Oxidation of toluene to benzaldehyde over VSb0.8Ti0.2O4 Effect of the operating conditions

In the present work, the kinetic toluene oxidation on VSb_0.8Ti_0.2O₄ based catalyst was studied. A reaction network, which involves three steps: the partial oxidation of toluene to benzaldehyde, a consecutive oxidation of benzaldehyde to carbon oxides and a parallel oxidation of toluene to carbon oxides, was proposed. The kinetic parameters were estimated assuming the redox mechanism proposed by Mars and van Krevelen. The products distribution was strongly affected by the reaction temperature. The adjustment of activation energies for total and partial oxidation of toluene led to the same values. The activation energy for the benzaldehyde oxidation was lower than the one for its formation.     

Multiplicity in the partial oxidation of propylene over a copper-molybdena catalyst

Measurement of rates of formation of acrolein and acetaldehyde in the partial oxidation of propylene over a copper molybdate catalyst were made under steady-state and transient modes. These measurements disclosed a rate of product formation multiplicity apparently attributable to the oxidation state of the catalyst and not to surface phenomena usually thought to be the source of hysteresis in catalytic systems.     

Transient kinetics of toluene partial oxidation over V/Ti oxide catalysts

Transient kinetics in the toluene oxidation over V/Ti oxide catalysts prepared by grafting and impregnation have been compared. V⁴⁺ cations are supposed to be the sites for the formation of electrophilic oxygen species participating in deep oxidation. Another oxygen species (probably nucleophilic) present on the oxidised catalyst surface are responsible for benzaldehyde formation. Selectivity of 80–100% can be obtained during the initial period of the reaction on the grafted catalysts in the presence of gaseous oxygen and during the interaction of toluene (without O₂ in the mixture) with partially reduced catalysts.     

The partial oxidation of some cyclohexenes and branched chain olefins over a silver catalyst

The oxidation of some cyclic and branched chain olefins over a silver catalyst effective for the conversion of ethylene to ethylene oxide has been investigated in a steady state flow system. The reaction of cyclohexene produces benzene and that of both 1-methylcyclohexene and 4-methylcyclohexene yields toluene. The selectivity to aromatics exceeds 20% for fractional conversions below 0.2, but it can be improved to almost 50% by inclusion of an optimum quantity of dichloroethane in the feed. Styrene is oxidised more slowly than the cyclohexenes and only carbon dioxide and water are produced. The oxidation of 3,3-dimethyl-1-butene and 3-methyl-1-butene occurs much faster than that of the cyclic molecules and some of the corresponding epoxides are produced. The selectivity with the dimethyl-butene is 9–13% for conversions to 0.2. The methylbutene requires a higher temperature for reaction and the epoxide yield is lower. Factors influencing reactivity and product distribution are discussed.     

Direct partial oxidation of methane over ZSM-5 catalyst: Zn-ZSM-5 catalyst studies

Extended studies on Zn-ZSM-5 catalyst for the production of liquid hydrocarbons in the direct partial oxidation (DPO) of CH₄ with O₂ are reported. Previously, it was reported that metal-containing ZSM-5 catalysts could produce C₅₊ hydrocarbons from pure CH₄/O₂ feeds without feed additives. Zn-ZSM-5 produced the highest C₅₊ yields of the catalysts tested. This work shows that the method of introducing Zn onto the catalyst, ion-exchange versus impregnation, does not significantly alter C₅₊ yields if low Zn content is maintained ( 0.4–0.5 wt%). Liquid hydrocarbon yields in this system doubled after 8 h on stream while overall C₂₊ yields increased by over 300%. Mechanistic implications of these findings are discussed. Finally, processing a natural gas feed over Zn-ZSM-5 gave higher C₅₊ yields over CH₄ feed but these yields were not improved over previously published results using HZSM-5.     

