Al_2O_3负载Cu,Fe或Ni掺杂氧化钼催化乙苯氧化脱氢(英文)

Molybdenum-based catalysts supported on Al_2O_3 doped with Ni, Cu, or Fe oxide were synthesized and used in ethylbenzene dehydrogenation to produce styrene. The molybdenum oxide was supported using an unconventional route that combined the polymeric precursor method(Pechini) and wet impregnation on commercial alumina. The samples were characterized by X-ray diffraction(XRD), N_2 adsorption-desorption isotherms, temperature-programmed reduction of H_2(H_2-TPR),and thermogravimetric(TG) analysis. XRD results showed that the added metals were well dispersed on the alumina support. The addition of the metal oxide(Ni, Cu, or Fe) of 2 wt% by wet impregnation did not affect the texture of the support. TPR results indicated a synergistic effect between the dopant and molybdenum oxide. The catalytic tests showed ethylbenzene conversion of 28%–53% and styrene selectivity of 94%–97%, indicating that the addition of the dopant improved the catalytic performance, which was related to the redox mechanism. Molybdenum oxides play a fundamental role in the oxidative dehydrogenation of ethylbenzene to styrene by its redox and acid–base properties. The sample containing Cu showed an atypical result with increasing conversion during the reaction, which was due to metal reduction. The Ni-containing solid exhibited the highest amount of carbon deposited, shown by TG analysis after the catalytic test, which explained its lower catalytic stability and selectivity.     

镧-镍复合氧化物纳米微粒的固相合成及其催化性能

The La-Ni complex oxide catalyst was prepared by solid state reactions under microwave. The structure and reducibility of the catalyst were characterized by using TG-DTA, XRD, TEM and TPR methods. At the same time the catalytic activity of oxidative dehydrogenation of ethylbenzene to styrene with carbon dioxide over the complex oxide nanoparticle was investigated.The Results show that the product is K2NiF4 nanoparticles,and the size is 13nm.The complex oxide sample had high activity for the oxidative dehydrogenation of ethylbenzene to styrene.     

Cu,Fe, or Ni doped molybdenum oxide supported on Al2O3 for the oxidative dehydrogenation of ethylbenzene

Molybdenum-based catalysts supported on Al2O3 doped with Ni, Cu, or Fe oxide were synthesized and used in ethylbenzene dehydrogenation to produce styrene. The molybdenum oxide was sup-ported using an u...     

Synthesis of 2-methylpyrazine from cyclocondensation of ethylene diamine and propylene glycol over promoted copper catalyst

The 2-methylpyrazine was synthesized by catalytic reaction of ethylene diamine and propylene glycol at 380 ℃. The alumina supported copper catalysts with promoter were prepared by impregnation method, characterized by ICP-AES, BET and TPR. The results demonstrated that the dehydrogenation was improved by addition of chromium promoter. The selectivity of 2-methylpyrazine reached 84.75%, while the conversions of reactants were also enhanced.     

MECHANISTIC STUDIES ON CATALYTIC DEHYDROGENATION OF ETHYL-BENZENE OVER IRON-OXIDE-BASED CATALYST SYSTEMS-I. ROLE OF LATTICE OXYGEN

The role of lattice oxygen in the catalytic dehydrogenation of ethylbenzene over industrial iron-oxide-based catalysts has been investigated mainly by means of isotopic exchanges attending the dehydrogenation reaction.The results indicated that although the exchange of lattice oxygen with steam oxygen appeared to take place to an appreciable extent,the direct catalytic dehydrogenation of ethylbenzene appeared to be the major reaction pathway,with catalytic dehydrogenation by oxygen-transfer reaction pathway playing only a minor role,as revealed different extents of hydrogeh-deute-rium isotopic exchange between ethylbenzene and steam D2Q at low and very high space velocities.The mechanisms of these two reaction pathways are discussed.For the oxygen-transfer dehydrogenation mechanism,electron transport between neighboring Active-sites operating cooperatively in opposite phases of their redox cycles may be a requisite factor.     

Investigation on the Performance of Supported Molybdenum Carbide for the Partial Oxidation of Methane

The performance of uspported and unsupported molybdenum carbide for the partial oxidation of methane (POM) to syngas was investgated.An evaluation of the catalysts indicates that bulk molybdenum carbied has a higher methane conversion during the initial stage but a lower selectivity to CO and H2/CO ratio in the products.The rapid deactivation of the catalyst is also a significant problem.However,the supported molybdenum carbide catalyst shows a much higher methane conversion,increased selectivity and significantly improved catalytic stability.The characterization by XRD and BET specific area measurements depict an improved dispersion of molybdenum carbide when using alumina as a carrier.The bulk or the supported molybdenum carbide exists in the β-Mo2C phase,while it is transformed into molybdenum dioxide postcatalysis which is an improtant cause of molybdenum carbide deactivation.     

