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1.
CeO2‐CrOy loaded on γ‐Al2O3 was investigated in this work for the oxidative dehydrogenation (ODH) of propane under oxygen‐free conditions. The ODH experiments of propane were conducted in a fluidized bed at 500°C‐600°C under 0.1 Mpa. The prepared catalyst was characterized by N2 adsorption‐desorption measurements, H2‐temperature‐programmed reduction, O2‐temperature‐programmed desorption, NH3‐temperature‐programmed desorption, x‐ray photoelectron spectroscopy, and x‐ray diffraction. The change in the selectivity of propylene resulted from the thermal cracking of the propane and the competition for lattice oxygen in the catalyst between propylene formation and propane and propylene combustion. Therefore, to achieve higher propylene yield in the industry, the reaction temperature should be 550°C‐575°C for the 17.5Cr‐2Ce/Al catalyst. The results of H2‐TPR (from 0.2218 mmol/g‐0.3208 mmol/g) revealed that the addition of CeO2 can enhance the oxygen capacity of CrOy. Compared with that for 17.5Cr/Al, the conversion can be enhanced from 22.4% to 28.5% and the selectivity of propylene can be improved from 72.2% to 75.9% for the 17.5Cr‐2Ce/Al catalyst. In addition, CeO2 can inhibit the evolution of lattice oxygen (O2?) to electrophilic oxygen species (O2?), causing the average COx (CO and CO2) selectivity to decrease from 9.64% to 6.31%. 相似文献
2.
Structure and catalytic consequence of Mg‐modified VOx/Al2O3 catalysts for propane dehydrogenation
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Tengfang Wu Gang Liu Liang Zeng Guodong Sun Sai Chen Rentao Mu Sika Agbotse Gbonfoun Zhi‐Jian Zhao Jinlong Gong 《American Institute of Chemical Engineers》2017,63(11):4911-4919
Supported VOx catalysts are promising nonoxidative propane dehydrogenation (PDH) materials for their commercially attractive activity and propylene selectivity. However, they frequently suffer from rapid deactivation caused by coke deposition. This article describes the promoting role of magnesium on the stability of VOx/Al2O3 catalysts for PDH. A series of VOx/Al2O3 and Mg‐modified VOx/Al2O3 catalysts were synthesized by an incipient wetness impregnation method. The catalysts were carefully characterized by Raman spectra, UV‐Vis spectra, STEM, TGA and in situ DRIFTS. We showed that the stability of a 12V/Al2O3 catalyst was significantly improved on addition of small amounts of MgO. Experimental evidences indicate that V2O5 nanoparticles emerge in the 12V/Al2O3 samples, and appropriate Mg addition helps dispersing the V2O5 nanoparticles into 2D VOx species thus decreasing coke formation and improving stability in nonoxidative dehydrogenation of propane. © 2017 American Institute of Chemical Engineers AIChE J, 2017 相似文献
3.
On the influence of the acid-base character of catalysts on the oxidative dehydrogenation of alkanes 总被引:1,自引:0,他引:1
P. Concepción A. Galli J. M. López Nieto A. Dejoz M. I. Vazquez 《Topics in Catalysis》1996,3(3-4):451-460
Vanadium oxides supported on metal oxide, i.e. Al2O3, MgO and Mg-Al mixed oxide, and V-containing microporous materials (VAPO-5 and MgVAPO-5) have been tested in the oxidative dehydrogenation of C2-C4 alkanes. In all cases, tetrahedral vanadium species (isolated and/or associated) were mainly observed from51V-NMR and diffuse reflectance spectroscopies. The reducibility of V5+-species, determined from the onset-reduction temperature, decreases as follows: VOx/AL > VAPO-5 > MgVAPO-5 =VOx/MG > VOx/MG + AL. The acid character of catalysts, determined from the FTIR spectra of pyridine adsorbed, decreases as: MgVAPO-5 > VOx/AL > VAPO-5 > VOx/MG + AL > VOx/MG. A similar trend between V-reducibility of the catalyst and its catalytic activity for the alkane conversion was observed. However, the selectivity to olefins depends on the acid-base character of catalyst and the alkane fed. In the ODH ofn-butane, the higher the acid character of the catalyst the lower the selectivity to C4-olefins, while in the ODH of ethane an opposite trend between the catalyst acidity and the selectivity to ethene was observed.On leave from the Department of Industrial Chemistry and Materials, V. le Risorgimento 4, 40136 Bologna, Italy. 相似文献
4.
