The Experts below are selected from a list of 324 Experts worldwide ranked by ideXlab platform
Kefa Cen - One of the best experts on this subject based on the ideXlab platform.
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catalytic performance of semi coke on Hydrogen Iodide decomposition in sulfur iodine thermochemical cycle for carbon dioxide free Hydrogen production
Energy Conversion and Management, 2018Co-Authors: Lijian Wang, Yanwei Zhang, Zhihua Wang, Yanqun Zhu, Kefa CenAbstract:Abstract Sulfur-iodine thermochemical water splitting cycle is a promising and carbon dioxide-free method for Hydrogen production. Among the reactions in this cycle, Hydrogen Iodide catalytic decomposition is the rate-determining step. In this study, catalytic reactivity test combined with characterizations of nitrogen physisorption, X-Ray diffraction, and Raman spectroscopy provide evidences that hydrofluoric acid modified semi-coke is a promising catalyst candidate for Hydrogen Iodide decomposition because of its high active and low cost. The raw semi-coke enhanced the Hydrogen Iodide conversion rate. After modification of hydrofluoric acid, the catalytic activity of semi-coke increased largely. Semi-coke modified by 40 wt% hydrofluoric acid showed better performance than commercial activated carbon catalyst. Combine the characterization results and catalytic reactivity, the graphitic edge carbon atoms in semi-coke are the active sites for Hydrogen Iodide decomposition. This finding pointed out the direction of carbon material catalyst design for Hydrogen Iodide decomposition.
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study of the mechanism of the catalytic decomposition of Hydrogen Iodide hi over carbon materials for Hydrogen production
International Journal of Hydrogen Energy, 2017Co-Authors: Yanwei Zhang, Zhihua Wang, Rui Wang, Jiayi Lin, Kefa CenAbstract:Abstract Quantum chemistry calculations using a reasonably simplified char model were performed to clarify the mechanisms of Hydrogen Iodide (HI) decomposition over carbon materials. The density functional theory at the B3LYP/3-21G** level was used to optimize the geometries of the reactants, products, stable intermediates, and transition states in possible reaction pathways. The main elementary reactions of the homogeneous decomposition of HI were simulated to verify the applicability of the chosen calculation method and basis set. The adsorptions of HI on two prototypical model chars were all irreversible chemisorption reactions. The results revealed that HI chemisorption preferentially occurred in the zigzag model compared with the energy barriers. Based on the chemisorption results, the decomposition process of HI in the zigzag model was calculated at the same level. The process of HI decomposition on carbon materials took place not directly but by a series of chemisorption and desorption reactions, which demonstrated that the desorption of I 2 and H 2 controls overall catalysis reaction. The initial carbon structure disappeared and turned into the iodine absorbed structure, which played a real catalytic role in the overall process. The two structures were compared by analyzing their electrostatic potentials (ESPs), which demonstrated that the iodine absorbed structure presented a higher activity than the initial carbon structure. A detailed mechanism of the catalytic decomposition of HI over the carbon materials was proposed based on the pathways that we obtained from the calculation results.
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influence of the structural and surface characteristics of activated carbon on the catalytic decomposition of Hydrogen Iodide in the sulfur iodine cycle for Hydrogen production
International Journal of Hydrogen Energy, 2013Co-Authors: Xiangdong Lin, Yanwei Zhang, Junhu Zhou, Zhihua Wang, Rui Wang, Kefa CenAbstract:Abstract Coal-based activated carbon (AC-COAL) catalysts subjected to acid treatment were tested to evaluate their performance on Hydrogen-Iodide (HI) decomposition for Hydrogen production in sulfur-iodine (SI or IS) cycle. The effects of acid treatment on catalysts and the relations between sample properties and catalytic activities were discussed. The AC-COAL obtained by non-oxidative acid treatments had the best catalytic activity. However, the catalytic activity of AC-COAL decreased after the treatment of nitric acid. Higher surface area, higher carbon contents, lower ash contents and fewer surface oxidation groups contributed to the catalytic activity of ACs. HI decomposition on the AC surface itself may be due to high densities of unpaired electrons associated with structural defects and edge plane sites with similar structural ordering. Moreover, the oxygen-containing groups reduced the electron transfer capability associated with the basal plane sites.
