Dehydrogenation of propane over a silica-supported vanadium oxide catalyst

The dehydrogenation of propane over a silica-supported vanadium oxide catalyst was investigated at 823 K under atmospheric pressure in the presence/absence of CO₂. The yield of propene and the selectivity to propene were higher in the dehydrogenation in the presence of CO₂ than those in the dehydrogenation in the absence of CO₂. On the other hand, the yield of aromatics and the selectivity to aromatics were much higher in the dehydrogenation in the absence of CO₂ than those in the dehydrogenation in the presence of CO₂. TPR measurements, NH₃ desorption studies and in-situ UV–vis studies on the catalyst were also performed to elucidate the effects of CO₂ on the behavior of the vanadium oxide in the catalyst during the dehydrogenation of propane.     

The kinetics and mechanism of the oxidation of carbon monoxide over an industrial vanadium oxide catalyst

The rate of catalytic oxidation of carbon monoxide was studied in a fixed bed reactor over the following range of conditions: 325 to 396°C, 0.11 to 1.75 mole % oxygen, 9.50 to 10.20 mole % carbon monoxide. Oxygen was the limiting component, most of the runs were taken to greater than 10% oxygen conversions, and therefore an integral approach was taken in the data analysis. The catalyst was vanadium oxide/potassium sulfate on silica, an industrial preparation which had been used in previous kinetic studies. The data were correlated successfully by the steady state adsorption model with Arrhenius activation energies of 22.1 k.cal/g. mole for the oxygen chemisorption step and 18.0 k.cal/g. mole for the reaction step. The rate constants obtained provide further support for the steady state adsorption model, previously used to evaluate the oxidation kinetics of naphthalene, toluene, benzene and orthoxylene on the same catalyst. The integrated rate equation appears to well describe the relationship between the various parameters with the conversion of the limiting component varying from less than 5% to over 50%. A brief comparison is reported between the steady state adsorption model and the more complex triangular mechanism postulated by Hirota and co-workers.     

Progress of vanadium phosphorous oxide catalyst for n-butane selective oxidation

The utilization of lighter alkanes into useful chemical products is essential for modern chemistry and reducing the CO₂ emission. Particularly, n-butane has gained special attention across the globe due to the abundant production of maleic anhydride (MA). Vanadium phosphorous oxide (VPO) is the most effective catalyst for selective oxidation of n-butane to MA so far. Interestingly, the VPO complex exists in more or less fifteen different structures, each one having distinct phase composition and exclusive surface morphology and physiochemical properties such as valence state, lattice oxygen, acidity etc., which relies on precursor preparation method and the activation conditions of catalysts. The catalytic performance of VPO catalyst is improved by adding different promoters or co-catalyst such as various metals dopants, or either introducing template or structural-directing agents. Meanwhile, new preparation strategies such as electrospinning, ball milling, hydrothermal, barothermal, ultrasound, microwave irradiation, calcination, sol–gel method and solvothermal synthesis are also employed for introducing improvement in catalytic performance. Research in above-mentioned different aspects will be ascribed in current review in addition to summarizing overall catalysis activity and final yield. To analyze the performance of the catalytic precursor, the reaction mechanism and reaction kinetics both are discussed in this review to help clarify the key issues such as strong exothermic reaction, phosphorus supplement, water supplement, deactivation, and air/n-butane pretreatment etc. related to the various industrial applications of VPO.     

Kinetics of o-Xylene oxidation over sintered vanadium pentoxide in a spinning catalyst basket reactor

Kinetics of vapor phase oxidation of o-xylene has been studied over sintered and compacted vanadium pentoxide in a continuous stirred tank catalytic reactor in the temperature range of 450–517°C at atmospheric pressure. The major product obtained is phthalic anhydride. The other products are maleic anhydride and carbon dioxide. The reaction rate data are well represented (with average absolute deviation less than 6%) by the following expression derived by applying the steady-state oxidation-reduction model of Mars and van Krevelen to a parallel reaction scheme and assuming first order with respect to both o-xylene and oxygen: Significantly, the activation energies for all three postulated reactions with rate constants k₁, k₂, and k₃ turn out to be identical having a value of 14.8 kcal/mole, which may be taken to imply that there is only one rate-influencing reaction step for all the products and not three as assumed in deriving this equation.     

Catalytic oxidation of benzene,toluene and p-xylene over colloidal gold supported on zinc oxide catalyst

Au was loaded (1.5 wt.%) on the supports (ZnO, Al₂O₃ and MgO) by a colloidal deposition method. For a range of low temperatures (50–300 °C), the catalytic activity of Au/ZnO was much greater than that of Au/Al₂O₃ and Au/MgO. In particular, for the Au/ZnO, the benzene conversion exceeded 80% at 150 °C. The results of catalyst characterization suggested that the high catalytic activity of the Au/ZnO might be attributed to the effects of strong metal–oxide interaction which is possibly originated from the small lattice parameter difference between Au {111} and ZnO {101} lattice planes.     

