n-Butane Oxidation over γ-Al2O3 Supported Vanadium Phosphate Catalysts

Four vanadium phosphate catalysts supported onγ-Al_2O_3(20 wt%)were synthesized via wetness impregnation of VOHPO_4·0.5H_2O precursor and calcined for different durations(6,10,30 and 75 h)at 673 K in a reaction flow of n-butane/air mixture.The samples calcined for 6 and 10 h produced only a single phase of(VO)_2P_2O_7.However,the VOPO_4 phase(β-VOPO_4)was detected and became more prominent with only a minor pyrophosphate peaks were found after 30 h of calcination.All these pyrophosphate peaks disappeared after 75 h of calcination.The formation of V~(5 )phase was also observed in the SEM micrographs.The redox properties and the nature of oxidants of the catalysts employed in this study were investigated by H_2-TPR analysis.Selective oxidation of n-butane to maleic anhydride(MA) over these catalysts shows that the percentage of n-butane conversion decreases with the transformation of the catalysts from V~(4 )to V~(5 )phases.An appropriate ratio of V~(5 )/V~(4 )can enhance the performance of the VPO catalyst.However,a higher amount of V~(5 )and its associated oxygen species are responsible to promote the MA selectivity.     

The Role of Lewis Acid Sites in γ-Al2O3 Oligomerization

Olefin oligomerization by γ-Al₂O₃ has recently been reported, and it was suggested that Lewis acid sites are catalytic. The goal of this study is to determine the number of active sites per gram of alumina to confirm that Lewis acid sites are indeed catalytic. Addition of an inorganic Sr oxide base resulted in a linear decrease in the propylene oligomerization conversion at loadings up to 0.3 wt %; while, there is a >95 % loss in conversion above 1 wt % Sr. Additionally, there was a linear decrease in the intensity of the Lewis acid peaks of absorbed pyridine in the IR spectra with an increase in Sr loading, which correlates with the loss in propylene conversion, suggesting that Lewis acid sites are catalytic. Characterization of the Sr structure by XAS and STEM indicates that single Sr²⁺ ions are bound to the γ-Al₂O₃ surface and poison one catalytic site per Sr ion. The maximum loading needed to poison all catalytic sites, assuming uniform surface coverage, was ∼0.4 wt % Sr, giving an acid site density of ∼0.2 sites per nm² of γ-Al₂O₃, or approximately 3 % of the alumina surface.     

Methane Decomposition over Ni/α-Al2O3 Promoted by La2O3 and CeO2

The decomposition of methane on Ni/a-Al2O3 modified by La2O3 and CeO2 with differ-ent contents has been investigated and the ralationship between methane decomposition and removal of carbon by CO2 over these catalyst has also been studied by pulse-chromatography. The catalysts were characterized by TPR and XRD. It was shown that Ni/a-Al2O3 could be promoted by adding La2O3, and the carbon species produced over this catalyst was activated and eliminated by CO2. But CeO2 would suppress the decomposition of methane over Ni crystallite. Both La2O3 and CeO2 can inhibit aggregation of the Ni particles. Decomposition of methane over the Ni-based catalysts is structure sensitive to a certain extent.     

Acid–Base Properties of γ-Al2O3 Suspension Studied by pK Spectroscopy

Theoretic fundamentals of the method of pK spectroscopy are formulated as applied to investigating acid–base properties of suspensions, hydrosols, and solutions of macromolecules. The computer-aided treatment of the data of potentiometric titration of the relevant substrates makes it possible to determine the molar fractions of corresponding acid–base groups (per total number of these groups) as a function of pK values of these groups. An appropriate computer program is tested with a model example and resulted in a pK spectrum meeting the model requirements. The method of pK spectroscopy is used to study acid–base properties of -Al₂O₃ suspension. In the pK spectrum obtained, four bands corresponding to four types of acid–base groups on the oxide surface are observed that appears to be a direct verification of the James–Parks model.     