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decomposition of Hydrogen Iodide via wood based activated carbon catalysts for Hydrogen production
International Journal of Hydrogen Energy, 2011Co-Authors: Zhihua Wang, Yanwei Zhang, Junhu Zhou, Yun Chen, Chao Zhou, Ronald Whiddon, Kefa CenAbstract:In this study, the catalytic activity of wood-based catalysts produced by different activation methods was evaluated for the decomposition of Hydrogen Iodide (HI) as part of the sulfur-iodine Hydrogen production process. The wood-based activated carbon catalysts showed strong improvement in the HI conversion compared to a blank, especially for carbon catalysts activated using H3PO4. Proximate analysis and ultimate analysis, XRD, BET, SEM, Boehm titration, TPD-MS, XPS were carried out to examine the characteristics of the catalysts. High carbon content (C-ad) seemed to favor high catalytic activity, while high ash content (A(ad)) reduced catalytic activity of samples likely due to displacement of catalytically active material. Oxygen-containing groups were not directly responsible for catalytic activity. HI conversion increased as the surface area and pore diameter increased. Unsaturated carbon atoms maybe the main active constituent, therefore, low area density of oxygen [O] that was closely related to unsaturated carbon atoms was beneficial to HI conversion. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved. (Less)
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catalytic decomposition of Hydrogen Iodide over pre treated ni ceo2 catalysts for Hydrogen production in the sulfur iodine cycle
International Journal of Hydrogen Energy, 2009Co-Authors: Yanwei Zhang, Junhu Zhou, Zhihua Wang, Jianzhong Liu, Kefa CenAbstract:The Ni/CeO2 catalysts with successive oxidization, reduction and re-oxidization have been tested for Hydrogen production in sulfur–iodine (SI or IS) cycle. The samples were characterized by BET, XRD, TEM, TPR and XPS. The oxidative/reductive atmosphere affected the structure and performance of the catalysts. It was suggested that a migration of Ce4+ from the bulk to the surface occurred during the reductive treatment. The diffusion process was reversed when the atmosphere was changed to an oxidative one. The reduced and re-oxidized samples seemed to be similar all the time and showed better catalytic activity in comparison with the as-received and oxidized samples. For the re-oxidized sample, the strongest interaction compared with other samples occurred between Ni and CeO2 and oxygen vacancies transferred from bulk to surface, which led to form more surface sites and oxygen vacancies. The metal Ni was found only on the surface of the reduced sample. The active site of metal Ni besides the surface site and oxygen vacancy were assumed to play an important role for Hydrogen production.
Ashok N Bhaskarwar - One of the best experts on this subject based on the ideXlab platform.
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catalytic performance of carbon nanotubes supported palladium catalyst for Hydrogen production from Hydrogen Iodide decomposition in thermochemical sulfur iodine cycle
Renewable Energy, 2018Co-Authors: Amit Singhania, Ashok N BhaskarwarAbstract:Abstract The current work presents the synthesis of carbon nanotubes supported palladium catalyst for Hydrogen production from Hydrogen-Iodide decomposition in thermochemical water-splitting sulfur-iodine (SI) cycle. XRD results showed that the Pd nanoparticles were highly dispersed on the CNT support. Raman results showed that Pd(3%) possessed the highest quantity of defects than other loaded Pd samples and CNT support. The order of catalytic activity for Hydrogen-Iodide decomposition is: Pd(3%)/CNT > Pd(5%)/CNT > Pd(1%)/CNT > CNT. This is due to high degree of defects present in Pd(3%)/CNT as compared to others. Pd(3%)/CNT also showed an excellent stability of 100 h for the reaction. The post-characterizations (BET, ICP-AES, XRD and TEM) of spent-Pd(3%)/CNT after 100 h were carried out in order to find out the changes in the specific surface area, elemental analysis, structure and particle size. No changes were observed in the specific surface area, elemental analysis, particle size, and structure of the spent catalyst as compared to the fresh one. This shows the Pd/CNT has a lot of potential of generating Hydrogen in the thermochemical SI cycle.
