Thermodynamic possibilities and constraints for pure hydrogen production by iron based chemical looping process at lower temperatures

Iron offers the possibility of transformation of a syngas or gaseous hydrocarbons into hydrogen by a cycling process of iron oxide reduction (e.g. by hydrocarbons) and release of hydrogen by steam oxidation. From the thermodynamic and chemical equilibrium point of view, the reduction of magnetite by hydrogen, CO, CH₄ and a model syngas (mixtures CO + H₂ or H₂ + CO + CO₂) and oxidation of iron by steam has been studied. Attention was concentrated not only on convenient conditions for reduction of Fe₃O₄ to iron at temperatures 400–800 K but also on the possible formation of undesired soot, Fe₃C and iron carbonate as precursors for carbon monoxide and carbon dioxide formation in the steam oxidation step. Reduction of magnetite at low temperatures requires a relatively high H₂/H₂O ratio, increasing with decreasing temperature. Reduction of iron oxide by CO is complicated by soot and Fe₃C formation. At lower temperatures and higher CO₂ concentrations in the reducing gas, the possibility of FeCO₃ formation must be taken into account. The purity of the hydrogen produced depends on the amount of soot, Fe₃C and FeCO₃ in the iron after the reduction step. Magnetite reduction is the more difficult stage in the looping process. Pressurized conditions during the reduction step will enhance formation of soot and carbon containing iron compounds.     

Enhanced sintering resistance of Fe2O3/CeO2 oxygen carrier for chemical looping hydrogen generation using core-shell structure

CeO₂-supported Fe₂O₃ is a satisfactory oxygen carrier for chemical looping hydrogen generation (CLHG). However, the sintering problem restrains its further improvement on redox reactivity and stability. In the present work, a core-shell-structured Fe₂O₃/CeO₂ (labeled Fe₂O₃@CeO₂) oxygen carrier prepared by the sol-gel method was studied in a fixed bed. The effect of the core-shell structure on the sintering resistance and redox performance was investigated with a homogenous composite sample of Fe₂O₃/CeO₂ as a reference. The results showed that the Fe₂O₃@CeO₂ exhibited much higher redox reactivity and stability than the Fe₂O₃/CeO₂ with no CO or CO₂ observed in the generated hydrogen, while the hydrogen yield for Fe₂O₃/CeO₂ decreased with redox cycles due to serious sintering. The satisfactory performance of Fe₂O₃@CeO₂ can be ascribed to its high sintering resistance, since the core-shell structure suppressed the outward migration of Fe cations from the bulk to the surface of the particles. On the other hand, the migration of Fe cations and their subsequent enrichment on the particle surface led to the serious sintering of Fe₂O₃/CeO₂. The crystallite size evolution of Fe₂O₃ and CeO₂ in redox cycles further demonstrated the higher sintering resistance of Fe₂O₃@CeO₂. Further, the particle size distribution (PSD) results indicated the agglomeration of Fe₂O₃/CeO₂ after cycles. In addition, the CeO₂ shell could facilitate the transport of oxygen ions between the iron oxide nanoparticle core and the shell surface. Therefore, the coating of nanoscale Fe₂O₃ with a CeO₂ shell did not reduce the redox reactivity and stability of Fe₂O₃@CeO₂, but rather promoted it, though less oxygen-ionic-conductive CeFeO₃ was generated.     

