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1.
A series of high-temperature close coupled catalysts Pd/Ce-Zr-M/Al2O3 (M = Y, Ca or Ba) were prepared by ultrasonic-assisted successive impregnation. The catalysts were subjected to a series of characterization measurements. The results of activity evaluation show that Y is the best promoter for propane total oxidation, especially at the calcination temperature of 1100 °C. It is interesting that although the BET specific surface areas and the dispersion of Pd species decrease, the Y-promoted catalyst calcined at 1100 °C shows higher catalytic activity than the corresponding one calcined at 900 °C and better sulfur-resisting performance. The results of TEM, TPHD and CO chemisorption indicate that Y can remarkably increase the dispersion of Pd species. However, the dispersion is hard to be connected with the activity increase as the calcination temperature is elevated from 900 to 1100 °C. The change of active phases and the interaction between Pd species and the supports may account for the activity enhancement. Combined with XRD, H2-TPR and O2-TPD results, it is deduced that the coexistence of metallic Pd and PdO species in the catalysts calcined at 1100 °C may be also favorable to C3H8 oxidation. In a word, Pd/Ce-Zr-Y/Al2O3 is indeed a promising high-temperature close coupled catalyst applicable to high temperature. 相似文献
2.
Mohamed A. Al-NakouaMuftah H. El-Naas Basim Abu-Jdayil 《Fuel Processing Technology》2011,92(10):1836-1841
Catalytic plate reactors offer many advantages over conventional reactors, including a major reduction in size and much better temperature control. This study examines the characteristics of thin catalyst coats prepared by the sol-gel method and calcined at different conditions. Employing the catalyst as a thin layer (< 100 μm) on the surface of plate reactors reduces mass and heat transfer limitations compared with pellet catalysts and can improve the effectiveness factor. A sol-gel of Ni/Al2O3 catalyst, with good rheological properties and good adherence onto stainless steel substrate, was prepared and characterized. The effects of calcination temperature, nickel content and calcination environment on the catalyst properties were investigated. The results revealed that the highest catalyst surface area was obtained at 400 °C for all calcined coatings. The presence of nitrogen gas during drying and calcining seemed to increase the catalyst surface areas and improve its adherence properties. Rheological evaluation of the prepared coats proved to be an effective tool in characterizing the thin coatings. The Ni/Al2O3 catalyst exhibited high activity and achieved more than 80% conversion for steam reforming of methane. The reactions were not diffusion limited based on the values of activation energy. 相似文献
3.
Biodiesel production via transesterification of mustard oil with methanol using solid oxide catalyst derived from waste shell of Turbonilla striatula was investigated. The shells were calcined at different temperatures for 4 h and catalyst characterizations were carried out by X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive spectrometer (EDS), Fourier transform infrared spectrometer (FT-IR), thermogravimetric analysis (TGA)/differential scanning calorimetry (DSC) and Brunauer-Emmett-Teller (BET) surface area measurements . Formation of solid oxide i.e. CaO was confirmed at calcination temperature of 800 °C. The effect of the molar ratio of methanol to oil, the reaction temperature, catalyst calcination temperature and catalyst amount used for transesterification were studied to optimize the reaction conditions. Biodiesel yield of 93.3% was achieved when transesterification was carried out at 65 ± 5 °C by employing 3.0 wt.% catalyst and 9:1 methanol to oil molar ratio. BET surface area indicated that the shells calcined in the temperature range of 700 °C-900 °C exhibited enhanced surface area and higher pore volume than the shells calcined at 600 °C. Reusability of the catalysts prepared in different temperatures was also investigated. 相似文献
4.
Carbon nanotubes (CNTs) were synthesized by the catalytic decomposition of acetylene over 40Fe:60Al2O3, 40Ni:60Al2O3 and 20Fe:20Ni:60Al2O3 catalysts. High density CNTs of 20 nm diameter were grown over the 20Fe:20Ni:60Al2O3 catalyst, whereas low growth density CNTs of 40 and 50 nm diameter were found over 40Fe:60Al2O3 and 40Ni:60Al2O3 catalysts. Smaller catalyst particles enabled the synthesis of highly dense, long and narrow-diameter CNTs. It was found that a homogeneous dispersion of the catalyst was an essential factor in achieving high growth density. The carbon yield and the quality of CNTs increased with increasing temperature. For the 20Fe:20Ni:60Al2O3 catalyst, the carbon yield reached 121% after 90 min at 700 °C. The CNTs were grown according to the tip growth mode. Based on reports regarding hydrocarbon adsorption and decomposition over different faces of Ni and Fe, the growth mechanism of CNTs over the 20Fe:20Ni:60Al2O3 catalyst are discussed. 相似文献
5.