Catalytic Combustion of Methane over MnOx／ZrO2-Al2O3 Catalysts

MnOx/Al2O3 and MnOx/ZrO2-Al2O3 catalysts were prepared by incipient wetness impregnation of Mn(CH3COO)2 on the corresponding supports, followed by the characterization using X-ray diffraction (XRD). temperature programmed reduction (TPR) and BET surface area techniques. The result shows the BET surface area of ZrO2-Al2O3 is lower than that of Al2O3 due to the loading of ZrO2.However tile resulted MnOx/ZrO2-Al2O3 catalyst exhibits higher activity for methane combustion than MnOx/Al2O3, because the addition of ZrO2 onto Al2O3 is beneficial for the dispersion of Mn species and the improvement of the lattice oxygen activity in MnOx. subsequently the activation of methane during combustion. The optimum loading of Zr in MnOx/ZrO2-Al2O3 is in the range of 5%-10% correlated with the calcination temperatures of catalyst supports.     

Synthesis of 2,2,4-trimethyl-1,2-dihydroquinolines over metal-modified 12-tungstophosphoric acid-supported γ-Al2O3 catalyst

Research on Chemical Intermediates - In spite of having significant pharmacological importance, scalable synthesis of 2,2,4-trimethyl-1,2-H-dihydroquinoline (TMQ) is always being cumbersome due to...     

A Green Synthesis of 2-Ethylanthraquinone by Dehydration of 2-(4''''-ethylbenzoyl) benzoic Acid over Solid Acid Catalysts

2-EAQ is an important intermediate for the synthesis of hydrogen peroxide, pharmaceu- ticals, pesticides, and dyes. With the increasing demand for hydrogen peroxide, it needs to enhance the yields of 2-EAQ. However, in the conventional process, concentrated H2SO41-2 is employed as the catalyst in the dehydration of BE acid for the synthesis of 2-EAQ, which produces a series of environmental impacts and safety concerns. For these reasons, a substitute process, which has little or no hazard…     

Regioselective Synthesis of 1,5-Disubstituted 1,2,3-Triazoles by Reusable AlCl3 Immobilized on γ-Al2O3

There is rapidly growing interest in the synthesis and use of substituted 1,2,3-triazoles. We report an easy and interesting procedure that demonstrates the effectiveness of surface-modified γ-Al₂O₃, which is reusable, efficient, catalytic, safe, and environmentally acceptable for the regioselective synthesis of 1,5-disubstituted-1,2,3-triazoles via [3 + 2] cycloaddition of phenyl and benzyl azides with a series of aryl nitroolefins in good yields. No adverse effect on substituents such as nitro, cyano, hydroxy, ether linkage, and halogens was observed. The catalyst could easily be recycled and was reused for nine runs without losing its activity.     

A Green Synthesis of 2-Ethylanthraquinone by Dehydration of 2-（4＇-ethylbenzoyl） benzoic Acid over Solid Acid Catalysts

The dehydration of 2-（4＇-ethylbenzoyl） benzoic acid （BE acid） to 2-ethylanthraquinone （2-EAQ） was investigated over solid acid catalysts. The results showed that H-beta zeolite catalyst modified by dilute HNO3 solution exhibited an excellent performance. In our study, the conversion of BE acid can reach 96.7%, and the selectivity to 2-EAQ is up to 99.6%.     

Autothermal Reforming of Methane over Ni Catalysts Supported on CuO-ZrO2-CeO2-Al2O3

Ni catalysts supported on various mixed oxides of Al2O3 with rare earth oxide and transitional metal oxides were synthesized. The studies focused on the measurement of the autothermal reforming of methane to hydrogen over Ni catalysts supported on the mixed oxide ZrxCe30-xAl70Oδ (x=5, 10, 15). The catalytic performance of Ni/Zr10Ce20Al70Oδ was better than that of other catalysts. XRD results showed that the addition of Zr to Ni/Ce30Al70Oδ prevented the formation of NiAl2O4 and facilitated the dispersion of NiO. Effects of CuO addition to Zr10Ce20Al70Oδ were also investigated. The activity of Ni catalyst supported on CuO-ZrO2-CeO2-Al2O3 was somewhat affected and the Ni/Cu5Zr10Ce20Al65Oδ showed the best catalytic performance with the highest CH4 conversion, yield of H2, selectivity for H2 and H2/CO production ratio in operation temperatures ranging from 650 to 750℃.     

