Impact of induced chlorine-poisoning on the catalytic behaviour of Ce0.5Zr0.5O2 and Ce0.15Zr0.85O2 in the gas-phase oxidation of chlorinated VOCs (original) (raw)
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Catalysis Today, 2005
The complete oxidation of volatile organic compounds of different chemical natures, such as 1,2-dichloroethane, trichloroethylene and n-hexane, over Ce–Zr mixed oxide catalysts has been studied in a conventional fixed bed flow reactor. Catalytic conversion was found to depend on Ce/Zr molar content. The combination of surface acidity and accessible lattice oxygen appeared to control the catalytic performance of the mixed oxides. Thus, Ce0.5Zr0.5O2 showed the highest combustion activity for the abatement of chlorohydrocarbons, whereas pure ceria was found to be the most active in the oxidation of the non-chlorinated compound. Destruction efficiency for the three VOCs decreased in the order: n-hexane > 1,2-dichloroethane > trichloroethylene.Significant ‘mixture effects’ were noticed when a given chlorinated feed was decomposed in the presence of n-hexane. On one hand, the destruction of the mixture induced an inhibition of the reactivity of each compound, leading to a marked increase in the ignition temperature. Competitive adsorption played an important role in the inhibition detected with CeO2-based catalysts. On the other hand, HCl selectivity was greatly enhanced through the increased presence of water in the reaction atmosphere generated as a reaction product.
Combustion of aliphatic C 2 chlorohydrocarbons over ceria–zirconia mixed oxides catalysts
Applied Catalysis A-general, 2004
The complete oxidation of chlorinated aliphatic hydrocarbons, such as 1,2-dichloroethane, and trichloroethylene, over CexZr1−xO2-based catalysts has been studied using a conventional fixed bed flow reactor. The mixed oxide catalysts exhibited a higher activity with respect to the pure oxides, and catalytic conversion was found to depend on Ce/Zr molar content. Thus, Ce0.5Zr0.5O2 showed the highest combustion activity for the abatement of both chlorohydrocarbons. The combination of surface acidity and accessible lattice oxygen appeared to control the catalytic performance of the mixed oxides.The major oxidation products were CO2, HCl and Cl2 along with trace amounts of other chlorinated by-products, namely vinyl chloride and tetrachloroethylene, and carbon monoxide. The selectivity toward CO2 and Cl2 was found to be noticeably promoted with increasing cerium content. Thus behaviour was related to the high activity of ceria in CO and HCl oxidation to give Cl2 by the Deacon reaction.
Catalysis Today, 2012
A series of Ce-Zr mixed oxides with different composition have been characterized and used as catalysts in the catalytic wet oxidation (CWO) of phenol. The addition of Zr significantly enhanced the redox and catalytic activity of ceria. However, a catalytic activity drop occurred for zirconium contents higher than 80%, which is related with a ZrO 2 segregation observed in Zr-rich oxides. The effects of the temperature of reaction, the oxygen partial pressure and the phenol/catalyst ratio on the activity for the oxidation of phenol and the selectivity to CO 2 were also investigated. The values for CO 2 selectivities were greatly influenced by the formation of a carbonaceous deposit adsorbed on the catalyst surface. The results indicated that these C-deposits can be totally oxidized by selecting appropriate operating conditions, thus obtaining catalytic systems with a very promising performance for phenol abatement. A mechanism is proposed to interpret the role of the carbonaceous deposits in the oxidation of phenol as a function of the reaction conditions.
Performance, structure, and mechanism of CeO2 in HCl oxidation to Cl2
Journal of Catalysis, 2012
Experimental and theoretical studies reveal performance descriptors and provide molecular-level understanding of HCl oxidation over CeO2. Steady-state kinetics and characterization indicate that CeO2 attains a significant activity level, which is associated with the presence of oxygen vacancies. Calcination of CeO2 at 1173 K prior to reaction maximizes both the number of vacancies and the structural stability of the catalyst. Xray diffraction and electron microscopy of samples exposed to reaction feeds with different O2/HCl ratios provide evidence that CeO2 does not suffer from bulk chlorination in O2-rich feeds (O2/HCl ≥ 0.75), while it does form chlorinated phases in stoichiometric or sub-stoichiometric feeds (O2/HCl ≤ 0.25). Quantitative analysis of the chlorine uptake by thermogravimetry and X-ray photoelectron spectroscopy indicates that chlorination under O2-rich conditions is limited to few surface and sub-surface layers of CeO2 particles, in line with the high energy computed for the transfer of Cl from surface to sub-surface positions. Exposure of chlorinated samples to a Deacon mixture with excess oxygen rapidly restores the original activity levels, highlighting the dynamic response of CeO2 outermost layers to feeds of different composition. Density functional theory simulations reveal that Cl activation from vacancy positions to surface Ce atoms is the most energy-demanding step, although chorineoxygen competition for the available active sites may render re-oxidation as the rate-determining step. The substantial and remarkably stable Cl2 production and the lower of CeO2 make it an attractive alternative to RuO2 for catalytic chlorine recycling in industry.
Journal of Alloys and Compounds, 2006
The treatment of halogenated containing compounds is one of the more promising applications of catalytic wet oxidation (CWO) reaction. The aim of this work is to compare the abatement of chemical oxygen demand (COD) and adsorbable organic halogen (AOX) parameters in three halogenated liquid wastes: a landfill leachate, a pulp and paper bleaching liquor and a heavily organic halogen polluted industrial wastewater, treated at 430-500 K in a batch bench-top pressure vessel. Two catalysts based on ceria were used: a pure CeO 2 and a SiO 2 -doped ceria characterized by different surface area and oxygen storage capacity. The efficiency of the catalytic process was examined controlling COD and AOX parameters; the catalysts deactivation was observed by the measurement of the surface area and the increase of the carbon content of the catalysts after the reactions.
