Multidisciplinary methods (co-precipitation,ultrasonic, microwave,reflux and hydrothermal) for synthesis and characterization of CaMn3O6 nanostructures and its photocatalytic water splitting performance

Production of hydrogen and oxygen from water splitting reaction under visible light is a simple method for conversion of solar-to-hydrogen energy and it is a hopeful clean and renewable method for H₂ fuel generation. However, there is still a lack of potential materials with significant activity under visible light. Because of safety, chemical inertness, low cost, stability and other characteristics, transition metal oxide semiconductors have been widely applied as photocatalysts for hydrogen generation. Albeit, wide usage of semiconductor photocatalysts were prevented by its inability to exploit solar energy of visible region. Here we show synthesis of a nano-sized mixed metal oxide (MMO) Ca₃MnO₆ through wet-chemistry methods such as co-precipitation, ultrasonic, microwave, reflux, and hydrothermal methods. The nano-sized Ca₃MnO₆ has initially selected based on morphology and respective particle diameters. The selected sample shows a well-defined single crystal, free from any impurities, complete structural formation, and a band gap energy (E_g) of around 5.3 eV. The best product synthesized in ultrasonic method which shows the best morphology, purity and the highest efficiency for splitting of water to hydrogen and oxygen. Irrespective of preparation methods and morphologies, all samples split water into hydrogen and oxygen, as confirmed from their respective photocatalytic analysis. When the selected sample combined with (NH₄)₂Ce(NO₃)₆, the single-crystal Ca₃MnO₆ nanoparticles split water into hydrogen and oxygen more efficiently under visible light. Our findings demonstrate the importance of nanostructured Ca₃MnO₆ single-crystal photocatalysts in solar water splitting.     

Ni/Al2O3 catalysts for CO2 methanation: Effect of silica and nickel loading

Samples containing from 1 to 33 wt.% of NiO on silica and alumina doped with silica (1 and 20 wt.% silica in the support) have been prepared and characterized by BET, XRD, FT-IR, UV–vis–NIR, FE-SEM, EDXS, and TPR techniques. Catalysts have been pre-reduced in situ before catalytic experiments and data have been compared with Ni/Al₂O₃ reference sample. Characterization results showed that SiO₂ support has a low Ni dispersion ability mainly producing segregated NiO particles and a small amount of dispersed Ni²⁺ in exchange sites. Instead, for the Si-doped alumina a “surface spinel monolayer phase” is formed by increasing Ni loading and, only when the support surface is completely covered by this layer, NiO is formed. Moreover, H₂-TPR results indicated that NiO particles are more easily reduced compared to Ni species. Low loading Ni/SiO₂ catalysts show high selectivity and moderate activity for RWGS (reverse Water Gas Shift) reaction, likely mainly due to nickel species dispersed in silica exchange sites, as evidenced by visible spectroscopy. High loading Ni/SiO₂ catalysts show both methanation and RWGS but evident short-term deactivation for methanation, attributed to large, segregated Ni metal particles, covered by a carbon veil. Ni on alumina -rich carriers, where nickel disperses forming a surface spinel phase, show high activity and selectivity for methanation, and short-term catalyst stability as well. This activity is attributed to small nickel clusters or metal particles interacting with alumina, formed upon reaction. The addition of SiO₂ in Al₂O₃ support decreases the activity of Ni catalysts in CO₂ methanation, because it reduces the ability of the support to disperse nickel in form of the surface spinel phase, thus reducing the amount of Ni clusters in the reduced catalysts.     

