Hydrogen Iodide Decomposition Research Articles

Research and development on membrane IS process for hydrogen production using solar heat

Thermochemical hydrogen production has attracted considerable interest as a clean energy solution to address the challenges of climate change and environmental sustainability. The thermochemical water-splitting iodine-sulfur (IS) process uses heat from nuclear or solar power and thus is a promising next-generation thermochemical hydrogen production method that is independent of fossil fuels and can provide energy security. This paper presents the current state of research and development (R&D) of the IS process based on membrane techniques using solar energy at a medium temperature of 600 °C. Membrane design strategies have the most potential for making the IS process using solar energy highly efficient and economical and are illustrated here in detail. Three aspects of membrane design proposed herein for the IS process have led to a considerable improvement of the total thermal efficiency of the process: membrane reactors, membranes, and reaction catalysts. Experimental studies in the applications of these membrane design techniques to the Bunsen reaction, sulfuric acid decomposition, and hydrogen iodide decomposition are discussed.

Performance of Activated‐Carbon‐Supported Ni, Co, and Ni–Co Catalysts for Hydrogen Iodide Decomposition in a Thermochemical Water‐Splitting Sulfur–Iodine Cycle

AbstractBimetallic Ni–Co/activated carbon (Ni–Co/AC) and monometallic Ni/AC and Co/AC catalysts were prepared to investigate their catalytic activity for hydrogen‐iodide decomposition in the sulfur–iodine (SI) cycle. Transmission electron microscopy (TEM) revealed an average size of approximately 3 nm particles for Ni–Co/AC. Ni–Co/AC possesses a higher ID/IG intensity ratio in Raman spectroscopy than the monometallic catalysts and support, which is an indication of high degree of defects. Hydrogen‐iodide decomposition was performed on a fixed vertical bed quartz reactor at a weight hourly space velocity (WHSV) of 12.9 h−1 and different temperatures (400–550 °C). Bimetallic catalysts exhibited better activity and stability than the monometallic catalysts. The composition of Ni/Co in the bimetallic Ni–Co catalyst played the key role in dictating the activity of catalyst. It was observed that the loading ratio of 3:1 for Ni/Co achieved the maximal hydrogen‐iodide conversion value. Bimetallic Ni(3 %)–Co(1 %)/AC showed excellent time‐on‐stream stability of 70 h for the hydrogen‐iodide decomposition reaction. The post‐reaction characterization studies (X‐ray diffraction and Brunauer–Emmett–Teller surface area measurements) confirmed that the bimetallic Ni–Co/AC catalyst has a stable structure and shows high corrosion resistance against the corrosive hydrogen iodide environment. Also, it was observed that the apparent activation energy of the bimetallic Ni–Co/AC catalyst was smaller than the monometallic Ni and Co catalysts. The effect of iodine on hydrogen‐iodide conversion was also studied.

Correction to: Catalytic Decomposition of Hydrogen-Iodide Over Nanocrystalline Ceria Promoted by Transition Metal Oxides for Hydrogen Production in Sulfur–Iodine Thermo-Chemical Cycle

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.

TiO2 as a catalyst for hydrogen production from hydrogen-iodide in thermo-chemical water-splitting sulfur-iodine cycle

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.

Effect of rare earth (RE – La, Pr, Nd) metal-doped ceria nanoparticles on catalytic hydrogen iodide decomposition for hydrogen production

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 < CeO2-N (N = Nd) < CeO2-P (P = Pr) < CeO2-L (L = La). CeO2-L shows higher catalytic activity and stability in comparison to the pure CeO2 material. It also showed an excellent time-on-stream stability for 35 h. The apparent activation energy of CeO2-L, CeO2-P, and CeO2-N was found to be 48.9, 54.8, and 61.4 kJ mol−1, respectively. The effect of iodine on hydrogen iodide conversion was also studied over a CeO2-L catalyst. Thus, RE-doped CeO2 catalysts show a lot of potential of generating hydrogen from hydrogen iodide in the SI cycle.