In situ growth of vanadia-titania nano/micro-porous layers with enhanced photocatalytic performance by micro-arc oxidation

Micro-arc oxidation process was used to synthesize V₂O₅-TiO₂ porous layers for the first time. Surface morphology and topography of the layers were investigated by scanning electron microscope (SEM) and atomic force microscope (AFM). X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) techniques were also employed to evaluate phase structure and chemical composition of the layers. It was found that the V₂O₅-TiO₂ layers consisted of anatase, rutile, and vanadium pentoxide phases fraction of which varied with the applied voltage and the electrolyte concentration. It was also revealed that pore size and surface roughness increased with the applied voltage and the electrolyte concentration. Optical properties of the layers were studied by a UV-vis spectrophotometer, and the band gap energies of the MAO-grown pure TiO₂ and V₂O₅-TiO₂ layers were respectively calculated as 3.21 and 2.56 eV. Furthermore, the composite layers exhibited a significantly enhanced photo-activity when compared to pure TiO₂ layers. The photocatalytic reaction rate constants of degradation of methylene blue on the surface of the V₂O₅-TiO₂ layers under ultraviolet and visible irradiations were measured as 0.0228 and 0.0117 min⁻¹, respectively. As a consequence, micro-arc oxidation was deduced to be an appropriate and efficient method for synthesis of V₂O₅-TiO₂ porous layers.     

The partial oxidation of norbornene over a silver catalyst under steady state conditions

The continuous oxidation of norbornene (C₇H₁₀) by molecular oxygen over a silver catalyst at 500–573 K has been investigated. In contrast to that observed during the temperature programmed reaction of norbornene and oxygen adsorbed on Ag(110) no norbornene epoxide is formed. Instead benzene is the sole partial oxidation product. A stable selectivity of 20 to 25% with fractional conversions up to 0.8 at 573 K could be obtained by inclusion of 15 to 30 ppm dichloroethane in the feed. Separate experiments withexo-norbornene epoxide showed that in the absence of oxygen it was almost completely isomerised to 3-cyclohexene-1-carboxyaldehyde with production of lesser amounts of norcamphor and norbornene. With oxygen present carbon dioxide and small amounts of benzene were also produced. It is concluded that norbornene epoxide cannot be a gas phase intermediate in the production of benzene from norbornene.     

Propane partial oxidation over M-substituted vanadyl phosphates dispersed on titania and silica

Mono-substituted M³⁺ compounds of vanadyl phosphate dihydrate VOPO₄·2H₂O, with formula [M(H₂O)]_xVO_1−xPO₄·nH₂O (M=Al, Fe, Cr, x=0.15–0.20, n=2–2.40), and a di-substituted compound with formula Fe_0.08Cr_0.08(H₂O)_0.16VO_0.84PO₄·2.9H₂O, either pure or supported, were characterised by XRD, EDAX, TG/DTA, physisorption and chemisorption measurements, and tested as catalysts in the partial oxidation of propane. Incorporation of the M³⁺ cation into VOPO₄ produces a marked increase in surface area, pore volume, and reducibility, with subsequent enhancement of the catalytic activity. Upon adsorption of these compounds on titania, a homogeneous distribution of highly dispersed species is obtained, whereas on silica small conglomerates of crystalline phases of VOP and FeVOP are formed, presumably by polymerisation on the acidic surface sites of the support. The titania-supported samples exhibit higher catalytic activity and better selectivity to partial oxidation products (acetic acid and propene), compared to silica-based materials; these effects are attributed to the higher dispersion and reducibility of the surface species. Propane oxidation over the supported materials undergoes transition to the ignited state, in which surface temperatures up to 900 K are attained, and homogenous reactions yield mainly propene and CO.     

以RTS为催化剂的湿法氧化脱硫技术

介绍了以RTS为催化剂的湿法氧化脱硫技术和实际运行效果。RTS催化剂脱硫效率高,不仅能脱除无机硫,还能脱除部分有机硫,析出的硫磺颗粒大且均匀。实践证明,该脱硫工艺运行与脱硫效果稳定,净化气中H2S含量为10-20mg／m^3。可满足使用高硫煤的脱硫需要。     

Vanadium peroxocomplexes as oxidation catalysts of sulfur organic compounds by hydrogen peroxide in bi-phase systems

New vanadium oxodiperoxocomplexes Bu₄N⁺[VO(O2)₂ L₂]⁻ were synthesized, where L=pyridine (1), 2-methylpyridine (2), 4-methylpyridine (3), 2-oxymethylpyridine (4). All complexes were characterized by NMR (¹H, ⁵¹V) and IR spectroscopy. The oxidation of sulfur organic compounds and diesel fuel desulfurization catalyzed by vanadium peroxocomplexes in bi-phase system was investigated in various solvents. The complexes manifested high catalytic activity and selectivity in oxidation of sulfides.     

