ABSTRACT
This work emphasizes the dry reforming of methane (DRM) reaction on citrate sol-gel-synthesized double perovskite oxides. Phase pure La2NiMnO6 shows very impressive DRM activity with H2/CO = 0.9, hence revealing a high prospect of next-generation catalysts. Although the starting double perovskite phase gets degraded into mostly binary oxide phases after a few hours of DRM activity, the activity continues up to 100 h. The regeneration of the original double perovskite out of decomposed phases by annealing at near synthesis temperature, followed by the spectacular retention of activity, is rather interesting and hitherto unreported. This result unravels unique reversible thermal switching between the original double perovskite phase and decomposed phases during DRM without compromising the activity and raises challenge to understand the role of decomposed phases evolved during DRM. We have addressed this unique feature of the catalyst via structure-property relationship using the in situ generated molecular level nanocomposite.
ABSTRACT
Cerium oxide particles with different morphologies, namely nanoparticles, nanofibers, nanocubes, and rice grains have been prepared by simple chemical routes. The shape and size of the synthesized morphologies have been studied using field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). X-ray diffraction (XRD) and selected area electron diffraction (SAED) techniques have been used to determine their crystal phases. Both nanoparticles and nanocubes of cerium oxide exclusively crystallize in fluorite structure of CeO2 as observed in XRD patterns, whereas nanofibers and rice grains are characterized by the presence of CeO2, Ce2O3, and Ce(OH)3 phases. X-ray photoelectron spectroscopy (XPS) has been employed to evaluate Ce species present in the different cerium oxide morphologies and to estimate their relative surface concentrations. As evident from Ce 3d core level spectra cerium oxide nanoparticles and nanocubes are basically CeO2 having Ce in the +4 oxidation state along with some amount of Ce3+ species. In contrast, Ce is in +3 oxidation state on its surface in cerium oxide nanofibers and rice grains that contain intermediate phases like Ce2O3 and Ce(OH)3 as endorsed by XRD patterns. CO oxidation has been carried out over these cerium oxide morphologies and among all morphologies lowest temperature CO oxidation has been demonstrated by the nanocube morphology.
ABSTRACT
Correction for 'Citrate combustion synthesized Al-doped CaCu3Ti4O12 quadruple perovskite: synthesis, characterization and multifunctional properties' by Kamalesh Pal et al., Phys. Chem. Chem. Phys., 2020, 22, 3499-3511, DOI: 10.1039/C9CP05005A.
ABSTRACT
The facile synthesis of the Al-doped CaCu3Ti4O12 quadruple perovskite, a well-known and vastly studied material for various technological applications, using the modified citrate combustion route along with structural, microstructural, and X-ray photoelectron spectroscopic (XPS) characterization and magnetic, dielectric and electrical properties has been investigated and reported here. The possible applications of the material as a Schottky barrier diode (SBD) in optoelectronic devices and as a catalyst in methanol steam reforming (MSR) reaction for hydrogen generation, hitherto unreported in the open literature, have also been explored. The compound is crystallized in the cubic body centered Im3[combining macron] space group and the particle size is found to be in nanodimension with rather narrow size distribution. The enhanced resistivity could be attributed to the grain boundary effect, and consequently, it exhibits better performance as a SBD compared to the undoped sample. Desired cationic composition with expected valence states within the probe range is confirmed by XPS analysis. A better catalytic activity towards MSR is noticed for the Al-doped CaCu3Ti4O12 compared to the undoped composition. These new findings, namely MSR activity and applicability in the Schottky device, have highlighted further the multifunctional nature of the material in energy related issues and would thus be of interest to the materials community searching for functional materials.