Hydrogen production via chemical looping steam reforming of ethanol by Ni-based oxygen carriers supported on CeO2 and La2O3 promoted Al2O3

This work studies the effects of Ce⁴⁺ and/or La³⁺ on NiO/Al₂O₃ oxygen carrier (OC) on chemical looping steam reforming of ethanol for hydrogen production - alternating between fuel feed step (FFS) and air feed step (AFS). Suitable amount of Ce- and La-doping increases OC carbon tolerance. The solubility limit is found at 50 mol% La in solid solution. At higher La-doping, La₂O₃ disperses on the surface and adsorbs CO₂ forming La₂O₂CO₃ during FFS. From the 1st cycle, 12.5 wt%Ni/7 wt%La₂O₃-3wt%CeO₂–Al₂O₃ (N/7LCA) displays the highest averaged H₂ yield (3.2 mol/mol ethanol) with 87% ethanol conversion. However, after the 5th cycle, 12.5 wt%Ni/3 wt%La₂O₃-7wt%CeO₂–Al₂O₃ (N/3LCA) exhibits more stability and presents the highest ethanol conversion (88%) and H₂ yield (2.7 mol/mol ethanol). Amorphous coke on the OCs decreases with increasing La³⁺ content and can be removed at 500 °C during AFS; nevertheless, fibrous coke and La₂O₂CO₃ cannot be eliminated. Therefore, after multiple redox cycles, highly La-doped OCs exhibits rather low stability.     

Effect of ceria addition on NiRu/CeO2Al2O3 catalysts in steam reforming of acetic acid

NiRu bimetallic catalysts with different amount of CeO₂ loaded on the γ-Al₂O₃ support were prepared. The properties of catalysts were characterized by means of N₂ adsorption-desorption, XRD, H₂-TPR and XPS techniques. Catalytic activities for the steam reforming of acetic acid over these catalysts were investigated at the temperature range from 650 °C to 750 °C. The addition of CeO₂ dramatically improved the activity and stability of the catalyst. Among these catalysts, the NiRu/10CeAl catalyst showed the highest catalytic activity as well as a good stability owing to the abundant Ce³⁺ on the surface of catalyst. The existence of Ce³⁺ promoted the formation of CO₂ from CO because of the mobilizable oxygen, which was favorable for the formation of hydrogen. The coke amount and species deposited on the catalysts after the activity tests were analyzed by DTG. As expected, the NiRu/10CeAl catalyst showed the best resistance to carbon formation. The temperature stepwise steam decoking experiment of the spent catalysts was conducted to elucidate the relationship between the existence of Ce³⁺ and the decoking abilities of various catalysts. It was verified that the existence of Ce³⁺ significantly promoted the decoking abilities of the catalysts.     

Thermo-catalytic conversion of greenhouse gases (CO2 and CH4) to CO-rich hydrogen by CeO2 modified calcium iron oxide supported nickel catalyst

In this study, the thermo-catalytic conversion of two principal greenhouse gases (methane and carbon dioxide) to carbon monoxide (CO)-rich hydrogen (H₂) is investigated over cerium oxide (CeO₂) promoted calcium ferrite supported nickel (Ni/CaFe₂O₄) catalyst. The CeO₂ promoted Ni/CaFe₂O₄ catalyst was prepared using wet-impregnation technique. To ascertain the physicochemical properties, the as-prepared catalyst was characterized using various instrument techniques. The characterization of the catalysts reveals that CeO₂-Ni/CaFe₂O₄ possesses suitable physicochemical properties for the conversion of methane (CH₄) and carbon dioxide (CO₂) to CO-rich H₂. The thermo-catalytic reaction revealed that the CeO₂ promoted Ni/CaFe₂O₄ catalyst displayed a higher CH₄ and CO₂ conversions of 90.04% and 91.2%, respectively, at a temperature of 1073 K compared to the unpromoted catalyst. The highest H₂ and CO yields of 78% and 76%, respectively, were obtained over the CeO₂-Ni/CaFe₂O₄ at 1073 K and CH₄/CO₂ ratio of 1. The CeO₂ promoted Ni/CaFe₂O₄ catalyst remained stable throughout the 30 hours time on stream (TOS) while that of the unpromoted Ni/CaFe₂O₄ catalyst sharply decreased after 22 hours TOS. The characterization of the used catalysts confirms the evidence of carbon depositions on the unpromoted Ni/CaFe₂O₄ which is solely responsible for its deactivation. Whereas, there was a slightly gasifiable carbon deposited on the CeO₂ promoted Ni/CaFe₂O₄ catalyst which could be ascribed to the interaction effect of the CeO₂ promoter on the Ni/CaFe₂O₄ catalyst.     