Deactivation kinetics of V/Ti-oxide in toluene partial oxidation

Deactivation kinetics of a V/Ti-oxide catalyst was studied in partial oxidation of toluene to benzaldehyde (BA) and benzoic acid (BAc) at 523–573 K. The catalyst consisted of 0.37 monolayer of VO_x species and after oxidative pre-treatment contained isolated monomeric and polymeric metavanadate-like vanadia species under dehydrated conditions as was shown by FT Raman spectroscopy. Under the reaction conditions via in situ DRIFTS fast formation of adsorbed carboxylate and benzoate species was observed accompanied by disappearance of the band of the monomeric species (2038 cm⁻¹) (polymeric species were not controlled). Slow accumulation of maleic anhydride, coupling products and/or BAc on the surface caused deactivation of the catalyst during the reaction. Temperature-programmed oxidation (TPO) after the reaction showed formation of high amounts of CO, CO₂ and water. Rate constants for the steps of the toluene oxidation were derived via mathematical modelling of reaction kinetics at low conversion and constant oxygen/toluene ratio of 20:1. The model allows predicting deactivation dynamics, steady-state rates and selectivity. The highest rate constant was found for the transformation of BA into BAc explaining a low BA yield in the reaction.     

甲烷部分氧化制合成气反应中床层热点问题研究进展

综述了甲烷部分氧化制合成气反应中催化剂床层热点问题,包括热点产生的原因,热点位置的测定,热点温度的影响因素,以及热点问题的解决方法,对于保护催化剂和反应器,降低反应的危险性起到借鉴作用.     

Competitive no,co and hydrocarbon oxidation reactions over a diesel oxidation catalyst

The oxidation of NO, CO and hydrocarbons (HC) individually, in mixtures, and with NO₂ were investigated over a monolith‐supported Pt/Al₂O₃ catalyst under oxidising conditions. Although competitive adsorption and inhibition by other species on oxidation reactions is a relatively well‐known phenomenon, this study represents a more comprehensive examination of such effects between key components in vehicle exhaust gases. NO₂ was completely reduced by CO and C₃H₆, under NO₂ limited conditions, at temperatures as low as 110°C and at temperatures above 140°C with dodecane and m‐xylene. NO₂ was then again observed once the extent of oxidation of the other species by oxygen was significant. Under the conditions tested, NO, CO and HC oxidation was inhibited by NO₂ in the feed gas mixture. HC were also found to inhibit the oxidation of NO and other HC species due to site adsorption competition. For CO, HC did not change the onset of oxidation, but did inhibit the extent after their light off began. At low temperatures, CO was initially found to inhibit NO oxidation, but at higher temperatures, once CO oxidation was significant, CO promoted NO conversion to NO₂. The observed inhibition effects of the different gases on HC oxidation were not additive, indicating one species would cause inhibition, but once its inhibition ended, another species could still then cause inhibition. The combined effect of C₃H₆, NO and NO₂ on CO conversion was found to be additive. This is because CO oxidation started prior C₃H₆. © 2011 Canadian Society for Chemical Engineering     

Kinetic studies of the partial oxidation of isooctane for hydrogen production over a nickel-alumina catalyst

The kinetics of the catalytic partial oxidation of isooctane for hydrogen (H₂) production over a stable Ni/γ-Al₂O₃ catalyst was investigated at atmospheric pressure in the temperature range of 863-913 K, ratio of weight of catalyst to the molar feed rate of isooctane in the range of , and molar feed ratio O₂/i-C₈H₁₈ of 4.0 in a 12.7 mm diameter Inconel micro-reactor housed in an electrically controlled furnace. The developed rate models were based on the Langmuir-Hinshelwood-Hougen-Watson (LHHW) and Eley-Rideal (ER) formulations. Out of the 18 models developed, 10 were eliminated due to poor predictive efficiency. A LHHW mechanism requiring the dissociative adsorption of isooctane and molecular adsorption of oxygen on a single site was the most likely pathway for the partial oxidation of isooctane. The reaction order of 1.5 indicates a strong coverage of nickel by isooctane.     

Role of steam in partial oxidation of propylene over a Pd/SDB catalyst

Step-response studies of propylene partial oxidation with oxygen over a hydrophobic Pd/SDB catalyst were conducted at 1000 kPa and 185°C in a fixed-bed reactor. CO₂ was found to be the only oxidation product when the feed contained only propylene and oxygen. CO₂ formation was significantly suppressed by addition of steam to the feed, and this addition leads to the formation of partial oxidation products: acrolein and acrylic acid. A competitive reaction mechanism involving water molecules is proposed to explain the significant influence of steam concentration on the rate of propylene oxidation and product selectivity.     

