Oxidative conversion of propane to acrylic acid and acetic acid over mixed oxide catalysts

The oxidative conversion of propane to acrylic acid and acetic acid over Mo? V? Sb? R? O (R?La, Ce, Nd and Sm) catalysts at different reaction conditions (viz. temperature, C₃H₈/O₂ ratio, H₂O/C₃H₈ ratio, space velocity, etc.) was investigated. The catalytic activity and selectivity of the Mo? V? Sb catalyst are strongly influenced by the addition of rare earth metals to the catalyst. The addition of water vapour to the feed of propane and oxygen enhances greatly the formation of oxygenated products, particularly acrylic acid and acetic acid. The ratio of selectivities of acrylic acid to acetic acid was found to depend on the rare earth metal used in the catalyst's preparation and the reaction conditions. High contact times, i.e. high degrees of propane conversion, are detrimental to the formation of acrylic acid but beneficial for acetic acid formation. Copyright © 2005 Society of Chemical Industry     

Activity performance and kinetics for glycerol carbonylation with urea over Zn-Co mixed metal oxide catalyst

Efficient carbonylation of glycerol using urea with Zn-Co mixed metal oxide (MMO) catalyst has been achieved. Various methods of catalyst preparation were explored for glycerol carbonate (GC) synthesis. The optimized method of catalyst preparation was found to be co-precipitation (CP) with a Zn:Co ratio of 70:30, achieving 81% glycerol conversion with 97% GC selectivity. X-ray diffraction (XRD) studies revealed the formation of ZnO, Co₃ O₄, and spinel ZnCo₂O₄ phases. Thermal treatment given to the catalyst allows insertion of Zn cations into Co₃O₄ lattice forming ZnCo₂O₄ phase which was also evidenced in X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. Herein, for the first time, reaction kinetics was studied to propose the rate equation, based on which a plausible reaction pathway is proposed involving two-site adsorption of glycerol (basic site) and urea (acidic site), which undergo carbonylation followed by cyclization into GC. A recycle study and hot filtration test have proven the reusability of the catalyst.     

Gas-phase dehydration of glycerol over commercial Pt/γ-Al2O3 catalysts

Gas-phase dehydration of glycerol to produce acrolein was investigated over commercial catalysts based onγ-Al2O3, viz. A-64, A-56, I-62, AP-10, AP-56, AP-64 and KR-104. To understand the effect of Cl?anions, HCl-impregnated sup-ports have been investigated in the dehydration reaction of glycerol at 375 °C. For comparison, various H-zeolites were also examined. It was found that the glycerol conversion over the solid acid catalysts was strongly dependent on their acidity and surface area. And the relationship between the catalytic activity and the acidity of the catalysts was discussed. The outstanding properties of Pt/γ-Al2O3 catalyst systems for the dehydration of glycerol were revealed. Pt/γ-Al2O3 catalyst (AP-64) showed the highest catalytic activity after 50 h of reaction with an acrolein selectivity of 65%at a conversion of glycerol of 90%. Based on these results, catalysts based onγ-Al2O3 appear to be most promising for gas phase dehydration of glycerol.     

Catalytic valorization of bioethanol over Cu-Mg-Al mixed oxide catalysts

The conversion of ethanol into 1-butanol and 1,1-diethoxyethane was studied over Cu-Mg-Al mixed oxide catalysts obtained from LDH precursors. The optimum yields are obtained for Cu loadings comprised between 5 and 10 at.%. A reaction scheme accounting for the main and secondary reaction products is proposed. The influences of the reaction temperature and of the reaction time on the catalytic performances have also been investigated. The negative effect of water, a by-product of the reaction, on this transformation was evidenced.     

Gas-phase hydrodechlorination of pentachlorophenol over supported nickel catalysts

The gas-phase hydrodechlorination of pentachlorophenol (PCP) over nickel/silica and nickel/Y zeolite catalysts at 573 K has been studied. Each catalyst was 100% selective in cleaving the C–Cl bonds, leaving the hydroxyl substituent and benzene ring intact. The variation of catalytic activity and selectivity (in terms of partial and full dechlorination) with time-on-stream is illustrated and catalyst deactivation is addressed. Dechlorination efficiency is quantified in terms of dechlorination rate constants, phenol selectivity/yield and the ultimate partitioning of chlorine in the parent organic and product inorganic host. Increasing the nickel loading on silica was found to raise the overall level of dechlorination while the use of a zeolite support introduced spatial constraints that severely limited the extent of dechlorination. Product composition was largely determined by steric effects where resonance stabilisation had little effect. The reaction pathways, with associated pseudo-first-order rate constants, are also presented. This revised version was published online in November 2006 with corrections to the Cover Date.     

