首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 46 毫秒
1.
The composition (CuO/ZnO/Al2O3 = 30/60/10) of a commercial catalyst G66B was used as a reference for designing CuO/ZnO/CeO2/ZrO2/Al2O3 catalysts for the oxidative (or combined) steam reforming of methanol (OSRM). The effects of Al2O3, CeO2 and ZrO2 on the OSRM reaction were clearly identified. CeO2, ZrO2 and Al2O3 all promoted the dispersions of CuO and ZnO in CuO/ZnO/CeO2/ZrO2/Al2O3 catalysts. Aluminum oxide lowered the reducibility of the catalyst, and weakened the OSRM reaction. Cerium oxide increased the reducibility of the catalyst, but weakened the reaction. Zirconium oxide improved the reducibility of the catalyst, and promoted the reaction. A lower CuO/ZnO ratio of the catalyst was associated with greater promotion of ZrO2. The critical CuO/ZnO ratio for the promotion of ZrO2 was approximately 0.75–0.8. Introducing of ZrO2 into CuO/ZnO/Al2O3 also improved the stability of the catalyst. Although Al2O3 inhibited the OSRM reaction, a certain amount of it was required to ensure the stability and the mechanical strength of the catalysts.  相似文献   

2.
Methanol, dimethyl ether and bioethanol steam reforming to hydrogen-rich gas were studied over CuO/CeO2 and CuO–CeO2/γ-Al2O3 catalysts. Both catalysts were found to provide complete conversion of methanol to hydrogen-rich gas at 300–350 °C. Complete conversion of dimethyl ether to hydrogen-rich gas occurred over CuO–CeO2/γ-Al2O3 at 350–370 °C. Complete conversion of ethanol to hydrogen-rich gas occurred over CuO/CeO2 at 350 °C. In both cases, the CO content in the obtained gas mixture was low (<2 vol.%). This hydrogen-rich gas can be used directly for fuelling high-temperature PEM FC. For fuelling low-temperature PEM FC, it is needed only to clean up the hydrogen-rich gas from CO to the level of 10 ppm. CuO/CeO2 catalyst can be used for this purpose as well. Since no individual WGS stage, that is necessary in most other hydrogen production processes, is involved here, the miniaturization of the multifuel processor for hydrogen production by methanol, ethanol or DME SR is quite feasible.  相似文献   

3.
Gold (Au) supported on CeO2–Fe2O3 catalysts prepared by the deposition-coprecipitation technique were investigated for steam reforming of methanol (SRM). The 3 wt% Au/CeO2–Fe2O3 sample calcined at 400 °C achieved 100% methanol conversion and 74% hydrogen yield due to a strong Ce–Fe interaction in the active solid solution phase, CexFe1−xO2. The sintering of Au particles was observed when the highest metal content of 5 wt% was registered, which worsened the SRM activity. According to the TPR and TPO analysis, it was found that the transformation of the α-Fe2O3 structure in the mixed oxides and the coke deposition were the main factors for the rapid deactivation of the catalyst.  相似文献   

4.
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   

5.
Single ZrO2 and mixed CeO2-ZrO2 oxides with different CeO2/ZrO2 ratios were prepared by the sol-gel method and the CeO2 by precipitation. The prepared support were impregnated with an aqueous solution of NiCl2·6H2O at an appropriate concentration to yield 3 wt.% of nickel respectively in the catalysts. Catalytic materials were characterized by BET (N2 adsorption-desorption), SEM-EDS, XRD and TPR. The oxidative steam reforming of methanol (OSRM) reaction was investigated on these catalysts for H2 production as a function of temperature. Depending of the CeO2/ZrO2 ratio; the catalysts composition has a significant influence on the surface area (BET), reduction properties and methanol conversion. XRD patterns of the Ni-base catalysts showed well defined diffraction peaks of the metallic Ni except on the Ni/CeO2 catalyst, suggesting that on this sample all of the active phase was highly dispersed. Ni/Ceria-rich catalysts were vastly active for OSRM, giving a total CH3OH conversion at 325 °C with GHSV = 0.3 × 105 h−1. They also showed close selectivity toward H2, with high selectivity to CO2 in all range of temperatures, this suggests that the reverse WGS reaction does not occur on these samples. It seems that the nickel is the phase mainly responsible of hydrogen production although the CeO2/ZrO2 support reduces the CO formation.  相似文献   

