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1.
    
Hydrogen energy is considered as one of the ideal solutions for the fulfilment of the ever increasing energy demand. It is mainly due to the following two reasons: firstly, it can be produced from a very abundant source, that is, water; and secondly, it does not leave any harmful effect on the environment. Thermochemical cycles are amongst the most promising ways to generate hydrogen from water in an environment‐friendly manner. Sulfur–iodine cycle is one of the most efficient thermochemical cycles. In this paper, we discuss synthesis of Pt/zirconia catalysts for HI decomposition reaction, which is one of the important steps of S–I thermochemical cycle. The catalysts were characterized by X‐ray diffraction, scanning electron microscopy (SEM), field emission gun‐SEM, transmission electron microscopy, N2 adsorption and H2 chemisorption. The catalytic activity and stability of these catalysts, for liquid phase decomposition of hydriodic acid was evaluated. Conversion is found to be dependent on the noble metal loading, with 18.7% conversion for 2% Pt/ZrO2 catalyst as compared with 2.7% of without catalyst, although the specific activity is highest for 0.5% Pt/ZrO2 catalyst. The catalyst was found to be stable under liquid phase HI decomposition reaction conditions. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

2.
    
Effects of additives to Pt‐CeO2/activated carbon (M563) catalysts on HI decomposition were studied. Among the additives studied, it was found that the addition of Cu to Pt‐CeO2 is the most effective for increasing the catalytic activity to HI decomposition. On this catalyst, almost the equilibrium hydrogen iodide (HI) conversion was achieved at temperature higher than 573 K. Cu addition increased Pt dispersion by anchoring effects. Therefore, in spite of decreased Brunauer‐Emmett‐Teller surface area of the catalyst, dispersion of Pt was much increased by addition of Cu resulting in the increased HI decomposition activity and stability. Because formed I2 adsorbed on the catalyst at initial ca 20 hours, HI conversion was higher than that of the equilibrium one; however, after 20 hours, stable HI decomposition conversion that was almost the same with equilibrium conversion was achieved in the examined temperature range.  相似文献   

3.
    
Pt‐TiO2 loaded on activated carbon was studied as an active and stable catalyst to HI decomposition for H2 formation in the sulfur‐iodine process. Although the activity of TiO2‐loaded catalyst was slightly lower HI conversion than that of CeO2 loaded one, the higher stability against HI decomposition reaction was achieved and almost equilibrium conversion was sustained over ~65 h examined. Moreover, effects of Rh or Ir addition on HI conversion were studied and it was found that Pt‐Rh bimetallic system was highly active and stable to HI decomposition. Scanning transmission electron micrograph observation suggested that the increased HI decomposition activity was assigned to the increased dispersion of Pt particles. High dispersion state of Pt was sustained after HI decomposition at 773 K by addition of Rh. Since the formation of PtI4 was suggested by X‐ray photoelectron spectroscopy measurement during HI decomposition, increased stability by addition of Rh seems to be assigned to the high chemical stability of Rh against iodine. Almost the equilibrium HI conversion on Pt‐Rh‐TiO2/M563 was sustained over 300 hours at 673 K.  相似文献   

4.
The sulfuric acid decomposition should be performed in the wide temperature ranges from 550 °C to 950 °C to absorb the sensible heat of He in SI process. Therefore, the catalysts for the reaction should be stable even in the very corrosive reaction condition of 650 °C. Here, the Pt/n-SiC catalyst was prepared for the purpose and compared with the Pt/SiC catalyst. The both catalysts showed the high stability in the temperature ranges from 650 to 850 °C. The n-SiC with the surface area of 187.1 m2/g was prepared using nano-sized SiO2, which resulted in amorphous SiC phase. The SiC support with the surface area of 19.2 m2/g for the comparison showed the well crystalline structure. In spite of the large surface area differences between the n-SiC and SiC support, the Pt particle sizes of the Pt/n-SiC (average Pt size: 26.4 nm) catalyst were not so much different from those of the Pt/SiC (average Pt size: 26.1 nm) catalyst after the calcination at 1000 °C for 3 h. However, the catalytic activity of the Pt/n-SiC was much higher than that of the Pt/SiC. XRD analysis indicated that the Pt particles on the Pt/n-SiC was more stable than those of the Pt/SiC in the sulfuric acid decomposition and XPS analysis showed that the Pt valence state on the Pt/n-SiC was higher than that on the Pt/SiC. The surface analysis showed that the surface of the n-SiC particles was covered by SiO2 and Si4C4−xO4. These experimental results indicate that the Pt metal particles on n-SiC were stabilized on the oxidized Si surface. Therefore, it is suggested that the Pt particles stabilized on the oxidized Si surface can be a reason for the higher activity of the Pt/n-SiC catalyst as compared with the Pt/SiC catalyst.  相似文献   

