Engineering the shape and size of catalyst particles and the interface between different components of heterogeneous catalysts at the nanometer level can radically alter their performances. This is particularly true with CeO2-based catalysts, where the precise control of surface atomic arrangements can modify the reactivity of Ce4+/Ce3+ ions, changing the oxygen release/uptake characteristics of ceria, which, in turn, strongly affects catalytic performance in several reactions like CO, soot, and VOC oxidation, WGS, hydrogenation, acid–base reactions, and so on. Despite the fact that many of these catalysts are polycrystalline with rather ill-defined morphologies, experimental and theoretical studies on well-defined nanocrystals have clearly established that the exposure of specific facets can increase/decrease surface oxygen reactivity and metal–support interaction (for supported metal nanoparticles), consequently affecting catalytic reactions. Here, we want to address the most recent developments in this...

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Ceria Catalysts at Nanoscale: How Do Crystal Shapes Shape Catalysis?

A series of cerium ion-doped titanium dioxide (Ce 3+ –TiO2) catalysts with special 4 f electron configuration was prepared by a sol–gel process and characterized by Brunauer-Emmett-Teller method, X-ray diffraction, X-ray photoelectron spectroscopy (XPS), UV–vis diffuse reflectance spectroscopy (DRS), and also photoluminescence (PL) emission spectroscopy. The photocatalytic activity of Ce 3+ –TiO2 catalysts was evaluated in the 2-mercaptobenzothiazole (MBT) degradation in aqueous suspension under UV or visible light illumination. The experimental results demonstrated that the overall photocatalytic activity of Ce 3+ –TiO2 catalysts in MBT degradation was signigicantly enhanced due to higher adsorption capacity and better separation of electron-hole pairs. The experimental results verified that both the adsorption equilibrium constant (Ka) and the saturated adsorption amount (Gmax) increased with the increase of cerium ion content. The results of XPS analysis showed that the Ti 3+ ,C e 3+ , and Ce 4+ ions reside in the Ce 3+ –TiO2 catalysts. The results of DRS analysis indicated that the Ce 3+ –TiO2 catalysts had significant optical absorption in the visible region between 400 and 500 nm because electrons could be excited from the valence band of TiO2 or ground state of cerium oxides to Ce 4 f level. In the meantime, the dependence of the electron-hole pair separation on cerium ion content was investigated by the PL analysis. It was found that the separation efficiency of electron-hole pairs increased with the increase of cerium ion content at first and then decreased when the cerium ion content exceeded its optimal value. It is proposed that the formation of two sub-energy levels (defect level and Ce 4 f level) in Ce 3+ –TiO2 might be a critical reason to eliminate the recombination of

for 2-mercaptobenzothiazole degradation in aqueous suspension for odour control

Fe doped CeO2 nanosheets as Fenton-like heterogeneous catalysts for degradation of salicylic acid

Catalytic partial oxidation of methane (CPO) to synthesis gas was performed over differently prepared CeO 2 supported nickel catalysts with 6 wt% Ni content. The samples were synthesized by microwave assisted procedures and by hydrothermal deposition procedure. Differences in the catalyst structural properties of the prepared catalysts were detected by XRD, TPR and XPS measurement. When tested at atmospheric pressure with feed gas mixture containing methane and oxygen in molecular ratio CH 4 /O 2  = 2, all the samples reached 98% conversion with CO selectivity values >95% in the 700–800 °C temperature range. The samples exhibited different behavior towards carbon formation during the tests. Moreover, according to XRD, XPS and TGA results, when the carbon was formed it did not cause catalyst deactivation. TPR profiles confirmed different degree of chemical interaction between NiO and CeO 2 support, depending on the preparation method. The building up or the easy removal of carbon during the CH 4 temperature programmed surface reaction (TPSR), substantiate the role of the CeO 2 lattice oxygen mobility, enhanced by metal-support interaction, in the removal of the deposited carbon through CO evolution. Structure-activity relationship established a close dependence of the CPO performance on the combination of NiO and CeO 2 crystallite sizes and the interaction between the two.

