Catalytic Activity In Total Oxidation Research Articles

Defective outermost layers of ceria catalysts determined by electrochemical methods as direct responsible for catalytic activity in total oxidation of a representative VOC

A large set of unsupported ceria catalysts has been synthesized, physicochemical and electrochemically characterized, and tested in a representative catalytic reaction (total oxidation of a volatile organic compound-VOC, propane). Interestingly, in spite of the diverse synthesis procedures employed, a clear relationship between the electrochemical properties of the active surface layer (related with the amount of oxygen vacancies) and the catalytic activity in the total oxidation of VOCs has been observed. Then, the resistance to the charge transfer in the outer layer of the catalysts (depth of ca. 1.5 nm), which is inversely related to the amount of oxygen vacancies in that range, clearly determines the catalytic activity in the total oxidation. If the near surface is considered (outer than 10 nm, observed by XPS) a poor relationship can be appreciated. However, if the whole bulk of the cerias (overall resistance) is considered, this electrochemical-thermocatalytic relationship is not observed.

Mn/Co bimetallic MOF-derived hexagonal multilayered oxide catalysts with rich interface defects for propane total oxidation: Characterization, catalytic performance and DFT calculation

Several hexagonal layered Mn/Co oxide catalysts were synthesized from Mn/Co-based metal–organic framework (MOF) precursors. The molar ratio of Mn/Co affects the physicochemical properties of catalysts, further affects their catalytic performance. The Mn/CoOx-3/2 sample with wide interlayer spacing exhibited the highest catalytic activity for total oxidation of propane, with a T90 of 270 °C at 120 L g−1 h−1. Low-temperature reducibility, oxygen mobility, water vapor tolerance, and oxygen defects play the key roles for improving catalytic activity. Oxygen defects were calculated using the density functional theory (DFT). The results show that the doping of Mn on Co oxide is conducive to the formation of oxygen vacancies. Therefore, benefiting from the layered structure and metal-doping for the catalysts, the formation of more abundant interfacial defects can further improve the catalytic performance. This study offers a simple way to synthesize regular layered multi-metal oxide, which can expose abundant interface defects and active sites.

Design Control of Copper-Doped Titania–Zirconia Catalysts for Methanol Decomposition and Total Oxidation of Ethyl Acetate

This study is focused on the design control of Cu–Zr–Ti oxide composites by the variation of the Zr/Ti ratio and the copper deposition procedure used. For the first time, these ternary composites were obtained by a combination of template-assisted hydrothermal techniques for the preparation of mesoporous ZrO2–TiO2 mixed oxides with diverse compositions, followed by the consecutive chemisorption and hydrolysis of copper ammonia complexes on them. The nitrogen physisorption, XRD, SEM, HRTEM, TPR, XPS, UV-Vis, and Raman spectroscopies were applied for the catalysts’ characterization. Methanol decomposition and the total oxidation of ethyl acetate, both of which with potential for sustainable environmental protection, were used as catalytic tests. The complex relationship between the phase composition, structure, and morphology of titania–zirconia mixed oxides and the state and catalytic behavior of the copper oxide species supported on them was investigated. In comparison with the conventional impregnation technique, the novel preparation procedure revealed the generation of more uniform and homogeneously dispersed needle-like copper oxide crystallites in the mesoporous TiO2–ZrO2 host matrix, which typically ensure improved catalytic performance. The synergistic activity between the loaded copper species and TiO2–ZrO2 support was discussed. All ternary composites exhibited superior catalytic activity in total oxidation of ethyl acetate. The specific behavior of the catalysts in methanol decomposition was related to the irreversible phase transformations by the influence of the reaction medium.

Mesoporous copper-ceria-titania ternary oxides as catalysts for environmental protection: Impact of Ce/Ti ratio and preparation procedure

Hydrothermally obtained mesoporous ceria-titania mixed oxides with different composition are modified with copper using incipient wetness impregnation and “chemisorption-hydrolysis” techniques. Their catalytic properties in methanol decomposition as a source of hydrogen and total oxidation of ethyl acetate as representative volatile organic pollutant are investigated. The effect of support composition and modification method on the formation of catalytic active sites is studied. The obtained results show that the catalytic behavior is determined by the activity of finely dispersed CuO crystallites and facile electron transfer in the “conjugated” TiCeCu redox centres in the interface layer. The mechanism of the formation of the interface layer and the growth of CuO crystallites during different modification procedures are discussed in details. The mesoporous CuCeTi oxides demonstrate excellent catalytic activity in total oxidation of ethyl acetate. Their catalytic behavior in methanol decomposition is strongly influenced by the reductive transformations, which are provoked by the reaction medium.