Catalytic Decomposition of Hydrogen-Iodide Over Nanocrystalline Ceria Promoted by Transition Metal Oxides for Hydrogen Production in Sulfur–Iodine Thermo-Chemical Cycle

Catalytic Decomposition of Hydrogen-Iodide Over Nanocrystalline Ceria Promoted by Transition Metal Oxides for Hydrogen Production in Sulfur–Iodine Thermo-Chemical Cycle

Hydrogen production tests by hydrogen iodide decomposition membrane reactor equipped with silica-based ceramics membrane

The decomposition of hydrogen iodide in the thermochemical water splitting iodine–sulfur process at an intermediate temperature (400 °C) using a catalytic membrane reactor was reported here, for the first time. The performance of a catalytic membrane reactor based on a hexyltrimethoxysilane-derived silica membranes (H2 permeance of 9.4 × 10−7 mol Pa−1 m−2 s−1 and H2/N2 selectivity of over 80.0.) was evaluated at 400 °C by varying the HI flow rates of 2.6, 4.7, 6.9, 8.4, and 9.7 mL min−1. The silica membranes were prepared by counter-diffusion chemical vapor deposition method on γ-alumina-coated α-alumina tubes. Hydrogen was successfully extracted from the membrane reactor using the silica membrane at 400 °C. A significant increase in HI conversion was achieved. The conversion achieved at an HI flow rate of 2.6 mL min−1 was approximately 0.60, which was greater than the equilibrium conversion in HI decomposition (0.22).

Pt-Ce0.9 Cu0.1 O2 /activated carbon as highly active and stable HI decomposition catalyst

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.

Development of catalysts for hydrogen production from hydrogen iodide decomposition in thermo-chemical water-splitting sulfur-iodine cycle: A review

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 specific surface area, oxygen vacancies (defects), and alloy formation between two metals. This article also summarized the different material of construction (MoC) used for HI reaction which are essential for building big pilot plants.

Hydrogen-iodide decomposition over Pd[sbnd]CeO2 nanocatalyst for hydrogen production in sulfur-iodine thermochemical cycle

A highly active and stable catalyst for hydrogen-iodide decomposition reaction in sulfur-iodine (SI) cycle has been prepared in the form of PdCeO2 nanocatalyst by sol-gel method with different calcination temperatures (300 °C, 500 °C, and 700 °C). XRD and TEM confirmed a size around 6–8 nm for PdCeO2 particles calcined at 300 °C. Raman study revealed large number oxygen vacancies in PdCeO2-300 when compared to PdCeO2-500 and PdCeO2-700. With increase in calcination temperature, the average particle size increased whereas the specific surface area and number of oxygen vacancies decreased. Hydrogen-iodide catalytic-decomposition was carried out in the temperature range of 400°C–550 °C in a quartz-tube, vertical, fixed-bed reactor with 55 wt % aqueous hydrogen-iodide feed over PdCeO2 catalyst using nitrogen as a carrier gas. PdCeO2-300 showed hydrogen-iodide conversion of 23.3%, which is close to the theoretical equilibrium conversion of 24%, at 550 °C. It also showed a reasonable stability with a time-on-stream of 5 h.

Preparation of an H2-permselective silica membrane for the separation of H2 from the hydrogen iodide decomposition reaction in the iodine–sulfur process

A high-performance, H2-permselective silica membrane derived from hexyltrimethoxysilane (HTMOS) was developed for application in the thermochemical water-splitting iodine–sulfur process. Silica membranes, referred to here as HTMOS membranes, were prepared via counter-diffusion chemical vapor deposition on γ-alumina-coated α-alumina support tubes with outer diameters of 10 mm. Special attention was devoted to obtain high H2/HI selectivity, high H2 permeance, and good stability in the presence of corrosive HI gas. The effects of the deposition conditions, temperature, and period were investigated. The HTMOS membrane prepared at 450 °C for 5 min exhibited high H2/HI selectivity (>175) with H2 permeance on the order of 10−7 mol Pa−1 m−2 s−1. On the basis of stability experiments, it was found that the HTMOS membrane was stable upon HI exposure at a temperature of 400 °C for 11 h.