Characterization of Fe2O3/CeO2 oxygen carriers for chemical looping hydrogen generation

Fe₂O₃ is currently the most proper active metal oxide for chemical looping hydrogen generation (CLHG). However, supports are necessary to improve the reactivity and redox stability. CeO₂ can enhance the oxygen mobility, leading to high redox reactivity and carbon deposition resistance, which can be an excellent alternative support for oxygen carriers. In this paper, Fe₂O₃/CeO₂ oxygen carriers prepared by the co-precipitation method with different Fe₂O₃ loadings were investigated on a batch fluidized bed regarding the hydrogen yield and purity, redox reactivity and stability in CLHG with CO as fuel. The results showed that Fe6Ce4 is the best given comprehensive performance with no CO or CO₂ observed in the obtained hydrogen (detection limit 0.01% in volume). The oxygen mobility property for the reducible support CeO₂ and the physical contact between un-integrated Fe₂O₃ and CeO₂ could improve the reduction of Fe₂O₃. In addition, the formation of the hematite-like solid solution and perovskite-type CeFeO₃ could bring about abundant oxygen vacancies and promote the oxygen mobility, which contributes to the elimination of carbon deposition, counteracts the negative effect of serious sintering and guarantees the reactivity and redox stability of the Fe₂O₃/CeO₂ oxygen carriers. The Fe₂O₃/CeO₂ oxygen carriers were characterized by carbon monoxide temperature-programmed reduction measurement and X-ray diffraction patterns, and Fe6Ce4 was also selected to be characterized by scanning electron microscopy images and energy dispersive X-ray spectrometer analysis.     

High-pressure hydrogen production with inherent sequestration of a pure carbon dioxide stream via fixed bed chemical looping

The proof of concept for the production of pure pressurized hydrogen from hydrocarbons in combination with the sequestration of a pure stream of carbon dioxide with the reformer steam iron cycle is presented. The iron oxide based oxygen carrier (95% Fe₂O₃, 5% Al₂O₃) is reduced with syngas and oxidized with steam at 1023 K. The carbon dioxide separation is achieved via partial reduction of the oxygen carrier from Fe₂O₃ to Fe₃O₄ yielding thermodynamically to a product gas only containing CO₂ and H₂O. By the subsequent condensation of steam, pure CO₂ is sequestrated. After each steam oxidation phase, an air oxidation was applied to restore the oxygen carrier to hematite level. Product gas pressures of up to 30.1 bar and hydrogen purities exceeding 99% were achieved via steam oxidations. The main impurities in the product gas are carbon monoxide and carbon dioxide, which originate from solid carbon depositions or from stored carbonaceous molecules inside the pores of the contact mass. The oxygen carrier samples were characterized using elemental analysis, BET surface area measurement, XRD powder diffraction, SEM and light microscopy. The maximum pressure of 95 bar was demonstrated for hydrogen production in the steam oxidation phase after the full oxygen carrier reduction, significantly reducing the energy demand for compressors in mobility applications.     

Gd,La co-doped CeO2 as an active support for Fe2O3 to enhance hydrogen generation via chemical looping water gas shift