Synergistic effect of CuO nanocrystals and Cu-oxo-Fe clusters on silica support in promotion of total catalytic oxidation of toluene as a model volatile organic air pollutant

Monometallic (CuO and FeOx) and bimetallic (CuFeOx) entities on different supports are promising transition-metal low-cost catalysts for catalytic oxidation of volatile organic compounds (VOC) from industrial air alternatively to noble-metal catalysts which are currently in use. In this work we report for the first time that the promotion of catalytic oxidation of toluene as a model VOC is due to the cooperative redox effect between CuO nanocrystals and finely dispersed Cu-oxo-Fe clusters on mesoporous silica with defined Fe/Cu molar ratio. This increases the number and reactivity of adsorbed electrophilic (O− and O2−) as well as nucleophilic lattice oxygen (O2-) species at the CuO crystal and and Cu-oxo-Fe cluster interface, thus providing up to twofold enhancement in catalytic activity for total oxidation of toluene. Catalysts were prepared via direct synthesis of Fe-functionalized disordered mesoporous silica containing only isolated iron sites followed by copper addition via impregnation.

The Study on the Reaction Order and Kinetics of Total Oxidation Reaction of m-xylene over LaMnO3 Perovskite Catalyst

Gases of m-xylene is one of the popurlar toxic pollutants in the exhaust gases, it is emitted into the environment from factories and engines because the fuel in the engine does not burn completely. The best solution in order to remove this toxic gases of m-xylene to protect the environment is transforming them completely into CO2 and H2O by catalysts. Perovskite of LaMnO3 is one of the catalysts that was synthesized and studied the catalytic properties in total oxidation of m-xylene in our previous report. Obtained results showed that the LaMnO3 perovskite has good catalytic characterizations such as large surface area and the amount of α-oxygen adsorbed on the catalyst is large too. So, it exhibits a good catalytic activity in total oxidation of m-xylene at relatively low reaction temperature. In present work, the reaction order and kinetics of this reaction are determined. The obtained results demonstrated that the reaction order value with respect to m-xylene is equal to about 1, to oxygene is proximately equal to 0 and the order of reaction is equal to about 1. Based on reaction order data, it was thought that the pathway of m-xylene oxidation by air oxygen over LaMnO3 may be followed through which the Langmuir - Hinshelwood mechanism.
 Keywords
 Catalyst, perovskite, oxidation, m-xylene, kinetics
 References
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Studies on non-modified and copper-modified coal ash zeolites as heterogeneous catalysts for VOCs oxidation.

The present study is aimed at investigations on the catalytic activity for total oxidation of volatile organic compounds (VOCs), such as toluene, acetone, n-hexane and dichlorobenzene onto zeolite-like materials synthesized from coal fly ash (FA) directed to development of an economically efficient approach for degradation of VOCs. Fly ash zeolites (FAZ) were prepared by alkaline conversion of FA collected from Thermal Power Plants supplied with lignite coal from "Maritza-East" basin in Bulgaria. Different synthesis procedures double stage fusion-hydrothermal activation, fusion-atmospheric crystallization and atmospheric aging were applied. The synthesis products were identified by X-ray diffraction, and were assigned to zeolite Na-X. Scanning electron microscopy images reveal submicron dimensions of the composing crystallites. Nitrogen adsorption/desorption measurements reveal a mixed micro-mesoporous structure and specific surface area between 116 and 396 m2/g for the obtained FAZ. Relationships between surface properties, iron content and the catalytic activity of FAZ were investigated and discussed. Copper-modified fly ash zeolites (Cu-FAZ) were prepared by incipient wetness impregnation technique with copper acetylacetonate. The loading of 5 wt. % copper on the zeolite samples was achieved. The catalytic activity of FAZ and Cu-FAZ in the total oxidation of model VOCs mixture containing n-hexane, acetone, toluene, 1,2 dichlorobenzene was evaluated.

Microstructure and total oxidising capacity for m-xylene of La<SUB align="right">1-xCa<SUB align="right">xCoO<SUB align="right">3 nanoparticles synthesised by combustion method

Nanoparticles of La1–xCaxCoO3 (x = 0, 0.1, 0.3 and 0.5) perovskites were synthesised by the combustion method using glycine agent and corresponding metal nitrates. The perovskites were characterised by thermogravimetric and differential thermal analysis (TG-DTA) and Brunauer-Emmett-Teller (BET) adsorption isotherms. The microstructure of samples was characterised by X-ray diffraction (XRD) combined with transmission electron microscopy (TEM), selected area electron diffraction (SAED) and energy dispersive X-ray (EDX). The grain size ranges from 20 nm to 30 nm. A high surface area from 15 m2/g to 21 m2/g was achieved for samples annealed at relatively low temperature (600°C). The perovskites exhibit a good catalytic activity in total oxidation of m-xylene at low reaction temperature.