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tio2 as a catalyst for Hydrogen production from Hydrogen Iodide in thermo chemical water splitting sulfur iodine cycle
Fuel, 2018Co-Authors: Amit Singhania, Ashok N BhaskarwarAbstract:Abstract In this work, TiO2 nanoparticles have been prepared by the sol–gel (at different calcination temperatures) and solution-combustion method for Hydrogen-Iodide decomposition in thermo-chemical water-splitting sulfur-iodine (SI) cycle for Hydrogen production. The sol-gel method derived TiO2 (TiO2-SGM-300 and TiO2-SGM-500) provide smaller nanoparticles as compared to the solution-combustion (TiO2-SCM). TEM revealed a particle size of around 4–5 nm of TiO2-SGM-300. XRD and Raman confirmed that TiO2-SGM-300 and TiO2-SGM-500 exhibited pure anatase phase, whereas a small amount of rutile phase was observed in TiO2-SGM-700 and TiO2-SCM samples. It is found that with increase in calcination temperatures during sol-gel method, the average particle size of TiO2 increases and specific surface area decreases. Commercial TiO2 (Degussa P-25) was used for the comparison purpose. As far as the author knows, TiO2 has been used here for the first time for Hydrogen-Iodide decomposition. The Hydrogen-Iodide decomposition experiments were carried out in a vertical-fixed bed quartz reactor at a WHSV of 12.9 h−1 under atmospheric pressure. The order of catalytic activity was as follows: TiO2-SGM-300 > TiO2-SCM > TiO2-COMM (commercial). Also, it was observed that the Hydrogen-Iodide conversion decreases with increase in calcination temperatures of TiO2 during sol–gel method. Their activity was as follows: TiO2-SGM-300 > TiO2-SGM-500 > TiO2-SGM-700. TiO2-SGM-300 catalyst also showed a reasonable time-on-stream stability of 6 h for Hydrogen-Iodide decomposition. The apparent activation energy of TiO2-SGM-300 is found to be 72.29 kJ mol−1. This shows that the TiO2 has a potential of generating Hydrogen from Hydrogen Iodide in SI cycle. This can further be explored as a catalyst support using some non-precious and precious metal catalysts for Hydrogen-Iodide decomposition.
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correction to catalytic decomposition of Hydrogen Iodide over nanocrystalline ceria promoted by transition metal oxides for Hydrogen production in sulfur iodine thermo chemical cycle
Catalysis Letters, 2018Co-Authors: Amit Singhania, Ashok N Bhaskarwar, Satinath Banerjee, Parvatalu Damaraju, Bharat BhargavaAbstract:In this study, CeO2, and CeO2-M (M=Fe, Co, and Ni) catalysts were prepared by sol–gel method for catalytic decomposition of Hydrogen-Iodide in sulfur–iodine (SI) cycle. These catalysts sample were characterized by Brunauer–Emmett–Teller (BET), X-ray diffraction (XRD), inductively coupled plasma-atomic emission spectroscopy (ICP-AES), transmission electron microscopy (TEM), and Raman spectroscopy. The powder XRD, and TEM results gave 4–5 nm average size particles of CeO2–Ni-300 sample. BET and Raman results showed a high specific surface area, and large number of oxygen vacancy in the Ni sample. The Hydrogen-Iodide decomposition experiments were carried out in the temperature range of 400–550 °C in a quartz-tube vertical fixed-bed reactor with 55 wt% HI feed over prepared CeO2-M catalysts using nitrogen as a carrier gas at atmospheric pressure. The experimental Hydrogen-Iodide decomposition results showed high catalytic activity of Ni sample as compared to Co and Fe samples. They followed the catalytic order: CeO2–Ni-300 > CeO2–Co-300 > CeO2–Fe-300 > CeO2-300. The effect of calcination temperatures (300, 500, and 700 °C) of CeO2–Ni sample (during sol–gel method) on Hydrogen-Iodide conversion was also studied and showed that the following catalytic order: CeO2–Ni-300 > CeO2–Ni-500 > CeO2–Ni-700. With increase in calcination temperatures the conversion decreased. CeO2–Ni-300 sample also gave a reasonable stability for time-on-stream of about 5 h. So, based on these results, CeO2–Ni-300 is an attractive candidate which has potential for producing large quantity of Hydrogen in SI cycle.
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effect of rare earth re la pr nd metal doped ceria nanoparticles on catalytic Hydrogen Iodide decomposition for Hydrogen production
International Journal of Hydrogen Energy, 2018Co-Authors: Amit Singhania, Ashok N BhaskarwarAbstract:Abstract In this work, high surface area rare earth (RE = La, Pr, and Nd) metal-doped ceria (CeO2) nanocatalysts have been synthesized by the citric-aided sol-gel method for Hydrogen-Iodide decomposition in thermochemical water-splitting sulfur-iodine (SI) cycle for Hydrogen production. This sol-gel method allows the insertion of rare earth metal M3+ ions into the CeO2 material. Incorporation of rare earth metals created a different synergistic effect between RE and Ce components such as increase of oxygen mobility, oxygen vacancy, and thermal stability of the CeO2 material. These doped-CeO2 materials were characterized by various physicochemical techniques, namely, XRD, BET, ICP-AES, TEM, TGA, and RAMAN spectroscopy. XRD and TEM studies revealed 5–10 nm particles of the RE-CeO2 material. Shifting of peaks and increase in lattice parameter values confirmed the formation of Ce-RE solid solutions (XRD and Raman). Incorporation of dopants resulted in an increase in the specific surface area (BET), thermal stability (TGA), and oxygen vacancy concentration (Raman). Among different dopants, CeO2-L (La-doped CeO2) material exhibits the highest specific surface area, thermal stability, and oxygen vacancy concentration, and smallest crystallite size. The catalytic activity of doped-CeO2 materials is explored for Hydrogen-Iodide decomposition. The order of catalytic activity is as follows: CeO2
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development of catalysts for Hydrogen production from Hydrogen Iodide decomposition in thermo chemical water splitting sulfur iodine cycle a review
Catalysis Reviews, 2017Co-Authors: Amit Singhania, Ashok N BhaskarwarAbstract:ABSTRACTHydrogen Iodide (HI) decomposition is an important part of thermo-chemical water-splitting sulfur-iodine (SI) cycle which can generate large amount of Hydrogen without releasing green-house carbon dioxide gas. HI-decomposition is a very slow reaction even at a high temperature of 500°C. The use of catalyst in this reaction increases the reaction rate. So, a highly active and stable catalyst is desired from long time. Development of active and stable non-noble catalysts for HI-decomposition reaction is a significant challenge. Recent developments and trends in catalysis towards the catalyst synthesis, activity, and stability are discussed in this review. The activity, stability, and kinetic studies of different support materials, different monometallic and bimetallic catalysts are summarized here. The effect of preparation methods of catalysts on their activity and stability is also discussed. The high activity of catalysts for HI reaction is related to nanosize particles, metal dispersion, high sp...
