl solution to change its surface and internal structure and the structure of sepiolite was cracked to produce SiO2 when the concentration of HCl is more than 2 mol/L. The Mo-Bi-Fe-Co-V-Sb-O/sepiolite catalyst was prepared through impregnationprecipitation method and characterized by means of X-ray diffraction, scanning electron microscopy and energy dispersive spectrum techniques. The effects of temperature, volume fractions of NH3 and O2, and space velocity of feed gas on catalytic activity were evaluated in a fixed bed reactor. The results show that propane conversion of 82% and selectivity to acrylonitrile of 38% can be obtained at 490 ℃, V（C3H8）∶V（NH3）∶V（O2）=1.00∶1.05∶2.50 and space velocity of 3 000 cm3·g-1·h-1.

Research on Preparation of 2,4-Dichlorobenzonitrile by Ammoxidation of 2,4-Dichlorotoluene

A process for ammoxidation of 2, 4-dichlorotoluene to prepare 2, 4-dichlorobenzonitrile which is a key intermediate of organic synthesis was studied. Having appraised and screened catalysts on an apparatus of umicroreactor-chromatograghy', the further experiments confirming the catalyst and find-ing the optimum technological conditions were carried out by using a fixed-bed reactor made of quartz (30mm inside diameter). The influence of temperature, the ratio of ammonia, the ratio of air and the space velocity of catalyst upon the conversion, molar yield and selectivity of the reaction were observed, respec-tively. Using catalyst of DC124, on the suitable conditions, the highest conversion is 98. 1 %, molar yield is 89. 5%. The 2, 4-dichlorobenzonitrile obtained is white sheet or needle crystal with the purity hlgher than 99%. The effect of two chlorine atoms at 2, 6 or 2,4 position on the reaction is discussed based on the research of the ammoxidation of 2, 6-dichlorotoluene and 2,4-dichlorotoluene.

Effect of Preparation Method on the Physicochemical Properties of MoVNbTe Catalyst for Propane Ammoxidation to Acrylonitrile

MoVNbTe catalyst has been found to be the most active and selective catalyst in the ammoxidation of propane to ACN, the selective oxidation of propane to acrylic acid and in the oxidative dehydrogenation of ethane to ethylene. However, in our previous work, when 0.5 mL of MoVNbTe catalyst prepared using slurry method was tested in the propane ammoxidation to ACN, it only shows 1% conversion of propane with about 55% selectivity to CAN, thus giving only 0.6% yields to ACN. The poor catalyst activity is attributed to insufficient formation of crystalline phases essential for the propane activation process. In an attempt to improve the physicochemical properties of this catalyst, several preparation methods have been used, namely hydrothermal, reflux, changing the solvent and changing the calcinations temperature. The modified catalysts have been characterized using X-Ray Diffraction （XRD） and N2 physisorption （BET）. The MoVNbTe catalyst prepared by hydrothermal method shows a remarkable improvement in the formation of crystalline phases.

Ammoxidation of 3-Picoline over V-Mo-P Oxide Catalyst Prepared from 11-Molybdo-l-Vanado Phosphoric Acid

V-Mo-P oxide catalyst system was directly prepared from ll-molybdo-l-vanado phosphoric acid by thermal decomposition. Supported V-Mo-P oxide catalysts were prepared by wet impregnation method. Catalysts were characterized by FTIR （Fourier transform infrared）, XRD （X-ray diffraction） and TPD （temperature programmed desorption）. The catalytic activity of V-Mo-P oxide catalysts were investigated for vapour phase ammoxidation of 3-picoline. The unsupported catalyst showed 92.1% yield where as V-Mo-P oxide/HZSM-5 showed the highest yield （80.4%） amongst the supported catalysts.

Influence of V/P Ratio on the Catalytic Performance of VPO/SiO_2 Catalysts for Ammoxidation of Chloro-Substituted Toluenes

A series of vanadium phosphate oxide(VPO) catalysts supported on silica(VPO/Si O2) with various mole ratios of V/P(nV:nP=1:0.8-1:3) were prepared through impregnation method. The catalytic activity was evaluated by ammoxidation reactions of several kinds of chloro-substituted toluenes(CT) in a fixed-bed reactor. The catalyst presented the best performance when nV:nP is 1:1.6. The prepared catalysts were characterized by N2 adsorption, hydrogen temperature programmed reduction(TPR) and ammonia temperature programmed desorption(TPD) and etc. The results reveal that P can decrease the bonding energy of V=O and increase the mobility of lattice oxygen which was beneficial for the improvement of the catalysts, while too much P can greatly decrease the average oxidation number of V which leads to deactivation of the catalysts. The surface acidity of the VPO/Si O2 catalysts is affected by nV:nP and the catalyst had the highest surface acidity when nV:nP is 1:1.6. The selectivity of catalysts is proportional to the surface acidity when nV:nP is lower than 1:3.0.

A New Synthetic Route for Preparation of 2-Chloro-6-fluoro- benzonitrile and 2-Chloro-6-fluorobenzoic Acid

An effective synthetic route for preparation of 2-chloro-6-fluorobenzonitrile, 2-chloro-6-fluorobenzamide and 2-chloro-6-fluorobenzoic acid has been described. It includes diazotization, fluorination, ammoxidation and hydrolysis reactions.

Synthesis of 2, 4-Dibromo-5-Fluorobenzonitrile

2,4-Dibromo-5-fluorobenzonitrile has been synthesized for the first time (81.5% yield). It may be used in synthesizing 2,4-dibromo-5-fluorobenzoic acid, the intermediates of fluoroquinolones. The ammoxidation procedure for preparation of the nitrile has been described in detail.

A New Synthetic Route for 2,4-Dibromo-5-fluorobenzoic Acid

A convenient and practical synthetic route for 2,4-dibromo-5-fluorobenzoic acid is described. Two intermediates, 2,4-dibromo-5-fluorobenzonitrile and 2,4-dibromo-5-fluorobenzamide, have not been reported before. This route can be easily industrialized.

Catalytic Amidation of 5-Hydroxymethylfurfural to 2,5-Furandicarboxamide over Alkali Manganese Oxides

2,5-Furandicarboxamide was firstly synthesized in yield of 85% via catalytic oxidative amidation of 5-hydroxy- methylfurfural with aqueous NH3 over alkali manganese oxides of a-MnO2/NaxMnO〉 The intermediates of 5-hydroxymethyl-furonitrile, 2,5-dicyanofuran, and 5-cyano-2-furancarboxamide were verified and their reactivities were further examined. The kinetic analysis results showed that the transformation of intermediate product of 5-cyano-2-furancarboxamide to 2,5-furan-dicarboxamide is a slower step, which is closely relative to the reaction temperature and basicity of catalyst.