A. Serrano-Lotina L. Rodríguez G. Muñoz A.J. Martin M.A. Folgado L. Daza 《Catalysis communications》2011,12(11):961-967
Hydrotalcite-like compound with general formula [M(II)1 − xM(III)x(OH)2]x+(An−x/n) · mH2O, where An− is the compensation anion, has been used as precursor of active catalysts for biogas reforming. This precursor was calcined at six different temperatures between 250 and 750 °C and the resulting catalysts were tested in order to evaluate the influence of the calcination temperature on the catalytic activity and stability. XRD characterization showed that from 250 °C the hydrotalcite structure is no longer detected, leading to Mg(Ni,Al)O solid solutions, where no peaks related to lanthanum appear. An increase on the calcination temperature increased the grain size and cell parameter value. 50 h-catalytic tests were carried out at 700 °C, CH4:CO2 molar ratio of 1:1 and a mass/feed alimentation ratio (W/F) of 0.4 mg min cm− 3. Used catalysts were characterized by temperature programmed oxidation (TPO), scanning electron microscopy (SEM) and Raman spectroscopy in order to obtain information about coke deposition. Catalytic tests highlighted the great influence of calcination temperature over catalytic activity and stability, having found that, as a general trend, calcination temperatures below 750 °C decrease both the stability and catalytic activity, with the exception of the catalyst calcined at 550 °C, where a higher activity was achieved but with a comparatively low stability. 相似文献
6.
H.Y WangE Ruckenstein 《Carbon》2002,40(11):1911-1917
The carbon formation during methane decomposition was investigated at 900 °C over the 48 wt% Co-MgO catalysts as a function of the calcination temperature Tc used in their preparation. Examination of the carbonaceous deposits by transmission electron microscopy revealed three kinds of structures: shapeless tangles, shell-like materials, and carbon filaments. In another set of experiments, the structural characteristics of the calcined catalysts were investigated using temperature-programmed reduction (TPR) and X-ray diffraction (XRD). Co3O4, Co2MgO4, and (Co, Mg)O (solid solution of CoO and MgO) were identified for Tc≤700 °C, Co3O4 and (Co, Mg)O for Tc=800 °C and only (Co, Mg)O for Tc=900 °C. It was found that the metal particles originated from the reduction of the solid solution favored the formation of filamentous carbon. A possible explanation is proposed. 相似文献
7.
Xiaoming Guo Dongsen Mao Guanzhong Lu Song Wang Guisheng Wu 《Catalysis communications》2011,12(12):1095-1098
Cu/ZnO/ZrO2 catalysts were prepared by a route of solid-state reaction and tested for the synthesis of methanol from CO2 hydrogenation. The effects of calcination temperature on the physicochemical properties of as-prepared catalysts were investigated by N2 adsorption, XRD, TEM, N2O titration and H2-TPR techniques. The results show that the dispersion of copper species decreases with the increase in calcination temperature. Meanwhile, the phase transformation of zirconia from tetragonal to monoclinic was observed. The highest activity was achieved over the catalyst calcined at 400 °C. This method is a promising alternative for the preparation of highly efficient Cu/ZnO/ZrO2 catalysts. 相似文献
8.
Gang WangHui Wang Weilong Li Zhaoyu RenJintao Bai Jinbo Bai 《Fuel Processing Technology》2011,92(3):531-540
Fe/Al2O3 catalysts with different Fe loadings (10-90 mol%) were prepared by hydrothermal method. Ethanol decomposition was studied over these Fe/Al2O3 catalysts at temperatures between 500 and 800 °C to produce hydrogen and multi-walled carbon nanotubes (MWCNTs) at the same time. The results showed that the catalytic activity and stability of Fe/Al2O3 depended strongly on the Fe loading and reaction temperature. The Fe(30 mol%)/Al2O3 and Fe(40 mol%)/Al2O3 were both the effective catalyst for ethanol decomposition into hydrogen and MWCNTs at 600 °C. Several reaction pathways were proposed to explain ethanol decomposition to produce hydrogen and carbon (including nanotube) at the same time. 相似文献
9.