6.
The effect of metal oxide (CeO2, Al2O3 and ZrO2) support and In2O3 co-supported Pt catalysts has been investigated on steam reforming of methanol in microreactors. CeO2, Al2O3 and ZrO2 were prepared by the sol-gel method and they were used as a support, which was impregnated with In2O3 as co-support followed by the introduction of Pt species via the wet impregnation method. The size and dispersion of the Pt nanoparticles on In2O3/support have been examined by transmission electron microscopy. From these TEM and XPS results, it was found that the addition of In2O3 supports the formation of a high concentration of metallic Pt nanoparticles with enhanced dispersion and controlled particle size on the surface. The activity and stability of all the developed catalysts were tested for the steam reforming of methanol in microreactors at different temperatures. Under reforming conditions without prior reduction, a Pt/CeO2 catalyst containing 15 wt % of Pt exhibited complete methanol conversion and high selectivity towards hydrogen at 350 °C. However, the CO formation was found to be very high (7.0 vol %) for this catalyst. Upon addition of In2O3 as a co-support to this formulation the formation of CO decreased considerably. Pt/In2O3/CeO2 catalyst containing 15 wt % of Pt and 15 wt % of In2O3 showed excellent catalytic performance at much lower concentration of CO. This change could be closely associated with the formation of metallic Pt nanoparticles with smaller size, higher dispersion with strong interaction between Pt, In2O3 and support, which creates more oxygen vacancies to activate the water molecule which then react with methanol to produce H2 and CO2 suppressing the CO formation. Moreover, CeO2 supported Pt/In2O3 catalyst displayed higher stability with lowest CO formation under continuous steam reforming operation of 100 h. The superior performance of this catalyst is thought to be due to the relative abundance of redox sites on the CeO2 surface, which is able to create an oxygen vacancy as it possesses higher oxygen storage capacity and oxygen exchange capacity. This work demonstrates that the nature of support plays a crucial role for the continuous activation of reactants and determines the catalytic stability during methanol steam reforming.  相似文献   

7.
Hydrogen production by oxidative steam reforming of methanol (OSRM) or autothermal steam reforming of methanol (ASRM) was investigated over Cu-loaded mesoporous CeO2 and Cu-loaded mesoporous CeO2–ZrO2 catalysts, synthesized via a nanocasting process using MCM-48 as a hard template, followed by a deposition–precipitation technique. Various Cu contents were loaded on the mesoporous CeO2 and CeO2–ZrO2 supports. The fresh and spent catalysts were characterized by N2 adsorption–desorption, X-ray diffraction, temperature-programmed oxidation, and X-ray photoelectron spectroscopy. The ASRM results showed that 9 wt% Cu loading onto mesoporous CeO2 and CeO2–ZrO2 provided the best catalytic performance with 100% methanol conversion and 60% H2 yield at 350° and 300 °C, respectively. Furthermore, the time-on-stream stability testing of the 9 wt% Cu loading catalyst was at 168 h, and the CO selectivity of these two catalysts indicated that the addition of ZrO2 into the catalyst reduced the CO selectivity during the ASRM process.  相似文献   

8.
Gold particle with an average size of dAu ~ 4 nm was dispersed on ZnO by the deposition precipitation method. The fabricated Au/ZnO catalyst was used to produce hydrogen from reforming of methanol. Four reforming reactions, i.e., decomposition of methanol (DM), steam reforming of methanol (SRM), partial oxidation of methanol (POM) and oxidative steam reforming of methanol (OSRM), were evaluated in a fixed bed reactor. A reaction temperature of TR > 623 K was required for catalyzing reactions of DM and SRM. Interestingly, high methanol conversion (CMeOH > 90%) was found from reforming reactions of POM and OSRM at an amazing low temperature of TR < 473 K. Besides, a presentable hydrogen yield (RH2 ~ 2.4) and a low selectivity of CO (SCO ~ 1%) were simultaneously attained from the reaction of OSRM. Therefore, the low temperature OSRM reaction over the Au/ZnO catalyst is suggested as a friendly reforming process for on-board production of hydrogen.  相似文献   

