Nữa nè:
oxide nanoparticles supported on mesoporous MgO and CeO2: A comparative physicochemical and catalytic study
Abstract
Iron (III) containing nanoparticles with superparamagnetic behaviour are prepared via deposition on various mesoporous supports (MgO, CeO2 and SBA-15). XRD, TEM-EDX, N2 physisorption, FTIR, and Moessbauer spectroscopy are used for their characterization. The reductive properties and catalytic behaviour in methanol decomposition of the materials are also studied. Depending on the chemical nature of the support, the predominant formation of: isolated iron species, strongly interacting with the support (for SBA-15), mixture of hematite and binary MgFe2O4 nanoparticles (for MgO) or almost homogeneously dispersed hematite particles (for CeO2) are observed. The state of iron species strongly affects their catalytic properties. The favorable effect of the support mesoporosity on the catalytic activity is most pronounced for the iron modified CeO2.
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Crystallography and porosity effects of CO conversion on mesoporous CeO2
Abstract
Catalytic properties and thermal stability were studied for samples of mesoporous ceria with different BET specific surface area. The catalytic conversion of carbon monoxide to carbon dioxide and how thermal treatments of the catalysts influence the catalytic properties have been investigated. The materials were studied by transmission electron microscopy and by conversion profile measurements of CO versus temperature using a plug flow micro reactor made in quartz glass only. In order to compare the catalytic properties associated with a specific structure or morphology directly, aliquots of surface area (0.6 m2) of the catalyst was used. Scanning electron microscopy and X-ray energy-dispersive spectrometry (XEDS) were used for surface morphology studies and elemental analysis. It was found that the proportion of {1 0 0} surfaces determine the catalytic properties of the material and these surfaces become important at calcination temperatures between 773 and 973 K. The internal mesoporous structure is destroyed at calcination temperatures around 873 K.
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Vapor phase hydrogenation of phenol over palladium supported on mesoporous CeO2 and ZrO2*1
Abstract
Mesoporous CeO2 and ZrO2 were synthesized using hexadecyltrimethyl ammonium bromide (C16TMABr) as the template. Their physicochemical properties were investigated using X-ray diffraction (XRD) and N2 adsorption–desorption methods. Palladium (Pd) 1–10 wt.% was loaded on the mesoporous CeO2 and ZrO2 by deposition–precipitation method. The Pd metal surface area, dispersion and crystallite sizes were determined by room temperature H2 chemisorption on reduced samples. The catalytic activity of Pd supported mesoporous CeO2 (Pd/CeO2-MS) and ZrO2 (Pd/ZrO2-MS) were evaluated for the first time in the vapor phase hydrogenation of phenol in the temperature range between 160 and 230 °C at atmospheric pressure. The reaction over 3% Pd/CeO2-MS at 180 °C offered cyclohexanone as the major product (about 50%) along with some amounts of cyclohexanol (about 35%) and cyclohexane (about 15%). The influences of Pd loading, temperature, H2/phenol ratio, contact time, and nature of solvent on the catalytic performance were investigated systematically. A 3% Pd/ZrO2-MS offered slightly lower phenol conversion but very high selectivity of cyclohexanone (above 90%). The Pd/CeO2-MS exhibited a stable activity, while Pd/ZrO2-MS underwent deactivation during on-stream operation. Under similar operating conditions, the catalytic performance of Pd/CeO2-MS and Pd/ZrO2-MS was found to be far better than that obtained using MgO, Al2O3 and MgO-Al2O3 derived from hydrotalcites (MgAl-CHT) as supports. The benefit of using mesoporous oxide support to Pd was also demonstrated by comparing the catalytic activity with the activities of commercial oxide supports.
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Investigations of mesoporous CeO2–Ru as a reforming catalyst layer for solid oxide fuel cells
Abstract
Two types of ceria (CeO2) materials: mesoporous powders and mesoporous flowerlike microspheres have been synthesized. The products were characterized by XRD, SEM, TEM and N2 sorption measurements. Solid oxide fuel cells (SOFCs) with a reforming catalyst layer applied on the anode side were fabricated and operated with iso-octane/air/H2O/CO2 fuel mixtures. The fuel cells with a porous catalyst layer yield much higher maximum power density than those without a catalyst layer. In particular, the performance of the fuel cell with a flowerlike mesoporous CeO2–Ru microsphere catalyst layer is obviously improved, producing maximum power density up to 0.654 W cm−2 at 600 °C. Electrochemical impedance spectroscopy (EIS) analysis showed the kinetic characteristic of anode reactions in the fuel cell with porous CeO2–Ru microsphere catalyst layers was significantly enhanced.
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