Majid L. Balogun Yahya Gambo Sagir Adamu Mohammed S. Ba-Shammakh Mohammad M. Hossain 《American Institute of Chemical Engineers》2023,69(3):e17903
A 4-step kinetic model of CO2-assisted oxidative dehydrogenation (ODH) of propane to C2/C3 olefins over a novel MoOx/La2O3–γAl2O3 catalyst was developed. Kinetic experiments were conducted in a CREC Riser Simulator at various reaction temperatures (525–600 °C) and times (15–30 s). The catalyst was highly selective towards propylene at all combinations of the reaction conditions. Langmuir-Hinshelwood type kinetics were formulated considering propane ODH, uni- and bimolecular cracking of propane to produce a C1-C2 species. It was found that the one site type model adequately fitted the experimental data. The activation energy for the formation of propylene (67.8 kJ/mol) is much lower than that of bimolecular conversion of propane to ethane and ethylene (303 kJ/mol) as well as the direct cracking of propane to methane and ethylene (106.7 kJ/mol). The kinetic modeling revealed the positive effects of CO2 towards enhancing the propylene selectivity over the catalyst. 相似文献
5.
The catalytic performance of bifunctional catalysts, MOx‐Al2O3‐PO4, that contain acidic centers and different transition metal oxide components were evaluated in the gas‐phase dehydration of glycerol using the TPD‐TG‐MS technique and a continuous flow reactor experiment. The initial catalytic activity and selectivity to acrolein and acetol significantly depends on the acidity and the type of transition metal oxide. The higher the total acidity, the higher the acrolein selectivity in the order W > Mo > Cu > V~ Fe ~Cr > Ce. On the other hand, Mn‐, Cr‐, and Fe‐containing catalysts favor the formation of products of oxidative C‐C cleavage. TPD‐TG‐MS investigations of catalysts loaded with glycerol are useful tools for fast‐screening of initial activities of catalysts in the gas‐phase dehydration of glycerol. 相似文献
6.
Isomerization of n‐hexane into bi‐ and tri‐branched products was studied at atmospheric pressure on Ni‐WOx/Al2O3‐SiO2 catalysts. Two groups of catalysts (A and B) were prepared by using the sol‐gel method. The objective of the present study is the selection of the catalyst having the best isomer (bi‐ and tri‐branched) yield under optimum operating conditions (reaction temperature, reduction temperature, flow duration, etc.). The results show that the introduction of tungsten (group B) modifies siginificantly the catalyst activity and that the optimum nickel amount in these catalysts is 15 wt. %. When a steady flow is achieved (100 min), the catalyst containing 15 % nickel and 10 % tungsten exhibits the highest and largest selectivity at a reaction temperature of 250°C and a reduction temperature of 430°C. 相似文献
7.
Tian Xing Yang Lang Jian‐Gang Chen Qun‐Xing Luo Chang Liu Jian Song Zhong‐Wen Liu Zhao‐Tie Liu 《加拿大化工杂志》2019,97(12):3115-3124
GaN‐containing titanosilicate catalysts were used for the first time for the oxidative dehydrogenation (ODH) of n‐butane at a relatively low reaction temperature (460 °C). Commercially available GaN powder with a wurtzite crystal structure showed superior reactivity and stability for the ODH of n‐butane. The catalytic property of GaN catalyst for ODH strongly depends on the GaN particle size. The effects of the GaN weight percentage and GaN particle size on the catalytic performance are investigated in a fixed bed reactor. Based on the physicochemical properties of the catalyst characterized via TEM, DLS, N2 adsorption‐desorption, XRF, O2‐TPD, XRD, XPS, and in‐situ FTIR, the textural and structural properties of catalyst were obtained. The catalytic results reveal that the presence of GaN increases the activity of the catalysts, indicating that GaN can be used as a new active phase for the ODH of n‐butane. XRD, XPS, O2‐TPD, DLS, TEM, and in‐situ FTIR results show that activated O species exist on the surface of the GaN catalyst and enhance the catalytic performance with a decreasing GaN particle size, suggesting that smaller GaN particles possess a remarkable capability to activate O species in O2 and C‐H bonds in light alkanes. 相似文献
8.