TmVO4/Fe2O3 nanocomposites: Sonochemical synthesis,characterization, and investigation of photocatalytic activity

Today, a unique method of treating environmental contaminants is drawing considerable attention. Organic dyes are significant wastes from myriad industries, including paper, food, and textiles, which have become a serious environmental concern and have the potential to be toxic to humans and living organisms. This study demonstrates the fabrication and characterization of thulium vanadate (TmVO₄) nanostructures and TmVO₄/Fe₂O₃ nanocomposites that were effectively applied in the photodecomposition efficiency of cationic and anionic organic contaminants. The TmVO₄/Fe₂O₃ nanocomposites were prepared through a sonochemical method, and triethylenetetramine (TETA) was employed as a precipitating and capping agent. The tests were performed using a probe as a sonication source (60 W, 18 kHz). The impact of TmVO₄ content (5, 10, 15, and 30%) on the modification of binary nanocomposites was studied in terms of morphological, optical, and photocatalytic properties. The recyclable magnetic TmVO₄/Fe₂O₃ nanocomposites with 15% TmVO₄ achieve 68.3% of eriochrome black t (EBT) utilizing visible origin. More notably, the binary TmVO₄/Fe₂O₃ nanocomposites reveal higher photocatalytic activity than the pure TmVO₄ and Fe₂O₃ nanoparticles.     

Investigating a HEX membrane reactor for CO2 methanation using a Ni/Al2O3 catalyst: A CFD study

In this contribution, viability of processing of the flue gas streams as a source of carbon dioxide for the thermo-catalytic conversion was investigated. For this purpose, a Ni/Al₂O₃ commercial catalyst with known chemical kinetics was utilized. Moreover, a transient mathematical model for dynamic catalyst deactivation was developed and validated with experimental results available in the open literature. The developed model was then utilized to understudy an air-cooled membrane reactor. Different tube configurations were understudied and compared to choose the conditions under which high conversion was feasible. Sensitivity analysis revealed that, the space velocity, cooling rate, and feed distribution were all considered to be critical factors. It was revealed that, the presence of membrane resulted in higher conversion through the undertaken reactor. It made it possible to enhance reaction yield of non-membrane reactor through evenly distributing hydrogen along its length. A designed heat-exchanger (HEX) membrane reactor achieved 99% CO₂ conversion when the coolant flow rate was reached to 10% of the coolant gravimetric flow rate, feed space velocity was set at 100 h⁻¹ and the feed pressure was set at 10 bars.     

Green synthesis,characterization and investigation of the electrochemical hydrogen storage properties of Dy2Ce2O7 nanostructures with fig extract

Nanostructured Dy₂Ce₂O₇ with good electrochemical hydrogen storage properties has been produced utilizing a novel and green method in the presence of fig extract, for the first time. Fig extract has been employed as novel kind of fuel in the production of pure Dy₂Ce₂O₇. By varying the notable factor, temperature for production, Dy₂Ce₂O₇ structures can be created that are different in morphological features and Coulombic efficiency as well as electrochemical hydrogen storage properties. Diverse techniques have been adopted to examine and characterize the formed Dy₂Ce₂O₇ with the aid of fig extract. Electrochemical hydrogen storage features of the diverse Dy₂Ce₂O₇ samples (formed with the aid of fig extract) have been compared with chronopotentiometry technique at potash solution. Our findings reveal that the nanostructured Dy₂Ce₂O₇ fabricated with the aid of fig extract at 400 ^°C can possess the best efficiency for store hydrogen. Usage of fig extract, the new and eco-friendly fuel, for synthesis of the nanostructured Dy₂Ce₂O₇ that is efficiently capable to store hydrogen (renewable type of energy carrier), can be helpful to decline and stop the environmental pollution.     

Facile synthesis of M-CuFe2O4 (M= Al2O3, CeO2, La2O3, ZrO2, Mn2O3) catalysts using a one-pot method and their applications in high-temperature water gas shift reaction