Amit Singhania - One of the best experts on this subject based on the ideXlab platform.
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catalytic performance of carbon nanotubes supported palladium catalyst for Hydrogen production from Hydrogen Iodide decomposition in thermochemical sulfur iodine cycle
Renewable Energy, 2018Co-Authors: Amit Singhania, Ashok N BhaskarwarAbstract:Abstract The current work presents the synthesis of carbon nanotubes supported palladium catalyst for Hydrogen production from Hydrogen-Iodide decomposition in thermochemical water-splitting sulfur-iodine (SI) cycle. XRD results showed that the Pd nanoparticles were highly dispersed on the CNT support. Raman results showed that Pd(3%) possessed the highest quantity of defects than other loaded Pd samples and CNT support. The order of catalytic activity for Hydrogen-Iodide decomposition is: Pd(3%)/CNT > Pd(5%)/CNT > Pd(1%)/CNT > CNT. This is due to high degree of defects present in Pd(3%)/CNT as compared to others. Pd(3%)/CNT also showed an excellent stability of 100 h for the reaction. The post-characterizations (BET, ICP-AES, XRD and TEM) of spent-Pd(3%)/CNT after 100 h were carried out in order to find out the changes in the specific surface area, elemental analysis, structure and particle size. No changes were observed in the specific surface area, elemental analysis, particle size, and structure of the spent catalyst as compared to the fresh one. This shows the Pd/CNT has a lot of potential of generating Hydrogen in the thermochemical SI cycle.
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tio2 as a catalyst for Hydrogen production from Hydrogen Iodide in thermo chemical water splitting sulfur iodine cycle
Fuel, 2018Co-Authors: Amit Singhania, Ashok N BhaskarwarAbstract:Abstract In this work, TiO2 nanoparticles have been prepared by the sol–gel (at different calcination temperatures) and solution-combustion method for Hydrogen-Iodide decomposition in thermo-chemical water-splitting sulfur-iodine (SI) cycle for Hydrogen production. The sol-gel method derived TiO2 (TiO2-SGM-300 and TiO2-SGM-500) provide smaller nanoparticles as compared to the solution-combustion (TiO2-SCM). TEM revealed a particle size of around 4–5 nm of TiO2-SGM-300. XRD and Raman confirmed that TiO2-SGM-300 and TiO2-SGM-500 exhibited pure anatase phase, whereas a small amount of rutile phase was observed in TiO2-SGM-700 and TiO2-SCM samples. It is found that with increase in calcination temperatures during sol-gel method, the average particle size of TiO2 increases and specific surface area decreases. Commercial TiO2 (Degussa P-25) was used for the comparison purpose. As far as the author knows, TiO2 has been used here for the first time for Hydrogen-Iodide decomposition. The Hydrogen-Iodide decomposition experiments were carried out in a vertical-fixed bed quartz reactor at a WHSV of 12.9 h−1 under atmospheric pressure. The order of catalytic activity was as follows: TiO2-SGM-300 > TiO2-SCM > TiO2-COMM (commercial). Also, it was observed that the Hydrogen-Iodide conversion decreases with increase in calcination temperatures of TiO2 during sol–gel method. Their activity was as follows: TiO2-SGM-300 > TiO2-SGM-500 > TiO2-SGM-700. TiO2-SGM-300 catalyst also showed a reasonable time-on-stream stability of 6 h for Hydrogen-Iodide decomposition. The apparent activation energy of TiO2-SGM-300 is found to be 72.29 kJ mol−1. This shows that the TiO2 has a potential of generating Hydrogen from Hydrogen Iodide in SI cycle. This can further be explored as a catalyst support using some non-precious and precious metal catalysts for Hydrogen-Iodide decomposition.
