Optimization of hydrogen production from three reforming approaches of glycerol via using supercritical water with in situ CO2 separation

A pathway for hydrogen production from supercritical water reforming of glycerol integrated with in situ CO₂ removal was proposed and analyzed. The thermodynamic analysis carried out by the minimizing Gibbs free energy method of three glycerol reforming processes for hydrogen production was investigated in terms of equilibrium compositions and energy consumption using AspenPlus™ simulator. The effect of operating condition, i.e., temperature, pressure, steam to glycerol (S/G) ratio, calcium oxide to glycerol (CaO/G) ratio, air to glycerol (A/G) ratio, and nickel oxide to glycerol (NiO/G) ratio on the hydrogen production was investigated. The optimum operating conditions under maximum H₂ production were predicted at 450 °C (only steam reforming), 400 °C (for autothermal reforming and chemical looping reforming), 240 atm, S/G ratio of 40, CaO/G ratio of 2.5, A/G ratio of 1 (for autothermal reforming), and NiO/G ratio of 1 (for chemical looping reforming). Compared to three reforming processes, the steam reforming obtained the highest hydrogen purity and yield. Moreover, it was found that only autothermal reforming and chemical looping reforming were possible to operate under the thermal self-sufficient condition, which the hydrogen purity of chemical looping reforming (92.14%) was higher than that of autothermal reforming (52.98%). Under both the maximum H₂ production and thermal self-sufficient conditions, the amount of CO was found below 50 ppm for all reforming processes.     

Enhanced hydrogen production via staged catalytic gasification of rice husk using Ca(OH)2 adsorbent and Ce–Ni/γAl2O3 catalyst in a fluidized bed

Hydrogen production from rice husk was carried out via a two-stage system combining CLG (calcium looping gasification) using Ca(OH)₂ adsorbent in a bubbling fluidized bed and catalytic reforming with Ce–Ni/γAl₂O₃ catalyst in a connected fixed bed. The results show that the maximum H₂ concentration (69.16 vol%) and H₂ yield (11.86 mmol g⁻¹rice husk) are achieved at Ca/C (Ca(OH)₂ to carbon molar ratio) = 1.5, H₂O/C (H₂O to carbon molar ratio) = 1.5, T_g (gasification temperature) = 500 °C, T_c (catalytic temperature) = 800 °C. The supplementation of fresh Ca(OH)₂ at Ca/C of 0.5 during calcination helps to activate the regenerated CaO by hydration, maintaining its carbonation activity and CO₂ adsorption. Ce–Ni/γAl₂O₃ catalyst promotes water gas shift (WGS), steam methane reforming (SMR), and C₂–C₃ hydrocarbons reforming, also exhibits excellent activity stability to maintain H₂ concentration and H₂ yield above 67.21 vol% and 11.67 mmol g⁻¹_{rice husk}, respectively, during 5 lifetime tests.     

Enhanced ethanol steam reforming by CO2 absorption using CaO,CaO*MgO or Na2ZrO3

This paper presents results of thermodynamic analysis and experimental evaluation of hydrogen production by steam reforming of ethanol (SRE) combined with CO₂ absorption using a mixture of a solid absorbent (CaO, CaO*MgO and Na₂ZrO₃) and a Ni/Al₂O₃ catalyst. Thermodynamic analysis results indicate that a maximum of 69.5% H₂ (dry basis) is feasible at 1 atm, H₂O/C₂H₅OH = 6 (molar ratio) and T = 600 °C. whereas, the addition of a CO₂ absorbent at 1 atm, T = 600 °C and H₂O/C₂H₅OH/Absorbent = 6:1:2.5, produced a H₂ concentration of 96.6, 94.1, and 92.2% using CaO, CaO*MgO, and Na₂ZrO₃, respectively. SRE experimental evaluation achieved a maximum of 60% H₂. While combining SRE and a CO₂ absorbent exhibited a concentration of 96, 94, and 90% employing CaO, CaO*MgO, and Na₂ZrO₃, respectively at 1 atm, T = 600 °C, SV = 414 h⁻¹ and H₂O/C₂H₅OH/absorbent = 6:1:2.5 (molar ratio).     