5.
Decomposition of hydrogen iodide (HI) is one of the key reactions in the sulfur–iodine (S–I) thermochemical water splitting promising for the massive hydrogen production. Much effort has been made to explore the preparation of high performance catalyst for this hydrogen-producing reaction. Although platinum has long been found to be an efficient metallic catalyst, it was prone to agglomerate at elevated temperature resulting in a decrease in the hydrogen yield. A series of bimetallic Pt–Ir/C catalysts were prepared by electroless plating to investigate the effect of Ir/Pt molar ratio on the HI conversion compared with Pt/C and Ir/C catalysts. The physical properties and morphology of the catalysts were characterized by BET, XRD, TEM and ICP-AES. The synergistic effect of platinum and iridium with respect to HI decomposition was confirmed by the fact that the bimetallic Pt–Ir/C-0.77 catalyst with 1 wt% Pt loading and 0.77 wt% Ir loading showed much higher catalytic activity and thermostability compared with Pt/C and Ir/C catalyst. Based on the experimental results obtained, it may be concluded that the bimetallic Pt–Ir/C catalyst was supposed to be a cost-effective and high performance catalyst promising to be employed for the hydrogen production via the S–I thermochemical water splitting cycle.  相似文献   

6.
Different Pt-Carbon catalysts have been synthesized by hard templating route and have been employed for production of hydrogen from liquid phase HI decomposition at 160 °C temperature. The physical properties and catalytic activities of these catalysts are compared with that of the platinum on activated carbon catalysts. These catalysts have been characterised by X-Ray diffraction, Raman, SEM and BET surface area. Eluant analysis has been carried out using ICP-OES for evaluation of the extent of noble metal leaching under the catalytic activity test conditions. From the present study we have concluded that MCM-41 based Pt/carbon has higher catalytic activity and stability than other Pt/carbon catalysts.  相似文献   

7.
    
Sulfuric acid (SA) decomposition is one of three key reactions in sulfur Iodine (SI) cycle to produce hydrogen. The catalysts for the decomposition should be active and stable in a wide temperature range of 550–900 °C. Pt based catalysts have been explored for the application, but suffered from the Pt loss in high temperature (∼850 °C). TiO2 and Al2O3 are used as a support. They can stabilize Pt metal at higher temperature, but are degraded at the temperature lower than 700 °C. SiO2 supports with a high surface area are relatively stable in a sulfuric acid vapor stream, but the lower interaction with Pt results in high Pt sintering and Pt loss. Both Pt loss and Pt sintering at the high temperature are originated from Pt vaporization. Here, Pt metallic components are placed at the inner wall of hollow mesoporous SiO2 spheres (Pt-HMSS) to preserve Pt components even at 850 °C. PtOx vapor vaporized during the SA decomposition can be re-dispersed on the inner wall of mesoporous SiO2 shell, which can suppress the Pt loss; (1) temperature at outer wall is higher than temperature at inner wall during the endothermic reaction on Pt at the inner wall, (2) the mesoporous shell afford the long path to suppress the diffusion of PtOx vapor at the inner wall to the outer wall. Pt catalyst at the outer walls of hollow mesoporous SiO2 spheres (HMSS-Pt) is prepared and tested for clarifying the hypothesis. Additionally, TiO2-Pt catalyst, one of highly stable catalytic systems for the SA decomposition, is also prepared and compared with the Pt-HMSS catalyst.  相似文献   

8.
    
The sulfur–iodine (SI) cycle is deemed to be one of the most promising alternative methods for large-scale hydrogen production by water splitting, free of CO2 emissions. Decomposition of hydrogen iodide is a pivotal reaction that produces hydrogen. The homogeneous conversion of hydrogen iodide is only 2.2% even at 773 K [1]. A suitable catalyst should be selected to reduce the decomposition temperature of HI and attain reaction yields approaching to the thermodynamic equilibrium conversion. However, residual H2SO4 could not be avoided in the SI cycle because of incomplete purification. The H2SO4 present in the HI feeding stream may lead to the poisoning of HI decomposition catalysts. In this study, the activity and sulfur poisoning of Ru and Ni catalysts loaded on carbon and alumina, respectively, were investigated at 773 K. HI conversion efficiency markedly decreased from 21% to 10% with H2SO4 (3000 ppm) present, which was reversible when H2SO4 was withdrawn in the case of Ru/C. In the case of Ru/C and Ni/Al2O3, catalyst deactivation depends on the concentration of H2SO4; the higher the concentration of H2SO4, the greater the severity of deactivation. Catalysts before and after sulfur poisoning were characterized by transmission electron microscopy (TEM), energy-dispersive X-Ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD). Experimental results and characterization of poisoned and fresh catalysts indicate that the catalyst deactivation could be ascribed to the competitive adsorption of sulfur species and change in its surface properties.  相似文献   