Support materials are indispensable to promote the durability of iron oxides for chemical looping applications. However, the dilution effect of supports on the active phase would lead to decreased bulk oxygen conduction, thus leading to compromised activity. Here, we propose several Gd³⁺, La³⁺ and Nd³⁺ doped CeO₂ as active supports for iron oxides and investigate the support effect to improve hydrogen generation via chemical looping water gas shift. The characterizations show that the dopants improve the oxygen vacancy concentration in the CeO₂ lattice and Fe₂O₃/Ce_0.8Gd_0.1La_0.1O_2-δ exhibits the most oxygen vacancy concentration among all the oxygen carriers. Pulse reactions of oxygen carriers show that an abundance of oxygen vacancy concentration can promote the lattice oxygen transfer in bulk, thus contributing to improved redox reactions. The high oxygen conductivity mitigates the dilution effect on the active phase. Therefore, Fe₂O₃/Ce_0.8Gd_0.1La_0.1O_2-δ shows the highest hydrogen yield (～9.49 mmol^?1.g^?1) and hydrogen generation rate (～0.632 mmol.g^?1.min^?1) with only a slight decrease at 650 °C over 100 cycles. Overall, this work highlights the influence of support properties on the redox reactivity of iron oxides for chemical looping applications.     

Numerical investigation of hydrogen production via autothermal reforming of steam and methane over Ni/Al2O3 and Pt/Al2O3 patterned catalytic layers

In this study a numerical analysis of hydrogen production via an autothermal reforming reactor is presented. The endothermic reaction of steam methane reforming and the exothermic combustion of methane were activated with patterned Ni/Al₂O₃ catalytic layer and patterned Pt/Al₂O₃ catalytic layer, respectively. Aiming to achieve a more compacted process, a novel design of a reactor was proposed in which the reforming and the combustion catalysts were modeled as patterned thin layers. This configuration is analyzed and compared with two configurations. In the first configuration, the catalysts are modeled as continuous thin layers in parallel, while, in the second configuration the catalysts are modeled as continuous thin layers in series (conventional catalytic autothermal reactor). The results show that the pattern of the catalyst layers improves slightly the hydrogen yield, i.e. 3.6%. Furthermore, for the same concentration of hydrogen produced, the activated zone length can be decreased by 38% and 15% compared to the conventional catalytic autothermal reforming and the configuration where the catalysts are fitted in parallel, respectively. Besides, the oxygen consumption is lowered by 5%. The decrement of the catalyst amount and the oxygen feedstock in the novel studied design lead to lower costs and compact process.     

Activating Fe2O3 using K2CO3-containing ethanol solution for corn stalk chemical looping gasification to produce hydrogen

Alkaline organic liquid waste was introduced to activate Fe₂O₃ and provide sufficient steam to boost biomass chemical looping gasification (CLG) for H₂ production. Experiments under different excess oxygen ratios, temperatures, and alkali contents were performed to investigate the reaction characteristics of alkaline organic waste - biomass CLG. The highest H₂ yield of 1.71 L and carbon conversion rate of 83.8% were obtained at the excess oxygen ratio of 0.2, the alkali concentration of 6%, and the reaction temperature of 800 °C. Moreover, the kinetic and thermodynamic analysis under the optimized condition have cast light on the fundamental understanding of alkaline organic liquid waste - biomass CLG. Results demonstrate that this novel approach has the potential to enhance energy conversion.     

Using chemical looping gasification with Fe2O3/Al2O3 oxygen carrier to produce syngas (H2+CO) from rice straw

The chemical looping gasification of rice straw using Fe₂O₃/Al₂O₃ as oxygen carrier was studied at reaction time of 5–25 min, steam-to-biomass (S/B) ratio of 2.0–4.8, reaction temperature of 750–950 °C, and oxygen carrier-to-biomass of 1.0. The gasification can be regarded completed in 20-min reaction. There exist an optimal S/B ratio of 2.8 and reaction temperature of 900 °C leading to maximum performances yielded are 1.22 Nm³/kg gas yield at 54.6% H₂+24.2% CO. The studied Fe₂O₃ oxygen carrier/rice straw is a feasible platform for syngas production from an agricultural waste.     