Catalytic test of supported Ni catalysts with core/shell structure for dry reforming of methane 总被引:1,自引:0,他引:1
Supported nickel catalysts with core/shell structures of Ni/Al2O3 and Ni/MgO-Al2O3 were synthesized under multi-bubble sonoluminescence (MBSL) conditions and tested for dry reforming of methane (DRM) to produce hydrogen and carbon monoxide. A supported Ni catalyst made of 10% Ni loading on Al2O3 and MgO-Al2O3, which performed best in the steam reforming of methane (97% methane conversion at 750 °C) and in the partial oxidation of methane (96% methane conversion at 800 °C), showed also good performance in DRM and excellent thermal stability for the first 150 h. The supported Ni catalysts Ni/Al2O3 and Ni/MgO-Al2O3 yielded methane conversions of 92% and 92.5%, respectively and CO2 conversions of 95.0% and 91.8%, respectively, at a reaction temperature of 800 °C with a molar ratio of CH4/CO2 = 1. Those were near thermodynamic equilibrium values. 相似文献
10.
Yunbao TuMing Meng Zhaosong SunLijie Zhang Tong DingTianyong Zhang 《Fuel Processing Technology》2012,93(1):78-84
The Au/MnOx-CeO2 catalysts used for CO preferential oxidation were prepared by deposition-precipitation with ultrasonic assistance. The effect of calcination temperature (150-350 °C) on the structures and catalytic performance of the catalysts was systematically investigated. It is found that the catalyst Au/MnOx-CeO2 calcined at 250 °C exhibits the best catalytic performance, giving not only the highest CO conversion of 90.9% but also the highest selectivity of oxygen to CO2 at 120 °C. The results of XRD, TEM and XPS indicate that this catalyst possesses the smallest particle size, the highest dispersion of Au species and the largest amount of surface adsorbed oxygen species, which are favorable to CO oxidation. The H2-TPR results reveal that the selectivity of oxygen to CO2 is mainly determined by the reducibility of Au species in the catalysts. The strong interaction between Au species and the support in Au/MnOx-CeO2-250 decreases its capability for H2 dissociation and oxidation, leading to high selectivity of oxygen to CO2. 相似文献
11.
Effects of titania on the catalytic property of Pd/Al2O3 towards methane combustion were examined. The results revealed that the catalytic activity of the Pd/Al2O3 catalyst was considerably improved by pre-coating the alumina support with titania at low temperature (below 700 °C). Hydrogen chemisorption and BET measurements revealed that the titania-modified alumina supports could modify the support characterization to achieve a high dispersion of palladium. Temperature-programmed reduction and temperature-programmed desorption study further demonstrated that the coating of Pd/Al2O3 catalysts with titania can weaken the bond strength of Pd-O and enhance their catalytic activity towards methane combustion at lower temperature. 相似文献
12.
《Diamond and Related Materials》2007,16(8):1656-1664
Supported-NiO catalysts were tested in the synthesis of carbon nanotubes and carbon nanofibers by catalytic decomposition of methane at 550 °C and 700 °C. Catalytic activity was characterized by the conversion levels of methane and the amount of carbons accumulated on the catalysts. Selectivity of carbon nanotubes and carbon nanofiber formation were determined using transmission electron microscopy (TEM). The catalytic performance of the supported-NiO catalysts and the types of filamentous carbons produced were discussed based on the X-ray diffraction (XRD) results and the TEM images of the used catalysts. The experimental results show that the catalytic performance of supported-NiO catalysts decreased in the order of NiO/SiO2 > NiO/HZSM-5 > NiO/CeO2 > NiO/Al2O3 at both reaction temperatures. The structures of the carbons formed by decomposition of methane were dependent on the types of catalyst supports used and the reaction temperatures conducted. It was found that Al2O3 was crucial to the dispersion of smaller NiO crystallites, which gave rise to the formation of multi-walled carbon nanotubes at the reaction temperature of 550 °C and a mixture of multi-walled carbon nanotubes and single-walled carbon nanotubes at 700 °C. Other than NiO/Al2O3 catalyst, all the tested supported-NiO catalysts formed carbon nanofibers at 550 °C and multi-walled carbon nanotubes at 700 °C except for NiO/HZSM-5 catalyst, which grew carbon nanofibers at both 550 °C and 700 °C. 相似文献
13.