Water gas shift reaction is an essential process of hydrogen production and carbon monoxide removal from syngas. In this study, the promotional effect of ZrO₂, CeO₂, La₂O₃, Al₂O₃, and Mn₂O₃ was investigated on the CO conversion and thermal stability of the copper ferrite in high-temperature water gas shift reaction (HTSR) and hydrogen purification. The powders were synthesized by a simple solid-state route and characterized by XRD, H2-TPR, SEM, FT-IR, TG-DTA, and BET analyses. Promoters (ZrO₂, CeO₂, La₂O₃, Al₂O3, and Mn₂O₃) could affect the WGSR performance in activity and stability. In the M-CuFe2O4 catalyst, alumina acts as a texture promoter and aids in the fine dispersion of copper ferrite. The results indicated that the surface area of the Al₂O₃–CuFe₂O₄ (210 m²/g) catalyst was higher than the other samples. This catalyst presented higher CO conversion in HTSR and had higher stability at 1000 min on stream. It was found that the incorporation of different contents of alumina had a significant influence on the textural and catalytic properties of the CuFe₂O₄-based catalysts. The 30%Al₂O₃–70%CuFe₂O₄ catalyst exhibited the highest CO conversion of 65% at 350 °C, uniform pore size distribution, and intense interaction between copper ferrite and alumina, causing the effective stabilization of the active phase in the catalyst structure. The findings of this study represent that the solid-state method, due to its simplicity and creation of a mesoporous structure, can also be applied for the preparation of many heterogeneous metal oxide catalysts.     

Production of H2- and CO-rich syngas from the CO2 gasification of cow manure over (Sr/Mg)-promoted-Ni/Al2O3 catalysts

The valorization of cow manure (CM), as bio-waste, under a CO₂ atmosphere could be an attractive strategy for tackling the environmental problems related to waste management and CO₂ emission and producing valuable syngas. For this purpose, highly loaded Ni–Al₂O₃ catalysts with alkaline-earth metals (Mg and Sr) were synthesized and applied to the gasification of CM under CO₂. The lowest yields of bio-oil (16.98 wt %) and coke (0.34 wt %) and the highest yield of syngas (55.09 wt %) were obtained from the catalytic decomposition of hydrocarbons when Sr was incorporated into Ni/Al₂O₃ (SN-AO). The highest selectivity for H₂ (34.23 vol %) and CO (37.16 vol %) were obtained applying SN-AO followed by Mg-promoted Ni/Al₂O₃ (MN-AO) and Ni/Al₂O₃ (N-AO) catalysts. With increasing gasification temperature from 750 °C to 850 °C, the syngas yield (from 55.09 to 70.17 wt %) and H₂ concentration (from 34.23 to 38.03 vol %) increased considerably because of the endothermic gasification process. The yield and selectivity of syngas (H₂ and CO) increased under CO₂ compared to those obtained under N₂, indicating the high potential of CO₂ for the thermal decomposition and dehydrogenation of the volatile matter.     

Syngas production via CO2 reforming of methane over plasma assisted synthesized Ni‐Co/Al2O3‐ZrO2 nanocatalysts with different Ni‐loadings

Ni‐Co/Al₂O₃‐ZrO₂ nanocatalysts with 5, 10 and 15 wt.% nominal Ni content have been prepared by impregnation followed by a non‐thermal plasma treatment, characterized and tested for dry reforming of methane. For nanocatalysts characterization the following techniques have been used: XRD, FESEM, TEM, EDX dot‐mapping, BET, FTIR and XPS. The dry reforming of methane was carried out at different temperatures (550‐850 °C) using a feed mixture of CH₄:CO₂ (1:1). Among the nanocatalysts studied, the catalyst with the medium Ni content (10 wt.%) was the most active in dry reforming of methane. This higher activity exhibited by Ni‐Co/Al₂O₃‐ZrO₂ catalyst with medium Ni content (10 wt.% ) can be attributed to small and well dispersed particles of Ni within the catalyst. Apart from the narrow surface particle size distribution in the case of Ni(10 wt.%)‐Co/Al₂O₃‐ZrO₂, the presence of small active components with average size of 7.5 nm is proposed to be the reason for the superior performance of the catalyst. Ni(10 wt.%)‐Co/Al₂O₃‐ZrO₂ nanocatalyst had maximum surface area and the lower surface area was observed in the case of Ni(5 wt.%)‐Co/Al₂O₃‐ZrO₂ and Ni(15 wt.%)‐Co/Al₂O₃‐ZrO₂ due to the formation of the larger agglomeration and higher mean particle size of nickel particles, respectively. Although, GHSV enhancment had inverse effect on product yield but yield reduction for Ni‐Co/Al₂O₃‐ZrO₂ catalyst with 10 wt.% Ni was less drastic at high GHSVs. According to XRD and XPS, existence of NiAl₂O₄ confirms strong interaction between Ni and support but higher loadings of Ni resulted in less NiAl₂O₄; loser interaction between support and active phase. Small particles of active components and well‐defined dispersion of them in Ni(10 wt.%)‐Co/Al₂O₃‐ZrO₂ nanocatalyst resulted in stability of the catalyst for either feed conversion or H₂/CO molar ratio. Copyright © 2013 John Wiley & Sons, Ltd.     