Synthesis of a new self-supported Mgy(CuxNi0.6-xMn0.4)1-yFe2O4 oxygen carrier for chemical looping steam methane reforming process

Novel self-supported Mg_y(Cu_xNi_0.6-xMn_0.4)_1-yFe₂O₄ with (y = 0, 0.05, 0.1, 0.15, and x = 0, 0.15, 0.3, 0.45, 0.6) oxygen carriers (OCs) are synthesized through the co-precipitation method. The synthesized OCs’ properties are characterized by X-ray powder diffraction (XRD), Raman spectra, transform infrared spectroscopy (FT-IR), Brunauer-Emmett-Teller (BET), transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDX), and Thermogravimetric Analysis (TGA). The synthesized OCs are assessed in Chemical Looping Steam Methane Reforming (CL-SMR) process subject to different mesh sizes, reaction temperatures, Steam/Carbon (S/C) molar ratios, Mg concentrations, and Cu and Ni concentrations. The characterization of the OCs and process results indicate the contributive effect of Mg incorporation on the Cu_xNi_0.6-xMn_0.4Fe₂O₄ support structure. The redox results reveal that Mg_0.1(Cu_0.3Ni_0.3Mn_0.4)_0.9Fe₂O₄ OC is of the highest activity, even at low reduction temperatures. This OC exhibits the highest activity and stability with lowest coke deposition during 24 redox cycles at 650 °C and S/C = 2.5. The highest CH₄ conversion of about 99.4% and H₂ yield of about 84.4% are obtained.     

Effects of supports on hydrogen production and carbon deposition of Fe-based oxygen carriers in chemical looping hydrogen generation

Chemical looping hydrogen generation (CLHG) can produce high purity hydrogen from fuel gases with inherent separation of CO₂. However, the performance of oxygen carrier in CLHG varies with the support materials. In this paper, the reactivity, carbon deposition, redox stability, hydrogen yield and purity, and sintering behavior of the Fe-based oxygen carriers were analyzed to investigate the effects of supports, i.e. Al₂O₃, SiO₂, MgAl₂O₄, ZrO₂ and YSZ (yttrium-stabilized zirconia). The results showed that the properties of the oxygen carriers, e.g. carbon deposition, reactivity and stability, mainly depended on the support and its interaction with iron oxides. The reactivity and hydrogen yield for the oxygen carriers investigated followed the order: Fe₂O₃/MgAl₂O₄ > Fe₂O₃/ZrO₂ > Fe₂O₃/YSZ > Fe₂O₃/Al₂O₃ > Fe₂O₃/SiO₂, and the order of hydrogen purity was identical with that of hydrogen yield as a result of carbon deposition. Furthermore, the hydrogen purity of the Fe-based oxygen carriers supported by MgAl₂O₄, ZrO₂, or YSZ could reach above 99.5% and Fe₂O₃/YSZ showed the lowest carbon deposition. The oxygen carriers, Fe₂O₃/MgAl₂O₄ and Fe₂O₃/SiO₂, were selected to be characterized by SEM images and XRD patterns before and after the redox cycles.     

Interaction of coal ashes with potassium-decorated Fe2O3/Al2O3 oxygen carrier in coal-direct chemical looping hydrogen generation (CLHG)

Coal-direct CLHG is a novel hydrogen production technology with inherent CO₂ capture. Potassium-decorated Fe₂O₃/Al₂O₃ oxygen carrier (OC) has been proved to be a potential OC for the technology. However, the ash in the coal could influence the OC performance. In this work, the effect of ash addition on the reactivity, the morphology structure and phase composition of OC, and the potassium migration in the reduction stage were investigated. Furthermore, the effect of OC on the ash fusion temperature was discussed. Results indicated that the OC reactivity had no significant change when SM (Shenmu) ash addition was less than 1% in the reduction stage and decreased when the addition was more than 2%. In the steam oxidation stage, the H₂ yield varied between 5.80–5.57 mmol/g when the SM ash addition was less than 10% and decreased to 4.31 mmol/g when the addition was 40%. FeO could react with SiO₂ deriving from coal ash to form Fe₂SiO₄, which could cause the loss of Fe and the OC sintering; K₂CO₃ could react with silicon-aluminum minerals which could cause the potassium loss. The ash with high CaO content had a less negative effect on the OC reactivity. With the increase of SM ash addition, the potassium in OC decreased, the potassium in char increased and the volatile potassium decreased after the reduction stage. After the OC addition, the deformation temperature decreased from 1242 °C to 1114 °C in the weak reduction atmosphere while increased from 1162 °C to 1300 °C in the air atmosphere.     

