Cerium incorporated iron oxide catalysts and a pure iron oxide catalytic material were prepared by the complexation technique and their catalytic performances were investigated for selective oxidation of H2S to elemental sulfur in a fixed-bed flow reactor. Ce−Fe mixed oxide catalyst having a Fe/Ce ratio of 1/1 (2Fe−2Ce) showed complete conversion and very high sulfur selectivity in the temperature range of 200−300 °C. Sulfur selectivity and stability of iron oxide catalyst was significantly enhanced by the incorporation of cerium into the catalyst structure. It was concluded that incorporation of ceria into the catalyst structure significantly improved the redox ability of the catalyst.

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In the present study, mono and bi-metallic catalysts containing Cr and Co were prepared by impregnating the hydrothermally prepared mesoporous KIT-6 support with 5–10 wt% total metal content. The well-ordered three-dimensional mesoporous structure of the KIT-6 support was confirmed by small angle X-ray diffraction (XRD) patterns. N2 adsorption-desorption analysis results showed that the mesoporous structure of KIT-6 was preserved after metal loading. Structural bonds of KIT-6 support and prepared catalysts were determined by Fourier-transform infrared (FT-IR) spectroscopy. The pyridine adsorbed diffuse reflectance FT-IR (DRIFT) spectroscopy results revealed the presence of Lewis acid sites on the surface of the catalysts. Activity experiments were carried out in a microwave-heated continuous-flow fixed bed reactor system at temperature range of 350–650 °C and feed ratios of Ethane/Argon: 1/2, 1/1, 2/1 with a gas hourly space velocity (GHSV) of 18,000 ml/h.gcat. The 5Cr@KIT-6 catalyst exhibited high ethane conversion (63.5%) while the highest ethylene/hydrogen ratio (0.98) was obtained with the 2.5Cr2.5Co@KIT-6 catalyst at 450 °C. It was concluded that high temperatures (above 450 °C) facilitate the formation of side reactions and the production of aromatic compounds. The high catalytic activities of mesoporous catalysts were thought to be due to hot spots in the microwave reactor system.

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Highlights:Graphical/Tabular Abstract  Preparation of hydroxyapatite using eggshell wastes  Evaluation of hydroxyapatite in the adsorption of Remazol N.Blue RGB dye  Investigation of adsorption kinetics of Remazol N.Blue RGB dye with hydroxyapatite Figure A. The removal of Remazol N.Blue RGB dye using hydroxyapatite synthesized from waste eggshellPurpose: In this study, it is aimed to remove Remazol N.Blue RGB (RB203) dye, which is commonly found in water and textile sector, using hydroxyapatite obtained from calcined waste eggshell. Theory and Methods:The colored wastewater from the textile industry reduces the light permeability of the water and leads to a decrease in the photosynthetic activity and increases the chemical oxidation need (COD) of the water. Adsorption is one of the most preferred methods for dye removal because of its low cost, cheapness, being easy to use, reusable and easily recovered adsorbents. In this study, hydroxyapatite was prepared by precipitation method for the removal of Remazol N.Blue RGB (RB203) from waters. Waste calcined eggshell was used as a calcium source and synthesis of hydroxyapatite materials were performed at three different pH medium (pH 9, 10 and 11). XRF, XRD and SEM analysis were carried out on eggshells before and after calcination. Synthesized hydroxyapatites were characterized by TGA-DTA, XRD and FTIR analysis. The effect of pH (2-12), amount of adsorbent (2-10 g / L) and dye concentration (25-200 mg / L) were investigated for adsorption experiments. Adsorption isotherm models (Langmuir, Freundlich, Temkin and Henry) were used to determine the adsorption mechanism. In order to examine the kinetics of the adsorption process, pseudo-first and second order kinetic equations were used. Results:In this study, waste eggshells were characterized and about 97% of eggshell was determined as CaCO3-calcite phase. It was observed in XRD results that CaCO3 was transformed into CaO phase during calcination at 900 o C. TGA-DTA analysis of synthesized hydroxyapatite revealed that the hydroxyapatite did not undergo structural change up to 1000° C. XRD and FTIR analysis showed that the prepared hydroxyapatite materials were pure hydroxyapatite-Ca10(PO4)6(OH)2. At the end of characterization studies pH 10 was considered as better condition to obtain hydroxyapatite structure. Adsorption of RB203 was carried out with the hydroxyapatite prepared from waste calcined eggshell at this pH medium. In the experiments, related with pH effect on the adsorption, the highest dye removal was obtained at pH 2 medium, because of anionic character of RB203 and positively charged hydroxyapatite. It was seen that the adsorption process of RB203 reached equilibrium in 120 minutes. When the adsorption isotherm models were compared in terms of correlation coefficients (R 2 ), it was seen that Langmuir, Freundlich and Temkin isotherm models were in good agreement with the experimental data. The highest adsorption capacity obtained with the Langmuir isotherm model was 27.93 mg/g. The adsorption kinetic r...