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1.
The catalytic performances of Mn-based catalysts have been investigated for the oxidative dehydrogenation of both ethane (ODE)
and propane (ODP). The results show that a LiCl/MnOx/PC (Portland cement) catalyst has an excellent catalytic performance for oxidative dehydrogenation of both ethane and propane
to ethylene and propylene, more than 60% alkanes conversion and more than 80% olefins selectivity could be achieved at 650°C.
In addition, the results indicate that Mn-based catalysts belong to p-type semiconductors, the electrical conductivity of
which is the main factor in influencing the olefins selectivity. Lithium, chlorine and PC in the LiCl/MnOx/PC catalyst are all necessary components to keep the excellent catalytic performance at a low temperature.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
2.
Vanadium-containing hexagonal mesoporous silica catalysts were tested in oxidative dehydrogenation of ethane. V-HMS catalysts (0.3–9.0 wt.% V) were prepared by impregnation with solution of vanadyl acetylacetonate, and by incorporation of vanadium in the synthesis process. The prepared catalysts achieved a different distribution of vanadium species (isolated monomeric units with tetrahedral coordination, oligomeric units connected by VOV bonds up to distorted tetrahedral coordination, two-dimensional polymeric units in octahedral coordination, and bulk vanadium oxides). The contribution deals with the understanding of the relationship between the distribution of vanadium species and their activity in ODH of ethane. It has been found that both monomeric and oligomeric vanadium species play important role in ODH of ethane. The activity correlated with the population of oligomeric tetrahedrally coordinated vanadium species, which were evidenced by the UV–vis band at 315 nm. To analyze this effect, V-HMS catalysts were characterized by means of UV–vis spectroscopy, H2-TPR and N2-adsorption. 相似文献
3.
通过脱氢反应将低碳烷烃转化为同碳数的烯烃是烷烃高值化利用和烯烃原料多元化的重要途径。烷烃氧化脱氢制烯烃的反应具有不受反应平衡限制、积炭少、反应温度低等优点,一直是研究的热点。通过利用浸渍法制备不同铬(Cr)负载量的Crx/SSZ-13系列催化剂,采用氮气物理吸附、氨程序升温脱附(NH3-TPD)、二氧化碳程序升温脱附(CO2-TPD)、氢气程序升温还原(H2-TPR)、紫外-可见吸收光谱(UV-Vis)以及高角度环形暗场-扫描透射电镜(HAADF-STEM)与耦合能谱分析(EDX-Mapping)等方法对催化剂进行了物性表征,并用微型固定床反应器评价催化剂对乙烷氧化脱氢制乙烯的催化性能,最终建立了Cr/SSZ-13催化剂的构效关系。研究发现,当n(二氧化硅)/n(氧化铝)=10时,Cr1.5/SSZ-13-10催化剂上含有丰富的Cr3+物种,其中配位不饱和Cr3+是优异的脱氢活性位,有利于二氧化碳氧化乙烷脱氢反应的进行。因此,Cr1.5/SSZ-13催化剂在650 ℃时表现出优异的催化性能,即二氧化碳转化率和乙烷转化率分别达到26.41%和53.2%,乙烯产率为38.83%。 相似文献
4.