The catalytic activities of Cu/MOx (MOx = Al2O3, TiO2, and ZnO) catalysts in the gas‐phase hydrogenolysis of glycerol were studied at 180–300 °C under 0.1 MPa of H2. Cu/MOx (MOx = Al2O3, TiO2, and ZnO) catalysts were prepared by the incipient wetness impregnation method. After reduction, CuO species were converted to metallic copper (Cu0). Cu/Al2O3 catalysts with high acidity, high specific surface areas and small metallic copper size favored the formation of 1,2‐propanediol with a maximum selectivity of 87.9 % at complete conversion of glycerol and a low reaction temperature of 180 °C, and favored the formation of ethylene glycol and monohydric alcohols at high reaction temperature of 300 °C. Cu/TiO2 and Cu/ZnO catalysts exhibited high catalytic activity toward the formation of hydroxyacetone with a selectivity of approx. 90 % in a wide range of reaction temperature. 相似文献
9.
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
10.
Alfred A Susu Emmanuel O Ogogo 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2006,81(4):694-705
A platinum/alumina catalyst was sintered in oxygen and hydrogen atmospheres using two metal loadings of the catalyst: 0.3% Pt and 0.6% Pt. After sintering, the aromatization selectivity was investigated with the reforming of n‐heptane as the model reaction at a temperature of 500 °C and a pressure of 391.8 kPa. The primary products of n‐heptane reforming on the fresh platinum catalysts were methane and toluene, with subsequent conversion of benzene from toluene demethylation. To induce sintering, the catalysts were treated with oxygen at a flow rate of 60 mL min?1, pressure of 195.9 kPa and temperatures between 500 and 800 °C. The 0.3% Pt/Al2O3 catalyst exhibited enhanced aromatization selectivity at various sintering temperatures while the 0.6% Pt/Al2O3 catalyst was inherently hydrogenolytic. The fact that aromatization was absent on the 0.6% Pt/Al2O3 catalyst was attributed to the presence of surface structures with dimensionality between two and three as opposed to essentially 2‐D structures on the 0.3% Pt/Al2O3 catalyst surface. On the 0.3% Pt/Al2O3 catalyst, the reaction product ranged from only toluene at a 500 °C sintering temperature to predominantly cracked product at a sintering temperature of 650 °C and no reaction at 800 °C. For sintering at about 650 °C, subsequent conversion of n‐heptane was complete and dropped thereafter. The turnover number was observed to change from 0.07 to 2.26 s?1 as the dispersion changed from 0.33 to 0.09. The Koros–Nowark (K–N) test was used to check for the presence of internal diffusional incursions and Boudart's criterion was used for structural sensitivity determination. The K–N test indicated the absence of diffusional resistances while n‐heptane reforming was found to be structure sensitive on the Pt/Al2O3 catalyst. Copyright © 2006 Society of Chemical Industry 相似文献
11.
Epoxidation of ethylene, propylene, 2‐methylpropene, trans‐2‐butene, 2‐methyl‐2‐butene, and 2,3‐dimethyl‐2‐butene were carried out in a flow‐through reactor in the homogeneous gas phase at pressures of 0.25–1.0 bar in the temperature range of 250–375 °C. Residence times in the reactor varied from 8.3 to 38 ms. The oxidizing agent needed in the feed gas is ozone. The O3 efficiency (reacted olefin/initial O3) was found to be strongly dependent on the reactivity of the olefin used. For C4–C6 olefins, the O3 efficiency was better than 75 % in each case. For 2‐methyl‐2‐butene and 2,3‐dimethyl‐2‐butene, the O3 efficiency exceeded the theoretical value of 100 % considerably. The selectivity to epoxide was about 90 % independent of the olefin used. Under conditions of nearly total olefin conversion, the high selectivity to the epoxide has been retained as unchanged. There were no indications for consecutive reactions of the epoxides. 相似文献
12.
James McGregor Zhenyu Huang Edward P.J. Parrott J. Axel Zeitler K. Lien Nguyen Jeremy M. Rawson Albert Carley Thomas W. Hansen Jean-Philippe Tessonnier Dang Sheng Su Detre Teschner Elaine M. Vass Axel Knop-Gericke R. Schlögl Lynn F. Gladden 《Journal of Catalysis》2010,269(2):329-339
The catalytic dehydrogenation (DH) and oxidative dehydrogenation (ODH) of light alkanes are of significant industrial importance. In this work both carbonaceous material deposited on VOx/Al2O3 catalysts during reaction and unsupported carbon nanofibres (CNFs) are shown to be active for the dehydrogenation of butane in the absence of gas-phase oxygen. Their activity in these reactions is shown to be dependent upon their structure, with different reaction temperatures yielding structurally different coke deposits. Terahertz time-domain spectroscopy (THz-TDS), among other techniques, has been applied to the characterisation of these deposits – the first time this technique has been employed in coke studies. TEM and other techniques show that coke encapsulates the catalyst, preventing access to VOx sites, without a loss of activity. Studies on CNFs confirm that carbonaceous materials act as catalysts in this reaction. Carbon-based catalysts represent an important new class of potential catalysts for DH and ODH reactions. 相似文献
13.