9.
Carbon-supported Pt/Sn catalysts were prepared by decorating carbon-supported Pt with Sn, by decorating carbon-supported Sn with Pt, and by co-deposition of Pt and Sn on carbon. All of the Pt/Sn catalysts exhibited greatly enhanced activities for ethanol oxidation relative to Pt alone, with the Sn decorated Pt catalyst showing the best performance. The latter catalyst was shown by XPS to contain no metallic Sn, emphasizing the importance of surface Sn oxide species in the activation of Pt for ethanol oxidation. Decoration of Sn with Pt is shown to be a feasible way to increase Pt utilization.  相似文献   

10.
    
The current research presented a novel type of stable and high-performance electrocatalyst for oxygen reduction reaction (ORR). For this purpose, N-micro/mesoporous carbon-supported Pt/Co nanoparticles (NPs) were synthesized through a two-step procedure. The Co–N-micro/mesoporous carbon support was first prepared by the direct carbonization of zeolitic imidazolate framework-67 (ZIF-67). Next, the N-micro/mesoporous carbon-supported Pt/Co NPs were synthesized by galvanic replacement of Pt (IV) ions with Co nanoparticles. The surface properties and chemical structure of the prepared electrocatalyst were measured by field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), N2 adsorption-desorption, energy dispersive spectrometry (EDS) techniques. The results confirmed the desirable properties of the prepared electrocatalyst which enhanced the ORR kinetic. The ORR performance of the prepared electrocatalyst was examined utilizing the catalyst coated membrane electrode (CCME) in the homemade half-cell. The ORR performance of N-micro/mesoporous carbon-supported Pt/Co NPs loaded on the gas diffusion electrode (Pt/Co-NC-GDE) was evaluated in an acidic solution. The electrochemical tests exhibited the superior current density and power density of the Pt/Co-NC-GDE (?58.7 mAcm?2 at 0.3 V/RHE and 17.6 mW cm?2) compared to those of Pt/C-GDE (?43.7 mAcm?2, and 13.1 mW cm?2). Furthermore, durability tests indicated the higher stability of Pt/Co-NC-GDE than Pt/C-GDE.  相似文献   

11.
    
In this work, for the first time, MgFe2O4 (MFO) is used to stabilize the N-doped 3D carbon nanosheets supported platinum catalysts (Pt/MFO/NPC). The spherical MFO nanoparticles are randomly dispersed on the surface of the 3D carbon nanosheets, with Pt particles uniformly distributed on them. The Pt/MFO/NPC catalyst possesses excellent stability and methanol tolerance in alkaline solution. The current retention reaches 87.0% after 20,000 s of stability test, which is significantly higher than that of commercial Pt/C (46.9%). In addition, the onset potential (Eonset) and half-wave potential (E1/2) values of Pt/MFO/NPC are larger than that of the commercial contrast, implying the improved kinetics of the Oxygen reduction reaction (ORR). The excellent catalytic activity and stability of Pt/MFO/NPC can be attributed to the combined effect of N-doping and strong metal-support interaction (SMSI) between MFO and Pt.  相似文献   

12.
    
The platinum‐supported catalysts have been prepared by ethylene glycol reduction method, and the catalysts were applied to the partial oxidation of ethanol (POE) for hydrogen production. Four types of support, including CNTs, Al2O3, ZrO2, and CeO2, were used on POE catalytic performance test. Prior to catalyst preparation, the influence of acidic pretreatment on CNTs purity, surface morphology, and pore structure were investigated. The acid‐treated CNTs and prepared catalysts were characterized with N2 physisorption, Raman, thermogravimetric, and transmission electron microscopy analysis. The experimental results show that the particle size and metal dispersion of platinum on CNTs, as well as POE activity, depend on pH value of reducing agent and reduction temperature in the stage of catalyst preparation. In the condition pH value of 10 and temperature at 120 °C for catalyst 5 wt% Pt/CNTs preparation, 2 nm platinum clusters were obtained. Using the as‐prepared catalyst to study the effects of POE reaction conditions on the ethanol conversion, hydrogen selectivity, and hydrogen production rate under constant gas hourly space velocity, the corresponding values at the optimum reaction temperature 400 °C and O2/C2H5OH molar ratio of 0.5 were 98.2%, 97.5%, and 202.3 mmol s?1 kg?1, respectively. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