复合金属氧化物催化剂用于二氯甲烷催化燃烧的性能研究

采用浸渍法制备了一系列CuCrZrAl复合金属氧化物催化剂并用于二氯甲烷的催化燃烧反应,研究比较了催化剂的活性、选择性以及稳定性,发现经过ZrO2改性的氧化铝载体制得的催化剂具有更好的稳定性,更高的选择性,无大量副产物生成。解释了CuCr或Cr在ZrO改性的载体上表现出来的优良性能的原因。     

Low temperature incineration of mixed wastes using bulk metal oxide catalysts

Volume reduction of low-level mixed wastes from former nuclear weapons facilities is a significant environmental problem. Processing of these materials presents unique scientific and engineering problems due to the presence of minute quantities of radionuclides which must be contained and concentrated for later safe disposal. Low-temperature catalytic incineration is one option that has been utilized at the Rocky Flats facility for this purpose.

This paper presents results of research regarding evaluation of bulk metal oxides as catalysts for low-temperature incineration of carbonaceous residues which are typical by-products of fluidized bed combustion of mixed wastes under oxygen-lean conditions. A series of 14 metal oxides were screened in a thermogravimetric analyzer, using on-line mass spectrometry for speciation of reaction product gases. Catalyst evaluation criteria focused on the thermal—redox activity of the metals using both carbon black and PVC char as surrogate waste materials. Results indicated that metal oxides which were P-type semiconductor materials were suitable as catalysts for this application. Oxides of cobalt, molybdenum, vanadium, and manganese were found to be particularly stable and active catalysts under conditions specific to this process (T < 650°C, low oxygen partial pressures).

Bench-scale evaluation of these metal oxides with respect to stability to chlorine (HCl) attack was carried out at 550°C using a TG/MS system. Cobalt oxide was found to be resistant to metal loss in a HCl/He gaseous environment while metal loss from Mo, Mn, and V-based catalysts was moderate to severe. XRD and SEM/EDX analysis of spent Co catalysts indicated the formation of non-stoichiometric cobalt chlorides. Regeneration of chlorinated cobalt was found to successfully restore the low-temperature combustion activity to that of the fresh metal oxide.     

The catalytic hydrogenation of benzene over supported metal catalysts: I. Gas-phase hydrogenation of benzene over ruthenium-on-silica

A study is reported of the gas-phase hydrogenation of benzene over a ruthenium-on-silica catalyst in the temperature range from 300 to 415 K and at a total pressure of 130 kPa. The texture of the catalyst is studied by TEM, physisorption of nitrogen, chemisorption of hydrogen and by mercury penetration. Surface analysis is performed by XPS/AES.The adsorption enthalpies of the reaction intermediates 1,4-cyclohexadiene and cyclohexene and of cyclohexane on ruthenium are determined.On the basis of the kinetics, a reaction mechanism is proposed in which the rate-determining step shifts from the first hydrogen addition to benzene at low temperatures to the hydrogen addition to cyclohexene at higher temperatures.An approximate diagram is constructed representing the change of the free enthalpy as a function of the extension of the reaction.     

Activated red mud-supported Zn/Al oxide catalysts for catalytic conversion of glycerol to glycerol carbonate: FTIR analysis

Catalytic conversion to glycerol carbonate (GC) from glycerol and urea was investigated with Zn/Al oxide catalysts supported by activated red mud (ARM), a waste material. Compared to an unsupported catalyst, ARM-supported Zn/Al oxide catalysts exhibited higher GC yields. ARM-supported Zn/Al oxide catalysts showed a volcano curve for the GC yield as a function of the Zn/Al loading. FTIR analysis revealed the ARM-supported Zn/Al oxide catalysts to be more selective, resulting in higher GC yield. The balance of active sites from ARM and Zn/Al oxide was related to rates of each reaction step in GC synthesis, which eventually influenced on the selectivity and yield of GC.     

Total oxidation of ethanol and propane over Mn-Cu mixed oxide catalysts

Mn-Cu mixed oxides were prepared by co-precipitation varying the aging time for 4, 18 and 24 h. The catalytic performance in propane and ethanol total oxidation on these samples was better than on Mn₂O₃ and CuO pure oxides. The increase of the aging time enhanced the activity and the selectivity to CO₂. The nature and disposition of the phases forming the catalytic system as well as the effect of the precipitated aging time was determined by means of specific surface area measurements, X-ray diffractometry (XRD), infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), temperature programmed reduction (TPR) and temperature programmed desorption of oxygen (O₂-TPD). The catalytic behaviour seems related to the existence of a Cu_1.5Mn_1.5O₄ mixed phase and the easier reducibility of the catalysts.     