9.
The precipitation processes of CuO–CeO2 catalysts preparation were modified, and their optimized copper content were also studied in detail. As indicated by the experimental results, the WGS catalytic activities of the CuO–CeO2 catalysts can be ranked as: stepwise precipitation (SP) > deposition–precipitation (DP) > co-precipitation (CP), suggesting that stepwise precipitation (i.e., a modified DP) is a convenient and effective method to prepare CuO–CeO2 WGS catalysts. The optimized copper contents of CuO–CeO2–SP and CuO–CeO2–CP catalysts are 20 wt.% and 25 wt.%, respectively. Their catalytic activities can be strongly correlated with the results from XRD, XPS, Raman, N2-physisorption, N2O chemisorption and H2-TPR. For DP and SP, a certain amount of copper has substitutively incorporated into ceria lattice with multiple Ce3+ and oxygen vacancies, which is considered as one relatively strong interaction between copper and ceria support. The substitutional incorporation of copper creates larger lattice distortion, lattice defect (embodying as larger lattice cell contraction of CeO2, microstrain and Raman shift) and stronger reducibility (i.e., lower reduction temperature of H2-TPR), as a consequence, higher surface energy and catalytic activity for WGS reaction. While for CP, copper nitrate and cerium nitrate were simultaneously precipitated, resulting in the burial of many copper species in ceria supports, i.e., occupancy incorporation of isolated copper into ceria lattice vacant site, which is considered as another weak interaction between copper and ceria support. Accordingly, combined with N2O chemisorption results, it is demonstrated that surface copper species of CuO–CeO2–CP are fewer and less active than those of CuO–CeO2–DP and CuO–CeO2–SP. Lastly, there is a direct relationship between the pore volume along with most probable pore size of the as-synthesized catalysts and their corresponding catalytic activities for WGS reaction.  相似文献   

10.
Ni–Cu catalysts supported on different materials were tested in ethanol steam reforming reaction for hydrogen production. These catalysts were evaluated at reaction temperature of 400 °C under atmospheric pressure. The reagents, with a water/ethanol molar ratio equal to 10, were fed at 70 dm3/(h gcat) (after vaporization). Analysis of the ethanol conversion, as well as evaluation and quantification of the reaction products, indicated the catalyst 10% Ni–1% Cu/Ce0.6Zr0.4O2 as the most appropriate for the ethanol steam reforming under investigated reaction conditions, among the studied catalysts. During 8 h of reaction this catalyst presented an average ethanol conversion of 43%, producing a high amount of H2 by steam reforming and by ethanol decomposition and dehydrogenation parallel reactions. Steam reforming, among the observed reactions, was quantified by the presence of carbon dioxide. About 60% of the hydrogen was produced from ethanol steam reforming and 40% from parallel reactions.  相似文献   

11.
Hydrogen production by steam reforming of methanol was studied over several Cu/SAB-15-based nanocatalysts in a parallel-type microchannel reactor. The catalysts were prepared through impregnation method and XRD, BET, FT-IR, FE-SEM, TEM, H2-TPR and TGA techniques were used to characterize surface and structural properties of the synthesized catalysts. The effects of reaction temperature, WHSV and S/C molar ratio on the methanol conversion and selectivities of the gaseous products were studied. Then, effects of the metallic promoters were investigated to improve performance of the catalysts. It was revealed that ZnO and CeO2 promoters have positive effects on decreasing CO selectivity and ZrO2 promotes methanol conversion. Furthermore, ZrO2 and CeO2 were declared to improve stability of the catalyst. Among the evaluated catalysts, Cu/ZnO/CeO2/ZrO2/SBA-15 can provide optimal methanol conversion with low CO concentration in the gaseous products. For this catalyst, the methanol conversion and hydrogen selectivity reached 95.2% and 94.6%, respectively.  相似文献   

12.
Novel zeolite-supported rhodium catalysts for ethanol steam reforming   总被引:1,自引:0,他引:1  
Renewable bioethanol is an interesting hydrogen source for fuel cells through steam reforming, but its C–C bond promotes parallel reactions, mainly coke and by-products formation. In this way, good ethanol reforming catalysts are still needed, which explains current research and development efforts around the world. Most catalysts proposed for ethanol reforming are based on oxide-supported noble metals with surface area below 100 m2 g−1 and reaction temperatures above 500 °C. Novel Rh and Rh–K catalysts supported on NaY zeolite with surface area above 440 m2 g−1 are presented in this work. Reaction temperature was fixed at 300 °C and H2O/EtOH molar ratio and reagent flow were varied. Ethanol conversion varied from 50 to 99%, with average increase of 50% due to K promoter, and hydrogen production yield achieved 68%.  相似文献   