13.
Corncob-derived activated carbon (CAC) was prepared by potassium hydroxide activation. The Pt/Pd-doped CAC samples were prepared by two-step reduction method (ethylene glycol reduction plus hydrogen reduction). The as-obtained samples were characterized by N2-sorption, TEM and XRD. The results show the texture of CAC is varied after doping Pt/Pd. The Pd particles are easier to grow up than Pt particles on the surface of activated carbon. For containing Pt samples, the pore size distributions are different from original sample and Pd loaded sample. The hydrogen uptake results show excess hydrogen uptake capacity on the Pt/Pd-doped CAC samples are higher than pure CAC at 298 K, which should be attributed to hydrogen spillover effects. The 2.5%Pt and 2.5%Pd hybrid doped CAC sample shows the highest hydrogen uptake capacity (1.65 wt%) at 298 K and 180 bar, The particle size and distribution of Pt/Pd catalysts could play a crucial role on hydrogen uptake by spillover. The total hydrogen storage capacity analysis show that total H2 storage capacities for all samples are similar, and spillover enhanced H2 uptakes of metal-doped samples could not well support total H2 storage capacity. The total pore volume of porous materials also is a key factor to affect total hydrogen storage capacity.  相似文献   

14.
    
Proton exchange membrane fuel cell is an energy conversion technology with an excellent potential to replace fossil fuel–based internal combustion engines. Evenly distributed Pt on conductive support is commonly used as an electrocatalyst. This catalyst support material is a key component of proton exchange membrane fuel cell as it greatly affects the cost, durability, and electrochemical activity of fuel cells. Although the carbon‐based support materials have evolved in the last few decades, there is still need to explore other alternatives as the corrosion of carbon is inevitable under the harsh environments within the catalyst layer of proton exchange membrane fuel cells. Moreover, the performance of noncarbon supports is also not satisfactory. Therefore, the advent of hybrid support materials, which are electrochemically stable and cost‐effective, is required. The hybrid supports exhibiting the characteristics of contributing component, or even showing synergistic effect, would circumvent the shortcomings associated with individual components. This review introduces the recent advances in hybrid support materials, including carbonaceous and noncarbonaceous one; discusses the pros and cons of different support materials; and highlights the improved properties of hybrid supports as compared with the individual components.  相似文献   

15.
Sulfonic acid groups were grafted onto the surface of carbon-nanotube supported platinum (Pt/CNT) catalysts to increase platinum utilization in polymer electrolyte fuel cells (PEFCs) by both thermal decomposition of ammonium sulfate and in situ radical polymerization of 4-styrenesulfonate. The resultant sulfonated Pt/CNT catalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectrometry, thermal gravimetric analysis (TGA) and electrochemical methods. The electrodes with the Pt/CNT catalysts sulfonated by the in situ radical polymerization of 4-styrenesulfonate exhibited better performance than did those with the unsulfonated counterparts, mainly because of the easier access with protons and well dispersed distribution of the sulfonated Pt/CNT catalysts, indicating that sulfonation is an efficient approach to improve performance and reduce cost for the Pt/CNT-based PEFCs. The electrodes with the Pt/CNT catalysts sulfonated by the thermal decomposition of ammonium sulfate, however, did not yield the expected performance as in the case of carbon black supported platinum (Pt/C) catalysts, probably due to the significant agglomeration of platinum particles on the CNT surface at high temperatures, indicating that the Pt/CNT catalysts are more sensitive to temperature than the Pt/C catalysts.  相似文献   