Elucidation of cobalt disturbance on Ni/Al2O3 in dissociating hydrogen towards improved CO2 methanation and optimization by response surface methodology (RSM)

In this study, nickel (Ni) and cobalt nickel (Co/Ni) supported on alumina were successfully synthesized by a facile electrolysis procedure and were tested for CO₂ methanation. By applying the Ni/Al₂O₃ catalyst, CO₂ conversion reached up to of 10 μmol/g.s, which is 1.4 times higher than Co/Ni/Al₂O₃, followed by the parent Al₂O₃. The addition of Co into Ni/Al₂O₃ has formed spinel phase in Co/Ni/Al₂O₃, as well as caused a slight increase in the basicity, which directed to the higher formation of formate species as observed by in-situ CO₂ + H₂ FTIR study. Both catalyst followed the dissociative mechanism during the CO₂ methanation. However, bigger metal particles in Co/Ni/Al₂O₃ caused slower hydrogen dissociation compared to Ni/Al₂O₃, leading to lower yield of CH₄. The optimization study via the response surface methodology (RSM) showed that the yield of CH₄ was significantly affected by reaction temperature, followed by treatment time, the ratio of H₂:CO₂ and lastly the gas hour space velocity (GHSV).     

CO2 methanation over nanocrystalline Ni catalysts supported on mechanochemically synthesized Cr2O3-M (M=Fe,Co, La,and Mn) carriers

In the present study, a series of Cr₂O₃ powders modified by different promoters such as Fe, Co, La, and Mn were synthesized using a facile and solvent-free mechanochemical method and the prepared powders were used as a catalyst carrier for the preparation of 20 wt%Ni catalysts in CO₂ methanation. The results indicated that among all catalysts, the nickel catalyst supported on the Mn-promoted Cr₂O₃ exhibited the best catalytic performance. The results showed that there was an optimum for the Mn content and the increment in Mn content up to 15 wt% improved the catalytic performance due to its positive influence on increasing nickel dispersion and catalyst reducibility. The 20 wt%Ni/15 wt%Mn–Cr₂O₃ catalyst possessed a CO₂ conversion of 72.12% and CH₄ selectivity of 100% at 350 °C (H₂/CO₂ = 3 M ratio, GHSV = 18,000 ml/g_cat.h) with high stability during 12 h on stream. The obtained results showed that the increment in H₂/CO₂ molar, and the decrement in GHSV value and calcination temperature improved the catalytic performance.     

Catalytic gasification of textile wastewater treatment sludge for hydrogen production in supercritical water with K2CO3/H2O2: Reaction variables,mechanism and kinetics

As the main by-product, sludge was generated during the process of textile wastewater treatment. Due to containing organic compounds, textile sludge has great potential to be effectively reused for production of clean energy. In this work, gasification of textile sludge in supercritical water for hydrogen production was investigated. In order to improve hydrogen production, H₂O₂ and K₂CO₃ were used as catalysts. Effects of reaction variables (including temperature, retention time, oxidation coefficient and alkali catalyst dosage) on hydrogen yield were studied. Experimental results indicate that hydrogen yield increases with rise of temperature. When reaction temperature reaches 500 °C, the maximum value of hydrogen yield being 10.6 mol/kg was obtained. When excessive H₂O₂ was added, decrease of hydrogen yield was achieved. However, the addition of K₂CO₃ is favor to hydrogen yield, which is about 1.5 times as much as that of without catalyst. Meanwhile, reaction mechanism and kinetics of textile sludge gasification in supercritical water were explored. Reaction activation energy and Arrhenius constants were obtained in the established kinetic model.     

