Influence of the preparation method on the activity of ceria zirconia mixed oxides for naphthalene total oxidation (original) (raw)
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Efficiency of manganese modified CTAB-templated ceria-zirconia catalysts in total CO oxidation
Applied Surface Science, 2019
CTAB templated Ce 0.8 Zr 0.2 O 2 (CZ), MnO x-Ce 0.8 Zr 0.2 O 2 (Mn-CZ), CeO 2 and MnO x oxide catalysts were prepared by precipitation and tested in CO oxidation. Manganese was added to CZ oxide at the precipitation stage (Mn-CZ) or by impregnation of the precipitated CZ oxide with manganese salt (Mn-CZ IM). Despite the decrease in the specific surface area after modification with Mn, both Mn-modified catalysts showed the significant improvement in the catalytic performance. Mn-CZ IM exhibited better catalytic activity than Mn-CZ, which was explained by the different distribution of manganese in CZ found by the complex SEM-EDS, XRD, TPR, Raman spectroscopy, XPS, and EPR study. In Mn-CZ both Mn 2+ and Mn 3+ ions are incorporated into the CZ lattice and form particles of MnO x phases uniformly distributed over the surface and in the bulk of CZ. In contrast, in Mn-CZ IM no manganese ions are embedded into the crystal lattice of CZ, while the surface of Mn-CZ IM comprises local areas mainly formed by CZ or MnO x. Such arrangement provides the additional adsorption sites and the second redox pair (Mn 3+ /Mn 2+) in addition to Ce 3+ /Ce 4+ , improving low-temperature efficiency, whereas the surface areas depleted with MnO x serve as a source of the active oxygen from the CZ lattice, enhancing CO oxidation at high temperatures.
Catalysis Today, 2008
The influence of cerium salt/urea ratio on the activity of nanocrystalline ceria catalysts prepared by homogeneous precipitation with urea for the complete oxidation of naphthalene has been evaluated. Ceria catalysts were prepared from five different cerium salt/urea ratios (2:1, 1:1, 1:2, 1:3 and 1:4). Catalyst characterization (by BET, XRD and TPR) only revealed subtle differences in the characteristics of these catalysts with cerium salt to urea ratio. However, Raman and scanning electron microscopy (SEM) results indicated differences in the oxygen defect concentration (FWHM of Raman band) and morphology of the catalysts with variation of the preparation ratio. Catalysts prepared with 2:1, 1:1 and 1:4 were significantly more active than those prepared from 1:2 and 1:3 ratios. A relationship between the concentration of oxygen defects and naphthalene oxidation activity has been established. The activity of the catalysts is thought to be related to a combination of oxygen defect concentration, surface reducibility and morphology.
Materials Today Chemistry, 2020
Mesoporous Ce 0.75 Zr 0.25 O 2 solid solution powders were successfully synthesized by a co-precipitation method. A combination of 10 wt% copper oxide, manganese oxide, and nickel oxide was added to the Ce 0.75 Zr 0.25 O 2 support by impregnation method and calcined in the air with a flow rate of 2 ml s À1 at 400 C for 4 h. All catalysts were characterized using Hydrogen Temperature Programmed Reduction (H 2-TPR), X-ray Diffraction (XRD), and Brunauer-Emmet-Teller (BET) isotherm methods to find the interaction between metals, the crystallinity of the catalyst, surface area and pore volume of the catalyst, respectively. The 3.3% CuO-3.3% MnO 2-3.3% NiO/Ce 0.75 Zr 0.25 O 2 catalyst showed higher catalytic activity for benzene oxidation with benzene conversion of 90% at 250 C and weight hourly space velocity (72,000 mL g À1 h À1) when compared to one metal oxide only. This finding presents a high activity and low-cost catalysts for removing a very lean concentration of benzene containing in the industrial flue gas at low temperatures.
Catalysis Communications, 2009
A study on the structural and morphological characterization of a ceria-zirconia-supported copper oxide (with nominal composition CuO x /Ce 0.5 Zr 0.5 O 2 ) and on its catalytic activity for the oxidation of propylene is reported. XRD and spectroscopic analyses show that the supported phase is highly dispersed over the support constituted by a fluorite-like ceria-zirconia solid solution. FT-IR spectra of adsorbed pyridine evidence the presence of Lewis acid sites. Propylene reacts with the catalyst surface and according to a Mars van Krevelen mechanism giving rise upon increasing the temperature to propanal, propanoate, small amounts of acrylate, acetate plus formiate and finally CO 2 .
Catalysis Letters, 2020
A set of cerium–manganese–copper oxide catalysts with various foreign metal contents was prepared via the solution combustion synthesis (SCS). The catalysts were characterized by complementary techniques such as N2 physisorption at − 196 °C, X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), H2-temperature-programmed reduction (H2-TPR), O2-temperature-programmed desorption (O2-TPD) and X-ray photoelectron spectroscopy (XPS). Their catalytic activity was tested towards the VOC oxidation using ethylene and propylene as probe molecules. As a whole, it has been observed that the Ce55Mn45 sample (Mn 45 at.%), containing MnOx clusters interacting with the ceria phase, was the most active catalyst for propylene oxidation, exhibiting a complete conversion at 250 °C. On the other hand, the ternary oxide catalyst (Ce55Mn22.5Cu22.5 with Mn = 22.5 at.% and Cu = 22.5 at.%) has exhibited the best results for the oxidation of ethylene. These findings suggest that the co-...
