Thermocatalytic decomposition of methane is an alternative route for the production of CO x -free hydrogen and carbon nanomaterials. In this work, a set of novel Ni, Co and Fe based bimetallic ...catalysts supported over mesoporous SBA-15 was synthesized by a facile wet impregnation route, characterized for their structural, textural and reduction properties and were successfully used for the methane decomposition. The fine dispersion of metal oxide particles on the surface of SBA-15, without affecting its mesoporous texture was clearly shown in the low angle X-ray diffraction patterns and the transmission electron microscopy (TEM) images. The nitrogen sorption analysis showed the reduced specific surface area and pore volume of SBA-15, after metal loading due to the partial filling of hexagonal mesopores by metal species. The results of methane decomposition experiments indicated that all of the bimetallic catalysts were highly active and stable for the reaction at 700 degree C even after 300min of time on stream (TOS). However, a maximum hydrogen yield of 56% was observed for the NiCo/SBA-15 catalyst within 30min of TOS. A high catalytic stability was shown by the CoFe/SBA-15 catalyst with 51% of hydrogen yield during the course of reaction. The catalytic stability of the bimetallic catalysts was attributed to the formation of bimetallic alloys. Moreover, the deposited carbons were found to be in the form of a new set of hollow multi-walled nanotubes with open tips, indicating a base growth mechanism, which confirm the selectivity of SBA-15 supported bimetallic catalysts for the formation of open tip carbon nanotubes. The Raman spectroscopic and thermogravimetric analysis of the deposited carbon nanotubes over the bimetallic catalysts indicated their higher graphitization degree and oxidation stability.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
•Synthesis and characterization of Pd promoted Ni/SBA-15 catalysts for methane decomposition.•Improved textural properties of Ni/SBA-15 after Pd deposition.•High catalytic activity and stability of ...the prepared catalysts.•Production of multi walled carbon nanotubes with open tips.•Crystalline characterization of carbon nanotubes by XRD, Raman and thermal analysis.
The catalytic performance of Ni/SBA-15 catalysts promoted with different loadings of Pd is investigated for the thermocatalytic decomposition of methane into COx-free hydrogen and nanocarbon. The catalysts are characterized in terms of their structural, textural and redox properties. The results showed that the Pd deposition increased the crystallinity of NiO and allowed the fine dispersion of NiO on the SBA-15 support. The decreased surface area of SBA-15 after Ni loading, due to pore blocking, increased after the Pd deposition. Moreover, it reduced the reduction temperatures of NiO interacting with the SBA-15 due to the spillover effect of hydrogen. Furthermore, the addition of Pd increased the catalytic efficiency of the catalysts. A maximum hydrogen yield of 59% is observed over the 0.4% Pd catalyst within 30min of time on stream. No deactivation is observed until 420min of streaming for all of the catalysts, indicating a high catalytic stability of the Ni/SBA-15 catalysts for methane decomposition. A new set of multi-walled carbon nanotubes with open tips were deposited over the catalysts, irrespective of the role of Pd and its loading. Moreover, a high graphitization degree and oxidation stability are observed for the nanotubes deposited over the 0.4% Pd catalyst.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
A single-step ammonium persulfate (APS)-assisted swelling, followed by oxidation, can prepare nanocrystalline cellulose (NCC) from cotton linters. The APS-swelling is the critical step in the ...process, and the effects of swelling time, temperature and solid–liquid ratios were thoroughly investigated. The optimal conditions for NCC preparation were a swelling time of 3.0 h, a swelling temperature of 25 °C, and a solid–liquid ratio of 1:50. Upon heating at 60 °C, the persulfate enters the amorphous region of the cellulose and produces active SO
4
·−
and H
2
O
2
, which effectively attack the two-phase structure of cellulose and oxidize the –OH group at the C-6 position. The swelling temperature of 25 °C plays a crucial role in breaking the hydrogen bonds between the molecular chains of cellulose. It permits the preparation of NCC with a high yield and crystallinity index. The crystalline structure of cellulose I
β
did not change after APS swelling and oxidation. The atomic force microscopic analysis confirmed the formation of spindle-shaped particles with a helical structure. Upon natural evaporation of the NCC suspension, brittle films were obtained, which exhibited a left-hand layered structure and high iridescence with a fingerprint-texture. These materials can be applied as strength additives and chiral templates.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Thermocatalytic decomposition of undiluted biogas into hydrogen-rich syngas and multiwalled carbon nanotubes over zirconia supported iron catalysts.