Chemical looping steam reforming of ethanol without and with in-situ CO2 capture

Chemical looping steam reforming (CLSR) of ethanol using oxygen carriers (OCs) for hydrogen production has been considered a highly efficient technology. In this study, NiO/MgAl₂O₄ oxygen carriers (OCs) were employed for hydrogen production via CLSR with and without CaO sorbent for in-situ CO₂ removal (sorption enhanced chemical looping steam reforming, SE-CLSR). To find optimal reaction conditions of the CLSR process, including reforming temperatures, the catalyst mass, and the NiO loadings on hydrogen production performances were studied. The results reveal that the optimal temperature of OCs for hydrogen production is 650 °C. In addition, 96% hydrogen selectivity and a 'dead time' (the reduced time of OCs) less than 1 minute is obtained with the 1 g 20NiO/MgAl₂O₄ catalysts. The superior catalytic activity of 20NiO/MgAl₂O₄ is due to the maximal quantity of NiO loadings providing the most Ni active surface centers. High purity hydrogen is successfully produced via CLSR coupling with CaO sorbent in-situ CO₂ removal (SE-CLSR), and the breakthrough time of CaO is about 20 minutes under the condition that space velocity was 1.908 h^?1. Stability CLSR experiments found that the hydrogen production and hydrogen selectivity decreased obviously from 207 mmol to 174 mmol and 95%–85% due to the inevitable OCs sintering and carbon deposition. Finally, stable hydrogen production with the purity of 89%～87% and selectivity of 96%～93% was obtained in the modified stability SE-CLSR experiments.     

Thermodynamic analysis of hydrogen production via glycerol steam reforming with CO2 adsorption

Thermodynamic equilibrium for glycerol steam reforming to hydrogen with carbon dioxide capture was investigated using Gibbs free energy minimization method. Potential advantage of using CaO as CO₂ adsorbent is to generate hydrogen-rich gas without a water gas shift (WGS) reactor for proton exchange membrane fuel cell (PEMFC) application. The optimal operation conditions are at 900 K, the water-to-glycerol molar ratio of 4, the CaO-to-glycerol molar ratio of 10 and atmospheric pressure. Under the optimal conditions, complete glycerol conversion and 96.80% H₂ and 0.73% CO concentration could be achieved with no coke. In addition, reaction conditions for coke-free and coke-formed regions are also discussed in glycerol steam reforming with or without CO₂ separation. Glycerol steam reforming with CO₂ adsorption has the higher energy efficiency than that without adsorption under the same reaction conditions.     

Thermodynamic analysis of H2 production from CaO sorption‐enhanced methane steam reforming thermally coupled with chemical looping combustion as a novel technology

In this novel paper, a technique for hydrogen production route of CaO sorption‐enhanced methane steam reforming (SEMSR) thermally coupled with chemical looping combustion (CLC) was presented (CLC‐SEMSR), which perceived as an improvement of previous methane steam reforming (MSR) thermally coupled with CLC technology (CLC‐MSR). The application of CLC instead of furnace achieves the inherent separation of CO₂ from flue gas without extra energy required. The required heat for the reformer is provided by thermally coupling CLC. The addition of CaO sorbents can capture CO₂ as it is formed from the reformer gas to the solid phase, displacing the normal MSR equilibrium restrictions and obtaining higher purity of H₂. The Aspen Plus was used to simulate this novel process on the basis of thermodynamics. The performances of this system examined included the composition of reformer gas, yield of reformer gas (Y_Rg), methane conversion (α_M), the overall energy efficiency (η), and exergy efficiency (φ) of this process. The effects of the molar ratio of CaO to methane for reforming (Ca/M) in the range of 0–1.2, the molar ratio of methane for combustion to methane for reforming (M(fuel)/M) in the range of 0.1–0.3, and the molar ratio of NiO to methane for reforming (Ni/M) in the range of 0.4–1.2 were investigated. It has been found to be favored by operating under the conditions of Ca/M = 1, M(fuel)/M = 0.2, and Ni/M = 0.8. The most excellent advantage of CLC‐SEMSR was that it could obtain higher purity of H₂ (95%) at lower operating temperature (655 °C), as against H₂ purity of 77.1% at higher temperature (900 °C) in previous CLC‐MSR. In addition, the energy efficiency of this process could reach 83.3% at the optimal conditions. Copyright © 2014 John Wiley & Sons, Ltd.     

