Results 1 - 10 of 2800
Results 1 - 10 of 2800. Search took: 0.028 seconds
|Sort by: date | relevance|
[en] Dehydrogenation of propane (DHP) was studied over a series of Cr2O3-Al2O3 and Cr2O3-SiO2 catalysts, prepared by incipient wetness impregnation and sol gel (SG) method, respectively, to gain a better understanding of the nature and distribution of chromium (Cr) species and their catalytic function. To this end, the catalysts were characterized by N2-physisorption and X-ray diffraction (XRD). N2-physisorption analysis of Cr2O3-SiO2 showed the relatively higher surface area of 391.1 m2/g, compared with Cr2O3-Al2O3 of 224.3 m2/g. The combination method of sol gel and sonothermal also produced smaller particles size of catalyst with higher microporosity of 23.5 % and smaller pores size of 6 nm. The good surface properties of Cr2O3-SiO2 enabled the high conversion of propane of 55 % at 550 degree Celsius. At higher temperature of 600 degree Celsius, the Cr species might be reduced into lower oxidation state and inhibit the catalytic behavior to produce hydrogen. (author)
[en] Topaz [Al2SiO4(F,OH)2] is a subduction-related mineral that is found in metasediments and has a large pressure and temperature stability field. Here, we use luminescence spectroscopy of Cr3+ to probe the Al site in topaz at pressures up to ~60 GPa, which corresponds to a depth of ~1400 km in the Earth. This technique allows us to probe all three unique Al environments (i.e., [AlO4(OH)2]7–, [AlO4(F)2]7–, and [AlO4OH,F]7–) simultaneously under high pressure. We find that the R-line luminescence from all three Al environments shift linearly to longer wavelength to ~40 GPa. Above ~40 GPa, they shift nonlinearly and begin to flatten out at ~48 GPa, with a pressure shift of ~0 cm–1/GPa from ~48–55 GPa. Our results, combined with previous high-pressure single-crystal X-ray diffraction studies to ~45 GPa, strongly indicate that there is a change in the compression mechanism in topaz above ~40 GPa. Furthermore, our high-pressure room-temperature results show that the metastable persistence of topaz on compression represents one of the most extreme cases among tetrahedrally coordinated silicates.
[en] Chromium and bromide ions inside the artificial crevice of Fe-18%Cr∼12%Ni-2%Mo alloy was successfully investigated by the in situ X-ray Absorption Fine Structure (XAFS) measurement. A cross-section of 0.1mm thick stainless steel foil sandwiched with Kapton films attached solution reservoir above contained 1M LiBr solution was dissolved at 0.8V (vs. Ag/AgCl) to form the artificial crevice. When the crevice reached several mm in depth, concentrations and coordination states of dissolved chromium ion and bromide ion were investigated by the transmission XAFS measurement, which was carried out at BL-7C in Photon Factory, KEK, JAPAN. Concentrations of chromium and bromide ions inside the artificial crevice were almost lineally decreased from metal/solution interface towards bulk solution. A concentration of bromide ion at the metal/solution interface was estimated as approximately 10M, which was close to solubility of FeBr2. Coordination states of dissolved chromium ion and bromide ion were also investigated at different positions from the metal/solution interface inside the artificial crevice, close to interface, the middle of the crevice and close to bulk solution. No change of coordination states of chromium ion was observed. Structures of bromide ion, on the other hand, were changed with positions. Distance between bromide ion and the nearest ion near the interface was shorter than those at middle of the artificial crevice or position close to bulk solution. These results are consistent with a theory that the change of the distance from bromide ion to the nearest atoms might relate to a formation of hydrobromo-complex near the metal/solution interface
[en] Complete text of publication follows. Continuous extraction device was used to follow the evolution of Cr(VI) enrichment with Aliquat 336 (trioctyl methyl ammonium chloride) in time. Only chloroform which ensures the needed difference in density was used in order to have a proper run of the extraction instrument. The extraction process was followed with a flame atomic absorption spectrometer (FAAS). The chromium content of the organic phase was measured with GFAAS method. A mixing vessel, volume 7,5 mL is connected with a reservoir of sample solution by a glass capillary. In the bottom of the mixing vessel there is 2 mL organic phase, chloroform in which complex forming agent is solved. A magnetic stirrer disintegrates the chloroform into small droplets. The sample is continuously sucked through this mixed phase into the flame of FAAS instrument. Using 100 mL of dichromate containing solution in the extraction device and 2 mL Aliquat 336 solution in chloroform for extraction we obtain a 50-fold enrichment. After this extraction the chromium content of the organic phase was determined with GFAAS method. The limit of detection of GFAAS for chromium was improved to 1 ng/L (1 ppt). This method is generally useful for planning continuous extractions, establishing the metal/complexing agent ratio and effective enrichment of elements in ultra trace level. The single drop microextraction was modified so, that instead of hanging 3-4 μL droplet a 30 μL drop was placed to the bottom of a flowing microvessel to stabilize the continuous extraction and for accurate pipetting the drop to the graphite tube of GFAAS instrument. After optimization of this method the performance was compared to conventional and the continuous liquid-liquid extractions.
[en] Two novel poly(amidoamine) (PAMAM) dendrimers, comprising rhodamine B unit in the core and 1-phenyl-3-methyl-5-pyrazolone unit at the periphery, have been synthesized and characterized. Both dendrimers displayed high selectivity and sensitivity towards Cr3+ ion. As considering the potential of being applied as fluorescent sensors for Cr3+ ion, we studied the complexes formed between the dendrimers and Cr3+ ion. Different PAMAM dendrimers had different recognition mechanism towards Cr3+ ion. For dendrimer G2, the recognition of Cr3+ was mainly due to the ring-opening of spirolactam. However, it significantly depended on the simultaneous effect of ring-opening of spirolactam and photoinduced electron transfer (PET) in the case of dendrimer G3. - Highlights: → First synthesize two novel PAMAM simultaneously containing rhodamine and pyrazolone. → Novel dendrimer show high selectivity and sensitivity towards Cr3+. → Recognition Cr3+ of dendrimer G2 is dominantly due to the ring-opening mechanism. → Sensing Cr3+ of dendrimer G3 is dependent on simultaneous mechanisms of ring-opening and PET.
[en] This study was carried out to investigate the feasibility and removal efficiency of Cd (II) and Cr(III) ions removal from the simulated wastewater solution by using slag media type filter. The results of the slag filter were compared to conventional sand filter at the point of view of effluent quality and removal performance. The obtained effective size and coefficient uniformity were 0.45mm and 1.67 in slag, 0.46mm and 1.35 in sand respectively. At pH 7, imulated wastewater, 100mg Cd/l was passed through both filter columns. The slag filter showed 60 to 80 percent removal efficiency of the initial Cd concentration, while the sand filter showed only 5 to 10 percent. Optimum pH value for Cd removal showed 7, obtained optimum back wash frequency of slag column was 1.5 times less than of sand. With the simulated wastewater having ionic concentration of pH 7 the removal efficiency of the slag column and metal concentration of 100ml/l revealed 99.7 percent during 62 hrs, while that of the sand column was 28.5 percent. (Author)