Integration of 2D printing technologies for AV2O6 (A=Ca,Sr, Ba)-MO (M=Cu,Ni, Zn) photocatalyst manufacturing to solar fuels production using seawater

The non-polluting nature of photocatalytic H₂ production makes of interest the study of semiconductors for this process. Scale-up of the photocatalytic hydrogen process to a pilot plant requires the photocatalyst's immobilization to enhance the charge transfer and facilitate its recovery. In this work, screen-printed films from the AV₂O₆ (A = Ca, Sr, Ba) semiconductor family were fabricated and evaluated in photocatalytic water splitting for H₂ production in distilled water and seawater under UVA light. The films exhibited ∼3.1 eV band gaps, high crystallinity, and heterogeneous morphologies. BaV₂O₆ film exhibited the highest H₂ production in distilled water (691 μmol/g), related to the synergistic effect between a higher crystallinity and traces of V⁺⁴ species that decrease the recombination of the photogenerated charges. Also, to take advantage of the dissolved species in seawater that could act as sacrificial agents, the BaV₂O₆ film was evaluated in seawater, in which H₂ production was up to 6 times higher (4374 μmol/g) than in distilled water. The BaV₂O₆ film was decorated with simple oxides (CuO, NiO, and ZnO) by the ink-jet printing technology to increase its photocatalytic performance for H₂ production. The highest efficiency with distilled water was obtained with the BaV₂O₆-CuO film, which reached an H₂ production up to 30 times higher than the bare BaV₂O₆, own to the n-p heterostructure formation that enhances the charge transport in the photocatalytic process. When the BaV₂O₆-CuO film was evaluated in seawater, a more constant H₂ production was observed; moreover, the efficiency was similar compared to the production in distilled water (20,563 μmol/g). To elucidate the seawater compounds that most influence the H₂ production, a two levels Plackett–Burman experiments design was carried out in simulated seawater. The analysis revealed that the SO₄²⁻ ions from the CaSO₄ could be decreasing the H₂ production by acting as Lewis's acid sites that trap the photogenerated e⁻ competing for its usage with the H⁺. Additionally, the Cl⁻ ions and the HCO₃⁻ reduction improved the HCOOH production from simulated seawater, reaching 26 times a higher production (23,333 μmol/g) than in distilled water.     

Li2MnO3/LiMnBO3/MnFe2O4 ternary nanocomposites: Pechini synthesis,characterization and photocatalytic performance

Li₂MnO₃/LiMnBO₃/MnFe₂O₄ ternary nanocomposites were synthesized via modified pechini sol-gel approach employing the mixture of metal cations, boric acid, ethylene glycol and ethylene diamine tetra acetic acid gelating agent. Shape and size of nanocomposites was controlled by changing molar ratio of metal ions, ethylene glycol and gelating agent. In order to confirmation of crystalline and structural features of products, analyses of X-ray diffraction, Fourier transform infrared and energy dispersive X-ray were carried out. Scanning electron microscopy and transmission electron microscopy images were taken for morphology investigation of nanostructure products. Band-gap of ternary nanocomposites calculated by UV–Vis data is 2.6 eV. Magnetic property of Li₂MnO₃/LiMnBO₃/MnFe₂O₄ ternary nanocomposites investigated through vibrating sample magnetometer presents ferromagnetic behavior. Moreover, photocatalytic activity of Li₂MnO₃/LiMnBO₃/MnFe₂O₄ and Li₂MnO₃/LiMnBO₃ nanocomposites was investigated in aqueous solution via UV and visible light for degradation acid red 88 dye. Some effective parameters such as dye concentration, irradiation and nanocomposite type were evaluated for optimum removal of water pollutant dye.     