Mesoporous vanadium oxide as catalyst for liquid-phase selective oxidation of diphenylmethane to benzophenone

The mesoporous vanadium oxide (MVO) was prepared from the surfactant cetyltrimethylammonium bromide along with benzyl alcohol as co-surfactant. It was found that the presence of benzyl alcohol in the synthetic mixture was essential to the formation and stability of MVO material. Characteristic mesoporous structure with uniform channel spacing as well as large surface area and pore volume of MVO sample were identified by XRD, SEM, TEM, and N₂ sorption techniques. The structure of vanadium–oxygen framework was explored using FT-IR and ⁵¹V MAS NMR spectroscopy; the MVO sample possessed distorted tetrahedron structure. Results from TPR studies indicated the easier reducibility of MVO as compared to bulk V₂O₅. In the liquid-phase selective oxidation of diphenylmethane to benzophenone in acetic acid as solvent, the MVO catalyst exhibited remarkably better catalytic performance than bulk V₂O₅; at 60 °C, the conversion and benzophenone selectivity reached 39.6 and 96.7% after 1 h reaction time, with a catalyst turnover frequency of 24.2 h⁻¹. These superior results were properly correlated to the physico-chemical properties of MVO catalyst.     

Selective oxidation of toluene ando-xylene on MgF2-supported monolayer vanadium oxide catalyst

Information on the reactions of selective oxidation of toluene ando-xylene on monolayer V₂O₅/MgF₂ catalyst was obtained using IR spectroscopy. Also adsorption of aldehyde derivatives of these reagents, i.e. benzaldehyde ando-tolualdehyde, was investigated in order to identify intermediate species, which were formed during the oxidation process. The measurements were carried out at different temperatures, under conditions similar to that of the catalytic reaction. On the surface of the catalyst many intermediate species, as aldehyde-like, keton-like and benzoate species, were detected. On the basis of the data obtained the mechanism of these reactions has been proposed.     

The oxidation of ethylene over a supported platinum catalyst

The complete oxidation of ethylene over a 0.3% Pt/Al₂O₃ catalyst, at ethylene concentration of ≤ 1.0 mol/m³ and oxygen concentrations of 0.16 to 8.6 mol/m³, was studied in a recycle reactor at temperatures of 362 to 472 K. The activity of the catalyst was influenced by pretreatment and reaction conditions causing fluctuations in rate measurements. Nevertheless, a simple rate function, r =Ae^?E/RT[O₂]/[C₂H₄], fitted the data as well as more complicated rate functions.     

Photocatalytic oxidation of alkane at a steady rate over alkali-ion-modified vanadium oxide supported on silica

Photocatalysts were applied to photocatalytic oxidation of propane in a fixed bed flow reactor. Titanium dioxide exhibited fairly high activity but the deep oxidation was predominant. Silica-supported vanadium oxide (VS) favors the partial oxidation to form propanone and variety of aldehydes and the fast deactivation took place accompanied by reduction of vanadium ions. On the other hand, alkali-ion-modified VS exhibited the highest activity and high selectivity to propanone. The activity was stable because vanadates in alkali-ion-modified VS do not change their structure or are not poisoned by water molecules throughout the reaction. The cleavage of C=C double bond to form aldehydes predominantly proceeded in the case of photo-oxidation of 1-butene over VS while in the case of photo-oxidation of Rb-modified VS, the oxidation of secondary carbon atom to form methyl vinyl ketone is favored. Methyl ethyl ketone was produced at a steady rate over Rb-VS in the photo-oxidation of n-butane.     

Simulation of the ammonia oxidation process over an oxide monolith catalyst

A mathematical model of ammonia oxidation over an oxide monolith honeycomb catalyst has been developed. Experimental data from a pilot unit operating under process conditions equal to those in a type UKL-7 commercial nitric acid plant were used to refine the parameters of the mathematical model. The results from calculating the NO yield are in satisfactory agreement with the pilot unit data. There is now computer program that allows us to calculate the conditions of an industrial reactor functioning.     

Influence of pressure on the kinetics of SO2 oxidation over a vanadium catalyst

The kinetics of SO₂ oxidation over a vanadium catalyst have been investigated in an integral reactor operated isothermally at pressures of one, five and ten atmospheres. The rate data have been analyzed by linear as well as non-linear least squares regression combined with other considerations to discriminate among possible reaction rate models.     

Catalytic ozone oxidation of benzene at low temperature over MnOx/Al-SBA-16 catalyst

The low-temperature catalytic ozone oxidation of benzene was investigated. In this study, Al-SBA-16 (Si/Al = 20) that has a three-dimensional cubic Im3m structure and a high specific surface area was used for catalytic ozone oxidation for the first time. Two different Mn precursors, i.e., Mn acetate and Mn nitrate, were used to synthesize Mn-impregnated Al-SBA-16 catalysts. The characteristics of these two catalysts were investigated by instrumental analyses using the Brunauer-Emmett-Teller method, X-ray diffraction, X-ray photoelectron spectroscopy, and temperature-programmed reduction. A higher catalytic activity was exhibited when Mn acetate was used as the Mn precursor, which is attributed to high Mn dispersion and a high degree of reduction of Mn oxides formed by Mn acetate than those formed by Mn nitrate.     