Madaan Neetika Haufe Rommy Shiju N. Raveendran Rothenberg Gadi 《Topics in Catalysis》2014,57(17):1400-1406
The catalytic activity of a VO x /Al2O3 catalyst for the oxidative dehydrogenation of n-butane is investigated. The effects of reaction temperature, oxygen to n-butane ratio and GHSV on the catalytic performance are examined and optimized. Interestingly, this simple catalyst gives good conversion and selectivity. Butane was 22–24 %, and the selectivity to C4 alkenes was 56 %, of which 20–22 % to 1,3-butadiene. Moreover, the catalyst is stable for at least 72 h on stream. Kinetic studies show that the activation barriers for the formation of (butene + butadiene), CO and CO2 amount to 70.2, 65 and 81.3 kJ/mol respectively.
相似文献14.
Bingtian Tu Hao Wang Xiao Liu Weimin Wang Zhengyi Fu 《Journal of the American Ceramic Society》2014,97(9):2996-3003
Spinel type Aluminum oxynitride (γ‐alon) solid solution exists in the Al2O3‐rich region of AlN–Al2O3 systems. The first‐principles calculations facilitate our investigations on composition‐dependence of structure and properties in γ‐alon without the limit of experimental solubility. The constant anion crystal structure of γ‐alon was described as the solid solution of spinel phase γ‐Al2O3 and the ideal Al3O3N with formula of Al(8+x)/3O4?xNx (0 ≤ x ≤ 1). The unit cell expands with increasing Al3O3N composition. The lattice parameter increases nonlinearly with the composition of Al3O3N, which deviates from Vegard's law. As x increases, the anions dilate from the AlIV along (1 1 1) direction, and two new narrow peaks (approximate –12.7 and –0.3 eV) become stronger and the conduction band presents a downward shift to low energy in the TDOS. The absorption edge in the UV region of ε2(ω) present slight red‐shift of 0.5 eV as x increases. Because the compressibility was improved by expansion of coordination polyhedron, the elastic properties were just slightly enhanced as the nitrogen concentration increases. It is suggested that the notable enhancement of mechanical properties in γ‐alon may be difficult to yield by varying the content of substituted nitrogen atoms. The calculated results provide the basis for understanding the crystal structure and intrinsic properties of γ‐alon with different compositions. 相似文献
15.
Anongsack Paseuth Kazuo Yamagata Akira Miura Mikio Higuchi Kiyoharu Tadanaga 《Journal of the American Ceramic Society》2017,100(1):343-353
Metastable c‐AlxT1?xN is an important and well‐established hard coating in the tool industry. To improve the mechanical and thermal properties, Al‐rich c‐AlxTi1?xN coatings with controllable preferred crystal orientations were fabricated via low‐pressure chemical vapor deposition (LP‐CVD) in an industrial plant, using an AlCl3–TiCl4–NH3–Ar–H2 precursor system. The c‐AlxTi1?xN coatings with (100)‐ and (111)‐preferred orientations and average x values of 0.82 and 0.73, respectively, comprised c‐Al(Ti)N/c‐Ti(Al)N nanolamellae with average compositions of c‐Al0.9Ti0.1N/c‐Al0.6Ti0.4N and c‐Al0.80Ti0.20N/c‐Al0.50Ti0.50N; the average lamellar periods were 7.7 and 4.5 nm, respectively. High‐resolution transmission electron microscopy indicated that the c‐Al(Ti)N/c‐Ti(Al)N nanolamellae were modulated along the <100> direction, implying coherent spinodal decomposition of c‐AlxTi1?xN in the as‐deposited state. The hardness of the c‐AlxTi1?xN coatings varied from 33 to 36 GPa, depending on the (100)‐ or (111)‐preferred orientation. Residual stress measurements in the as‐deposited state showed tensile stress values of 1.8 and 4.6 GPa for the (100)‐ and (111)‐oriented c‐AlxT1?xN coatings, respectively. This stress may be generated by the difference in the thermal expansion coefficient of the c‐AlxT1?xN coating and the carbide substrate and by coherency stress in the c‐Al(Ti)N/c‐Ti(Al)N nanolamellae. In situ high‐temperature X‐Ray diffraction results revealed high thermal stability up to 1000°C. 相似文献
16.