Steam reforming of ethanol to hydrogen over nickel metal catalysts

In the present work acid‐treated Ni catalyst was investigated for the steam reforming (SR) of bio‐ethanol. Influential factors, such as reaction temperature, water‐to‐ethanol molar ratio and liquid hourly space velocity (LHSV), were investigated. The conversions were always complete at temperatures above 773 K, regardless of the changes of the reaction conditions. The yield to hydrogen increased with the increase in temperature and H₂O/C₂H₅OH molar ratios. The hydrogen yield up to 84% was reached under conditions: 923 K, LHSV of 5.0 ml g⁻¹ h⁻¹, H₂O/C₂H₅OH ratio of 10 over the acid‐treated Ni catalyst. The effects of the influential factors on the side reactions and the distribution of byproducts were discussed. Copyright © 2010 John Wiley & Sons, Ltd.     

Production of hydrogen by ethanol steam reforming over nickel–metal oxide catalysts prepared via urea–nitrate combustion method

A series of Ni/MgO catalysts have been prepared by a urea–nitrate combustion method, studied for the ethanol steam reforming, and compared with Ni/ZnO and Ni/Al₂O₃. The results show that Ni/MgO is superior to the latter two types of catalysts, especially in terms of H₂ yield. Influential factors, including Ni loading, temperature, water‐to‐ethanol molar ratio, and liquid hourly space velocity, are investigated with the Ni/MgO catalyst. The conversions are always complete at temperatures above 773 K, regardless of the changes of the other reaction conditions. The hydrogen yield increases with increasing temperature and H₂O/C₂H₅OH molar ratios, with up to 75% being obtained at 873 K, liquid hourly space velocity (LHSV) of 5.0 ml g^–1 h^–1 and H₂O/C₂H₅OH molar ratio of 10. Copyright © 2010 John Wiley & Sons, Ltd.     

Oxidative steam reforming of ethanol over Ru–Al2O3 catalyst in a dense Pd–Ag membrane reactor to produce hydrogen for PEM fuel cells

This study focuses on the influence of oxygen addition on ethanol steam reforming (ESR) reaction performed in a dense Pd–Ag membrane reactor (MR) for producing hydrogen directly available for feeding a polymer electrolyte membrane fuel cell (PEMFC). In particular, oxygen addition can prevent ethylene and ethane formation caused by dehydration of ethanol as well as carbon deposition. The MR is operated at 400 °C, H₂O:C₂H₅OH = 11:1 as feed molar ratio and space velocity (GHSV) ∼2000 h⁻¹. A commercial Ru-based catalyst was packed into the MR and a nitrogen stream of 8.4 × 10⁻² mol/h as sweep gas was flowed into the permeate side of the reactor. Both oxidative ethanol steam reforming (OESR) and ESR performances of the Pd–Ag MR were analyzed in terms of ethanol conversion to gas, hydrogen yield, gas selectivity and CO-free hydrogen recovery by varying O₂:C₂H₅OH feed molar ratio and reaction pressure. Moreover, the experimental results of the OESR and ESR reactions carried out in the same Pd–Ag MR are compared in order to point out the benefits due to the oxygen addition. Experimentally, this work points out that, overcoming O₂:C₂H₅OH = 1.3:1, ethanol conversion is lowered with a consequent drops of both hydrogen yield and hydrogen recovery. Vice versa, a complete ethanol conversion is achieved at 2.5 bar and O₂:C₂H₅OH = 1.3:1, whereas the maximum CO-free hydrogen recovery (∼30%) is obtained at O₂:C₂H₅OH = 0.6:1.     