Reaction pathways in the selective oxidation of propane over a mixed metal oxide catalyst

The catalytic properties of a Mo–V–Te–Nb–O mixed metal oxide catalyst were investigated in the selective oxidation of propane and its corresponding partial oxidation intermediates. Propane oxidation pathways are proposed based on experimental findings.     

The effect of the nature of vanadium species on benzene total oxidation

The nature of the vanadium species present on V₂O₅/Al₂O₃ catalysts was investigated by using solid state ⁵¹V NMR, diffuse reflectance spectroscopy (DRS), X-ray diffraction (XRD) and temperature programmed reduction (TPR). ⁵¹V NMR and DRS analyses indicated the presence of V⁵⁺ in tetrahedral symmetry at low vanadium loading. A surface polymeric vanadium species and/or the bulk crystalline V₂O₅ were mainly observed at high vanadium loading as also detected by XRD. The positions of the absorption edges determined through the UV–VIS spectra allowed distinguishing between various tetrahedral symmetries. After TPR, the average oxidation state of vanadium depended on the vanadium content. The nature of vanadium species was related to the catalyst behavior on the benzene oxidation reaction. The catalysts containing high vanadium content were more active suggesting that a high amount of V⁴⁺ is responsible for the higher activity.     

从废钒催化剂中回收钒氧化物的研究

研究了将废钒催化剂经过氧化焙烧、水浸、渣碱浸、离子交换等工序制备偏钒酸铵或五氧化二钒的新工艺.探讨了工艺参数对附加剂配方、氧化焙烧、浸钒、离子交换及偏钒酸铵沉淀影响的规律性,为推广工业生产提供适宜的工艺条件.在此工艺条件下,可以制备出质量优于GB/T 3283-1987冶金99级标准的五氧化二钒产品,具有较好的经济效益和社会效益,市场前景广阔.     

Kinetics of oxidation of 2-methylpropene over chlorine modified copper oxide catalyst

The vapour phase air oxidation of 2-methylpropene to methacrolein over a copper oxide catalyst supported on pumice, modified by a continuous supply of chlorine, was investigated in an isothermal integral flow reactor at atmospheric pressure between 300 and 450 °C. The effects of several variables, weight ratio of modifier (CI) to 2-methylpropene in the feed, feed ratio of oxygen to 2-methylpropene, reaction temperature and the reciprocal of space velocity on the conversion and product distribution were determined by gas chromatography. The results indicate that the promotional effect of the modifier is mainly due to successful suppression of further oxidation of aldehyde to undesired products. Though several mechanisms were postulated, the rate of reaction was most satisfactorily correlated by a mechanism, which assumes the rate controlling step to be the surface reaction between charged adsorbed 2-methylpropene and oxygen.     

A vanadium phosphorus oxide catalyst synthesized in rotating packed bed for high-efficiency selective oxidation of n-butane

Oxidation of n-butane to produce maleic anhydride (MA) by the vanadium phosphorus oxide (VPO) catalyst is important for the fine chemical industry. However, the improvement in MA yield exceeding 60% is still a big challenge. In this article, a VPO catalyst with increased MA yield originated from the tailored structure of VPO precursor prepared in a rotating packed bed (RPB) reactor with excellent micro-mixing efficiency. The activated VPO-RPB catalyst displayed the coexistence of X₁-VOPO₄ and α_I-VOPO₄ phases and enhanced reducibility of V⁴⁺ state. Remarkably, the MA yield in n-butane oxidation catalyzed by VPO-RPB reached up to 66%, showing an increment by 14% compared with VPO-STR prepared in a stirring tank reactor (STR). The VPO-RPB showed the repeatable catalytic performance and achieved a promising scale-up production. This work provides the experimental evidence of a dual-phase (X₁-VOPO₄ and α_I-VOPO₄) mechanism for n-butane oxidation, and reveals the structure–activity dependence of VPO catalyst.     

关于硫酸生产钒催化剂的几点思考

探讨与硫酸生产钒催化剂有关的几个问题：催化剂开发的前沿机遇和研究资源的社会共享，钒催化剂检测标准与质量管理和监督，催化反应器设计与性能保证值，催化剂供应商与技术服务。建议利用国家重点实验室这一社会资源开展催化剂基础研究以寻求新的催化剂开发机遇，制定科学的检测标准，发挥国家认可实验室的作用加强催化剂质量的管理与监督，进行催化反应动力学研究和催化反应器模拟研究，完善催化剂供应的技术服务，全面提高我国催化剂产品的技术创新能力和市场竞争力。