Applied Catalysis B: Environmental, 2011
A Ce-Zr-Cu oxide system with a flower-like morphology was prepared by a slow co-precipitation method in the absence of any structure directing agent. Four portions of the oxide were thermally treated at four different temperatures (350 • C, 450 • C, 550 • C, 650 • C). The resulting materials samples were characterized by quantitative XRD, adsorption-desorption of N 2 at-196 • C, SEM and TEM microscopy, -H 2 -TPR, XPS and Operando-XANES. All samples were tested in the preferential CO oxidation (CO-PROX) in the 40-190 • C temperature range. Thermal treatments were found to induce slight structural changes without altering the starting morphology of the samples. The samples treated at higher temperature 550-650 • C showed a quite interesting CO-PROX activity and selectivity in a temperature range suitable for a practical use within the FEMFC technology. (M. Lenarda).
Chinese Journal of Catalysis, 2011
Ceria-zirconia (CZ) and ceria-terbia (CT) and alumina-supported ceria-zirconia (CZA) and ceria-terbia (CTA) solid solutions were synthesized by coprecipitation and deposition precipitation methods, respectively. Structural characteristics and catalytic activity of the synthesized samples have been investigated using X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy (RS), and Brunauer-Emmett-Teller (BET) surface area measurements. To evaluate the catalytic properties, total oxygen storage capacity and CO oxidation activity measurements were carried out. The XRD analyses revealed the formation of Ce 0.75 Zr 0.25 O 2 phase for CZ and Ce 0.5 Zr 0.5 O 2 and Ce 0.6 Zr 0.4 O 2 phases for CZA samples, respectively. While the formation of only Ce 0.8 Tb 0.2 O 2-phase was noted for both CT and CTA samples. All the supported and unsupported samples adopted a fluorite-type structure and exhibited cell parameters with respect to Vegard's rule. The HRTEM results indicated well-dispersed particles of the size around 5 nm. The RS measurements suggested the presence of oxygen vacancies due to defective structure formation. The XPS studies revealed the presence of cerium in both Ce 4+ and Ce 3+ oxidation states in different proportions. It was found that CO oxidation for CTA occurs at very much lower temperature than CT, CZ, and CZA samples. Details of these findings by correlating with the structural characterization studies are consolidated.
The Role of Different Types of CuO in CuO–CeO2/Al2O3 for Total Oxidation
Catalysis Letters, 2014
The binary metal oxide, CuOACeO 2 /c-Al 2 O 3 , has been compared with the single oxide components CuO/ c-Al 2 O 3 and CeO 2 /c-Al 2 O 3 for toluene total oxidation. The nature of the active sites was determined by means of several spectroscopic techniques, while the transient response technique TAP (Temporal Analysis of Products) was used to investigate the catalytic performance.
Colloids and Surfaces A-physicochemical and Engineering Aspects, 2003
Copper was introduced to zirconium-based catalysts using three methods before calcination at 600 • C: (i) coprecipitation of copper nitrate and zirconium oxychloride, (ii) wet impregnation of copper nitrate on zirconium oxyhydroxide (ZrO(OH) 2 ), (iii) or on zirconium oxyhydroxide previously calcined at 600 • C (ZrO 2 ). Two atomic ratios (Cu/Zr = 0.01 and 0.1) were prepared. The crystallization phase of the catalysts was evidenced by X-ray diffraction (XRD). Copper stabilizes the metastable tetragonal phase of zirconia for the samples prepared by coprecipitation and by impregnation over oxyhydroxide. Electron paramagnetic resonance (EPR) study of Fe 3+ isolated ions allowed also to evidence the stabilization of this phase. Moreover, this technique evidenced the presence of two types of paramagnetic copper species that occupy the same sites: the isolated copper ions in octahedral environment, which is lacunal in the case of the coprecipitates and the clusters. The activity of these catalysts for the complete oxidation of propene was investigated. The impregnated samples have shown better catalytic activities than the coprecipitated ones. EPR study and surface area measurements by the BET method, after the catalytic test, were done in order to detect an eventual deactivation of the catalysts. A decrease in the surface area due to water formation during oxidation reaction, accompanied by a structural change on the surface of the catalyst from tetragonal to monoclinic phase, was detected for the coprecipitates and that impregnated over oxyhydroxide samples. The catalysts copper impregnated over ZrO(OH) 2 previously calcined at 600 • C have combined the best activity and the best resistance towards deactivation. (J.-F. Lamonier). their release begins to be severely regulated. VOCs coming from automobiles must decrease by 24% in Europe between 1993 and 2010 [1]. Moreover, for industries, in compliance with the stringent environmental regulations, catalytic oxidation can effectively destroy VOC at much lower temperatures than thermal oxidation. The advantage of low oxidation
Applied Catalysis A: General, 2005
CeO 2 nano-crystals were synthesized by a sol-gel process and then used as support for CuO/CeO 2 (sol-gel) catalysts prepared via impregnation method. For comparison, the commercial CeO 2 was also used as a support for CuO/CeO 2 (commercial) catalysts prepared via the same method. The samples were characterized by means of BET, XRD, UV-vis, TPR and XPS. The catalytic properties of the CuO/CeO 2 catalysts for low-temperature CO oxidation were studied by using a microreactor-GC system. The prepared spherical CeO 2 nano-crystals have much smaller particle size, better crystallinity and larger surface area than the commercial CeO 2 . XPS analysis indicated the presence of reduced copper species in the CuO/CeO 2 catalysts. TPR showed that there are different copper species in the catalysts. The influence of calcination time, temperature and CuO loadings on the catalytic activity of CuO/CeO 2 catalysts has been studied. The CuO/CeO 2 (sol-gel) catalysts exhibited higher catalytic activity than the CuO/CeO 2 (commercial) catalysts. Compared with CuO/CeO 2 catalysts prepared via other techniques, our catalysts exhibited similar or even better catalytic performance. # Fig. 4. XRD patterns of CuO/CeO 2 catalysts with various CuO loadings: (a) CuO/CeO 2 (sol-gel); (b) CuO/CeO 2 (commercial).