Hydrogen production from bio-oil: A thermodynamic analysis of sorption-enhanced chemical looping steam reforming

The steam reforming of pyrolysis bio-oil is one proposed route to low carbon hydrogen production, which may be enhanced by combination with advanced steam reforming techniques. The advanced reforming of bio-oil is investigated via a thermodynamic analysis based on the minimisation of Gibbs Energy. Conventional steam reforming (C-SR) is assessed alongside sorption-enhanced steam reforming (SE-SR), chemical looping steam reforming (CLSR) and sorption-enhanced chemical looping steam reforming (SE-CLSR). The selected CO₂ sorbent is CaO(s) and oxygen transfer material (OTM) is Ni/NiO. PEFB bio-oil is modelled as a surrogate mixture and two common model compounds, acetic acid and furfural, are also considered. A process comparison highlights the advantages of sorption-enhancement and chemical looping, including improved purity and yield, and reductions in carbon deposition and process net energy balance.The operating regime of SE-CLSR is evaluated in order to assess the impact of S/C ratio, NiO/C ratio, CaO/C ratio and temperature. Autothermal operation can be achieved for S/C ratios between 1 and 3. In autothermal operation at 30 bar, S/C ratio of 2 gives a yield of 11.8 wt%, and hydrogen purity of 96.9 mol%. Alternatively, if autothermal operation is not a priority, the yield can be improved by reducing the quantity of OTM. The thermodynamic analysis highlights the role of advanced reforming techniques in enhancing the potential of bio-oil as a source of hydrogen.     

Thermodynamic and experimental aspects on chemical looping reforming of ethanol for hydrogen production using a Cu‐based oxygen carrier

An investigation on the chemical looping reforming of ethanol process using Gibbs free energy minimization method was performed. It is found that the temperature, oxygen/ethanol molar ratio (OER), and pressure have pronounced influences on the product yields in chemical looping reforming of ethanol process. The ethanol conversion and H₂ yield are 100% and 2.25 mol mol^?1 ethanol, respectively, at 700 °C, OER of 1 and 1 atm. The higher temperatures promote H₂ and CO production, but the higher pressures and OERs have negative effect on the H₂ and CO generation. Favorable operation conditions are 1 atm, 700 °C, and OER = 1. The experimental tests were carried out in a fixed bed using a Cu‐based oxygen carrier prepared by impregnation method. Working at 1 atm, the H₂ concentration increased with an increase in temperature; however, it remained approximately with an increase in gas hourly space velocity. The H₂/CO molar ratio was between 3 and 5 in the period of 0–30 min at 1 atm and 700 °C. Copyright © 2013 John Wiley & Sons, Ltd.     

Study on the preparation of Ni–La–Ce oxide catalyst for steam reforming of ethanol

Two schemes for design and preparation of Ni–La–Ce oxide catalysts for steam reforming of ethanol were proposed in this work. The one via citrate complexing method was designed as NiO supported on ceria-lanthanum oxide (CL) solid solution, in which the strong interaction between NiO and CL solid solution was beneficial to inhibit the aggregation of NiO particles, and the abundant of oxygen vacancies existed in CL solid solution was in favor of carbon elimination from catalyst surface. The other was schemed as LaNiO₃ with perovskite structure loaded on CeO₂ support by using impregnation method, in which the particles of metal Ni derived from reduction of LaNiO₃ were highly dispersed, and the formation of La₂O₂CO₃ in the reaction process could act as the carbon scavenger. Both of the catalysts exhibited very good performance for steam reforming of ethanol (SRE), complete C₂H₅OH conversion was obtained with 70.3% of H₂ selectivity at 400 °C over the catalyst obtained from former method and complete C₂H₅OH conversion was achieved at 450 °C with 67% of H₂ selectivity over the catalyst from latter method. The catalyst made according to the citrate complexing method was more active for SRE and more selective for H₂ production. Both of the catalysts displayed very good anti-sintering ability which was tested at 650 °C and at a high space velocity of 180,000 ml g_cat⁻¹ h⁻¹ with reaction mixture of H₂O/C₂H₅OH = 3 in mole ratio. The results indicated that both of oxygen vacancy and La₂O₂CO₃ possessed the ability to remove the deposited carbon, and compared with La₂O₂CO₃ the oxygen vacancy could reduce one third more of the carbon deposited according to TG tests.     