M.V. Martínez-Huerta X. Gao H. Tian I.E. Wachs J.L.G. Fierro M.A. Baares 《Catalysis Today》2006,118(3-4):279-287
The influence of vanadium oxide loading in the supported VOx/Al2O3 catalyst system upon the dehydrated surface vanadia molecular structure, surface acidic properties, reduction characteristics and the catalytic oxidative dehydrogenation (ODH) of ethane to ethylene was investigated. Characterization of the supported VOx/Al2O3 catalysts by XPS surface analysis and Raman spectroscopy revealed that vanadia was highly dispersed on the Al2O3 support as a two-dimensional surface VOx overlayer with monolayer surface coverage corresponding to 9 V/nm2. Furthermore, Raman revealed that the extent of polymerization of surface VOx species increases with surface vanadia coverage in the sub-monolayer region. Pyridine chemisorption-IR studies revealed that the number of surface Brønsted acid sites increases with increasing surface VOx coverage and parallels the extent of polymerization in the sub-monolayer region. The reducibility of the surface VOx species was monitored by both H2-TPR and in situ Raman spectroscopy and also revealed that the reducibility of the surface VOx species increases with surface VOx coverage and parallels the extent of polymerization in the sub-monolayer region. The fraction of monomeric and polymeric surface VOx species has been quantitatively calculated by a novel UV–Vis DRS method. The overall ethane ODH TOF value, however, is constant with surface vanadia coverage in the sub-monolayer region. The constant ethane TOF reveals that both isolated and polymeric surface VOx species possess essentially the same TOF value for ethane activation. The reducibility and Brønsted acidity of the surface VOx species, however, do affect the ethylene selectivity. The highest selectivity to ethylene was obtained at a surface vanadia density of 2.2 V/nm2, which corresponds to a little more than 0.25 monolayer coverage. Below 2.2 V/nm2, exposed Al support cations are responsible for converting ethylene to CO. Above 2.2 V/nm2, the enhanced reducibility and surface Brønsted acidity appear to decrease the ethylene selectivity, which may also be due to higher conversion levels. Above monolayer coverage, crystalline V2O5 nanoparticles are also present and do not contribute to ethane activation, but are responsible for unselective conversion of ethylene to CO. The crystalline V2O5 nanoparticles also react with the Al2O3 support at elevated temperatures via a solid-state reaction to form crystalline AlVO4, which suppresses ethylene combustion of the crystalline V2O5 nanoparticles. The molecular structure–chemical characteristics of the surface VOx species demonstrate that neither the terminal VO nor bridging VOV bonds influence the chemical properties of the supported VOx/Al2O3 catalysts, and that the bridging VOAl bond represents the catalytic active site for ethane activation. 相似文献
5.
Oxidative dehydrogenation of ethane to ethylene was investigated over a series of MoO3 added V2O5–Al2O3 catalysts. The catalysts were characterized by BET, XRD, Laser-Raman and FT-IR spectroscopies and TPR technique. Catalytic tests were carried out in a fixed bed stainless steel reactor in the temperature range from 450 to 600 °C. Results revealed that the loading of molybdophosphoric acid (MPA) and the method of preparation had a clear influence on the catalytic performance. Among all, 10 wt.% MPA/V2O5–Al2O3 solid was found to possess superior activity and selectivity (X-C2H6 ~ 35% and S-C2H4 ~ 65%). Formation of Mo–V mixed oxide phases on Al2O3 appeared to be responsible for this improved performance. This best catalyst also exhibited good long-term stability over a period of ca. 36 h. 相似文献
6.
《Catalysis communications》2011,15(1):107-110
This work presents the results of propane oxidative dehydrogenation on alumina-supported V–Mo oxides and Sr–V–Mo oxide catalysts. The reaction was conducted at atmospheric pressure and 500 °C. Catalysts composed of 2:4 vanadium to molybdenum ratio showed the best performance. The presence of strontium in the catalyst's matrix enhanced its performance (increase in conversion and selectivity) and decreased its reducibility by changing the nature of its surface as confirmed by BET, XRD and TGA techniques. Moreover, the presence of strontium improved the stability of the catalyst. Hence, Sr–V–Mo stands as a promising catalyst for oxidative dehydrogenation of propane. 相似文献
7.
Jeddou El-Idrissi Mohamed Kacimi François Bozon-Verduraz Mahfoud Ziyad 《Catalysis Letters》1998,56(4):221-225
A series of catalysts were prepared by loading titanium dioxide with chromium and different amounts of phosphorus. Investigation
in the oxidative dehydrogenation of ethane showed that chromium notably increases the activity of TiO2 principally toward the total oxidation of the hydrocarbon. Addition of phosphorus to the system simultaneously improved the
global conversion and the ethylene selectivity. Moreover, a fairly good correlation between the catalysts acidity, the P/Cr
ratios and the activity in the ODH reaction was established. It was also found that an excess of phosphorus, although it increases
the acidity, decreases the conversion as if phosphorus effect was optimum for P/Cr ratios equal to 1.6. EPR and UV-visible
characterizations of the samples before and after the catalytic tests showed that the improvement of the catalysts performances
might be due to the isolated octahedral Cr3+ species that appear on the support.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
8.