Ni/CeO2 catalysts for methane partial oxidation: Synthesis driven structural and catalytic effects

Synthesis and enhanced photocatalytic property of Ni doped ZnS nanoparticles

Morphology controlled synthesis and photocatalytic activity of zinc oxide nanostructures

In this communication, we investigate the Heterogeneous Fenton-like oxidation of methylene blue in model waste water over ceria based nanocatalysts Modification of ceria nanoparticles with oxides of Fe, Cu, Zr, La and Dy is carried out via wet impregnation and deposition precipitation methods The synthesized catalytic systems are well characterized by X-Ray Diffraction technique, Electron microscopy (TEM &SEM), Raman spectral study, FTIR spectroscopy, UV-DR Spectra and BET surface area analysis Among the prepared catalysts, copper oxide modified ceria system is found to be the most effective for the mineralization of methylene blue It is concluded that oxygen vacancies and Ce 3+ ions in the catalyst have prominent role in deciding the performance of M/CeO 2 catalysts in Fenton-like oxidation reactions Besides this, the decisive role of redox potential of the doped metal ions on the efficiency of nanoceria in Fenton-like oxidation has also been examined for the first time in literature A correlation between redox potential of doped metal ions and the oxidation activity is also established

Modulated heterogeneous Fenton-like activity of ‘M’ doped nanoceria systems (M = Cu, Fe, Zr, Dy, La): Influence of reduction potential of doped cations

Herein we present the exceptionally high oxygen buffer action of ceria quantum dots of size 3.7 nm. Ceria nanoparticles were obtained via a facile ammonia precipitation route, and were characterized using TEM, XRD, BET surface area analysis, XPS analysis and TPR study using H2 as the probe molecule. A supercharging effect that leads to low temperature oxygen release is observed in these ultra-fine ceria particles. Existence of under stoichiometry in the ceria nanostructures with practically no oxygen vacancies has been substantiated with experimental proof.

Supercharged ceria quantum dots with exceptionally high oxygen buffer action

Herein, we project the efficiency of cerium oxide nanostructures in humidity sensing. Truncated octahedral particles, rods, cubes and octahedral particles have been synthesized by adopting different synthesis routes to this effect. The obtained systems are well characterized by Fourier Transform Infrared spectroscopy (FTIR), X-Ray Diffraction (XRD) analysis, Electron microscopic analysis (SEM &TEM), Brunauer Emmet Teller (BET) surface area analysis, Raman spectroscopy and photoluminescence spectroscopy. The exponential decrease in the resistance of thin films of ceria nanostructures upon increase in relative humidity in the surroundings is investigated. The promising response of ceria nano systems towards humidity suggests their utility in environmental applications.

Nanoceria based thin films as efficient humidity sensors

We project a reduced graphene oxide-fluorescein sensor moiety that offers a quick, selective and sensitive optical response to the presence of a noxious heavy metal ion, mercury (Hg2+) in aqueous solution. A turn off and turn on optical response is envisaged by the unit on competitive adsorption of fluorescein and mercury ions on reduced graphene oxide sheets. The crux behind the sensing of Hg2+ ion by the reduced graphene oxide-fluorescein unit lies behind the decrease in absorbance/fluorescence intensity of the dye on complexing with reduced graphene oxide and the corresponding restoration of the optical response upon highly selective competitive adsorption of Hg2+ ions by reduced graphene oxide sheets. Quantification of these optical responses was attained by colorimetric and fluorimetric measurements, which yielded ppb level and ppt level mercury ion assay. The LOD values were 240 ppb and 780 ppt respectively for these analytical methods. The moiety is highly selective and specific for mercury ions over alkali, alkaline earth metals and its congeners. The significant advance in this investigation is the fabrication of a reduced graphene oxide-fluorescein unit as a qualitative read out tool for naked eye detection of Hg2+ ions in ppm levels noting the colour and for the visual detection of ppt levels of Hg2+ through fluorescence in UV light. A highly efficient GFU immobilized filter paper strip was developed which could sense Hg2+ under UV light in a concentration as low as ppb level. Moreover, investigations on tap water samples spiked with Hg2+ ions underlines that the reduced graphene oxide-fluorescein moiety can swiftly monitor Hg2+ levels in complex solutions and demonstrates its potential utility in practical applications.

T. Divya

Papers

Morphology controlled synthesis and photocatalytic activity of zinc oxide nanostructures

Modulated heterogeneous Fenton-like activity of ‘M’ doped nanoceria systems (M = Cu, Fe, Zr, Dy, La): Influence of reduction potential of doped cations

Supercharged ceria quantum dots with exceptionally high oxygen buffer action

Nanoceria based thin films as efficient humidity sensors

An elegant and handy selective sensor for ppt level determination of mercury ions