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•A series of Fe/ZrO2 catalysts ...with different amount of iron were successfully prepared by an urea-assisted solid-state combustion method.•H2-rich syngas and multiwalled carbon nanotubes with high crystallinity were produced in the catalytic biogas decomposition.•A maximum CH4 conversion of 92% and a CO2 conversion of 89% with a H2/CO ratio of 2.25 was achieved at 900°C over 50% Fe/ZrO2 catalyst.
A set of Fe/ZrO2 catalysts were successfully synthesized by a facile urea-assisted solid-state combustion method, and their catalytic test was evaluated for the thermal decomposition of undiluted-biogas into hydrogen-rich syngas and multiwalled carbon nanotubes (MWCNTs). The as-prepared catalysts were characterized by X-Ray diffraction (XRD), Scanning and Transmission electron microscopy (SEM and TEM), Nitrogen-physisorption, X-ray photoelectron spectroscopy and Temperature programmed reduction analyses. The iron was found in the form of hematite and metallic-iron in the fresh and reduced catalysts respectively. A suitable metal-support interaction due to the fine surface dispersion of iron species on ZrO2 was observed in the catalysts. The N2-physisorption analysis indicated the reduced surface area of the catalysts after iron loading. However, it does not influence the catalytic efficiency since the metal amount and metal-support interaction was determined to play the main role. The Fe/ZrO2 catalysts exhibited improved catalytic efficiency. With increasing the amount of iron and increasing the reaction temperature, the CH4 and CO2 conversions were increased significantly. A highest CH4 and CO2 conversions of 92% and 89% respectively, with an H2/CO ratio of ∼2.25 were obtained for the 50%Fe/ZrO2 catalyst at 900°C. The enhanced catalytic performance could be attributed to the fine-surface dispersion of iron-nanocrystals on ZrO2. Moreover, the MWCNTs were characterized by XRD, SEM, TEM and Raman analyses for their structural properties.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Hydrogen is an alternative source of renewable energy that can be produced by methane decomposition without any CO
x
formation. In this work, an impregnation method was used to prepare a set of ...Ni-based catalysts (5% to 50%) supported on mesostructured silica nanoparticles (MSNs) for its application in methane decomposition. The use of MSN as an effective support for nickel in methane decomposition was reported here for the first time. The physical, chemical and structural properties of the catalysts was studied and the results indicated that NiO was the active species in the fresh catalyst that were effectively distributed on the mesoporous surface of MSN. The reduction temperature of Ni/MSN catalysts were shifted to low temperatures with increased loading of nickel. The hydrogen yield increased with the increment of Ni amount in the catalysts. The catalytic activity of the 50% Ni/MSN catalyst showed that this catalyst was highly efficient and stable compared with other catalysts. The catalyst showed the highest hydrogen yield of 68% and remained more or less the same during 360 min of reaction. Approximately 62% of hydrogen yield was observed at the end of reaction. Further analysis on the spent catalysts confirmed that carbon nanotubes was formed over Ni/MSN catalyst with high graphitization degree.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
In this article, we report on the synthesis, characterization and photocatalytic activity of quasi spherical ZnO nanoparticles obtained by an egg white assisted facile sol–gel type wet method. The ...material was characterized for its structural, textural and optical properties. The hexagonal wurtzite crystalline structure of ZnO with high phase purity was confirmed by the X-ray diffraction analysis. The mesoporous texture generated from the inter-agglomeration of ZnO nanoparticles was clearly shown in the transmission electron microscopy (TEM) images. The N
2
sorption analysis indicated a specific surface area of 18 m
2