Ethanol steam reforming on Ni/CaO catalysts for coproduction of hydrogen and carbon nanotubes

Catalytic steam reforming of ethanol is considered as a promising technology for producing H₂ in the modern world. In this study, using a fixed‐bed reactor, steam reforming of ethanol was performed for production of carbon nanotubes (CNTs) and H₂ simultaneously at 600°C on Ni/CaO catalysts. Commercial CaO and a synthetic CaO prepared using sol‐gel were scrutinized for ethanol's catalytic steam reforming. Analysis results of N₂ isothermal adsorption indicate that the CaO synthesized by sol‐gel has more pore volume and surface area in comparison with the commercial CaO. When Ni was loaded, the Ni/CaO catalyst shows an encouraging catalytic property for H₂ production, and an increase in Ni loading could improve H₂ production. The Ni/CaO catalyst with sol‐gel CaO support has presented a higher hydrogen production and better catalytic stability than the catalysts with the commercial CaO support at low Ni loading. The highest hydrogen yield is 76.8% at Ni loading content of 10% for the Ni/sol‐gel CaO catalyst with WHSV of 3.32/h and S/C ratio of 3. The carbon formed after steam reforming primarily consists of filamentous carbons and amorphous carbons, and CNTs are the predominant type of carbon deposition. The deposited extent of carbon on the used Ni/CaO catalyst lessen upon more Ni loading, and the elongated CNTs are desired to be formed at the surface of the Ni/sol‐gel CaO catalyst. Thus, an efficient process and improved economic value is associated with prompt hydrogen production and CNTs from ethanol steam reforming.     

Steam reforming of shale gas in a packed bed reactor with and without chemical looping using nickel based oxygen carrier

The catalytic steam reforming of shale gas was examined over NiO on Al₂O₃ and NiO on CaO/Al₂O₃ in the double role of catalysts and oxygen carrier (OC) when operating in chemical looping in a packed bed reactor at 1 bar pressure and S:C 3. The effects of gas hourly space velocity GHSV (h^?1), reforming temperatures (600–750 °C) and catalyst type on conventional steam reforming (C-SR) was first evaluated. The feasibility of chemical looping steam reforming (CL-SR) of shale gas at 750 °C with NiO on CaO/Al₂O₃ was then assessed and demonstrated a significant deterioration after about 9 successive reduction-oxidation cycles. But, fuel conversion was high over 80% approximately prior to deterioration of the catalyst/OC, that can be strongly attributed to the high operating temperature in favour of the steam reforming process.     

Nickel-alumina washcoating on monoliths for the partial oxidation of ethanol to hydrogen production

Preparation of nickel-alumina washcoating on a honeycomb monolith for the ethanol partial oxidation taking at very low residence time was presented. The catalyst presented good dispersion of γ-Al₂O₃ and NiO over the cordierite surface and could be efficient to the ethanol dehydrogenation reaction at low temperatures, as well as it is suitable to intensify hydrogen production due to its good activity for reforming reaction at higher temperatures. As temperature increased, all ethanol was converted by decomposition and this catalyst showed good ability to promote the water-gas shift reaction. The hydrated ethanol increased the ethanol conversion and H₂ production. The high CO₂/CO molar ratio suggested that the water-gas shift inverse reaction equilibrium was achieved. The NiO/Al₂O₃/cordierite was run during few days presenting a large amount of carbon deposition. The FEG-SEM images are in agreement with DTA/TG and Raman results indicating the presence of well-defined filamentous carbon structures.     