Metathesis of Butylene-2 and Ethylene to Propylene over 3.0Mo／（Hβ＋γ-Al2O3） Catalysts with Different γ-Al2O3 Contents

A series of 3. OMo/(Hβ γ-Al2O3) samples with γ-Al2O3 contents in the range of 0-100% (mass fraction) was studied by means of XRD, NH3-TPD, TPR and BET determinations for characterizing their structures. The Hβ zeolite structure in the 3.0Mo/Hβ sample can be effectively stabilized by adding some γ-Al2O3 to Hβ zeolite. γ-Al2O3 mainly favors the formation of polymolybdate or multilayered Mo oxide, while Hβ mainly forms the Al2(MoO4)3 species, as evaluated by the TPR technique. When used as the catalyst for the metathesis of butylene-2 and ethylene to propylene, there exists a close correlation between the specific surface area and stability of the catalyst. The specific surface area of the catalyst shows the maximum when (Hβ γ-Al2O3) contains 30%γ-Al2O3, which is in agreement with that of the time needed for the reaction stablization. In the case of maximum surface area, the rate of coke deposition is the minimum.     

Ammonia Decomposition over Bimetallic Nitrides Supported on γ-Al2O3

A series of monometallic nitrides and bimetallic nit-rides were prepared by temperature-programmed reaction with NH3. The effects of Co, Ni and Fe additives and the synergic action between Fe, Co, Ni and Mo on the ammonia decomposition activity were investigated. TPR-MS, XRD were also carded out to obtain better insight into the structure of the bimetallic nitride. The results of ammonia decomposition activity show that bimetallic nitrides are more active than monometallic nitrides or bimetallic oxides.     

Mechanism on The Disproportionating Synthesis of Dichlorodimethyl- silane by ZSM-5(5 T)@γ-Al2O3 Series Core-Shell Catalysts

In view of the wide application of organosilicon bifunctional structure in industry, the most effective disproportionation solution is used by the new catalyst to prepare the largest and the most versatile organic silicon monomer dimethyldichlorosilane. However, there are still remaining doubts on the disproportionation mechanism of the catalyst. The Density Functional Theory (DFT) was used to theoretically calculate the disproportionation mechanism of 5 T clusters ZSM-5@γ-Al₂O₃ series catalysts at the B3LYP/6–311++G(3df, 2pd) level. The properties were verified and the catalytic effects of different active sites pre- and post- modified by AlCl₃ were calculated and compared. The active center of HZSM-5@γ-Al₂O₃ was proton, and that of AlCl₃/ZSM-5@γ-Al₂O₃ changed to lewis acidic center. The presence of the lewis acid center enhances the total activity of the catalyst to some extent. The catalytic activity of the 5 T cluster ZSM-5@γ-Al₂O₃ catalyst modified by AlCl₃ was higher, which was the same as the experimental results.     

Tungsten Promoted Ni／Al2O3 Catalysts for Carbon Dioxide Reforming of Methane to Synthesis Gas

A series of tungsten promoted alumina supported nickel catalysts has been prepared for the carbon diox-ide reforming of methane to synthesis gas. The catalysts have been characterized by means of XRD, TEM,and Laser Raman spectroscopy. It is shown that the addition of tungsten to the nickel catalyst can stabilize the catalyst and increase the resistance to carbon deposition. Adding a suitable amount of tungsten can also increase the catalyst activity to be close to that of supported noble metal catalysts. The carburisation of the tungsten modified nickel catalyst decreases the catalyst activity at lower reaction temperatures (＜1123K),but has no effect on the catalyst performance at higher reaction temperatures. The alumina supported nickel catalyst modified by 0. 67% (mass fraction) WO3 has the equivalent equilibrium constant of the dry reforming reaction to that of alumina supported 5% (mass fraction) Ru at 873 K, and also has a lower activation energy for dry reforming than the latter.     

Environment-friendly synthesis of N-phenylpiperidine from aniline and 1,5-pentanediol over γ-Al2O3 catalyst

An efficient environment-friendly synthesis of N-phenylpiperidine was developed from aniline and 1,5-pentanediol over γ-Al2O3 catalyst under atmospheric pressure. The conversion of 1,5-pentanediol reached 97% and the selectivity for N-phenylpiperidine attained 94%. The structure of the catalyst was characterized by NH3-TPD and BET. The influences of calcination temperature of the catalyst and reaction temperature on activity and selectivity of the catalyst were investigated.     