In contrast to previous claims, the addition of niobia to catalysts containing vanadia supported on titania resulted in much enhanced activity for low-temperature SCR of NO with NH3 only at low vanadia loadings. Niobia promoted catalysts could also be demonstrated to show higher selectivities to N2, especially at high temperatures and low vanadia loading. This enhancement of the activity cannot be explained only on the basis of the observation that niobia stabilized the surface area of the catalyst: calculations of the activation energy suggest that a different mechanism of the reaction may be at work at low vanadia loadings. 相似文献
9.
10.
Shaobin Wang K Murata T Hayakawa S Hamakawa K Suzuki 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1999,74(10):988-992
Alkali‐metal doped sulfated zirconia catalysts were tested for the oxidative dehydrogenation of ethane into ethene. The effects of metal precursor compounds and acidic anion promoters on the catalytic activity in this reaction were studied. It was found that sulfation of zirconia increases the selectivity of ethane towards ethene. Lithium‐, sodium‐, and potassium‐doped sulfated zirconia catalysts showed quite different activities in this reaction. Sulfated zirconia doped with lithium catalysts were found to be effective for the oxidative dehydrogenation of ethane, giving over 90% selectivity to ethene and 25% ethene yield at 650 °C. © 1999 Society of Chemical Industry 相似文献
11.
《Catalysis communications》2008,9(12):2186-2193
Non-oxidative dehydrogenation of ethane into ethylene at 700 °C over reductively pretreated Cr–Mg–Al and Cr–Mg mixed oxide catalysts has been studied. The catalysts were prepared from layered double hydroxide (LDH) precursors that contained various species of chromium (i.e., cationic Cr(III), complex of Cr(III) with an anionic chelating agent, and chromate anion). Synthesized materials were characterized with powder X-ray diffraction, X-ray photoelectron spectroscopy and Raman spectroscopy techniques. It was shown that the surface area of the LDH-derived mixed oxides, their catalytic performance, coking ability, and susceptibility to sintering were highly dependent on the method used for introducing chromium into the LDH precursors of the catalysts. 相似文献
12.
Andrey Tsyganok Richard G. Green Javier B. Giorgi Abdelhamid Sayari 《Catalysis communications》2007,8(12):2186-2193
Non-oxidative dehydrogenation of ethane into ethylene at 700 °C over reductively pretreated Cr–Mg–Al and Cr–Mg mixed oxide catalysts has been studied. The catalysts were prepared from layered double hydroxide (LDH) precursors that contained various species of chromium (i.e., cationic Cr(III), complex of Cr(III) with an anionic chelating agent, and chromate anion). Synthesized materials were characterized with powder X-ray diffraction, X-ray photoelectron spectroscopy and Raman spectroscopy techniques. It was shown that the surface area of the LDH-derived mixed oxides, their catalytic performance, coking ability, and susceptibility to sintering were highly dependent on the method used for introducing chromium into the LDH precursors of the catalysts. 相似文献
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14.
The catalytic oxidative dehydrogenation of ethane with alkali and alkaline earth metal chloride modified LiCl supported on Dy2O3/MgO (MD) was studied. Eutectic mixtures of alkali and alkaline earth metal chloride with LiCl are formed on the support surface decreasing so the melting point of pure LiCl to temperatures as low as 366 °C (Li-K-MD). All samples had weak basicity decreasing in the order: Li-K-MD < Li-Sr-MD Li-Ba-MD < Li-Na-MD < Li-MD. Physisorbed and chemisorbed CO2 species are identified for all materials studied by in situ IR spectroscopy. Bidentate carbonate species are the most abundant on Li-MD, while on modified samples bi- and unidentate carbonate species exist. The catalyst activity increases with decreasing basicity. Catalyst selectivity increases with increasing reaction temperature and is constant above a threshold temperature. The maximum ethene selectivity is directly correlated with the melting point of the eutectic melt on the catalyst support. 相似文献
15.