16.
Although several technologies, such as reactive distillation and catalytic membrane reactor, have been proposed to improve HI conversion efficiency, they still experience several challenges for the application in HI section. In this study, an electrochemical cell was employed for hydriodic acid decomposition under the presence of iodine. Several commercial proton-exchange membranes (PEMs), namely, Nafion 117 and Nafion 115, were used as separators for the electrochemical cell. Anodization of iodide anion occurred at the graphite electrode in the anode compartment. Hydrogen was generated by the reduction reaction of hydrogen cations, which migrated from anolyte to catholyte. In electrolysis experiments, PEM showed good performance in terms of high transport number of proton and low iodine permeation. Several parameters, such as operating temperature, HI molarity, and I2 molarity in anolyte, which affected current efficiency, iodine permeance, and electric resistance of test cell, were investigated. High operating temperature and I2 molarity in anolyte enhanced the permeability of iodine, which had several negative influences on electrochemical cell performance. Although current efficiency was negatively affected by increasing temperature and I2 molarity, it still remained above 0.85 in the range of 30 °C–75 °C. Ohmic resistance, which is a component of cell resistance, offered by PEM was investigated with Nafion 117 and 115. Apart from graphite plates, activated carbon papers were adopted as electrodes to reduce the overpotentials due to their high specific surface characteristic.  相似文献   

17.
The third section of closed loop Iodine Sulphur (IS) thermochemical cycle, dealing with HIx processing, suffers from low equilibrium decomposition of HI to hydrogen with a conversion value of only ~22% at 700 K. Here, we report a significant enhancement in conversion of HI into hydrogen (up to ~95%) using a zeolite membrane reactor for the first time. The all silica DDR (deca dodecasil rhombohedral) zeolite membrane with dense, interlocked structure was synthesized on the seeded clay alumina substrate by sonication mediated hydrothermal process. The synthesized membranes along with seed crystals were characterized by X-ray diffraction (XRD), field emission scanning electron microscope (FESEM) and energy dispersive X-ray spectroscopy (EDX). Corrosion studies were carried out by exposing the membrane samples to simulated HI decomposition reaction environment (at 450 °C) for different durations of time upto 200 h. The FESEM, EDX and XRD analyses indicated that no significant changes occurred in the morphology, composition and structure of the membranes. Iodine adsorption on to the membrane surface was observed which got increased with the exposure duration as confirmed by secondary ion mass spectrometry studies. A packed bed membrane reactor (PBMR) assembly was fabricated with integration of in-house synthesized zeolite membrane and Pt-alumina catalyst for carrying out HI decomposition studies. The tube side was chosen as reaction zone and the shell side as the permeation zone. The HI decomposition experiments were carried out for different values of temperature and feed flow rates. DDR zeolite based PBMR was found to enhance the single-pass conversion of HI up to ~95%. The results indicate that for achieving optimal performance of PBMR, it should be operated with space velocities of 0.2–0.3 s?1 and temperature in the range of 650 K–700 K with permeate side vacuum of 0.12 kg/cm2. It is believed that the in-house developed zeolite PBMR shall be a potential technology augmentation in making the IS thermochemical cycle energy efficient.  相似文献   

18.
Pt/C double catalyst layer (DCL) electrodes are prepared by pulsed electrophoresis deposition (PED) method from a Pt colloidal solution as a plating bath. The PED is optimized by varying the deposition time in a galvanostatic mode. The catalyst layers of the electrodes prepared by this method are structurally characterized by EDX and SEM studies. The catalytic activities of Pt/C DCL electrodes are evaluated by cyclic voltammetry technique. The loading amount of the Pt catalyst is controlled by varying the deposition time. With the same Pt catalyst loading, the DCL electrode has enhanced catalytic activity than single catalyst layer (SCL) electrode.  相似文献   

19.
Eight commercial activated carbon catalysts were examined for their catalytic activity to decompose hydroiodic acid (HI) to produce hydrogen; a key reaction in the sulfur-iodine (S-I) thermochemical water splitting cycle. Activity was examined under a temperature ramp from 473 to 773 K. No statistically significant correlation was found between the measured catalyst sample properties and catalytic activity. Four of the eight samples were examined for one week of continuous operation at 723 K. All samples appeared to be stable over the period of examination.  相似文献   

20.
The structure function of hollow carbon nanoparticles (HCNP) as support of Pt particles in the dehydrogenation of cyclohexane was studied. The catalysts and supports were characterized by the XRD, TEM, TG-MS and N2 adsorption/desorption technologies. The results indicated that the short-channel of HCNP can improve the activity and stability of Pt/HCNP, which was confirmed and explained by the temperature programmed desorption (TPD) experiments. The extent of coke deposited on HCNP was much less than that on MCNT, which can be attributed to fast diffusion and quick removal of benzene from active sites through the short path of HCNP. The HCNP with short channel is very important for improving catalyst performance in the storage system of liquid organic hydrides.  相似文献   

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