Environment-friendly synthesis of N-phenylpiperidine from aniline and 1,5-pentanediol over γ-Al2O3 catalyst

An efficient environment-friendly synthesis of N-phenylpiperidine was developed from aniline and 1,5-pentanediol over γ-Al2O3 catalyst under atmospheric pressure. The conversion of 1,5-pentanediol reached 97% and the selectivity for N-phenylpiperidine attained 94%. The structure of the catalyst was characterized by NH3-TPD and BET. The influences of calcination temperature of the catalyst and reaction temperature on activity and selectivity of the catalyst were investigated.     

TG Study of the Dispersion Threshold of Mn2O3 on γ-Al2O3

Mn₂O₃/-Al₂O₃ catalysts were prepared by the impregnation method, and the maximum monolayer dispersion capacity or dispersion threshold value of Mn₂O₃ on the surface of -Al₂O₃ was determined to be 13.08% from the decomposition mass loss of supported Mn(NO₃)₂ in the monolayer state. This was compared with the values estimated from a close-packed monolayer model and an interaction model. It was confirmed that the high activities and selectivities of the catalysts for benzoic acid hydrogenation to benzaldehyde are due to the monolayer dispersion of the Mn₂O₃ on the surface of -Al₂O₃.This revised version was published online in November 2005 with corrections to the Cover Date.     

Surface reactions of dimethyl ether on γ-Al2O3

The surface reactions of dimethyl ether (DME) on industrial alumina (γ-Al₂O₃) were studied by chromatographic analysis of the products at the outlet of the flow reactor and (independently) by diffuse reflectance IR spectroscopy. The major products of the reactions at 250°С were found to be methanol formed in the reaction of DME with hydroxyl groups (the 3720 and 3674 cm^–1 bands in the diffuse reflectance spectrum) and various methoxy groups (the 1121, 1070, 695, and 670 cm^–1 bands in the differential spectra). The presence of molecularly adsorbed methanol was confirmed by experiments with methanol fed in a high-temperature IR cell. The interaction of the resulting methanol molecule with the hydroxyl group led to the formation of a water molecule in the gas phase and a methoxy group on the oxide surface. Strong adsorption of molecular DME was revealed, which was favored by an increase in the temperature of the preliminary calcination of oxide from 250 to 450–500°С; treatment of alumina with water vapor after its preliminary contact with DME led to a recovery of the hydroxyl coating and a replacement of molecularly adsorbed DME with hydroxyl. The thermal effect recorded in a flow reactor was positive during the adsorption of DME and negative during the desorption of weakly bonded DME. Schemes of formation of methoxy groups in the interaction of DME and methanol with surface hydroxyls were suggested.     

Effective Removal of CF4 by Combining Nonthermal Plasma with γ-Al2O3

Conversion of CF₄ was experimentally evaluated with three systems including catalytic hydrolysis, NTP-alone and plasma catalysis. Firstly, activity of γ-Al₂O₃ for CF₄ conversion was tested via catalytic hydrolysis. Experimental results indicate that the highest CF₄ conversion (72%) could be achieved with γ-Al₂O₃ in the presence of 45% H₂O_(g) with the operating temperature of 900 °C and the apparent activation energy is calculated as 85 kJ/mol using power rate law model. For plasma-based systems, results indicate that CF₄ conversions achieved with plasma catalysis remain 100% with the applied voltage ranging from 12 to 23 kV, while the highest CF₄ conversion achieved with NTP-alone is 86%. For the effects of various parameters on plasma-based systems, the results indicate that plasma catalysis also has better resistivity for higher total flow rate, CF₄ concentration and O₂ contents. Especially, CF₄ conversion could maintain at 100% with the operating applied of 23 kV as CF₄ concentration is increased to 10,000 ppm. On the other hand, CF₄ conversion achieved with NTP-alone is 18% at the same conditions. In addition, negative effect of O₂ on plasma catalysis could be reduced by the addition of Ar due to its good discharge properties and high excitation threshold energy (13 eV). The kinetics of plasma catalysis is investigated for CF₄ conversion by a simplified model, and the results indicate that overall energy constant achieved with plasma catalysis reaches 0.015 mg J^?1. Overall, plasma catalysis is demonstrated with good potential for the reduction of CF₄ emission.