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1.
The effect operating conditions (temperature, space time, steam/ethanol molar ratio, ethanol partial pressure and time on stream) have on the activity and stability of a Ni/SiO2 catalyst for H2 production by ethanol steam reforming has been studied in a fluidized bed reactor. This catalyst allows obtaining total conversion above 500 °C, with a steam/ethanol molar ratio of 6 and a space time of 0.138 gcatalysth/gethanol. Catalyst deactivation in the 300–500 °C range is due to coke deposition, whose nature (determined by TPH and TPO analysis) mainly depends on reaction temperature. The coke deposited at 300 °C is amorphous and blocks metallic sites, whereas at higher temperatures the coke is mainly filamentous and, although its content increases as reaction temperature is raised to 500 °C, it has a low effect on catalyst deactivation because it does not block metal sites. Above 600 °C the decrease in coke content due to gasification is noticeable, although at this temperature an incipient Ni sintering is observed, which is significant at 700 °C.  相似文献   

2.
The ammonia decomposition process for hydrogen production was studied experimentally in a fixed bed tubular micro-reactor (I.D. = 1 cm and h = 20 cm) filled with 15 ml of ACTA Hypermec 10010 Ru catalyst. With the aim of pointing out the best process conditions, experiments were carried out varying the reaction temperature between 400 and 500 °C, the feeding gas pressure between 1 and 10 bar and the GHSV (Gas Hourly Space Velocity) between 300 and 2400 h−1. To maintain the temperature as uniform as possible along the reactor axis, a 3 zone heater was used and each zone was controlled independently. An acid H2SO4 trap was used downstream the reactor to remove by neutralization the residual ammonia from the product gas. Moreover, the residual ammonia amount in the gas and thus the NH3 dissociation were evaluated for the catalyst in different operative conditions by measuring the PH of the trap and its changing rate over time. Dissociations close to the chemical equilibrium were obtained for every GHSV and temperature we tested with a pressures of 1 and 5 bar in the reactor. In particular, the dissociation was always higher than 99% at 1 bar, while at 5 bar it varied from 96% at 400 °C to 99% at 500 °C. At 10 bar the chemical equilibrium was reached for all GHSVs only at 450 °C and 500 °C with dissociations equal to 95.5% and 97.2%. At 400 °C a dissociation close to the chemical equilibrium (92%) was reached only for a GHSV of 300 h−1 while for the remaining GHSVs the dissociation was always lower, down to 80.8% for a GHSV equal to 2400 h−1.  相似文献   

3.
Ammonia can be a hydrogen source for many applications including fuel cells. Using Ru or Cs–Ru as the catalyst, hydrogen is generated from ammonia by decomposition reaction. These catalysts are deposited on carbon powder by either chemical reduction or precipitation method in this study. Different carbon powder pre-treatment solutions and catalyst deposition conditions are evaluated. Nitric acid pre-treatment followed by precipitation at pH of 6 produces the highest catalyst loading from solution with given concentration of catalyst precursor. Hydrogen generation rate is measured at different catalyst compositions, ammonia inlet flow rates, decomposition temperatures, amount of catalyst packing, and ratio of Cs/Ru. The optimal condition for the ammonia decomposition reaction is Cs/Ru weight ratio at 3, ammonia inlet flow at 6 ml min−1, reaction temperature at 400 °C. At this condition, the ammonia conversion rate reaches 90% and hydrogen generation rate reaches 29.8 mmol/min-gcat.  相似文献   