Yasuhiko Hayashi Toru IijimaM. Miyake M. SatohN.L. Rupesinghe K.B.K. TeoM. Tanmemura 《Diamond and Related Materials》2011,20(7):859-862
This paper presents the growth evolutions in terms of the structure, growth direction and density of rapid grown carbon nanotube (CNT) forests observed by scanning and transmission electron microcopies (SEM/TEM). A thermal CVD system at around 700 °C was used with a catalyst of Fe films deposited on thin alumina (Al2O3) supporting layers, a very fast raising time to the growth temperature below 25 °C/s, and a carbon source gas of acetylene diluted with hydrogen and nitrogen without water vapor. Activity of Fe catalyst nanoparticles was maintained for 5 min during CVD process, and it results in CNT forests with heights up to 0.6 mm. SEM images suggest that the disorder in CNT alignment at the initial stage of CNTs plays a critical role in the formation of continuous CNT growth. Also, the prolonged heating process leads to increased disorder in CNT alignment that may be due to the oxidation process occurring at the Fe nanoparticles. TEM images revealed that both double- and few-walled CNTs with diameters of 5-7 nm were obtained and the CNT density was controlled by thickness of Fe catalytic layer. The number of experiments at the same conditions showed a very good repeatability and reproducibility of rapid grown CNT forests. 相似文献
14.
Akaraphol Petchmala Bunjerd Jongsomjit Joongjai Panpranot Artiwan Shotipruk 《Fuel》2010,89(9):2387-2392
Sulfated zirconia (SO4-ZrO2) catalysts, prepared with three different sulfur loading contents (0.75%, 1.8% and 2.5%) at two calcination temperatures (500 °C and 700 °C), were tested for use in the transesterification of purified palm oil (PPO) and the esterification of palm fatty acid (PFA) in near-critical and super-critical methanol. Techniques including BET, XRD, NH3- and CO2-TPD revealed that the sulfur content and calcination temperature strongly affects the catalyst base-acid site, specific surface area, average pore size, phase structure, and thus the catalytic reactivity. The most suitable sulfur loading content was found to be 1.8% and the optimum calcination temperature 500 °C. The results show that the use of SO4-ZrO2 reduces esterification reaction times, the amount of methanol necessary and the required reaction temperature. The reactions at 250 °C in the presence of the SO4-ZrO2 catalyst at 0.5 w/w% catalyst to PPO or PFA were found to give the highest FAMEs conversions. Under these conditions, 90% and 75% conversions were achieved within 10 and 1 min from PPO (at 25:1 MeOH:PPO molar ratio) and PFA (at 6:1 MeOH:PFA molar ratio), respectively. 相似文献
15.
CaCu3Ti4O12 nano-sized powders were successfully prepared by sol-gel technique and calcination at 600-900 °C. The thermal decomposition process, phase structures and morphology of synthesized powders were characterized by IR, DSC-TG, XRD, TEM, respectively. It was found that the main weight-loss and decomposition of precursors occurred below 450 °C and the complex perovskite phase appeared when the calcination temperature was higher than 700 °C. Using above synthesized powders as starting materials, CCTO-based ceramics with excellent dielectric properties (?25 = 5.9 × 104, tan δ = 0.06 at 1.0 kHz) were prepared by sintering at 1125 °C. According to the results, a conduction mechanism was proposed to explain the origin of giant dielectric constant in CCTO system. 相似文献
16.
Pimjai Saengkwamsawang Samuk Pimanpaeng Vittaya Amornkitbamrung Santi Maensiri 《Ceramics International》2014
Al2O3 nanopowders were synthesized by a simple chitosan-polymer complex solution route. The precursors were calcined at 800–1200 °C for 2 h in air. The prepared samples were characterized by XRD, FTIR and TEM. The results showed that for the precursors prepared with pH 3–9 γ-Al2O3 and δ-Al2O3 are the two main phases formed after calcination at 800–1000 °C. Interestingly, when the precursor prepared with pH 2 was used, α-Al2O3 was formed after calcination at 1000 °C, and pure α-Al2O3 was obtained after calcination at 1200 °C. The crystallite sizes of the prepared powders were found to be in the range of 4–49 nm, as evaluated by the XRD line broadening method. TEM investigation revealed that the Al2O3 nanopowders consisted of rod-like shaped particles and nanospheres with particle sizes in the range of 10–300 nm. The corresponding selected-area electron diffraction (SAED) analysis confirmed the formation of γ- and α-Al2O3 phases in the samples. 相似文献
17.