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correction to catalytic decomposition of Hydrogen Iodide over nanocrystalline ceria promoted by transition metal oxides for Hydrogen production in sulfur iodine thermo chemical cycle
Catalysis Letters, 2018Co-Authors: Amit Singhania, Ashok N Bhaskarwar, Satinath Banerjee, Parvatalu Damaraju, Bharat BhargavaAbstract:In this study, CeO2, and CeO2-M (M=Fe, Co, and Ni) catalysts were prepared by sol–gel method for catalytic decomposition of Hydrogen-Iodide in sulfur–iodine (SI) cycle. These catalysts sample were characterized by Brunauer–Emmett–Teller (BET), X-ray diffraction (XRD), inductively coupled plasma-atomic emission spectroscopy (ICP-AES), transmission electron microscopy (TEM), and Raman spectroscopy. The powder XRD, and TEM results gave 4–5 nm average size particles of CeO2–Ni-300 sample. BET and Raman results showed a high specific surface area, and large number of oxygen vacancy in the Ni sample. The Hydrogen-Iodide decomposition experiments were carried out in the temperature range of 400–550 °C in a quartz-tube vertical fixed-bed reactor with 55 wt% HI feed over prepared CeO2-M catalysts using nitrogen as a carrier gas at atmospheric pressure. The experimental Hydrogen-Iodide decomposition results showed high catalytic activity of Ni sample as compared to Co and Fe samples. They followed the catalytic order: CeO2–Ni-300 > CeO2–Co-300 > CeO2–Fe-300 > CeO2-300. The effect of calcination temperatures (300, 500, and 700 °C) of CeO2–Ni sample (during sol–gel method) on Hydrogen-Iodide conversion was also studied and showed that the following catalytic order: CeO2–Ni-300 > CeO2–Ni-500 > CeO2–Ni-700. With increase in calcination temperatures the conversion decreased. CeO2–Ni-300 sample also gave a reasonable stability for time-on-stream of about 5 h. So, based on these results, CeO2–Ni-300 is an attractive candidate which has potential for producing large quantity of Hydrogen in SI cycle.
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effect of rare earth re la pr nd metal doped ceria nanoparticles on catalytic Hydrogen Iodide decomposition for Hydrogen production
International Journal of Hydrogen Energy, 2018Co-Authors: Amit Singhania, Ashok N BhaskarwarAbstract:Abstract In this work, high surface area rare earth (RE = La, Pr, and Nd) metal-doped ceria (CeO2) nanocatalysts have been synthesized by the citric-aided sol-gel method for Hydrogen-Iodide decomposition in thermochemical water-splitting sulfur-iodine (SI) cycle for Hydrogen production. This sol-gel method allows the insertion of rare earth metal M3+ ions into the CeO2 material. Incorporation of rare earth metals created a different synergistic effect between RE and Ce components such as increase of oxygen mobility, oxygen vacancy, and thermal stability of the CeO2 material. These doped-CeO2 materials were characterized by various physicochemical techniques, namely, XRD, BET, ICP-AES, TEM, TGA, and RAMAN spectroscopy. XRD and TEM studies revealed 5–10 nm particles of the RE-CeO2 material. Shifting of peaks and increase in lattice parameter values confirmed the formation of Ce-RE solid solutions (XRD and Raman). Incorporation of dopants resulted in an increase in the specific surface area (BET), thermal stability (TGA), and oxygen vacancy concentration (Raman). Among different dopants, CeO2-L (La-doped CeO2) material exhibits the highest specific surface area, thermal stability, and oxygen vacancy concentration, and smallest crystallite size. The catalytic activity of doped-CeO2 materials is explored for Hydrogen-Iodide decomposition. The order of catalytic activity is as follows: CeO2
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development of catalysts for Hydrogen production from Hydrogen Iodide decomposition in thermo chemical water splitting sulfur iodine cycle a review
Catalysis Reviews, 2017Co-Authors: Amit Singhania, Ashok N BhaskarwarAbstract:ABSTRACTHydrogen Iodide (HI) decomposition is an important part of thermo-chemical water-splitting sulfur-iodine (SI) cycle which can generate large amount of Hydrogen without releasing green-house carbon dioxide gas. HI-decomposition is a very slow reaction even at a high temperature of 500°C. The use of catalyst in this reaction increases the reaction rate. So, a highly active and stable catalyst is desired from long time. Development of active and stable non-noble catalysts for HI-decomposition reaction is a significant challenge. Recent developments and trends in catalysis towards the catalyst synthesis, activity, and stability are discussed in this review. The activity, stability, and kinetic studies of different support materials, different monometallic and bimetallic catalysts are summarized here. The effect of preparation methods of catalysts on their activity and stability is also discussed. The high activity of catalysts for HI reaction is related to nanosize particles, metal dispersion, high sp...