Magnetically recyclable ZnCo2O4/Co3O4 nano-photocatalyst: Green combustion preparation,characterization and its application for enhanced degradation of contaminated water under sunlight

Finding the appropriate photocatalyst for elimination of organic contaminants is a challenge for remediation of environment. Herein, we tried to synthesis of ZnCo₂O₄/Co₃O₄ nanocomposite using the Stevia extract as a natural reagent that can act as green fuel in auto-combustion sol-gel method and control the size of product by steric-hindrance induced by its structure. The chelating role of this natural reagent was investigated by changing the amount of this extract for synthesis of different samples. Analyses confirmed the effect of this parameter on morphology and size of products. The photocatalytic activities of different samples under visible irradiation were investigated and the effect of size of photocatalyst on degradation percent of dye was studied. The good performance of ZnCo₂O₄/Co₃O₄ nanocomposite was detected by degradation of Acid violet 7 about 93.5% in 70 min and 2-phenol about 100% in 18 min. Photocatalyst was easily recycled through magnetic properties of products and stability of it under irradiation was confirmed by degradation of dye after 10 times recycling.     

The role of additives (Ba,Zr, and Nd) on Ce/Cu/Al2O3 catalyst for water-gas shift reaction

Enhanced catalytic performance is required to increase the efficiency of hydrogen production from waste-derived synthesis gas via the high-temperature water-gas shift reaction (HT-WGSR). Herein, the effects of barium, zirconium, and neodymium doping on the physico-chemical properties of a Ce/Cu/Al₂O₃ catalyst as well as its catalytic performance for HT-WGSR are investigated. Ce/Cu/Al₂O₃ catalysts with various additives (barium, zirconium, and neodymium) prepared via a sequential impregnation method have been characterized by using N₂ adsorption-desorption isotherms, X-ray powder diffraction (XRPD), N₂O-titration, X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and hydrogen temperature-programmed reduction (H₂-TPR). Advantageously, barium and zirconium addition enhance the HT-WGSR activity and stability of the Ce/Cu/Al₂O₃ catalyst, whereas neodymium doping has a negative effect. Regarding the correlation of catalytic performance with the characterization results, it was found that catalytic activity and stability strongly depended on their oxygen vacancy concentration and strong-metal to support interaction.     

Tuning the alloy degree for Pd-M/Al2O3 (M=Co/ Ni /Cu) bimetallic catalysts to enhance the activity and selectivity of dodecahydro-N-ethylcarbazole dehydrogenation

Hydrogen is a promising candidate to substitute the fossil fuels. However, the efficient hydrogen storage technologies restrict the commercial applications. Developing new catalysts with high activity and selectivity is important for the dehydrogenation reaction in N-ethylcarbazole/dodecahydro-N-ethylcarbazole (NECZ/12H-NECZ) hydrogen storage system. In this work, a series of Pd-M/Al₂O₃ (M = Co, Ni and Cu) bimetallic catalysts are synthesized successfully and show good performance in the dehydrogenation reaction of 12H-NECZ than the commercial Pd/Al₂O₃ catalyst. The Pd₁Co₁/Al₂O₃ catalyst (Practical Pd content = 2.4136 wt%) showed the highest catalytic performance with 95.34% H₂ release amount, TOF of 230.5 min⁻¹ and 85.4% selectivity of NECZ. Combined with the characterization analysis, it can be proposed that the dehydrogenation performance of 12H-NECZ is dependent on the alloy phases, reasonable electronic structures and nanoparticle size of catalysts. The fine-tuned alloy degree and appropriate nanoparticle size of Pd₁Co₁/Al₂O₃ bring the 17.7% increase of H₂ release amount and 99.5% increase of NECZ selectivity than those of Pd/Al₂O₃. For the bimetallic catalysts, the enhancement of selectivity of NECZ is mainly from the increase of the kinetic constant of rate-limiting step.     