Study of the mechanism of the catalytic decomposition of hydrogen iodide (HI) over carbon materials for hydrogen production

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 I2 and H2 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.

Hydrogen production from the decomposition of hydrogen iodide over nanosized nickel-oxide-zirconia catalysts prepared by solution-combustion techniques

NiO/ZrO2 prepared by solution-combustion method (SCM) showed near equilibrium conversions of hydrogen iodide to hydrogen and iodine at 500°C–550°C without any performance degradation over 50h. XRD data of the catalyst after 10h of reaction were compared with the same after a TPR step in H2/Ar on another catalyst sample, to verify Ni-ex-solution. Ni is clearly visible in the XRD after TPR, although it was not observed under reaction conditions (HI/H2O/N2), even after 10h. Instead, the onset of monoclinic ZrO2 is observed after reaction, which was not visible after TPR.

Catalytic performance of bimetallic Ni-Pt nanoparticles supported on activated carbon, gamma-alumina, zirconia, and ceria for hydrogen production in sulfur-iodine thermochemical cycle

Bimetallic Ni-Pt nanoparticles supported on four different supports (activated carbon (AC)), γ-alumina, zirconia, and ceria) were prepared by modified impregnation-reduction technique for decomposition of hydrogen iodide to hydrogen and iodine, in the thermochemical water-splitting sulfur-iodine (SI) cycle. The catalysts were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), and Brunauer–Emmett–Teller (BET) method to find their structure, morphology, and surface area, respectively. High metal dispersions (Ni-Pt) were obtained with particle sizes of the order of 10 nm or lesser, in the high-surface-area supports. The hydrogen iodide-decomposition results showed catalytic activity of Ni-Pt nanoparticles in the following order on different supports: Ni(2.5%)-Pt(2.5%)/AC > Ni(2.5%)-Pt(2.5%)/γ-alumina > Ni(2.5%)-Pt(2.5%)/Zirconia > Ni(2.5%)-Pt(2.5%)/Ceria. Bimetallic Ni(2.5%)-Pt(2.5%)/AC also showed excellent stability for 100 h in the hydrogen iodide-decomposition reaction, and with a higher performance relative to the corresponding Pt supported catalyst under the same operating conditions.

Study of Bunsen reaction in agitated reactor operating in counter current mode for iodine-sulphur thermo-chemical process

The iodine-sulphur (IS) thermo-chemical process is being studied as a potential process for production of hydrogen by water splitting. It consists of three chemical reactions: 1) Bunsen reaction, which is the acid production step, 2) sulphuric acid decomposition to produce oxygen; 3) hydrogen iodide decomposition to produce hydrogen. In this work, a detailed parametric study of the Bunsen reaction is presented, which was carried out in agitated reactor (ABR) in counter current mode of operation. Experiments have been carried out in the reactor at different temperatures by varying the sulphur dioxide (SO2) flow rate and partial pressure of SO2. Bunsen reaction rate and SO2 conversion are calculated experimentally from feed rate and scrubbing rate of SO2. It has been observed that the reaction rate and SO2 conversion increase with increase in SO2 flow, increase in SO2 partial pressure and decrease in temperature. 'Tanks-in-series' model, one of the non-ideal reactor models, has been proposed to describe the ABR reaction system. The model has been validated with experimental results. This approach can be useful for the design and scaling up of the agitated reactor.