13.
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   

14.
Τhe feasibility of tailoring the iso-octane steam reforming activity of Cu/CeO2 catalysts through the use of Co as a second active metal (Cu20−xCox, where x = 0, 5, 10, 15, 20 wt%), is investigated. Characterization studies, involving N2 adsorption–desorption at −196 °C (BET), X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), X-ray Photoelectron Spectroscopy (XPS) and Temperature Programmed Reduction (H2-TPR), were carried out to reveal the impact of the morphological, structural and surface properties of the catalysts on the reforming performance. The results showed that reforming activity was monotonically increased upon increasing cobalt loading. The Co/CeO2 catalyst demonstrated the optimum performance with a H2 yield of 70–80% in the 600–800 °C temperature interval. The Co/CeO2 catalyst exhibited also excellent stability at temperatures above 700 °C, while Cu-based catalysts rapidly deactivated in long term stability tests. A close correlation between surface/redox properties and steam reforming efficiency was established. The lower reducibility of Co/CeO2 catalysts, associated with the formation of Co3+ species, in Co3O4-like phase, can be accounted for the enhanced carbon tolerance of Co-based catalysts. Furthermore, the high concentration of surface oxygen species on Co/CeO2 catalysts can be considered for their enhanced performance. On the other hand, the Cu-induced easier reducibility of bimetallic catalysts, in conjunction with carbon deposition and active phase sintering can be accounted for their inferior steam reforming performance. Irreversible changes in the redox properties of Cu-based catalysts, taking place under reaction conditions, could be resulted to ceria deactivation thus hindering the redox process to keep on.  相似文献   

15.
We studied ethanol steam reforming over Ir/Ce0.9Pr0.1O2 and Ir/CeO2 catalysts comparatively with respect to activity and stability. We found that PrOx-doping have significantly promoted the oxygen storage capacity and thermal stability of the catalysts by incorporation into the ceria lattice. Ethanol was readily converted to hydrogen, methane and carbon oxides at 773 K over the Ir/Ce0.9Pr0.1O2 catalyst, and this is 100 K lower than that found for the Ir/CeO2 catalyst. Moreover, the PrOx-doped catalyst was stable toward ethanol steam reforming at 923 K for 300 h without an apparent variation in ethanol conversion and product distribution. However, the severe aggregation of ceria particles and heavy coke deposition were observed on the Ir/CeO2 catalyst, resulting in remarkable deactivation under the same reaction conditions.  相似文献   

16.
Nano-rod(R), nano-particle(P) and sponginess(S) of ceria samples were used to study catalytic performance of hydrogen production by methanol steam reforming. The samples were prepared by hydrothermal method, precipitation method, and sol-gel method, respectively, and the CuO was supported on the different morpholopy of CeO2 samples by wet impregnation. SEM, TEM, XRD, XRF, BET, H2-TPR, XPS and N2O titration methods were used to study correlation between the structure and the catalytic performance for methanol steam reforming. The results showed that the morphology of the prepared CeO2 support dramatically influenced the performance of catalysts. Due to the stronger interaction between copper oxide and ceria support, the CuO/CeO2-R catalyst had exhibited the better catalytic activity than those of the CuO/CeO2P and CuO/CeO2S catalysts. Moreover, higher Cu dispersion, lower reduction temperature of CuO, and higher content of active species Cu+ were also advantageous to raising catalytic effects. Besides, with the highest content of surface Ce3+, the CuO/CeO2-R had estimated the content of oxygen vacancy on the surface of the catalyst. The existence of surface oxygen vacancy had a positive effect on the methanol steam reforming.  相似文献   

17.
Cu and Ni were supported on ZrO2 by co-impregnation and sequential impregnation methods, and tested in the oxidative steam reforming of methanol (OSRM) reaction for H2 production as a function of temperature. Surface area of the catalysts showed differences as a function of the order in which the metals were added to zirconia. Among them, the Cu/ZrO2 catalyst had the lowest surface area. XRD patterns of the bimetallic catalysts did not show diffraction peaks of the Cu, Ni or bimetallic Cu–Ni alloys. In addition, TPR profiles of the bimetallic catalysts had the lowest reduction temperature compared with the monometallic samples. The reactivity of the catalysts in the range of 250–350 °C showed that the bimetallic samples prepared by successive impregnation had highest catalytic activity among all the catalysts studied. These results were also confirmed by theoretical calculations. The reactivity of the monometallic and bimetallic structures obtained by molecular simulation followed the next order: NishellCucore/ZrO2 ≅ CushellNicore/ZrO2 > Ni/Cu/ZrO2 > Cu/Ni/ZrO2 > Cu–Ni/ZrO2 > Cu/ZrO2 > Ni/ZrO2. These findings agree with the experimental results, indicating that the bimetallic catalysts prepared by successive impregnation show a higher reactivity than the Cu–Ni system obtained by co-impregnation. In addition, the selectivity for H2 production was higher on these catalysts. This result could be associated also to the presence of the bimetallic Cu–Ni and core–shell Ni/Cu nanoparticles on the catalysts, as was evidenced by TEM–EDX analysis, suggesting that the OSRM reaction may be a structure–sensitive reaction.  相似文献   