Yanwei Zhang - One of the best experts on this subject based on the ideXlab platform.
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catalytic performance of semi coke on Hydrogen Iodide decomposition in sulfur iodine thermochemical cycle for carbon dioxide free Hydrogen production
Energy Conversion and Management, 2018Co-Authors: Lijian Wang, Yanwei Zhang, Zhihua Wang, Yanqun Zhu, Kefa CenAbstract:Abstract Sulfur-iodine thermochemical water splitting cycle is a promising and carbon dioxide-free method for Hydrogen production. Among the reactions in this cycle, Hydrogen Iodide catalytic decomposition is the rate-determining step. In this study, catalytic reactivity test combined with characterizations of nitrogen physisorption, X-Ray diffraction, and Raman spectroscopy provide evidences that hydrofluoric acid modified semi-coke is a promising catalyst candidate for Hydrogen Iodide decomposition because of its high active and low cost. The raw semi-coke enhanced the Hydrogen Iodide conversion rate. After modification of hydrofluoric acid, the catalytic activity of semi-coke increased largely. Semi-coke modified by 40 wt% hydrofluoric acid showed better performance than commercial activated carbon catalyst. Combine the characterization results and catalytic reactivity, the graphitic edge carbon atoms in semi-coke are the active sites for Hydrogen Iodide decomposition. This finding pointed out the direction of carbon material catalyst design for Hydrogen Iodide decomposition.
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study of the mechanism of the catalytic decomposition of Hydrogen Iodide hi over carbon materials for Hydrogen production
International Journal of Hydrogen Energy, 2017Co-Authors: Yanwei Zhang, Zhihua Wang, Rui Wang, Jiayi Lin, Kefa CenAbstract:Abstract Quantum chemistry calculations using a reasonably simplified char model were performed to clarify the mechanisms of Hydrogen Iodide (HI) decomposition over carbon materials. The density functional theory at the B3LYP/3-21G** level was used to optimize the geometries of the reactants, products, stable intermediates, and transition states in possible reaction pathways. The main elementary reactions of the homogeneous decomposition of HI were simulated to verify the applicability of the chosen calculation method and basis set. The adsorptions of HI on two prototypical model chars were all irreversible chemisorption reactions. The results revealed that HI chemisorption preferentially occurred in the zigzag model compared with the energy barriers. Based on the chemisorption results, the decomposition process of HI in the zigzag model was calculated at the same level. The process of HI decomposition on carbon materials took place not directly but by a series of chemisorption and desorption reactions, which demonstrated that the desorption of I 2 and H 2 controls overall catalysis reaction. The initial carbon structure disappeared and turned into the iodine absorbed structure, which played a real catalytic role in the overall process. The two structures were compared by analyzing their electrostatic potentials (ESPs), which demonstrated that the iodine absorbed structure presented a higher activity than the initial carbon structure. A detailed mechanism of the catalytic decomposition of HI over the carbon materials was proposed based on the pathways that we obtained from the calculation results.
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catalytic performance of different carbon materials for Hydrogen production in sulfur iodine thermochemical cycle
Applied Catalysis B-environmental, 2015Co-Authors: Yanwei Zhang, Zhihua Wang, Rui Wang, Junhu ZhouAbstract:Abstract This study examines four carbon materials through a series of characterization methods and a Hydrogen Iodide (HI) decomposition test. Applying a traditional structure to carbon materials facilitates the quantitative analysis of the four samples. The X-ray diffraction and Raman spectroscopy results indicate that lesser stacked graphite-like layers and shorter lateral diameter La result in higher disordering structure. However, the quantity of active sites is not determined only by the degree of disordering. The aliphatic carbon in the inter-layer correlations decreases the amount of graphite carbon and occupies its edge, thereby inhibiting the formation of edge sites in carbon materials. A low ratio of amorphous carbon with a high degree of disordering corresponds to a high concentration of surface active sites associated with the edges of graphite-like layers. The catalytic performance combined with characterization results demonstrates that the edges of graphite carbon are active sites in HI decomposition. A computational chemistry study is also conducted to illustrate the dominant role of edge sites in the reaction. The calculation results build a detailed mechanism of the catalytic decomposition of HI over the carbon materials and verify that the adsorbed I on the edge sites facilitate the HI decomposition.