Zn-Co bimetallic supported ZSM-5 catalyst for phosgene-free synthesis of hexamethylene–1,6–diisocyanate by thermal decomposition of hexamethylene–1,6–dicarbamate

A set of mono-and bimetallic(Zn-Co) supported ZSM-5 catalysts was first prepared by PEG-additive method. The physicochemical properties of the catalysts were investigated by FTIR, XPS, XRD, N_2adsorption-desorption measurements, SEM, EDS and NH3-TPD techniques. The physicochemical properties showed that the Zn Co_2O_4 spinel oxide was formed on the ZSM-5 support and provided effectual synergetic effect between Zn and Co species for the bimetallic catalyst. Furthermore, bimetallic supported ZSM-5 catalyst exhibited weak, moderate and strong acidic sites, while the monometallic supported ZSM-5 catalyst showed only weak and moderate or strong acidic sites. Their catalytic performances for thermal decomposition of hexamethylene–1,6–dicarbamate(HDC) to hexamethylene–1,6–diisocyanate(HDI) were then studied. It was found that the bimetallic supported ZSM-5 catalysts,especially Zn-2Co/ZSM-5 catalyst showed excellent catalytic performance due to the good synergetic effect between Co and Zn species, which provided a suitable contribution of acidic sites. HDC conversion of 100% with HDI selectivity of 91.2% and by-products selectivity of 1.3% could be achieved within short reaction time of 2.5 h over Zn-2Co/ZSM-5 catalyst.     

Effect of support modification on the characterization and catalytic activity of Mo/Al_2O_3 catalysts

Molybdenum catalysts(15 wt% Mo O3loading) supported on alumina,alumina–magnesia,and alumina–chromia were prepared via impregnation technique and studied for the reaction of methyl-cyclohexane dehydrogenation. The catalysts were evaluated by means of FT-IR,XRD,DSC,TPR,and N2adsorption–desorption isotherms. The results clarified that Mo/alumina–magnesia catalyst possesses small crystallite size and high surface area(240 m2/g) and is selective toward the formation of dehydrogenated product(96.5%). The yield to ring-opening products is higher on Mo/alumina–chromia catalyst due to its higher acidity and larger metal crystals,which favor the ring-opening reaction and lower metallic activity with selectivity toward ringopening products(32%).     

Rh/ZnO-Al2O3催化剂用于巴豆醛选择性加氢（英文）

Gas phase hydrogenation of crotonaldehyde was performed over 1 wt% Rh/ZnO-Al2O3 catalysts with various Zn/Rh atomic ratios. Monometallic Rh/Al2O3 was also prepared for comparison. The samples were prepared by the successive impregnation of Al2O3 with chlo-ride precursors of zinc and rhodium. The solids have been characterized by H2 chemisorption,temperature-programmed reduction,scanning electron microscopy,and cyclohexane dehydrogenation. Their catalytic behaviour in the gas phase crotonaldehyde hydrogenation reaction after reduction treatment in flowing hydrogen at 723 K was investigated. The relationship between catalytic activity,selectivity for crotyl alcohol,and physicochemical properties of the catalysts was examined. Results obtained showed that the presence of Zn clearly promotes the hydrogenation of the carbonyl bond. The catalyst with Zn/Rh atomic ratio of 5 displayed good catalytic stability and the highest selectivity for crotyl alcohol(70%) along with alloy formation.     

Effects of the crystallization time on the mesoporous structure,texture, morphology and styrene oxidation performances of V-MCM-41

The new V-MCM-41 molecular sieves with good ordered hexagonal mesoporous structure and crystallinity were synthesized through in-situ hydrothermal preparation method. The effects of the crystallization time were discussed. The synthesized samples were characterized by X-ray diffraction, N2adsorption/desorption, Fourier transformed infrared and scanning electron microscopy. The different structures, textures, morphologies of V-MCM-41 obtained with different crystallization times were observed and analyzed on the basis of the characterized results. The results showed that the V-MCM-41 molecular sieve obtained at 110 °C for 48 h crystallization times was of good spherical morphology, ordered hexagonal structure, most uniform pore size distribution and high surface area compared with other samples. Meanwhile, the V-MCM-41 molecular sieve with the high skeleton Si condensation and the good crystallinity was obtained. The heteroatom could be incorporated into MCM-41 framework with increasing crystallization times, which was beneficial to improve the catalytic activity and selectivity of pure siliceous MCM-41. The V-MCM-41 showed the good catalytic selectivity in catalytic oxidation of styrene using hydrogen peroxide, and the selectivity of the benzaldehyde and phenylacetic acid reached 30.68%and 49.44%, respectively.     