Thermodynamic analysis of aqueous phase reforming of three model compounds in bio-oil for hydrogen production

Thermodynamic analysis with Gibbs free energy minimization was performed for aqueous phase reforming of methanol, acetic acid, and ethylene glycol as model compounds for hydrogen production from bio-oil. The effects of the temperature (340-660 K) and pressure ratio Psys/PH₂O (0.1-2.0) on the selectivity of H₂ and CH₄, formation of solid carbon, and conversion of model compounds were analyzed. The influences of CaO and O₂ addition on the formation of H₂, CH₄, and CO₂ in the gas phase and solid phase carbon, CaCO₃, and Ca(OH)₂ were also investigated. With methanation and carbon formation, the conversion of the model compounds was >99.99% with no carbon formation, and methanation was thermodynamically favored over hydrogen production. H₂ selectivity was greatly improved when methanation was suppressed, but most of the inlet model compounds formed solid carbon. After suppressing both methanation and carbon formation, aqueous phase reforming of methanol, acetic acid and ethylene glycol at 500 K and with Psys/PH₂O = 1.1 gave H₂ selectivity of 74.98%, 66.64% and 71.38%, respectively. These were similar to the maximum stoichiometric hydrogen selectivity of 75.00% (methanol), 66.67% (acetic acid), and 71.43% (ethylene glycol). At 500 K and 2.90 MPa, as the molar ratio of CaO/BMCs increased, the normalized variation in H₂ increased and that for CH₄ decreased. Formation of solid carbon was effectively suppressed by addition of O₂, but this was at the expense of H₂ formation. With the O₂/BMCs molar ratio regulated at 1.0, oxidation and CO₂ capture increased the normalized variation in H₂ to 33.33% (methanol), 50.00% (acetic acid), and 60.00% (ethylene glycol), and the formation of solid carbon decreased to zero.     

Towards H2-rich gas production from unmixed steam reforming of methane: Thermodynamic modeling

In this work, the Gibbs energy minimization method is applied to investigate the unmixed steam reforming (USR) of methane to generate hydrogen for fuel cell application. The USR process is an advanced reforming technology that relies on the use of separate air and fuel/steam feeds to create a cyclic process. Under air flow (first half of the cycle), a bed of Ni-based material is oxidized, providing the heat necessary for the steam reforming that occurs subsequently during fuel/steam feed stage (second half of the cycle). In the presence of CaO sorbent, high purity hydrogen can be produced in a single reactor. In the first part of this work, it is demonstrated that thermodynamic predictions are consistent with experimental results from USR isothermal tests under fuel/steam feed. From this, it is also verified that the reacted NiO to CH₄ (NiO_reacted/CH₄) molar ratio is a very important parameter that affects the product gas composition and decreases with time. At the end of fuel/steam flow, the reforming reaction is the most important chemical mechanism, with H₂ production reaching ∼75 mol%. On the other hand, at the beginning of fuel/steam feed stage, NiO reduction reactions dominate the equilibrium system, resulting in high CO₂ selectivity, negative steam conversion and low concentrations of H₂. In the second part of this paper, the effect of NiO_reacted/CH₄ molar ratio on the product gas composition and enthalpy change during fuel flow is investigated at different temperatures for inlet H₂O/CH₄ molar ratios in the range of 1.2-4, considering the USR process operated with and without CaO sorbent. During fuel/steam feed stage, the energy demand increases as time passes, because endothermic reforming reaction becomes increasingly important as this stage nears its end. Thus, the duration of the second half of the cycle is limited by the conditions under which auto-thermal operation can be achieved. In absence of CaO, H₂ at concentrations of approximately 73 mol% can be produced under thermo-neutral conditions (H₂O/CH₄ molar ratio of 4, with NiO_reacted/CH₄ molar ratio at the end of fuel flow of ∼0.8, in temperature range of 873-1073 K). In the presence of CaO sorbent, using an inlet H₂O/CH₄ molar ratio of 4 at 873 K, H₂ at concentrations over 98 mol% can be obtained all through fuel/steam feed stage. At 873 K, carbonation reaction provides all the heat necessary for H₂ production when NiO_reacted/CH₄ molar ratio reached at the end of fuel/steam feed is greater or equal to1. In this way, the heat released during air flow due to Ni oxidation can be entirely used to decompose CaCO₃ into CaO. In this case, a calcite-to-nickel molar ratio of 1.4 (maximum possible value) can be used during air flow. For longer durations of fuel/steam feed, corresponding to lower NiO_reacted/CH₄ molar ratios, some heat is necessary for steam reforming, and a calcite-to-nickel molar ratio of about 0.7 is more suitable. With the USR technology, CaO can be regenerated under air feeds, and an economically feasible process can be achieved.     