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influence of the structural and surface characteristics of activated carbon on the catalytic decomposition of Hydrogen Iodide in the sulfur iodine cycle for Hydrogen production
International Journal of Hydrogen Energy, 2013Co-Authors: Xiangdong Lin, Yanwei Zhang, Junhu Zhou, Zhihua Wang, Rui Wang, Kefa CenAbstract:Abstract Coal-based activated carbon (AC-COAL) catalysts subjected to acid treatment were tested to evaluate their performance on Hydrogen-Iodide (HI) decomposition for Hydrogen production in sulfur-iodine (SI or IS) cycle. The effects of acid treatment on catalysts and the relations between sample properties and catalytic activities were discussed. The AC-COAL obtained by non-oxidative acid treatments had the best catalytic activity. However, the catalytic activity of AC-COAL decreased after the treatment of nitric acid. Higher surface area, higher carbon contents, lower ash contents and fewer surface oxidation groups contributed to the catalytic activity of ACs. HI decomposition on the AC surface itself may be due to high densities of unpaired electrons associated with structural defects and edge plane sites with similar structural ordering. Moreover, the oxygen-containing groups reduced the electron transfer capability associated with the basal plane sites.
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decomposition of Hydrogen Iodide via wood based activated carbon catalysts for Hydrogen production
International Journal of Hydrogen Energy, 2011Co-Authors: Zhihua Wang, Yanwei Zhang, Junhu Zhou, Yun Chen, Chao Zhou, Ronald Whiddon, Kefa CenAbstract:In this study, the catalytic activity of wood-based catalysts produced by different activation methods was evaluated for the decomposition of Hydrogen Iodide (HI) as part of the sulfur-iodine Hydrogen production process. The wood-based activated carbon catalysts showed strong improvement in the HI conversion compared to a blank, especially for carbon catalysts activated using H3PO4. Proximate analysis and ultimate analysis, XRD, BET, SEM, Boehm titration, TPD-MS, XPS were carried out to examine the characteristics of the catalysts. High carbon content (C-ad) seemed to favor high catalytic activity, while high ash content (A(ad)) reduced catalytic activity of samples likely due to displacement of catalytically active material. Oxygen-containing groups were not directly responsible for catalytic activity. HI conversion increased as the surface area and pore diameter increased. Unsaturated carbon atoms maybe the main active constituent, therefore, low area density of oxygen [O] that was closely related to unsaturated carbon atoms was beneficial to HI conversion. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved. (Less)
Zhihua Wang - One of the best experts on this subject based on the ideXlab platform.
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catalytic performance of semi coke on Hydrogen Iodide decomposition in sulfur iodine thermochemical cycle for carbon dioxide free Hydrogen production
Energy Conversion and Management, 2018Co-Authors: Lijian Wang, Yanwei Zhang, Zhihua Wang, Yanqun Zhu, Kefa CenAbstract:Abstract Sulfur-iodine thermochemical water splitting cycle is a promising and carbon dioxide-free method for Hydrogen production. Among the reactions in this cycle, Hydrogen Iodide catalytic decomposition is the rate-determining step. In this study, catalytic reactivity test combined with characterizations of nitrogen physisorption, X-Ray diffraction, and Raman spectroscopy provide evidences that hydrofluoric acid modified semi-coke is a promising catalyst candidate for Hydrogen Iodide decomposition because of its high active and low cost. The raw semi-coke enhanced the Hydrogen Iodide conversion rate. After modification of hydrofluoric acid, the catalytic activity of semi-coke increased largely. Semi-coke modified by 40 wt% hydrofluoric acid showed better performance than commercial activated carbon catalyst. Combine the characterization results and catalytic reactivity, the graphitic edge carbon atoms in semi-coke are the active sites for Hydrogen Iodide decomposition. This finding pointed out the direction of carbon material catalyst design for Hydrogen Iodide decomposition.