4.
This paper presents an experimental investigation for an improved process of sorption-enhanced steam reforming of methane in an admixture fixed bed reactor. A highly active Rh/CeαZr1−αO2 catalyst and K2CO3-promoted hydrotalcite are utilized as novel catalyst/sorbent materials for an efficient H2 production with in situ CO2 capture at low temperature (450–500 °C). The process performance is demonstrated in response to temperature (400–500 °C), pressure (1.5–6.0 bar), and steam/carbon ratio (3–6). Thus, direct production of high H2 purity and fuel conversion >99% is achieved with low level of carbon oxides impurities (<100 ppm). A maximum enhancement of 162% in CH4 conversion is obtained at a temperature of 450 °C and a pressure of 6 bar using a steam/carbon molar ratio of 4. The high catalyst activity of Rh yields an enhanced CH4 conversion using much lower catalyst/sorbent bed composition and much smaller reactor size than Ni-based sorption enhanced processes at low temperature. The cyclic stability of the process is demonstrated over a series of 30 sorption/desorption cycles. The sorbent exhibited a stable performance in terms of the CO2 working sorption capacity and the corresponding CH4 conversion obtained in the sorption enhanced process. The process showed a good thermal stability in the temperature range of 400–500 °C. The effects of the sorbent regeneration time and the purge stream humidity on the achieved CH4 conversion are also studied. Using steam purge is beneficial for high degree of CO2 recovery from the sorbent.  相似文献   

5.
In this study, the continuous sorption-enhanced steam reforming of glycerol to high-purity hydrogen production by a simultaneous flow concept of catalyst and sorbent for reaction and regeneration using two moving-bed reactors has been evaluated experimentally. A Ni-based catalyst (NiO/NiAl2O4) and a lime sorbent (CaO) were used for glycerol steam reforming with and without in-situ CO2 removal at 500 °C and 600 °C. The simultaneous regeneration of catalyst and sorbent was carried out with the mixture gas of N2 and steam at 900 °C. The product gases were measured by a GC gas analyzer. It is obvious that the amounts of CO2, CO and CH4 were reduced in the sorption-enhanced steam reforming of glycerol, and the H2 concentration is greatly increased in the pre-CO2 breakthrough periods within 10 min both 500 °C and 600 °C. The extended time of operation for high-purity hydrogen production and CO2 capture was obtained by the continuous sorption-enhanced steam reforming of glycerol. High-purity H2 products of 93.9% and 96.1% were produced at 500 °C and 600 °C and very small amounts of CO2, CH4 and CO were formed. The decay in activity during the continuous reaction-regeneration of catalyst and sorbent was not observed.  相似文献   

6.
In this study, the delafossite type CuCrO2 nanopowder was used as a precursor for preparing Cu-based catalyst for steam reforming of methanol (SRM). The efficiency of hydrogen generation was greatly improved by reducing the size of CuCrO2 to nanoscale. The reduction temperature of Cu metal particles from CuCrO2 decreased from 600 °C to 200 °C due to this size effect. Additionally, because of lowered activation energy, CuCrO2 nanopowder could be reduced by methanol vapor. Thus the CuCrO2 nanopowder, prepared by GNP method, had much higher SRM efficiency than bulk CuCrO2 and the commercial SRM catalyst, even without H2 activation process. The SEM images revealed that the powder retained a cotton candy-like porous structure after reduction treatment. The TEM images showed that the Cu particles were about 5 nm in diameter and well dispersed on Cr2O3 after the reduction of CuCrO2 nanopowder at 500 °C. The catalyst was evaluated by the generation rate with steam reforming of methanol, and the peak hydrogen generation rate read as high as 2550 ml/min g-cat at 360 °C with hydrogen activation. CuCrO2 nanopowder showed high catalytic activity even without reduction treatment, and hydrogen generation rate read as high as 1740 ml/min g-cat at 360 °C.  相似文献   