Catalytic activity of MCM-48-, SBA-15-, MCF-, and MSU-type mesoporous silicas modified with Fe3+ species in the oxidative dehydrogenation of ethylbenzene in the presence of N2O

MCM-48, SBA-15, MCF, and MSU mesoporous silicas were used as supports for a deposition of Fe oxide species. Iron was introduced using two different methods: the wetness impregnation and the molecular designed dispersion (MDD). The obtained catalysts were characterized with respect to their textural parameters (BET), chemical composition (electron microprobe analysis), and reducibility (TPR). The coordination environment of Fe was determined using EPR and UV-vis/DRS. The samples were tested as catalysts in the oxidative dehydrogenation of ethylbenzene to styrene in the presence of N(2)O. An influence of Fe dispersion and reducibility on the catalytic activity was discussed. Isolated Fe(3+) species appeared to be more selective in the styrene formation, whereas iron oxide clusters showed a higher selectivity in total oxidation of aromatic hydrocarbons. The reaction system was well described by the Mars- van Krevellen mechanism.     

A STUDY ON MEMBRANE PROCESS WITH |?-ALUMINA MEMBRANE REACTOR FOR ETHYLBENZENE DEHYDROGENATION TO STYRENE

The membrane reaction of ethylbenzene(EB) dehydrogenation to styrene(ST) has been studied by using K2O/Fe2O3 industrial catalyst and alumina ceramic membrane developed by our institute. In comparison with the packed bed reactor (that is, plug flow reactor, abbr. PFR) in industrial practice, the yield of styrene was increased by 5%~10% in the membrane reactor. Furthermore, mathematical modeling of membrane reaction has been studied to display the principle of optimal match between the catalytic activity and the membrane permeability.     

乙苯氧化脱氢反应Fex/TiO2的催化性能研究

新型氧化钛负载铁催化剂Fex/TiO2在低温乙苯空气氧化脱氢制苯乙烯反应中具有良好的催化活性。350 ℃,使用Fe7/TiO2催化剂,当Fe的质量分数为7%时,可获得14.6%乙苯单程转化率和99.0%的苯乙烯选择性。通过X衍射、表面吸附、热分析及扫描电镜仪器分析表征,考察氧化钛负载铁催化剂在乙苯低温氧化脱氢反应中的催化作用。350 ℃乙苯可被活化,催化剂活性的高低取决于活性物种Fe(III)的分布状态和质量分数。     

乙苯脱氢氧化铁系催化剂的活性相及钾的助催作用

与机械混合法相比,用KOH水溶液浸渍法制成的K_2O-Fe_2O_3催化剂性能较佳。负载型多元催化剂的性能与C-64I相近。SEM、XPS和EDAX证实,经使用后,上述负载型多元催化剂表面形态明显改变,表面铁/钾原子比上升。连续升温XRD证实,在乙苯脱氢通常所采用的温度区间,载于表面的KOH会迅速和氧化铁相互作用生成K_2Fe_2O_4。本文认为K_3Fe_2O_4可能是活性相并据此对实验结果作出较为合理的解释。     

Co-doping a metal (Cr,Mn, Fe,Co, Ni,Cu, and Zn) on Mn/ZSM-5 catalyst and its effect on the catalytic reduction of nitrogen oxides with ammonia

Selective catalytic reduction (SCR) of NO_x by NH₃ over a series of Mn–M/Z catalysts (M = Cr, Mn, Fe, Co, Ni, Cu, Zn, and Z = the ZSM-5 Zeolite) synthesized by wet impregnation method was investigated. Mn–Fe/Z, Mn–Co/Z, and Mn–Cu/Z catalysts exhibited approximately 100 % NO_x conversion over a wide temperature range (200–360 °C) in a defined atmospheric condition, which was noticeably greater than that of Mn–Cr/Z (340–360 °C). Furthermore, the effect of addition of second metal oxide species to the initial Mn/Z catalyst on the structure of catalysts was studied by several characterization techniques. BET measurements revealed high surface area and pore volume of the Mn–Cu/Z catalyst. In addition, the XRD and UV–Vis DR results showed that addition of co-doped metal oxide species improved the dispersion of metal ions and inhibited crystallization of metal oxides. UV–Vis studies also were in good accordance with DTA/TG results confirming the formation of cobalt oxide and copper oxide clusters in Mn–Co/Z and Mn–Cu/Z catalysts, respectively. The FTIR spectra of pyridine adsorption, in addition, suggested the Mn–Cu/Z catalyst contained the most Lewis acid sites leading to more NO_x adsorption capacity.     