Gibbs free energy minimization as a way to optimize the combined steam and carbon dioxide reforming of methane

Gibbs free energy minimization was applied to study thermodynamic equilibrium of the combined steam and carbon dioxide reforming of methane. Coke deposition, the content of methane and carbon dioxide in syn-gas as well as H₂/CO ratio were investigated as a function of CO₂/CH₄ and H₂O/CH₄ mole ratios at different temperatures and pressures. The ranges of the molar ratios CH₄/CO₂/H₂O in the feed with H₂/CO = 2.1-2.2 were identified at which reforming of methane is not complicated by coke deposition. For each range optimized CH₄/CO₂/H₂O molar ratios characterized by the lowest content of methane and carbon dioxide in syn-gas were found.     

Effects of CaO addition on Ni/CeO2–ZrO2–Al2O3 coated monolith catalysts for steam reforming of N-decane

A series of 10 wt%Ni/CeO₂–ZrO₂–Al₂O₃ (10%Ni/CZA) coated monolith catalysts modified by CaO with the addition amount of 1 wt%~7 wt% are prepared by incipient-wetness co-impregnation method. Effects of CaO promoter on the catalytic activity and anti-coking ability of 10%Ni/CZA for steam reforming of n-decane are investigated. The catalysts are characterized by N₂ adsorption-desorption, XRD, SEM-EDS, TEM, NH₃-TPD, XPS, H₂-TPR and Raman. The results show that specific surface area and pore volume of as-prepared catalysts decrease to some extent with the increasing addition of CaO. However, the proper amounts of CaO (≤3 wt%) significantly enhance the catalytic activity in terms of n-decane conversion and H₂ selectivity mainly due to the improved dispersion of NiO particles (precursor of Ni particles). As for anti-coking performance, reducibility of CeO₂ in composite oxide support CZA is promoted by CaO resulting in providing more lattice oxygen, which favors suppressing coke formation. Moreover, the addition of CaO reduces the acidity of 10%Ni/CZA, especially the medium and strong acidity. But far more importantly, a better dispersion of NiO particles obtained by proper amounts of CaO addition is dominant for the lower carbon formation, as well as the higher catalytic activity. For the spent catalysts, amorphous carbon is the main type of coke over 10%Ni–3%CaO/CZA, while abundant filamentous carbon is found over the others.     

Thermodynamic evaluation of methanol steam reforming for hydrogen production

Thermodynamic equilibrium of methanol steam reforming (MeOH SR) was studied by Gibbs free minimization for hydrogen production as a function of steam-to-carbon ratio (S/C = 0–10), reforming temperature (25–1000 °C), pressure (0.5–3 atm), and product species. The chemical species considered were methanol, water, hydrogen, carbon dioxide, carbon monoxide, carbon (graphite), methane, ethane, propane, i-butane, n-butane, ethanol, propanol, i-butanol, n-butanol, and dimethyl ether (DME). Coke-formed and coke-free regions were also determined as a function of S/C ratio.Based upon a compound basis set MeOH, CO₂, CO, H₂ and H₂O, complete conversion of MeOH was attained at S/C = 1 when the temperature was higher than 200 °C at atmospheric pressure. The concentration and yield of hydrogen could be achieved at almost 75% on a dry basis and 100%, respectively. From the reforming efficiency, the operating condition was optimized for the temperature range of 100–225 °C, S/C range of 1.5–3, and pressure at 1 atm. The calculation indicated that the reforming condition required from sufficient CO concentration (<10 ppm) for polymer electrolyte fuel cell application is too severe for the existing catalysts (T_r = 50 °C and S/C = 4–5). Only methane and coke thermodynamically coexist with H₂O, H₂, CO, and CO₂, while C₂H₆, C₃H₈, i-C₄H₁₀, n-C₄H₁₀, CH₃OH, C₂H₅OH, C₃H₇OH, i-C₄H₉OH, n-C₄H₉OH, and C₂H₆O were suppressed at essentially zero. The temperatures for coke-free region decreased with increase in S/C ratios. The impact of pressure was negligible upon the complete conversion of MeOH.