7.
An integrated reactor system which combines oxygen permeable La0.6Sr0.4Co0.8Ni0.2O3−δ (LSCN) perovskite ceramic hollow fiber membrane with Ni based catalyst has been successfully developed to produce hydrogen through oxy-CO2 reforming of methane (OCRM). Dense La0.6Sr0.4Co0.8Ni0.2O3−δ hollow fiber membrane was prepared using phase inversion-sintering method. OCRM reaction was tested from 650 °C to 800 °C with a quartz reactor packed with 0.5 g Ni/Al2O3 catalyst around the LSCN hollow fiber membrane. CH4 and CO2 were used as reactants and air as the oxygen source was fed through the bore side of the hollow fiber membrane. In order to gauge the effectiveness of this membrane reactor system, air flow was closed at 800 °C and dry reforming of methane (DRM) was tested for comparison. The results show that the oxygen fluxes of LSCN membrane swept by helium are nearly 3 times less than those swept by OCRM reactants. With increasing temperature and oxygen supply, methane conversion in the OCRM reactor reaches 100%, but CO2 conversion decreases from 87% to 72% due to the competition reaction with POM. CO selectivity is as high as nearly 100% at reaction temperatures of 700 °C–800 °C while H2 selectivity reaches a maximum of 88% at 700 °C. At 800 °C, when air supply was closed and DRM was conducted for comparison, CO selectivity decreased to 91%, resulting in carbon deposition which was around 4 times more than those obtained under OCRM reaction and H2/CO ratio decreased from 0.93 to 0.74, showing better carbon resistance and higher H2 selectivity of the Ni-based catalyst over the integrated oxygen separation-OCRM reaction across the LSCN hollow fiber membrane reactor.  相似文献   

8.
Heterogeneous transesterification of waste cooking palm oil (WCPO) to biodiesel over Sr/ZrO2 catalyst and the optimization of the process have been investigated. Response surface methodology (RSM) was employed to study the relationships of methanol to oil molar ratio, catalyst loading, reaction time, and reaction temperature on methyl ester yield and free fatty acid conversion. The experiments were designed using central composite by applying 24 full factorial designs with two centre points. Transesterification of WCPO produced 79.7% maximum methyl ester yield at the optimum methanol to oil molar ratio = 29:1, catalyst loading = 2.7 wt%, reaction time = 87 min and reaction temperature = 115.5 °C.  相似文献   

9.
Bioethanol was reformed in supercritical water (SCW) at 500 °C and 25 MPa on Ni/Al2O3 and Ni/CeZrO2/Al2O3 catalysts to produce high-pressure hydrogen. The results were compared with non-catalytic reactions. Under supercritical water and in a non-catalytic environment, ethanol was reformed to H2, CO2 and CH4 with small amounts of CO and C2 gas and liquid products. The presence of either Ni/Al2O3 or Ni/CeZrO2/Al2O3 promoted reactions of ethanol reforming, dehydrogenation and decomposition. Acetaldehyde produced from the decomposition of ethanol was completely decomposed into CH4 and CO, which underwent a further water-gas shift reaction in SCW. This led to great increases in ethanol conversion and H2 yield on the catalysts of more than 3-4 times than that of the non-catalytic condition. For the catalytic operation, adding small amounts of oxygen at oxygen to ethanol molar ratio of 0.06 into the feed improved ethanol conversion, at the expense of some H2 oxidized to water, resulting in a slightly lower H2 yield. The ceria-zirconia promoted catalyst was more active than the unpromoted catalyst. On the promoted catalyst, complete ethanol conversion was achieved and no coke formation was found. The ceria-zirconia promoter has important roles in improving the decomposition of acetaldehyde, the enhancement of the water-gas shift as well as the methanation reactions to give an extremely low CO yield and a tremendously high H2/CO ratio. The SCW environment for ethanol reforming caused the transformation of gamma-alumina towards the corundum phase of the alumina support in the Ni/Al2O3 catalyst, but this transformation was slowed down by the presence of the ceria-zirconia promoter.  相似文献   

10.
This paper focuses on the yields of both main product NaBH4 and byproduct MgH2 of the thermochemical process. The influence of parameters such as i) the isothermal reaction temperature in the range 480 °C–660 °C, ii) the stoichiometric ratio of solid reactants NaBO2:Mg prepared from 1:2 to 1:8, iii) H2 pressure supplied from 2 to 31 bars and iv) the reaction time kept at isotherm from 0 to 16 h have been systematically investigated. The yields are estimated by in-situ and ex-situ evaluations. Two temperature regimes for MgH2 and NaBH4 formation are recognized from 370 °C to 450 °C and above 500 °C respectively. With regard to NaBH4 regeneration, temperature is the most important factor that positively accelerates the apparent reaction rate between 500 °C and 650 °C providing a sufficient H2 pressure. To efficiently obtain high NaBH4 yield mixtures with molar stoichiometric ratio between solid reactants not less than 1:4 is suggested. Experimental results also reveal that at 12 bars of H2 pressure high NaBH4 yield is obtained. Hence, more efficient way to improve mass transfer of solid reactants (e.g. advance reactor enhances mobility of reactants) rather than increasing H2 pressures is advised. Under optimized condition, 100% conversion of NaBO2 can be achieved within 1.5 h.  相似文献   