Effect of size of catalytically active phases in the dehydrogenation of alcohols and the challenging selective oxidation of hydrocarbons

The size of the active phase is one of the most important factors in determining the catalytic behaviour of a heterogeneous catalyst. This Feature Article focuses on the size effects in two types of reactions, i.e., the metal nanoparticle-catalysed dehydrogenation of alcohols and the metal oxide nanocluster-catalysed selective oxidation of hydrocarbons (including the selective oxidation of methane and ethane and the epoxidation of propylene). For Pd or Au nanoparticle-catalysed oxidative or non-oxidative dehydrogenation of alcohols, the size of metal nanoparticles mainly controls the catalytic activity by affecting the activation of reactants (either alcohol or O(2)). The size of oxidic molybdenum species loaded on SBA-15 determines not only the activity but also the selectivity of oxygenates in the selective oxidation of ethane; highly dispersed molybdenum species are suitable for acetaldehyde formation, while molybdenum oxide nanoparticles exhibit higher formaldehyde selectivity. Cu(II) and Fe(III) isolated on mesoporous silica are highly efficient for the selective oxidation of methane to formaldehyde, while the corresponding oxide clusters mainly catalyse the complete oxidation of methane. The lattice oxygen in iron or copper oxide clusters is responsible for the complete oxidation, while the isolated Cu(I) or Fe(II) generated during the reaction can activate molecular oxygen forming active oxygen species for the selective oxidation of methane. Highly dispersed Cu(I) and Fe(II) species also function for the epoxidation of propylene by O(2) and N(2)O, respectively. Alkali metal ions work as promoters for the epoxidation of propylene by enhancing the dispersion of copper or iron species and weakening the acidity.     

An Overview on the Dehydrogenation of Alkylbenzenes with Carbon Dioxide over Supported Vanadium–Antimony Oxide Catalysts

Utilization of carbon dioxide as a soft oxidant for the catalytic dehydrogenation of ethylbenzene (CO₂-EBDH) has been recently attempted to explore a new technology for producing styrene selectively. This article summarizes the results of our recent attempts to develop effective catalyst systems for the CO₂-EBDH on the basis of alumina-supported vanadium oxide catalysts. Its initial activity and on-stream stability were essentially improved by the introduction of antimony oxide as a promoter into the alumina-supported catalyst. Insertion of zirconium oxide into alumina support substantially increased the catalytic activity. Modification of alumina with magnesium oxide yielded an increase of catalyst stability of alumina-supported V–Sb oxide due to the coking suppression. Carbon dioxide has been confirmed to play a beneficial role of selective oxidant in improving the catalytic performance through the oxidative pathway, avoiding excessive reduction and maintaining desirable oxidation state of vanadium ion (V⁵⁺). The positive effect of carbon dioxide in dehydrogenation reactions of several alkylbenzenes such as 4-diethylbenzene, 4-ethyltoluene, and iso- and n-propylbenzenes was also observed. Along with the easier redox cycle between fully oxidized and partially reduced vanadium species, the optimal surface acidity of the catalyst is also responsible for achieving high activity and catalyst stability. It is highlighted that supra-equilibrium EBDH conversions were obtained over alumina-supported V–Sb oxide catalyst in CO₂-EBDH as compared with those in steam-EBDH in the absence of carbon dioxide.     

Molecular-level understanding of the catalytic cycle of dehydrogenation of ethylbenzene to styrene over iron oxide-based catalyst

Dehydrogenation of ethylbenzene (EB) to styrene over iron oxide-based catalyst is an important industrial catalytic process. A great deal of insight into this reaction has been accomplished by surface science studies of the model catalysts. However, molecular understanding still lacks in the removal of the resultant hydrogen from the oxide surface. Employing gas-phase atomic hydrogen, we successfully prepared hydroxyls on an alpha-Fe2O3(0001) film with biphase surface structure under ultrahigh-vacuum conditions. Upon heating, hydroxyls react to form hydrogen and water, the latter of which results in the partial reduction of Fe2O3. These results add important insight into the complete understanding of the catalytic cycle of dehydrogenation of ethylbenzene to styrene over iron oxide-based catalyst.     

Role of carbon dioxide in the ethylbenzene dehydrogenation coupled with reverse water–gas shift

The dehydrogenation of ethylbenzene (EB) to styrene (ST) in the presence of carbon dioxide instead of steam is believed to be an energy-saving and environmentally friendly process. However, the reaction mechanism for this coupling system still remains unclear. Therefore, the role of carbon dioxide was investigated by means of catalytic reactions and temperature-programmed desorption (TPD) of carbon dioxide over a series of Fe and V supported catalysts as well as thermodynamic analysis. The results showed that the ethylbenzene conversion is associated with the conversion of carbon dioxide, and that there exists a synergistic effect between the ethylbenzene dehydrogenation and the reverse water–gas shift. However, the difference in the behaviour of the catalysts between the single reverse water–gas shift and the coupled ethylbenzene dehydrogenation may suggest that the catalysts are different in the reaction mechanisms for the coupled ethylbenzene dehydrogenation. Carbon dioxide can be activated through either basic sites or redox sites on the catalyst. Based on these results, the role of carbon dioxide and reaction mechanisms are proposed.