Nanoscale Research Letters, 2016
In the present work, ceria, ceria-zirconia (Ce = 80 at.%, Zr = 20 at.%), ceria praseodymia (Ce = 80 at.%, Pr = 20 at.%) and ceria-zirconia-praseodymia catalysts (Ce = 80 at.%, Zr = 10 at.% and Pr = 10 at.%) have been prepared by the multi-inlet vortex reactor (MIVR). For each set of samples, two inlet flow rates have been used during the synthesis (namely, 2 ml min −1 , and 20 ml min −1) in order to obtain different particle sizes. Catalytic activity of the prepared materials has been investigated for CO and soot oxidation reactions. As a result, when the catalysts exhibit similar crystallite sizes (in the 7.7-8.8 nm range), it is possible to observe a direct correlation between the O v /F 2g vibrational band intensity ratios and the catalytic performance for the CO oxidation. This means that structural (superficial) defects play a key role for this process. The incorporation of Zr and Pr species into the ceria lattice increases the population of structural defects, as measured by Raman spectroscopy, according to the order: CeO 2 < Ce 80 Zr 20 < Ce 80 Zr 10 Pr 10 < Ce 80 Pr 20. On the other hand, the presence of zirconium and praseodymium into the ceria lattice does not have a direct beneficial effect on the soot oxidation activity for these catalysts, in contrast with nanostructured ones (e.g., Ce-Zr-O nanopolyhedra, Ce-PrO nanocubes) described elsewhere (Andana et al.
CO and Soot Oxidation over Ce-Zr-Pr Oxide Catalysts
Nanoscale Research Letters, 2016
A set of ceria, ceria-zirconia (Ce 80 at.%, Zr 20 at.%), ceria-praseodymia (Ce 80 at.%, Pr 20 at.%) and ceria-zirconia-praseodymia (Ce 80 at.%, Zr 10 at.% and Pr 10 at.%) catalysts has been prepared by the solution combustion synthesis (SCS). The effects of Zr and Pr as dopants on ceria have been studied in CO and soot oxidation reactions. All the prepared catalysts have been characterized by complementary techniques, including XRD, FESEM, N 2 physisorption at −196°C, H 2-temperature-programmed reduction, and X-ray photoelectron spectroscopy to investigate the relationships between the structure and composition of materials and their catalytic performance. Better results for CO oxidation have been obtained with mixed oxides (performance scale, Ce80Zr10Pr10 > Ce80Zr20 > Ce80Pr20) rather than pure ceria, thus confirming the beneficial role of multicomponent catalysts for this prototypical reaction. Since CO oxidation occurs via a Mars-van Krevelen (MvK)-type mechanism over ceria-based catalysts, it appears that the presence of both Zr and Pr species into the ceria framework improves the oxidation activity, via collective properties, such as electrical conductivity and surface or bulk oxygen anion mobility. On the other hand, this positive effect becomes less prominent in soot oxidation, since the effect of catalyst morphology prevails.
Removal of oxygenated volatile organic compounds by catalytic oxidation over Zr–Ce–Mn catalysts
Journal of Hazardous Materials, 2011
The composition-activity relationship of Zr-Ce-Mn-O materials was investigated for the catalytic removal of Oxygenated Volatile Organic Compounds (OVOC) emitted by stationary sources. Using a sol-gel method, very high surface specific areas, small crystallite sizes and high redox properties were obtained for Zr 0.4 Ce 0.6−x Mn x O 2 catalytic systems after calcination at 500 • C. The textural and redox properties were improved when Mn content increased in the material, especially for x = 0.36. As a result the most active and selective catalyst in the butanol (model of OVOC) oxidation was obtained for the nominal composition Zr 0.4 Ce 0.24 Mn 0.36 O 2 due to a high oxygen mobility and surface Mn 4+ concentration.
Catalytic properties of Ce x Zr1–x O2 prepared using a template in the oxidation of CO
Russian Journal of Physical Chemistry A, 2016
The catalytic activity in CO oxidation of Ce x Zr 1-x O 2 double oxides prepared using pine sawdust and cetyltrimethylammonium bromide (CTAB) as templates is compared. It is found by means of SEM and the low-temperature adsorption of N 2 that biomorphic oxides reproduce the macropore structure of the template. It is shown via XRD and Raman spectroscopy that all samples contained mixed ceria-zirconia oxide. The double oxides form a cubic phase with a lattice of the fluorite type at a ratio of Ce : Zr = 4, regardless of the nature of the template; when Ce : Zr = 1, the biomorphic mixed oxide forms a tetragonal phase. According to Raman spectroscopy and XRD it was shown that the distortion of the oxygen sublattice is higher in biomorphic samples. Energy dispersive analysis shows that Ca impurities were present in the biomorphic samples, introducing additional distortions in the lattice of double oxide and leading to the formation of anionic vacancies. It is found that when Ce : Zr = 4, the conversion of CO on biomorphic oxide in the range of 100-350°C is higher than that observed for Ce x Zr 1-x O 2 (CTAB); reducing the Ce : Zr ratio in the biomorphic sample to 1 results in a marked decrease in CO conversion at 100-200°C. It is concluded that these differences are due to changes in the mobility of the lattice oxygen.