18.
Cu(BDC) metal–organic framework (MOF) was used as a support for the copper (Cu) catalyst applied in the methanol steam reforming (MSR) process at low temperatures (130–250 °C) with a feed WHSV = 9.2 h?1 within the monolithic reactor. Also, the effects of diverse promoters were examined on the catalytic activities of the Cu/X–Cu(BDC) (X = Ce, Zn, Gd, Sm, La, Y, Pr) catalysts. Results showed that the Ce/Sm–Cu(BDC) supports exhibited highest activities, lowest reduction temperatures and largest specific surface areas, which caused highest distributions of the active copper metal nanoparticles on the supports. The reactor tests displayed that the activities of Cu/X–Cu(BDC) (X = Ce, Zn, Gd, Sm, La, Y, Pr) catalysts followed the order X = Ce > Sm > Y > La > Pr > Cu(BDC) > Zn > Gd. The highest activities of Ce and Sm containing catalysts were attributed to the presence of CeO2 and Sm2O3 caused the oxygen vacancies on the catalyst surface which had positive effects on the methanol reforming process. The time-on-stream stability tests showed the highest resistance of the Cu/Ce–Cu(BDC) catalyst to the carbon formation during 32 h. Consequently, the Cu/Ce–Cu(BDC) with the highest stability, methanol conversion and carbon monoxide selectivity could be used in practical industrial applications.  相似文献   

19.
We tested 3 wt% gold (Au) catalysts on CeO2–ZrO2 mixed oxides, prepared by co-precipitation (CP) and the sol–gel (SG) technique, for steam reforming of methanol (SRM). Uniform Ce1−xZrxO2 solid solution was dependent on the Zr/Ce ratio, where the incorporation of Zr4+ into the Ce4+ lattice with a ratio of 0.25 resulted in smaller ceria crystallites and better reducibility, and was found to be efficient for SRM activity. The catalytic activity was suppressed when the ratio was ≥0.5, which led to the segregation of Zr from solid solution and sintering of Au nanoparticles. It was found that the CP technique produced better catalysts than SG in this case. For the bimetallic catalysts, the co-operation of Au–Cu supported on Ce0.75Zr0.25O2 (CP) exhibited superior activities with complete methanol conversion and low CO concentration at 350 °C. Furthermore, the size of the alloy particle was strongly dependent on the pH level during preparation.  相似文献   

20.
The Cu-based catalysts with different supports (CeO2, ZrO2 and CeO2–ZrO2) for methanol steam reforming (MSR) were prepared by a co-precipitation procedure, and the effect of different supports was investigated. The catalysts were characterized by means of N2 adsorption–desorption, X-ray diffraction, temperature-programmed reduction, oxygen storage capacity and N2O titration. The results showed that the Cu dispersion, reducibility of catalysts and oxygen storage capacity evidently influenced the catalytic activity and CO selectivity. The introduction of ZrO2 into the catalyst improved the Cu dispersion and catalyst reducibility, while the addition of CeO2 mainly increased oxygen storage capacity. It was noticed that the CeO2–ZrO2-containing catalyst showed the best performance with lower CO concentration, which was due to the high Cu dispersion and well oxygen storage capacity. Further investigation illuminated that the formation of CO on CuO/ZnO/CeO2–ZrO2 catalyst mainly due to the reverse water gas shift. In addition, the CuO/ZnO/CeO2–ZrO2 catalyst also had excellent reforming performance with no deactivation during 360 h run time and was used successfully in a mini reformer. The maximum hydrogen production rate in the mini reformer reached to 162.8 dm3/h, which can produce 160–270 W electric energy power by different kinds of fuel cells.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号