11.
La(0.9−x)CexFeO3 perovskite-like catalysts were investigated for the production of hydrogen from simulated coal-derived syngas via the water-gas shift reaction in the temperature range 450-600 °C and at 1 atm. These catalysts exhibited higher activity at high temperatures (T ≥ 550 °C), compared to that of a commercial high temperature iron-chromium catalyst at 450 °C. Addition of a low Ce content (x = 0.2), has little influence on the formation of the LaFeO3 perovskite structure, but enhances catalytic activity especially at high temperatures with 19.17% CO conversion at 550 °C and 40.37% CO conversion at 600 °C. The LaFeO3 perovskite structure and CeO2 redox properties play an important role in enhancing the water-gas shift activity. Addition of a high Ce content (x = 0.6) inhibits the formation of the LaFeO3 perovskite structure and decreases catalyst activity.  相似文献   

12.
Hydrogen production via steam reforming of methanol has been studied over a series of CuO/ZnO/Al2O3 catalysts synthesized by the combustion method using urea as fuel. Furthermore, the effect of alumina loading on the properties of the catalyst has been investigated. XRD analysis illustrated the crystallinity of the Cu and Zn oxides decreases by enhancing alumina loading. BET showed the surface area improvement and FESEM images revealed lower size distribution by increasing the amount of alumina. EDX results gave approximately the same metal oxide compositions of primary gel for the surface of the nanocatalysts. Catalytic performance tests showed the well practicability of catalysts synthesized by the combustion method for steam reforming of methanol process. Alumina addition to the CuO/ZnO catalyst caused the higher methanol conversion and the lower CO generation. Among different compositions the sample with molar component of CuO/ZnO/Al2O3 = 4/4/2.5 showed the best performance which without CO generation at 240 °C its methanol conversion decreased from 90 to 60% after 90 h.  相似文献   

13.
The Ni-H3PW12O40/nano-hydroxyapatite catalyst with H3PW12O40 (HPW) loading was prepared by impregnation method and performed through hydrocracking of Jatropha oil in a fixed-bed reactor. The catalyst was characterized by N2 adsorption–desorption, powder X-ray diffraction (XRD), Fourier transform infrared (FT-IR), X-ray photoelectron spectroscopy (XPS), temperature-programmed desorption of ammonia (NH3-TPD), thermogravimetric analysis (TGA). The conversion of Jatropha oil over Ni-HPW (30 wt%)/nHA was 100%, the liquid yield of liquid product was 83.4%, the ratio of i/n-paraffins was 1.64 at 360 °C, 3 MPa, H2/oil (v/v) = 600 and LHSV = 2 h−1. The pour point of final product oil was −28 °C and the catalyst was used without sulfurization.  相似文献   