Guofeng Zhao Yakun Li Qiaofei Zhang Miaomiao Deng Fahai Cao Yong Lu 《American Institute of Chemical Engineers》2014,60(3):1045-1053
Microstructured Ag‐based catalysts were developed by galvanically depositing Ag onto 80‐μm‐Cu‐fibers for the gas‐phase oxidation of alcohols. By taking advantages including large voidage, open porous structure and high heat/mass transfer, as‐made catalysts provided a nice combination of high activity/selectivity and enhanced heat transfer. The best catalyst was Ag‐10/80‐Cu‐fiber‐400 (Ag‐loading: 10 wt%; Cu‐fiber pretreated at 400 °C in air), being effective for oxidizing acyclic, benzylic and polynary alcohols. For benzyl alcohol, conversion of 94% was achieved with 99% selectivity to benzaldehyde at 300 °C using a high WHSV of 20 h?1. Computational fluid dynamics (CFD) calculation and experimental result illustrated significant enhancement of the heat transfer. The temperature difference from reactor wall to central line was about 10–20 °C for the Ag‐10/80‐Cu‐fiber‐400, much lower than that of 100–110 °C for the Ag‐10‐Cu‐2/Al2O3 at equivalent conversion and selectivity. Synergistic interaction between Cu2O and Ag was discussed, being assignable to the activity improvement. © 2014 American Institute of Chemical Engineers AIChE J, 60: 1045–1053, 2014 相似文献
17.
New calcium‐free Na2O–Al2O3–P2O5 bioactive glasses with potential applications in bone tissue engineering
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Oliwia Jeznach Marcin Gajc Karolina Korzeb Andrzej Kłos Krzysztof Orliński Ryszard Stępień Małgorzata Krok‐Borkowicz Łucja Rumian Krzysztof Pietryga Katarzyna Reczyńska Elżbieta Pamuła Dorota A. Pawlak 《Journal of the American Ceramic Society》2018,101(2):602-611
Sodium aluminophosphate glasses were evaluated for their bone repair ability. The glasses belonging to the system 45Na2O–xAl2O3‐(55‐x)P2O5, with x = (3, 5, 7, 10 mol%) were prepared by a melt‐quenching method. We assessed the effect of Al2O3 content on the properties of Na2O–Al2O3–P2O5 (NAP) glasses, which were characterized by density measurements, DSC analyses, solubility, bioactivity in simulated body fluid and cytocompatibility with MG‐63 cells. To the best of our knowledge, this is the first investigation of calcium‐free Na2O–Al2O3–P2O5 system glasses as bioactive materials for bone tissue engineering. 相似文献
18.
19.
The synthesis technology of linear alkylbenzenes (LABs) was studied through the preparation of an Al‐SBA‐15 catalyst, the optimization of alkylation conditions, and the regeneration of deactivated catalyst. The hydro‐refining over the Pd/Al2O3 catalyst was carried out to remove unsaturated hydrocarbon impurities from the LAB. The results of the alkylation reactions over the Al‐SBA‐15 catalyst in a liquid fixed bed reactor showed that the olefin conversion remained above 98 % for time on stream of 3000 h, and the LAB selectivity was above 93 % under the following conditions: temperature of 260 °C; pressure of 5.0 MPa; weight hourly space velocity (WHSV) of 1.0 h?1; and the molar ratio of benzene to olefin of 25:1. Through the burning coke regeneration, the catalytic performance of the deactivated alkylation catalyst was satisfactorily restored. The quality of the LAB synthesized through alkylation and hydro‐refining was better than that of the industrial LAB produced using the hydrofluoric acid catalytic process. 相似文献
20.
Bi2O3 and mixtures with different additives (Cr2O3, MoO3, NH4VO3, SnO2, and V2O5) have been chosen to study the oxidative dehydrodimerization of isobutene. The catalytic performances were investigated by variation of the residence time, isobutene to oxygen molar ratio, and pressure. The best results for 2,5‐dimethyl‐1,5‐hexadiene (DMH) yield (13 %) were achieved with Bi2O3 as the catalyst. The selectivity of DMH reaches values of over 90 %. 相似文献