Manoj Pudukudy

CeO2-TiO2 as a visible light active catalyst for the photoreduction of CO2 to methanol

The performance of CeO2-TiO2 photocatalyst for the photocatalytic reduction of CO2 into methanol was studied under visible light irradiation. The as-prepared catalysts were characterized for their structural, textural and optical properties using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), X-ray photoelectron spectroscopy (XPS), nitrogen physisorption analysis, UV-vis spectroscopy and photoluminescence (PL) spectroscopy. The characterization results indicated that the presence of CeO2 stabilized the anatase phase of TiO2, decreased its crystallite size, increased the surface area, reduced the band gap energy and lowered the rate of electron-hole pair recombination. The CeO2-TiO2 photocatalyst showed an increased methanol yield of 18.6 µmol/g under visible light irradiation, compared to the bare TiO2 (6.0 µmol/g).

Sol-gel synthesis, characterisation, and photocatalytic activity of porous spinel Co3O4 nanosheets

Mesoporous spinel Co3O4 nanosheets were synthesised via a simple sol-gel route using the Pluronic P123 triblock copolymer as the stabilising agent. Their structural, morphological, and textural properties were characterised. FTIR spectrum revealed the formation of cobalt oxide without any surface adsorbed impurities. Face centered cubic phase of spinel Co3O4 with the mean crystalline size of 26 nm was assigned by the X-ray diffraction analysis without the formation of other phases. Porous nanosheets and cave-like morphologies were identified from the scanning electron microscopy (SEM) images. Highly agglomerated more or less spherical particles with well separated lattice fringes, representing the oriented growth of nanocrystals, were noticed on the transmission electron microscopy photographs. Surface area analysis revealed that the spinel has high surface area of about 25 m2 g−1 with monomodal mesoporosity. The average pore size distribution was found to be about 15.8 nm. The as-prepared spinel photocatalyst showed a mild photocatalytic activity in the degradation of methylene blue (2.5 mg L−1) under UV light irradiation with air as the oxidising agent. Photocatalytic activity of the as-prepared reusable Co3O4 was found to be higher than that of the commercial spinel powder.

Methane decomposition over unsupported mesoporous nickel ferrites: effect of reaction temperature on the catalytic activity and properties of the produced nanocarbon

The thermocatalytic decomposition of methane is a promising route for the simultaneous production of COx-free hydrogen and nanocarbon. In this work, unsupported mesoporous nickel ferrites were successfully synthesized via a facile co-precipitation method and used to catalyze the decomposition of methane. The as-prepared nickel ferrites were characterized by using X-ray diffraction, energy dispersive X-ray spectroscopy, scanning and transmission electron microscopy, X-ray photoelectron spectroscopy, N2 adsorption and temperature-programmed reduction analysis. The NiFe2O4 catalyst was found to be highly phase pure and porous. The porosity is resulted from the inter-aggregation of more or less spherical nickel ferrite particles. Moreover, these particles had a total specific surface area of 21 m2 g−1 with a monomodal mesoporous distribution. The catalytic performance of the catalysts was evaluated for methane decomposition at various reaction temperatures, and the dependence of the properties of the nanocarbon on reaction temperature was investigated in detail. Upon increasing the temperature from 700 °C to 900 °C, the yields of hydrogen and nanocarbon increased significantly. A maximum hydrogen yield of 68% was observed over the catalyst at 900 °C within the first 20 minutes of time on the stream. After that, its activity slightly declined, and at the end of 360 minutes, the hydrogen yield was measured to be 47%. At 700 °C and 800 °C, maximum hydrogen yields of 41% and 58% were achieved within 90 minutes of time on stream. No deactivation was observed for the catalyst at any of the temperatures tested, which was attributed to the formation of NiFe bimetallic alloys, which in turn increased the carbon diffusion rate and prevented deactivation of the catalyst. The effect of reaction temperature on the crystalline, morphological and graphitization properties of the deposited nanocarbon was studied. Metal-encapsulated carbon particles with a nano-onion-like appearance and multi-layered graphene sheets were deposited over the catalyst at 700 °C and 900 °C, respectively. Moreover, the crystallinity and graphitization degree of the deposited nanocarbon was found to increase with increasing reaction temperature.

Synthesis, Characterization, and Photocatalytic Performance of Mesoporous α-Mn 2 O 3 Microspheres Prepared via a Precipitation Route

α-Mn2O3 microspheres with high phase purity, crystallinity, and surface area were synthesized by the thermal decomposition of precipitated MnCO3 microspheres without the use of any structure directing agents and tedious reaction conditions. The prepared Mn2O3 microspheres were characterized by Fourier transform infrared (FTIR) spectroscopy, powder X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM), and Brunauer-Emmett-Teller (BET) and photoluminescence (PL) studies. The complete thermal transformation of MnCO3 to Mn2O3 was clearly shown by the FTIR and XRD analysis. The electron microscopic images clearly confirmed the microsphere-like morphology of the products with some structural deformation for the calcined Mn2O3 sample. The mesoporous texture generated from the interaggregation of subnanoparticles in the microstructures is visibly evident from the TEM and BET studies. Moreover, the Mn2O3 microstructures showed a moderate photocatalytic activity for the degradation of methylene blue dye pollutant under UV light irradiation, using air as the potential oxidizing agent.

Catalytic decomposition of undiluted methane into hydrogen and carbon nanotubes over Pt promoted Ni/CeO2 catalysts

The catalytic decomposition of methane is a strategic process to produce COx-free hydrogen and carbon nanomaterials. In this work, for the first time, highly porous ceria was prepared by a urea-assisted solid state combustion method and used as a support for the preparation of a set of platinum-promoted nickel catalysts. The amount of Pt varied from 0.05% to 0.2% while retaining 20% nickel in the catalysts. The prepared catalysts were completely characterized for their structural, textural and redox properties, and their catalytic performance was tested for undiluted methane decomposition. A fine surface dispersion of nickel oxide over ceria was observed in the prepared catalysts. No peaks related to Pt were observed in the catalysts, indicating its good surface dispersion. An enhancement was observed in the properties of the Ni/CeO2 catalyst after the addition of Pt as a promoter. The crystallinity of NiO was not altered by the addition of Pt, whereas the specific surface area of the catalysts was increased with the incremental addition of Pt. Furthermore, the reduction temperature of nickel oxide was shifted to low temperature in the Pt-promoted catalysts due to the hydrogen spillover effect. The surface composition and chemical states of the Pt-promoted Ni/CeO2 catalysts were further studied using XPS. The Pt-promoted Ni/CeO2 catalysts exhibited high catalytic efficiency for methane decomposition due to their improved catalytic properties. The addition of Pt increased the hydrogen yield, and a significant increase in the hydrogen yield was observed for the incremental amount of Pt in the catalysts. Moreover, by increasing the reaction temperature from 650 °C to 750 °C, the hydrogen yield increased significantly. A maximum hydrogen yield of 65% was observed for the 0.2% Pt@Ni/CeO2 catalyst at 750 °C. The enhanced activity and stability of the catalysts were attributed to the synergistic effects of Ni and Pt due to their fine surface dispersion over ceria with a proper metal–support interaction. Multiwalled carbon nanotubes with different diameters were deposited over the catalysts. The carbon nanotubes deposited over the Ni/CeO2 catalyst were found to be more homogeneous than the Pt-promoted catalysts. Moreover, a wide hollow channel was observed in the carbon nanotubes deposited over the Pt-promoted catalyst.