14.
A novel nickel catalyst supported on Al2O3@ZrO2 core/shell nanocomposites was prepared by the impregnation method. The core/shell nanocomposites were synthesized by depositing zirconium species on boehmite nanofibres. This contribution aims to study the effects of the pore structure of supports and the zirconia dispersed on the surface of the alumina nanofibres on the CO methanation. The catalysts and supports were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), H2 temperature-programmed reduction (H2-TPR), nitrogen adsorption–desorption, and thermogravimetry and differential thermal analysis (TG-DTA). The catalytic performance of the catalysts for CO methanation was investigated at a temperature range from 300 °C to 500 °C. The results of the characterization indicate that the metastable tetragonal zirconia could be stably and evenly dispersed on the surface of alumina nanofibres. The interlaced nanorods of the Al2O3@ZrO2 core/shell nanocomposites resulted in a macropore structure and the spaces between the zirconia nanoparticles dispersed on the alumina nanofibres formed most of the mesopores. Zirconia on the surface of the support promoted the dispersion and influenced the reduction states of the nickel species on the support, so it prevented the nickel species from sintering as well as from forming a spinel phase with alumina at high temperatures, and thus reduced the carbon deposition during the reaction. With the increase of the zirconia content in the catalyst, the catalytic performance for the CO methanation was enhanced. The Ni/Al2O3@ZrO2-15 exhibited the highest CO conversion and methane selectivity at 400 °C, but they decreased dramatically above or below 400 °C due to the temperature sensitivity of the catalyst. Ni/Al2O3@ZrO2-30 exhibited a high and constant rate of methane formation between 350 °C and 450 °C. The excellent catalytic performance of this catalyst is attributed to its reasonable pore structure and good dispersion of zirconia on the support. This catalyst has great potential to be further studied for the future industrial use.  相似文献   

15.
Perovskite-type oxide catalysts LaNiO3 and La1−xCexNiO3 (x ≤ 0.5) were prepared by the Pechini method and used as catalysts for carbon dioxide reforming of methane to form synthesis gas (H2 + CO). The gaseous reactants consisted of CO2 and CH4 in a molar ratio of 1:1. At a GHSV of 10,000 hr−1, CH4 conversion over LaNiO3 catalyst increased from 66% at 600 °C to 94% at 800 °C, while CO2 conversion increased from 51% to 92%. The achieved selectivities of CO and H2 were 33% and 57%, respectively, at 600 °C. To prevent the deposition of carbon and the sintering nickel species, some of the Ni in perovskite-type oxide catalyst was substituted by Ce. Ce provided lattice oxygen vacancies, which activated C–H bonds, and increased the selectivity of H2 to 61% at 600 °C. XRD analysis indicates that the catalyst exhibited a typical perovskite spinel structure and formed La2O2CO3 phases after CO2 reforming. The FE-SEM results reveal carbon whisker of the LaNiO3 catalyst and the BET analysis indicates that the specific surface area increases after the reforming reaction. The H2-TPR results confirm that Ce metals can store and provide oxygen.  相似文献   

16.
A series of Au catalysts supported on CeO2–TiO2 with various CeO2 contents were prepared. CeO2–TiO2 was prepared by incipient-wetness impregnation with aqueous solution of Ce(NO3)3 on TiO2. Gold catalysts were prepared by deposition–precipitation method at pH 7 and 65 °C. The catalysts were characterized by XRD, TEM and XPS. The preferential oxidation of CO in hydrogen stream was carried out in a fixed bed reactor. The catalyst mainly had metallic gold species and small amount of oxidic Au species. The average gold particle size was 2.5 nm. Adding suitable amount of CeO2 on Au/TiO2 catalyst could enhance CO oxidation and suppress H2 oxidation at high reaction temperature (>50 °C). Additives such as La2O3, Co3O4 and CuO were added to Au/CeO2–TiO2 catalyst and tested for the preferential oxidation of CO in hydrogen stream. The addition of CuO on Au/CeO2–TiO2 catalyst increased the CO conversion and CO selectivity effectively. Au/CuO–CeO2–TiO2 with molar ratio of Cu:Ce:Ti = 0.5:1:9 demonstrated very high CO conversion when the temperature was higher than 65 °C and the CO selectivity also improved substantially. Thus the additive CuO along with the promoter and amorphous oxide ceria and titania not only enhances the electronic interaction, but also stabilizes the nanosize gold particles and thereby enhancing the catalytic activity for PROX reaction to a greater extent.  相似文献   