Carbon as a catalyst in oxidation reactions and hydrogen halide elimination reactions

Carbon catalyses many reactions, mainly oxidation reactions with oxygen and with halogens, e.g. $\text{SO}{}_2\text{+}\text{1}\text{20}{}_2\text{→ SO}{}_3$, or CO + Cl₂→ COCl₂. It is known, however, that different carbons behave quite differently in the reduction of oxygen on fuel cell cathodes. Therefore the catalytic activity of carbons has been studied in other reactions. A convenient test reaction is the oxidation of dilute aqueous sulphurous acid. It became apparent that all catalytically active carbons contain small quantities of nitrogen, and inactive carbons such as wood charcoal or carbon blacks can be rendered highly active by treatment with N H₃ or HCN at elevated temperatures. Photoelectron spectra indicate that the catalytic activity increases parallel to the incorporation of a nitrogen species which is pyridine-like, i.e. incorporated in the aromatic layers. Treatment with NH₃ at 900 °C leads also to massive gasification of the carbons, increasing their surface area. Other reactions studied included the oxidation of aqueous oxalic acid and of methanol to formaldehyde. A quite different type of reaction is the elimination of hydrogen chloride from 1-chloroalkanes, e.g. 1 -chlorobutane. Again, activity changes in parallel to nitrogen content. Reaction products are olefins, dimers of the alkyl groups, and a polymer on the catalyst surface. The formation of alkyl dimers, e.g. n-octane in the case of n-butylchloride, suggests that radicals are involved in the reaction.     

Total oxidation of toluene on ferrite-type catalysts

Ferrite catalysts were prepared following two routes, i.e. the hydrothermal one and the calcination of an oxide mixture. In the first route sodium hydroxide, ferrous sulfate and the sulfate of the substituting ion (Mn, Ni) were used. The ferrites obtained using this route was Ni_xFe_3−xO₄ (x = 0.5) and Mn_xFe_3−xO₄ (x  0.65). Following the second route were prepared three samples: NiFe₂O₄, Ni_0.5Zn_0.5Fe₂O₄ and MnFe₂O₄. Two of them contain the corresponding ferrites while the latter is a presintered oxide mixture (Fe₂O₃–Mn₂O₃). All the samples were fully characterized using chemical analysis, X-ray fluorescence spectroscopy and EDX, nitrogen adsorption–desorption isotherms at −196 °C, X-ray diffraction (XRD), FTIR, scanning electron microscopy and XPS. The catalytic activity evaluation was made using a mixture of 1700 ppm vol. of toluene and air flowing at 100 ml min⁻¹ raising the temperature up to 600 °C in steps of 25 °C. Among these systems the sample representing the presintered Fe₂O₃–Mn₂O₃ mixture showed the highest activity.     

Rectorite as catalyst for wet air oxidation of phenol

Rectorite was characterized by XRF, BET, XRD, FT-IR, SEM and TPR, and investigated as catalyst for wet air oxidation of phenol in a batch reactor at 150 °C. The iron impurity, mainly presented as highly dispersed hematite, acted as active centers and showed good performance without significant iron leaching. The catalyst can be also used as adsorbent to remove leached iron in solution.     

Development of a dual functional structured catalyst for partial oxidation of methane to syngas

Rh-LaCoO₃ structured catalysts for the oxidative production of syngas from methane were developed by deposition of the active components on La-γ-Al₂O₃ washcoated honeycomb monoliths. SEM/EDS analysis showed a good adhesion of the washcoat layer and a uniform distribution of La and Co, while Rh was favourably located on the outer shell. Catalytic partial oxidation of methane was tested under both isothermal and pseudo-adiabatic conditions showing that the process can be conducted with high yield and selectivity and stable performance at short contact times over the novel catalysts, characterised by a limited content of noble metal and no need for pre-reduction. Further experiments of CO₂ autothermal reforming indicated the possibility to enhance CO production and to reduce the H₂/CO ratio through secondary endothermic reactions consuming CO₂, which are autothermally self-sustained in a single catalytic reactor operated at short contact time by the heat generated through partial oxidation reactions.     

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.