Structure-dependent activity and stability of Al2O3 supported Rh catalysts for the steam reforming of n-dodecane

Steam reforming of liquid hydrocarbon fuels is an appealing way for the production of hydrogen. In this work, the Rh/Al₂O₃ catalysts with nanorod (NR), nanofiber (NF) and sponge-shaped (SP) alumina supports were successfully designed for the steam reforming of n-dodecane as a surrogate compound for diesel/jet fuels. The catalysts before and after reaction were well characterized by using ICP, XRD, N₂ adsorption, TEM, HAADF-STEM, H₂-TPR, CO chemisorption, NH₃-TPD, CO₂-TPD, XPS, Al²⁷ NMR and TG. The results confirmed that the dispersion and surface structure of Rh species is quite dependent on the enclosed various morphologies. Rh/Al₂O₃-NR possesses highly dispersed, uniform and accessible Rh particles with the highest percentage of surface electron deficient Rh⁰ active species, which due to the unique properties of Al₂O₃ nanorod including high crystallinity, relatively large alumina particle size, thermal stability, and large pore volume and size. As a consequent, Rh/Al₂O₃-NR catalyst exhibited superior catalytic activity towards steam reforming reactions and hydrogen production rate over other two catalysts. Especially, Rh/Al₂O₃-NR catalyst showed the highest hydrogen production rate of 87,600 mmol g_fuel^?1 g_Rh^?1min^?1 among any Rh-based catalysts and other noble metal-based catalysts to date. After long-term reaction, a significant deactivation occurred on Rh/Al₂O₃–NF and Rh/Al₂O₃-SP catalysts, due to aggregation and sintering of Rh metal particles, coke deposition and poor hydrothermal stability of nanofibrous structure. In contrast, the Rh/Al₂O₃-NR catalyst shows excellent reforming stability with negligible coke formation. No significantly sintering and aggregation of the Rh particles is observed after long-term reaction. Such great catalyst stability can be explained by the role of hydrothermal stable nanorod alumina support, which not only provides a unique environment for the stabilization of uniform and small-size Rh particles but also affords strong surface basic sites.     

CeO2 modified Fe2O3 for the chemical hydrogen storage and production via cyclic water splitting

The chemical hydrogen storage (hydrogen reduction) and production (water splitting) behaviour of Ce-modified Fe₂O₃ mixed oxides were investigated. Fe_1−xCe_xO_2−δ (x = 0, 0.05, 0.1, 0.2, 0.3, 0.4 and 1) oxides prepared by chemical precipitation were characterized by XRD (X-ray diffraction), H₂-TPR (hydrogen temperature-programmed reduction) and H₂O-TPO (steam temperature-programmed oxidation) tests. XRD results showed that two kinds of Fe–Ce–O solid solutions (Ce-based and Fe-based) coexisted in Fe–Ce mixed oxides. H₂-TPR experiment suggested that Ce addition could reduce hydrogen reduction temperature while H₂O-TPO experiments over reduced oxides showed that Fe–Ce mixed oxides could split water to produce hydrogen at a lower temperature and complete in a shorter time. Both redox reactions (hydrogen reduction and water splitting) were sensitive to the temperature and active at a high temperature. The successive redox cycles were carried out over the Fe_0.7Ce_0.3O_2−δ mixed oxide at 750 °C. It kept a stable production of hydrogen in the successive redox process at the condition of serious agglomeration of the materials. The highest hydrogen storage amount was up to 1.51 wt% for the Fe–Ce sample with a 30% substitution of Ce for Fe.     