17.
Hydrogen production was studied in the catalytic steam reforming of a synthetic and a real aqueous fraction of bio-oil. Ni/Al coprecipitated catalysts with varying nickel content (23, 28 and 33 relative atomic %) were prepared by an increasing pH technique and tested during 2 h under different experimental conditions in a small bench scale fixed bed setup. The 28% Ni catalyst yielded a more stable performance over time (steam-to-carbon molar ratio, S/C = 5.58) at 650 °C and a catalyst weight/organic flow rate (W/morg) ratio of 1.7 g catalyst min/g organic. Using the synthetic aqueous fraction as feed, almost complete overall carbon conversion to gas and hydrogen yields close to equilibrium could be obtained with the 28% Ni catalyst throughout. Up to 63% of overall carbon conversion to gas and an overall hydrogen yield of 0.09 g/g organic could be achieved when using the real aqueous fraction of bio-oil, but the catalyst performance showed a decay with time after 20 min of reaction due to severe coke deposition. Increasing the W/morg ratio up to 5 g catalyst min/g organic yielded a more stable catalyst performance throughout, but overall carbon conversion to gas did not surpass 83% and the overall hydrogen yield was only ca. 77% of the thermodynamic equilibrium. Increasing reaction temperatures (600–800 °C) up to 750 °C enhanced the overall carbon conversion to gas and the overall yield to hydrogen. However, at 800 °C the catalyst performance was slightly worse, as a result of an increase in thermal cracking reactions leading to an increased formation of carbon deposits.  相似文献   

18.
In this experimental study, a membrane reactor housing a composite membrane constituted by a thin Pd-layer supported onto Al2O3 is utilized to perform methanol steam reforming reaction to produce high-grade hydrogen for PEM fuel cell applications. The influence of various parameters such as temperature, from 280 to 330 °C, and pressure, from 1.5 to 2.5 bar, is analyzed. A commercial Cu/Zn-based catalyst is packed in the annulus of the membrane reactor and the experimental tests are performed at space velocity equal to 18,500 h−1 and H2O:CH3OH feed molar ratio equal to 2.5:1. Results in terms of methanol conversion, hydrogen recovery, hydrogen yield and products selectivities are given. As a best result of this work, 85% of methanol conversion and a highly pure hydrogen stream permeated through the membrane with a CO content lower than 10 ppm were reached at 330 °C and 2.5 bar. Furthermore, a comparison between the experimental results obtained in this work and literature data is proposed and discussed.  相似文献   

19.
Ceria-supported Pt, Ir and Co catalysts are prepared herein by the deposition–precipitation method and investigated for their suitability in the steam reforming of ethanol (SRE) at a temperature range of 250–500 °C. SRE is tested in a fixed-bed reactor under an H2O/EtOH molar ratio of 13 and 20,000 h−1 GHSV. Possible pathways are proposed according to the assigned temperature window to understand the different catalysts attributed to specific reaction pathways. The Pt/CeO2 catalyst shows the best carbon–carbon bond-breaking ability and the lowest complete ethanol conversion temperature of 300 °C. Acetone steam reforming over the Ir/CeO2 catalyst at 400 °C promotes a hydrogen yield of up to 5.3. Lower reaction temperatures for the water–gas shift and acetone steam reforming are in evidence for the Co/CeO2 catalyst, whereas the carbon deposition causes its deactivation at temperature over 500 °C.  相似文献   

20.
In this work, CO2 capture and H2 production during the steam gasification of coal integrated with CO2 capture sorbent were investigated using a horizontal fixed bed reactor at atmospheric pressure. Four different temperatures (650, 675, 700, and 750 °C) and three sorbent-to-carbon ratios ([Ca]/[C] = 0, 1, 2) were studied. In the absence of sorbent, the maximum molar fraction of H2 (64.6%) and conversion of coal (71.3%) were exhibited at the highest temperature (750 °C). The experimental results verified that the presence of sorbent in the steam gasification of coal enhanced the molar fraction of H2 to more than 80%, with almost all CO2 was fixed into the sorbent structure, and carbon monoxide (CO) was converted to H2 and CO2 through the water gas shift reaction. The steam gasification of coal integrated with CO2 capture largely depended on the reaction temperature and exhibited optimal conditions at 675 °C. The maximum molar fraction of H2 (81.7%) and minimum CO2 concentration (almost 0%) were obtained at 675 °C and a sorbent-to-carbon ratio of 2.  相似文献   

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