The catalytic hydrogenation of benzene over supported metal catalysts.: II. Gas-phase hydrogenation of benzene over copper-on-silica

A study has been made of the kinetics and mechanism of the gas-phase hydrogenation of benzene over a copper-on-silica catalyst in the temperature range from 300 to 450 K and at 130 to 395 kPa total pressure. Attention has been given also to the kinetics of the hydrogenation of the reaction intermediates 1,4-cyclohexadiene and cyclohexene.Two different catalysts were prepared on Shell silica spheres as a support, one according to the Dutch Patent No. 143,139 and the other according to European Patent No. 0006313. Their texture and analytical composition were studied by means of TEM, nitrogen physisorption and capillary condensation, adsorptive decomposition of nitrous oxide, atomic absorption spectrometry and XPS/AES analysis.The catalyst prepared according to European Patent No. 0006313 had a high mechanical strength, a perfect chemical stability and a high sintering resistance. The mean copper particle diameter was 5.5 nm. The other catalyst displayed poor mechanical strength and fragmented during testing.A reaction mechanism is formulated on the analogy of the mechanism proposed for the hydrogenation of benzene over ruthenium [11].The catalytic activity of copper is compared with that of several other transition metals and presented in the form of modified Tanaka-Tamaru plots.     

Cu-Zr-Ce-O复合氧化物催化剂上CO选择性氧化性能

将共沉淀法制备的Cu-Zr-Ce-O复合氧化物催化剂应用于富氢气体中CO的选择性氧化反应,研究了ZrO₂掺杂量及预处理方法对催化剂性能的影响,并通过H₂-TPR、CO-TPR等手段对催化剂进行了表征.结果表明,掺杂ZrO₂的Cu₁Zr₁Ce₉O_δ催化剂在160～200℃之间具有99％以上的CO转化率和相对较高的选择性.掺杂适量的ZrO₂能够提高催化剂的热稳定性和储氧能力,促进催化剂表面吸附氧向晶格氧的转化.经氧气预处理的Cu₁Zr₁Ce₉O_δ催化剂活性最高.催化剂上Cu⁺/Cu²⁺氧化还原离子对和表面的晶格氧含量均影响催化剂的活性,但在富氢气氛下,表面的晶格氧对催化剂的性能影响较大.     

Effects of methane and oxygen on decomposition of nitrous oxide over metal oxide catalysts

Catalytic activities of various metal oxides for decomposition of nitrous oxide were compared in the presence and absence of methane and oxygen, and the general rule in the effects of the coexisting gases was discussed. The reaction rates of nitrous oxide were well correlated to the heat of formation of metal oxide, i.e., a V-shaped relationship with a minimum at −ΔH_f⁰ around 450 kJ (O mol)⁻¹ was observed in N₂O decomposition in an inert gas. In the case of metal oxides having the heat of formation lower than 450 kJ (O mol)⁻¹, CuO, Co₃O₄, NiO, Fe₂O₃, SnO₂, In₂O₃, Cr₂O₃, the activities were strongly affected by the presence of methane and oxygen. On the other hand, the activities of TiO₂, Al₂O₃, La₂O₃, MgO and CaO were almost independent. The reaction rate of nitrous oxide was significantly enhanced by methane. The promotion effect of methane was attributed to the reduction of nitrous oxide with methane: 4N₂O+CH₄→2N₂+CO₂+2H₂O. The activity was suppressed in the presence of oxygen on the metal oxides having lower heat of formation. On the basis of Langmuir–Hinshelwood mechanism, the effect of oxygen on nitrous oxide decomposition was rationalized with the strength of metal–oxygen bond.     

Cyclohexanol conversion as a test of the acid-base properties of metal oxide catalysts

Cyclohexanol conversion on oxide catalysts is proposed as a test for the acid-base properties of oxide catalysts. The quantity of cyclohexene formed reflects the existence of Broensted acid sites. The dehydrogenation to cyclohexanone might be related to basic sites if at least one proton is released from the organic molecule. In some cases dehydrogenation to phenol occurred.     

Solvent free synthesis of chalcone and flavanone over zinc oxide supported metal oxide catalysts

Liquid phase Claisen–Schmidt condensation between 2′-hydroxyacetophenone and benzaldehyde to form 2′-hydroxychalcone, followed by intramolecular cyclisation to form flavanone was carried out over zinc oxide supported metal oxide catalysts under solvent free condition. The reaction was carried out over ZnO supported MgO, BaO, K₂O and Na₂O catalysts with 0.2 g of each catalyst at 140 °C for 3 h. Magnesium oxide impregnated zinc oxide was observed to offer higher conversion of 2′-hydroxyacetophenone than other catalysts. Further MgO impregnated with various other supports such as HZSM-5, Al₂O₃ and SiO₂ were also used for the reaction to assess the suitability of the support. The order of activity of the support is ZnO > SiO₂ > Al₂O₃ > HZSM-5. Various weight percentage of MgO was loaded on ZnO to optimize maximum efficiency of the catalyst system. The impregnation of MgO (wt%) in ZnO was optimized for better conversion of 2′-hydroxyacetophenone. The effect of temperature and catalyst loading was studied for the reaction.     