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study of the mechanism of the catalytic decomposition of Hydrogen Iodide hi over carbon materials for Hydrogen production
International Journal of Hydrogen Energy, 2017Co-Authors: Yanwei Zhang, Zhihua Wang, Rui Wang, Jiayi Lin, Kefa CenAbstract:Abstract Quantum chemistry calculations using a reasonably simplified char model were performed to clarify the mechanisms of Hydrogen Iodide (HI) decomposition over carbon materials. The density functional theory at the B3LYP/3-21G** level was used to optimize the geometries of the reactants, products, stable intermediates, and transition states in possible reaction pathways. The main elementary reactions of the homogeneous decomposition of HI were simulated to verify the applicability of the chosen calculation method and basis set. The adsorptions of HI on two prototypical model chars were all irreversible chemisorption reactions. The results revealed that HI chemisorption preferentially occurred in the zigzag model compared with the energy barriers. Based on the chemisorption results, the decomposition process of HI in the zigzag model was calculated at the same level. The process of HI decomposition on carbon materials took place not directly but by a series of chemisorption and desorption reactions, which demonstrated that the desorption of I 2 and H 2 controls overall catalysis reaction. The initial carbon structure disappeared and turned into the iodine absorbed structure, which played a real catalytic role in the overall process. The two structures were compared by analyzing their electrostatic potentials (ESPs), which demonstrated that the iodine absorbed structure presented a higher activity than the initial carbon structure. A detailed mechanism of the catalytic decomposition of HI over the carbon materials was proposed based on the pathways that we obtained from the calculation results.
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catalytic performance of different carbon materials for Hydrogen production in sulfur iodine thermochemical cycle
Applied Catalysis B-environmental, 2015Co-Authors: Yanwei Zhang, Zhihua Wang, Rui Wang, Junhu ZhouAbstract:Abstract This study examines four carbon materials through a series of characterization methods and a Hydrogen Iodide (HI) decomposition test. Applying a traditional structure to carbon materials facilitates the quantitative analysis of the four samples. The X-ray diffraction and Raman spectroscopy results indicate that lesser stacked graphite-like layers and shorter lateral diameter La result in higher disordering structure. However, the quantity of active sites is not determined only by the degree of disordering. The aliphatic carbon in the inter-layer correlations decreases the amount of graphite carbon and occupies its edge, thereby inhibiting the formation of edge sites in carbon materials. A low ratio of amorphous carbon with a high degree of disordering corresponds to a high concentration of surface active sites associated with the edges of graphite-like layers. The catalytic performance combined with characterization results demonstrates that the edges of graphite carbon are active sites in HI decomposition. A computational chemistry study is also conducted to illustrate the dominant role of edge sites in the reaction. The calculation results build a detailed mechanism of the catalytic decomposition of HI over the carbon materials and verify that the adsorbed I on the edge sites facilitate the HI decomposition.
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influence of the structural and surface characteristics of activated carbon on the catalytic decomposition of Hydrogen Iodide in the sulfur iodine cycle for Hydrogen production
International Journal of Hydrogen Energy, 2013Co-Authors: Xiangdong Lin, Yanwei Zhang, Junhu Zhou, Zhihua Wang, Rui Wang, Kefa CenAbstract:Abstract Coal-based activated carbon (AC-COAL) catalysts subjected to acid treatment were tested to evaluate their performance on Hydrogen-Iodide (HI) decomposition for Hydrogen production in sulfur-iodine (SI or IS) cycle. The effects of acid treatment on catalysts and the relations between sample properties and catalytic activities were discussed. The AC-COAL obtained by non-oxidative acid treatments had the best catalytic activity. However, the catalytic activity of AC-COAL decreased after the treatment of nitric acid. Higher surface area, higher carbon contents, lower ash contents and fewer surface oxidation groups contributed to the catalytic activity of ACs. HI decomposition on the AC surface itself may be due to high densities of unpaired electrons associated with structural defects and edge plane sites with similar structural ordering. Moreover, the oxygen-containing groups reduced the electron transfer capability associated with the basal plane sites.
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decomposition of Hydrogen Iodide via wood based activated carbon catalysts for Hydrogen production
International Journal of Hydrogen Energy, 2011Co-Authors: Zhihua Wang, Yanwei Zhang, Junhu Zhou, Yun Chen, Chao Zhou, Ronald Whiddon, Kefa CenAbstract:In this study, the catalytic activity of wood-based catalysts produced by different activation methods was evaluated for the decomposition of Hydrogen Iodide (HI) as part of the sulfur-iodine Hydrogen production process. The wood-based activated carbon catalysts showed strong improvement in the HI conversion compared to a blank, especially for carbon catalysts activated using H3PO4. Proximate analysis and ultimate analysis, XRD, BET, SEM, Boehm titration, TPD-MS, XPS were carried out to examine the characteristics of the catalysts. High carbon content (C-ad) seemed to favor high catalytic activity, while high ash content (A(ad)) reduced catalytic activity of samples likely due to displacement of catalytically active material. Oxygen-containing groups were not directly responsible for catalytic activity. HI conversion increased as the surface area and pore diameter increased. Unsaturated carbon atoms maybe the main active constituent, therefore, low area density of oxygen [O] that was closely related to unsaturated carbon atoms was beneficial to HI conversion. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved. (Less)