A. K. M. Fazle Kibria Young Hwan Mo Min Hee Yun Moon J. Kim Kee Suk Nahm 《Korean Journal of Chemical Engineering》2001,18(2):208-214
Multi-wall carbon nanotubes (MWNTs) were synthesized by catalytic decomposition of acetylene over Fe, Ni and Fe-Ni bimetallic
catalysts supported on alumina under various controlled conditions. The growth density and diameter of CNTs were markedly
dependent on the activation time of catalysts in H2 atmosphere, reaction time, reaction temperature, flow rate of acetylene, and catalyst composition. Bimetallic catalysts were
apt to produce narrower diameter of CNTs than single metal catalysts. For the growth of CNTs at 600 ‡C under 10/100 seem flow
of C2H2/H2 mixture, the narrowest diameter about 20 nm was observed at the reaction time of 1 h for 20Fe : 20Ni : 60Al2O3 catalyst, but at that of 1.5 h for 10Fe : 30Ni : 60Al2O3 catalyst. It was considered that the diameter and density of CNTs decreased with the increase of the growth time mainly due
to hydrogen etching. The growth of CNTs followed the tip growth mode. 相似文献
18.
Using thermogravimetry (TG) under conditions that minimize inhibition by the hydrogen produced, the intrinsic catalytic rates of skeletal Ni, pure and alloyed with solute metals Fe, Co, or Cu, were evaluated in methane decomposition to carbon nanofibers. In “standard” tests, i.e., after pre-reduction in H2 and exposure to CH4 directly at 450 °C, several catalysts reached stable activities exceeding 4 mg C/mg cat./h, comparable with literature values obtained at 500 °C or above. TG evidence is presented for partial bulk carburization of Ni in CH4 below 350 °C, which leads to substantially increased coking rates. TEM evidence supports the view that carburization promotes catalyst particle disintegration, thereby inducing faster and more stable nanofiber growth. Irregularities in alloy response to carburization are interpreted in terms of the stability of the respective mixed-metal carbides. TEM also shows that alloying changes the metal nanocrystallite shape (habit), with consequences for the carbon nanofiber structure. Evidence for the easy dissociation of CH4 is corroborated by direct catalyst activation in the absence of H2. Reduction begins in pure hydrocarbon around 300 °C and leads to coking activities at 450 °C comparable to those for samples pre-reduced in H2. Skeletal metal catalysts offer distinct advantages in low-temperature natural gas conversion. 相似文献
19.
Katabathini Narasimharao Maqsood Ahmad MalikMohamed M. Mokhtar Sulaiman N. BasahelShaeel A. Al-Thabaiti 《Ceramics International》2014
Sulfated TiO2 nanotubes and a series of iron oxide loaded sulfated TiO2 nanotubes catalysts with different iron oxide loadings (1 wt%, 3 wt%, 5 wt% and 7 wt%) were prepared and calcined at 400 °C. The physico-chemical properties of the catalysts were studied by using XRD, N2-physisorption, Raman spectroscopy, SEM-EDX, TEM, XPS, and pyridine adsorption using FTIR and H2-TPR techniques. It was observed that iron oxide was highly dispersed on the sulfated TiO2 nanotube support due to its strong interaction. The activity of these catalysts in the catalytic removal of NO with propane was also studied in the temperature range of 300–500 °C. Highest activity (90% NO conversion) was observed with 5 wt% iron oxide supported on sulfated TiO2 catalyst at 450 °C. Selective catalytic reduction of NO activity of the catalysts was correlated with iron oxide loading, reducibility, and the Brönsted and Lewis acid sites of the catalysts. The catalyst also showed good stability under studied reaction conditions that no deactivation was observed during the 50 h of reaction. 相似文献
20.
Se-Jin Kyung 《Carbon》2006,44(8):1530-1534
Carbon nanotubes (CNTs) were grown using a modified atmospheric pressure plasma with NH3(210 sccm)/N2(100 sccm)/C2H2(150 sccm)/He(8 slm) at low substrate temperatures (?500 °C) and their physical and electrical characteristics were investigated as the application to field emission devices. The grown CNTs were multi-wall CNTs (at 450 °C, 15-25 layers of carbon sheets, inner diameter: 10-15 nm, outer diameter: 30-50 nm) and the increase of substrate temperature increased the CNT length and decreased the CNT diameter. The length and diameter of the CNTs grown for 8 min at 500 °C were 8 μm and 40 ± 5 nm, respectively. Also, the defects in the grown CNTs were also decreased with increasing the substrate temperature (The ratio of defect to graphite (ID/IG) measured by FT-Raman at 500 °C was 0.882). The turn-on electric field of the CNTs grown at 450 °C was 2.6 V/μm and the electric field at 1 mA/cm2 was 3.5 V/μm. 相似文献