Preparation,characterization, and properties of Pt/Al2O3/cordierite monolith catalyst for hydrogen generation from hydrolysis of sodium borohydride in a flow reactor

High-purity hydrogen can be generated by hydrolysis of sodium borohydride and used for operating portable proton exchange membrane fuel cells. The monolith supported catalyst is suitable for practical NaBH₄-based hydrogen generation system due to its simple reactor structure miniaturizing for small size applications and easy separation from the spent solution. In the present study, a structured catalyst was prepared by wash-coating the Al₂O₃ sol over the wall of cordierite monolith followed by depositing Pt using incipient wet impregnation method; then the monolithic catalysts were characterized by XRF, XRD, SEM, HRTEM and XPS. The catalytic activity of the Pt-based monolithic catalyst towards hydrolysis of NaBH₄ was tested using a flow reactor under ambient conditions in an autothermal manner. The characterization results show that Pt nanoparticles are highly dispersed on the surface of the Al₂O₃-coated layer. A continuous and stable hydrogen generation can be obtained by feeding the reactant (10 wt% NaBH₄–5 wt % NaOH) into the tube reactor loaded with the monolithic catalyst at feed rates of 0.5–2.0 mL min⁻¹.     

An investigation of the simultaneous presence of Cu and Zn in different Ni/Al2O3 catalyst loads using Taguchi design of experiment in steam reforming of methane

Nowadays, increasing environmental pollution as well as restrictions on the use of fossil fuels have shifted the attention toward using hydrogen as a new source of clean and effective energy. Additionally, hydrogen and syngas are employed as feedstock for the production of valuable materials in the petrochemical industry. Methane steam reforming is the main procedure for the hydrogen and syngas production. In this study, Taguchi design of experiment (L9) was used to investigate the effects of simultaneous presence of copper (Cu) and Zinc (Zn) metals on different Ni/Al₂O₃ catalyst loads. It should be noted that some of the catalysts were characterized using XRD, BET, SEM and TGA analyses. According to the Taguchi design, it was concluded that the increment of Cu content enhances the catalyst stability and increases the CO selectivity. Increasing Zn content advocated CH₄ conversion, H₂ yield, and less selectivity toward the CO production. The XRD, BET and SEM test results revealed that the addition of Cu resulted in better distribution of active support phase. The TGA results indicated that the addition of Cu and Zn stabilized the catalyst activity; in this case, Cu was more effective than Zn. The overall results demonstrated that 15% load of Ni on Al₂O₃ support, simultaneous addition of Cu and Zn loads of 1% and 5%, respectively, enhanced the catalyst stability and activity and improved the catalyst performance in the selective hydrogen production as well.     

Syngas production by catalytic partial oxidation of methane over (La0.7A0.3)BO3 (A = Ba,Ca, Mg,Sr, and B = Cr or Fe) perovskite oxides for portable fuel cell applications

Hydrogen is a clean energy carrier for the future. More efficient, economic and small-scale syngas production has therefore important implications not only on the future sustainable hydrogen-based economy but also on the distributed energy generation technologies such as fuel cells. In this paper, a new concept for syngas production is presented with the use of redox stable lanthanum chromite and lanthanum ferrite perovskites with A-site doping of Ba, Ca, Mg and Sr as the pure atomic oxygen source for the catalytic partial oxidation of methane. In this process, catalytic partial oxidation reaction of methane occurs with the lattice oxygen of perovskites, forming H₂ and CO syngas. The oxygen vacancies due to the release of lattice oxygen ions are regenerated by passing air over the reduced nonstoichiometric perovskites. Studies by XRD, temperature-programmed reduction (TPR) and activity measurements showed the enhanced effects of alkaline element A-site dopants on reaction activity of both LaCrO₃ and LaFeO₃ oxides. In both series, Sr and Ca doping promotes significantly the activity towards the syngas production most likely due to the significantly increased mobility of the lattice oxygen in perovskite oxide structures. The active oxygen species and performance of the LaACrO₃ and LaAFeO₃ perovskite oxides with respect to the catalytic partial oxidation of methane are discussed.