Steam conversion of glycerol on Ni and Au-Ni catalysts

During primary screening, catalysts which enable production of syngas or hydrogen from glycerol with high yields under soft conditions were revealed. Nickel and nickel-gold catalysts on various supports support were studied in the reaction of steam conversion of glycerol. Nickel catalysts on acidic supports (F-Al₂O₃ and B₂O₃-Al₂O₃) were ascertained to provide 73% selectivity toward H₂ at temperatures as low as 520°C, glycerol conversion amounting to 48%, which allows one to consider these catalysts to be applicable for H₂ production from glycerol. 30% Ni/Al₂O₃ catalyst produced according to the original sol-gel procedure allows one to obtain syngas with a composition suitable for methanol production at relatively low temperatures (520–570°C) and almost complete glycerol conversion. A strongly pronounced synergetic effect was ascertained for 0.27% Au-0.09% Ni/Al₂O₃. Glycerol conversion on this catalyst at 570°C attains 67%; the composition of the resultant gas mixture is applicable for methanol production.     

金属氧化物催化CO还原NO的研究进展

一氧化碳（CO）广泛存在于烧结/球团/焦化烟气或汽车尾气中,应用CO-选择性催化还原（SCR）技术同时脱除烟气中CO和NO是烟气治理的理想方案之一。目前,在NO-CO反应研究中较多的是贵金属催化剂,但由于其价格昂贵、高温失活、易中毒等问题难以在工业中实现应用。本文将近几年来金属氧化物催化CO还原NO的研究成果进行了系统的梳理与总结,重点介绍Fe基、Ce基、Co基、Cu基这4种金属氧化物催化剂的研究进展,分析催化剂的制备方法、掺杂助剂种类和比例、NO-CO反应条件等因素与催化活性之间的关系,总结催化剂抗水抗硫性能及可能的CO-SCR反应机理,并探讨O₂存在的条件下对催化剂活性的影响,为提高金属氧化物催化剂抗氧性研究提供理论参考。     

Direct conversion of triglycerides to olefins and paraffins over noble metal supported catalysts

Deoxygenation of methyl esters and triglycerides was studied for production of either α-olefins or diesel components. The reactions were carried out in a reactive distillation fashion in which products are quickly removed from the reaction mixture in flowing He. The effects of He flow rate, reaction temperature, active component and support were studied. PtSnK supported on silica was found to be the best catalyst for selective production of α-olefins. Palm kernel oil and coconut oil were also deoxygenated to produce α-olefins or diesel components, depending on reaction conditions.     

Partial oxidation of propene over metal oxide catalysts pretreated with NO2

Titania pretreated with NO₂ has been found to catalyze the partial oxidation of propene into oxygenates such as acetone and acrolein at around 623 K, while fresh TiO₂ produces only carbon oxides. Temperature‐programmed desorption (TPD) revealed that nitrogen oxides adsorbed on TiO₂ are stable at temperatures below 673 K. Even after the propene oxidation at 573 K for 2 h, nitrogen oxides were confirmed still to exist on the TiO₂ surface. At temperatures higher than 673 K, however, the desorption and/or the reduction of the adsorbed nitrogen oxides took place, and concomitantly the catalytic ability giving oxygenates disappeared. This revised version was published online in July 2006 with corrections to the Cover Date.     

Total oxidation of selected mono-carbon VOCs over hydrotalcite originated metal oxide catalysts

Hydrotalcite originated Cu–Mg–Al, Co–Mg–Al and Cu–Co–Mg–Al oxide systems were tested as catalysts for the total oxidation of mono-carbon VOCs (methane, methanol, and formic acid). Both calcination temperature of the hydrotalcite precursors as well as doping of the catalysts with potassium promoter influenced their catalytic activity. Increased calcination temperature, which resulted in a decrease of the surface area of the samples and formation of the spinel phases, activated the Co–Mg–Al catalyst, while the opposite effect was observed for the Cu–Mg–Al and Cu–Co–Mg–Al catalysts. On the other hand doping of the catalysts with potassium promoter significantly activated the Cu–Mg–Al and Cu–Co–Mg–Al catalysts in the processes of methanol and formic acid conversion, while only slightly influenced the catalytic performance of the Co–Mg–Al sample.