ABSTRACT
We report an experimental study for the structural and magnetic properties of highly pure LaFe0.5Mn0.5O3 perovskite phase. The impurity free LaFe0.5Mn0.5O3 has been prepared by sol-gel technique at 500 °C and annealed at different temperatures up to 1000 °C. Previous works on LaFe0.5Mn0.5O3 revealed presence of secondary phases along with contradicting magnetic properties. Such as, Bhame et al (2005 Phys. Rev. B 72 054426-7) reported the superparamagnetic or spin-glass like behavior for 200 °C treated sample that persisted even at 700 °C sample. However, Wei et al (2012 Mater. Chem. Phys. 136 755-61) claimed room temperature ferromagnetism in all the samples annealed in the range of 600 °C-700 °C where the saturation magnetization decreases with the increase in temperature. These contradicting results lead us to revisit the effect of annealing temperature on the magnetic properties of LaFe0.5Mn0.5O3. We noticed a gradual increase in magnetization with increase in annealing temperatures without any signature of long range spin ordering for pure single phase samples. The increased magnetic moment with annealing temperatures has been attributed to the suppression of surface contribution of disordered spin. The low temperature magnetic behaviors can be explained by the interacting cluster glass behavior for the pristine as well as for 1000 °C annealed samples.
ABSTRACT
Here, we report the luminescence based sensing of trace amounts of nitroaromatic explosive organic compounds. The luminescence emission of nanosized spinel oxide ZnCr2O4 with high chemical and thermal stabilities has been used as a potential probe to detect such organic explosives. Low temperature solution combustion synthesized ZnCr2O4 oxide with an average particle size of â¼9 nm exhibits strong luminescence emission at 410 nm upon excitation at 260 nm in an aqueous suspension. The presence of nitroaromatics in ZnCr2O4 suspension dramatically suppresses the luminescence emission providing an opportunity to detect it quantitatively. The detection limit for 2,4,6-trinitrophenol (TNP) is as low as 23 ppb. A number of organic compounds have been investigated for a comprehensive understanding. The astonishing sensitivity of ZnCr2O4 nanoparticles towards nitro explosives is appealing for sensing application. A plausible explanation of such luminescence quenching has been ascribed to a two-fold mechanism. The underling mechanism is further substantiated by a similar study on ZnO nanoparticles.
ABSTRACT
Nanocrystalline Ce(1)(-)(x)Ti(x)O(2) (0 < or = x < or = 0.4) and Ce(1-)(x)(-)(y)Ti(x)Pt(y)O(2)(-)(delta) (x = 0.15, y = 0.01, 0.02) solid solutions crystallizing in fluorite structure have been prepared by a single step solution combustion method. Temperature programmed reduction and XPS study of Ce(1)(-)(x)Ti(x)O(2) (x = 0.0-04) show complete reduction of Ti(4+) to Ti(3+) and reduction of approximately 20% Ce(4+) to Ce(3+) state compared to 8% Ce(4+) to Ce(3+) in the case of pure CeO(2) below 675 degrees C. The substitution of Ti ions in CeO(2) enhances the reducibility of CeO(2). Ce(0.84)Ti(0.15)Pt(0.01)O(2)(-)(delta) crystallizes in fluorite structure and Pt is ionically substituted with 2+ and 4+ oxidation states. The H/Pt atomic ratio at 30 degrees C over Ce(0.84)Ti(0.15)Pt(0.01)O(2)(-)(delta) is 5 and that over Ce(0.99)Pt(0.01)O(2)(-)(delta) is 4 against just 0.078 for 8 nm Pt metal particles. Carbon monoxide and hydrocarbon oxidation activity are much higher over Ce(1-)(x)(-)(y)Ti(x)Pt(y)O(2) (x = 0.15, y = 0.01, 0.02) compared to Ce(1)(-)(x)Pt(x)O(2) (x = 0.01, 0.02). Synergistic involvement of Pt(2+)/Pt degrees and Ti(4+)/Ti(3+) redox couples in addition to Ce(4+)/Ce(3+) due to the overlap of Pt(5d), Ti(3d), and Ce(4f) bands near E(F) is shown to be responsible for improved redox property and higher catalytic activity.