Vasant R. Choudhary Shafeek A. R. Mulla Vilas H. Rane 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1998,71(2):167-172
Sr-promoted rare earth (viz. La, Ce, Pr, Nd, Sm, Eu, Gd, Dy, Er and Yb) oxide catalysts (Sr/rare earth ratio = 0·1) are compared for their performance in the oxidative coupling of methane (OCM) to C2 hydrocarbons and oxidative dehydrogenation of ethane (ODE) to ethylene at different temperatures (700 and 800°C) and CH4 (or C2H6)/O2 ratios (4–8), at low contact time (space velocity = 102000 cm3 g−1 h−1). For the OCM process, the Sr–La2O3 catalyst shows the best performance. The Sr-promoted Nd2O3, Sm2O3, Eu2O3 and Er2O3 catalysts also show good methane conversion and selectivity for C2 hydrocarbons but the Sr–CeO2 and Sr–Dy2O3 catalysts show very poor performance. However, for the ODE process, the best performance is shown by the Sr–Nd2O3 catalyst. The other catalysts also show good ethane conversion and selectivity for ethylene; their performance is comparable at higher temperatures (≥800°C), but at lower temperature (700°C) the Sr–CeO2 and Sr–Pr6O11 catalysts show poor selectivity. © 1998 SCI. 相似文献
16.
The addition of various metals to Pt-coated ceramic foam monoliths was examined for the autothermal oxidative dehydrogenation of ethane to ethylene at 900°C at contact times of 5 ms. The addition of Sn or Cu to Pt-monoliths enhanced both C2H6 conversions and C2H4 selectivities significantly, giving higher C2H4 yields. No deactivation or volatilization of the catalysts was observed. For Pt-Sn, an increase in the Sn/Pt ratio from 1/1 to 7/1 increased both the conversion and the selectivity. For Pt-Sn (Sn/Pt = 7/1) versus Pt alone the conversion increased by up to 6% and the selectivity up to 5% for an increase in optimal yield from 54.5% with Pt to 58.5% with Pt-Sn. XRD and XPS measurements showed that Pt existed in the form of PtSn and Pt3Sn alloys. The 1/1 Pt-Cu catalyst showed comparable performance, with conversion increasing by 5% and selectivity by 3%. The addition of several other metals to Pt-monoliths decreased both C2H6 conversion and C2H4 selectivity in the order, Sn>Cu>Pt alone>Ag>Mg>Ce>Ni>La> Co. For oxidative dehydrogenation ofn-butane and isobutane, Pt-Sn and Pt-Cu also showed higher conversion than Pt.This research was partially supported by NSF under Grant CTS-9311295. 相似文献
17.
自2016年Hermans课题组发现六方氮化硼(h-BN)在丙烷氧化脱氢制丙烯(ODHP)反应中优异的烯烃选择性,各类硼基材料引起了研究者强烈的研究兴趣并广泛地用于ODHP反应。与传统金属与金属氧化物基催化剂不同,非金属硼基催化体系能够有效抑制CO x 等过度氧化产物,提高烯烃产率,具有较广阔的工业应用前景。本综述对硼基丙烷氧化脱氢催化剂从催化剂的设计、合成策略和反应性能等方面进行了系统地讨论,阐明了催化剂的构效关系;总结了反应路线、关键中间体、决速步以及催化动力学行为,加深了硼基催化剂催化丙烷氧化脱氢活性位点和机理的理解。指出三配位B—O/B—OH活性位点的有效构建及实现表面与气相自由基反应的协同催化是提高硼基催化剂丙烷脱氢性能的关键。基于目前的研究现状和存在的问题,对硼基催化剂体系研发前景和未来工业化应用进行了展望。 相似文献
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19.
CO2是导致全球变暖的主要温室气体,又是宝贵的可再生C1资源,将其转化为有价值的化学品,在环境保护和碳资源合理利用方面具有双重意义。作为页岩气的重要组成部分,乙烷高效催化转化制乙烯不仅具有重要的理论研究意义,而且具有广阔的工业应用前景。在CO2气氛下乙烷氧化脱氢制乙烯(CO2-ODHE)已成为增产乙烯的有效手段之一。该文重点阐述了在CO2-ODHE反应中不同类型的催化剂及影响该反应催化活性和稳定性的主要因素和关键问题,并对比介绍了乙烷直接氧化脱氢(O2-ODHE)和乙烷化学链氧化脱氢(CL-ODHE)。最后,结合反应机制提出了构筑高效催化剂可能的方向和发展前景。 相似文献
20.
Hollow-fibre carbon membranes with different pore sizes were tested as catalyst supports in the hydrogenation of CO. The factors which contributed to the uniformity of the porous structure and to an increase in the specific surface area of the membranes also resulted in enhanced performances of the catalysts. 相似文献