Production of hydrogen by steam reforming of phenol over Ni/Al2O3-ash catalysts

An improved method for hydrogen production by the steam reforming of phenol over novel fly ash-based catalysts is investigated. The Ni/Al₂O₃-ash catalysts are prepared by an equal-volume impregnation method and characterized by XRD, FESEM, BET and H₂-TPR techniques. The effects of various process parameters including mixing ratio of fly ash, temperature, support, gas hourly space velocity (GHSV) and steam-to-carbon molar ratio (S/C) on the catalytic activity are investigated. The results show that fly ash mixing at 50 wt% and choosing γ-Al₂O₃ as the support own the best performance. A maximum hydrogen yield of 83.8% is achieved at 450 °C with a S/C of 10 and a GHSV of 4968 h^?1 with a maximum phenol conversion of 98.6%. The stability of the Ni-ash1-γA1 catalyst is further investigated and it is shown to continuously and stably react for more than 20 h at 450 °C with excellent catalytic reaction stability.     

Evaluation of iron based chemical looping for hydrogen and electricity co-production by gasification process with carbon capture and storage

Integrated Gasification Combined Cycle (IGCC) is one of power generation technologies having the highest potential for carbon capture with low penalties in efficiency and cost. Syngas produced by gasification can be decarbonised using chemical looping methods in which an oxygen carrier (usually a metallic oxide) is recycled between the syngas oxidation reactor (fuel reactor) and the chemical agent oxidation reactor (steam reactor). In this way, the resulted carbon dioxide is inherently separated from the other products of combustion and the syngas energy is transferred to an almost pure hydrogen stream suitable to be used not only for power generation but also for transport sector (PEM fuel cells).     

Cooperative role of cobalt and gallium under the ethanol steam reforming on Co/CeGaOx

The performance of gallium promoted cobalt-ceria catalysts for ethanol steam reforming (ESR) was studied using H₂O/C₂H₅OH = 6/1 mol/mol at 500 °C. The catalysts were synthetized via cerium-gallium co-precipitation and wetness impregnation of cobalt. A detailed characterization by N₂-physisorption, XRD, H₂-TPR and TEM allowed the normalization of contact time and rationalization of the role of each catalysts component for ESR. The gallium promoted catalyst, Co/Ce₉₀Ga₁₀O_x, was more efficient for the ethanol conversion to H₂ and CO₂, and the production of oxygenated by-products (such as, acetaldehyde and acetone) than Co/CeO₂. The catalytic performance is explained assuming that: (i) bare ceria is able to dehydrogenate ethanol to ethylene; (ii) Ce–O–Ga interface catalyzes ethanol reforming; (iii) both Ce–O–Co and Ce–O–Ga interfaces takes part in acetone production; and (iv) cobalt sites further allow C–C scission. It is suggested that a cooperative role between Co and Ce–O–Ga sites enhance the H₂ and CO₂ yields under ESR conditions.     

Enhancement effect of zero-valent iron nanoparticle and iron oxide nanoparticles on dark fermentative hydrogen production from molasses-based distillery wastewater

This study investigates the effect of two different iron compounds (zero-valent iron nanoparticle: nZVI and iron oxide nanoparticles: nIO) and pH on fermentative biohydrogen production from molasses-based distillery wastewater. The nZVI and nIO of optimum particle sizes of 50 nm and 55 nm respectively were synthesized and applied for fermentative hydrogen (H₂) production. The addition of nIO & nZVI at (0.7 g/L, pH: 6) resulted in the highest H₂ yield, H₂ production rate, H₂ content and COD reduction. Moreover, the kinetic parameters of H₂ production potential (P) and H₂ production rate (R_m) increased to 387 mL, and 22.2 mL/h, respectively for nZVI, these values were 363 mL and 21.8 mL/h for nIO. The results obtained indicated the positive effect of nZVI and nIO addition on enhanced fermentative H₂ production. The addition of nZVI & nIO resulted in 71% and 69.4% enhancement in biohydrogen production respectively.