Two-dimensional simulation of hydrogen iodide decomposition reaction using fluent code for hydrogen production using nuclear technology

The operating characteristics of hydrogen iodide (HI) decomposition for hydrogen production were investigated using the commercial computational fluid dynamics code, and various factors, such as hydrogen production, heat of reaction, and temperature distribution, were studied to compare device performance with that expected for device development. Hydrogen production increased with an increase of the surface-to-volume (STV) ratio. With an increase of hydrogen production, the reaction heat increased. The internal pressure and velocity of the HI decomposer were estimated through pressure drop and reducing velocity from the preheating zone. The mass of H2O was independent of the STV ratio, whereas that of HI decreased with increasing STV ratio.

Study of effect of high pressures and elevated temperatures on Bunsen reaction of Iodine–Sulfur thermo-chemical process

Hydrogen production by water splitting method is one of the promising solutions for the future energy systems. Among all hydrogen production processes, thermo-chemical Iodine–Sulfur process is one of the efficient and environmentally attractive methods. Iodine–Sulfur process consists of three chemical reactions: (i) Bunsen reaction, which is the acid production step, (ii) sulfuric acid decomposition to produce oxygen and (iii) hydrogen iodide decomposition to produce hydrogen. A detailed parametric study of Bunsen reaction has been carried out through semi-batch experiments. Experiments are carried out in a metallic tubular Bunsen reactor at different pressure and temperature with pure sulfur dioxide (SO2). It has been observed that the overall reaction rate increases with increase in pressure and decreases with increase in temperature. Further studies have been carried out with nitrogen in SO2, to understand the effect of gas film resistance on the overall reaction rate and conversion.

Equilibrium conversion and reaction analysis in sulfur‐iodine thermochemical hydrogen production cycle

Equilibrium conditions of the main reactions of the SI cycle were studied in this paper. The extent of reaction for two main reactions of this cycle including sulfuric acid decomposition and hydrogen iodide decomposition was evaluated as a function of temperature, pressure, and initial mole number of reactants. In the reaction modelling of sulfuric acid and sulfur trioxide decompositions, two models including simple and multiple reaction models were considered. In the simple model, it was assumed that two decomposition reactions proceeded independently. However, in the multiple reaction model, both reactions were considered simultamneously. It was shown that the Bunsen reaction completely proceeded in the range of operating conditions of the Bunsen reactor. Also, sulfuric acid was demonstrated to be decomposed at a higher rate when the reaction temperature and initial concentration of the sulfuric acid and sulfur trioxide increased. Furthermore, the operating pressure had to be maintained at lower values and the generated sulfur dioxide had to be withdrawn from the reactor in order to have a higher yield of product in this reactor. Finally, in the hydrogen iodide decomposition, the operating pressure, temperature, and concentration of hydrogen iodide had to be maintained at higher values to have a complete reaction. Moreover, the generated hydrogen was shown to be withdrawn from the hydrogen iodide reactor to prevent from backward reaction.

Catalytic performance of different carbon materials for hydrogen production in sulfur–iodine thermochemical cycle

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.

Numerical simulations of HI decomposition in packed bed membrane reactors

Numerical simulations to develop an understanding of transport processes inside PBMRs (packed bed membrane reactors) and to evaluate effectiveness of PBMRs in increasing the conversion of HI (hydrogen iodide) decomposition reaction of IS (iodine–sulfur) thermochemical cycle are reported. The computational approach used in the simulations has been validated using the data reported for HI decomposition in a packed bed reactor (PBR). The validated computational approach has been used for parametric studies. Effects of different parameters (temperature, pressure, space velocity, membrane permeability, permselectivity, packed bed porosity and reactor diameter) on HI conversion are reported. The parameters having the maximum impact on the conversion are identified. The findings show that using a PBMR instead of a PBR leads to significant enhancement in conversion and the parameters having high impact on conversion are wall temperature, feed temperature, reactor diameter and packed bed porosity. Based on the findings of parametric studies, ranges of the parameters having maximum impact on conversion are suggested, e.g. the reactor wall temperature is recommended to be in the range of 690–700 K, the bed porosity is recommended to be in the range of 0.2–0.4.