/g, with monomodal mesoporosity. The optical studies had shown the decreased optical band gap (3.28 eV) of the sample with the existence of a number of crystal defects, especially oxygen vacancies in the sample. The aquatic dye pollutants were effectively degraded under UV irradiation over the ZnO nano photocatalysts. They were also found to be reusable up to five consecutive runs without loss in catalytic activity, indicating their high photostability against photocorrosion.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Copper and iron-based bimetallic nickel catalysts supported on Mesostructured Silica Nanoparticles (MSNs) with compositions of 50% Ni–5% Cu/MSN and 50% Ni–5% Fe/MSN were prepared using an ...impregnation method, and they were compared with a monometallic 50% Ni–MSN catalyst for their activity and stability in methane decomposition reaction. The influence of promoters, such as Cu and Fe, at different reaction temperatures (700 °C, 800 °C and 900 °C) was investigated. The results revealed that the Cu and Fe-promoted catalysts significantly increased the hydrogen yield in methane decomposition compared with the unpromoted catalyst. This could be attributed to the formation of Ni–Cu and Ni–Fe bimetallic alloys in the catalysts, respectively, and this favored the stability of the catalysts. With increasing reaction temperature, the hydrogen yield also increased. However, the hydrogen yield and the lifetime of the nickel catalyst were enhanced upon the addition of iron compared to copper at all the reaction temperatures. The analysis conducted over the spent catalysts validated the formation of multi-walled carbon nanotubes with a bamboo-like internal channel over the catalysts along with a high crystallinity and graphitization degree of the carbon produced.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
•Rapid synthesis of ZnO nanogranules by facile solid state mixing method.•Role of citric acid in the structural, textural and morphological properties of ZnO nanogranules.•High crystallinity of ZnO ...nanogranules with excellent optical properties.•Superb photocatalytic activity for dye degradation compared to the commercial ZnO.•Highly reusable ZnO nanogranules for the degradation of industrial dyes.
In this article, ZnO nanogranules were synthesised rapidly by the thorough solid state mixing of nitrate precursor with citric acid followed by aging and calcination at two different temperatures of 400°C and 600°C. Here, citric acid played a superior role in the development of porous ZnO nanostructures. The ZnO nanogranules obtained in this way were characterised by different techniques. X-ray diffraction patterns indicated a hexagonal wurtzite structure of ZnO with high crystallinity and nanocrystalline size. Scanning and transmission electron microscopy images indicated the uniformly well separated hexagonal morphology of the ZnO nanoparticles, with granular shape. BET surface area-porosity analysis confirmed the presence of a mesoporous network in both samples, with high surface area and a monomodal pore size distribution. Room temperature Photoluminescence spectra of the samples exhibited characteristic blue and green emission bands in accordance with the calcination temperature. The photocatalytic performance of the ZnO nanogranules was studied using methylene blue degradation and found that the ZnO prepared at 400°C exhibited higher photocatalytic activity due to its high surface area and more oxygen vacancies. High concentrations of several hazardous dye pollutants were effectively degraded, when the solution was passed over 50mg of ZnO nanogranules under UV-light illumination.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
A controlled acidic precipitation is reported for the direct synthesis of nanosheets self-assembled hierarchical tungstic acid microspheres, and their annealing-dependent thermal conversion into WO
3
...microstructures is studied for the first time. The synthesis was carried out without the use of any structure directing agents and hydrothermal conditions. The microspheres were found to be consisting of many single-crystalline and highly oriented nanosheets that were hierarchically self-aggregated in spherical form for the minimization of surface energy. An experimentally validated time-dependent formation and growth mechanism was proposed for the development of microspheres. The characterization results indicated that the morphology-preserved thermal decomposition of H
2
WO
4
into WO
3
microspheres occurred at 400 °C, whereas a morphology distortion was noticed for the sample synthesized at 600 °C. The increase in annealing temperature further increased the crystallinity of WO
3
without changing its monoclinic crystal structure. However, it has a diminishing effect in the specific surface area, pore size and pore volume of the annealed samples. Moreover, the adsorption of methylene blue in aqueous medium was carried out to evaluate its potential environmental application. The WO
3
microspheres synthesized at 400 °C showed high adsorption capacity (63 mg/g) compared to the same at 600 °C (56 mg/g). The high activity could be ascribed to the synergistic effects of high surface area, low particle size, porosity, specific morphology and more negative zeta potential. The adsorption further followed pseudo-second-order kinetics with a best fit of the experimental and theoretical values.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