The Determing Activation Energy of Total Oxidation Reaction of m-xylene over La0,7Sr0,3BO3 (B = Mn, Fe, Ni) Perovskite Catalysts

Perovskite-type oxides containing rare earth ions and transition metals are of interest for catalytic oxidation and reduction reactions associated with automotive exhaust emission control. They are known to exhibit a good catalytic activity in the total oxidation reaction of carbon monoxide or hydrocarbon and removal of nitrogen oxides. By partially substitution of A and B ions of the perovskite with others, a wide variety of mixed oxides A1-xA’xB1-yB’yO3 can be obtained, allowing the systematic modification of the catalytic properties. We presented the preparation and the catalytic properties of and La0.7Sr0.3BO3 (B = Mn, Fe, Ni) perovskites in total oxidation of m-xylene in previous report. Obtained results showed that they exhibit a good catalytic activity in total oxidation of m-xylene at relatively low reaction temperature. In present work, the activation energy of total oxidation reaction of m-xylene over these catalysts are determined. The results show that the activation energy of studied catalyst is ranging about from 11.5 to 13.4 kcal/mol. The replacement of Mn by Fe and Ni in La0.7Sr0.3MnO3 perovskite catalyst reduces the catalytic property of La0.7Sr0.3MnO3 catalyst and increases the activation energy of the total oxidation reaction of m-xylene.

Synthesis and microstructure of La1−xCaxCoO3 nanoparticles and their catalytic activity for CO oxidation

Perovskite nanoparticles of La1−xCaxCoO3 (x = 0, 0.2, 0.3, 0.5) were synthesized by the combustion method using polyvinyl alcohol (PVA) and corresponding metal nitrates. Microstructure of samples was characterized by high resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED) combined with x-ray diffraction (XRD). The nanoparticles were characterized by thermogravimetric and differential thermal analysis (TG-DTA) and BET (Brunauer–Emmet–Teller). A high surface area (15–21 m2 g−1) at low temperature (600 °C) of samples was obtained. The optimal preparative conditions were PVA/metals 2:1 by mole, pH = 3 and 80 °C for gel formation. Perovskites exhibit a good catalytic activity in total oxidation of CO at the low temperature (<250 °C) of reaction.

Synthesis of nanometric LaCr0.5Mn0.5O3 perovskite at low temperature by the polyvinyl alcohol gel combustion method

Nanosized LaCr0.5Mn0.5O3 perovskite was synthesised with relatively high surface area (15.5 m2/g) at low temperature (650 °C) by the combustion method using polyvinyl alcohol (PVA) and corresponding metal nitrates. The perovskite was characterised by X-ray diffraction, thermogravimetric and differential thermal analysis, field emission scanning electron microscopy and Brunauer–Emmett–Teller technique. The optimal preparative conditions were PVA/metals 3:1 by mole, pH = 3–4 and 80 °C for gel formation. Perovskite exhibits a good catalytic activity in total oxidation of m-xylene at the low temperature of reaction (250 °C).

Impact of silica structure of copper and iron-containing SBA-15 and SBA-16 materials on toluene oxidation

Copper and iron modified SBA-15 and SBA-16 materials were prepared by incipient wetness impregnation technique and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), N2 physisorption, temperature-programmed reduction (TPR-TGA), UV–Vis diffuse reflectance and Mössbauer spectroscopy. Formation of finely dispersed copper and iron-oxide species was observed on both supports, whereas copper ferrite could be evidenced only on SBA-15. It was found that the structural and surface properties of the mesoporous supports determine the type of formed metal oxides, their dispersion, reducibility and the catalytic activity in total oxidation of toluene. On SBA-16 support penetration of metal salt into the bimodal channel system is hindered therefore separate copper- and iron-oxide phases are formed on the outer surface of catalysts. The catalytic activity and stability are lower due to the easier agglomeration of particles. On SBA-15 support finely dispersed metal-oxides can be found in the mesoporous channels. Their interaction is favored to form bimetallic phases enhancing the catalytic activity and stability in total oxidation of toluene.

The physico-chemical and catalytic properties of ferrite-containing MCM-41 and SBA-15 materials

Cobalt and iron modified MCM-41 and SBA-15 materials were prepared by incipient wetness impregnation technique and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), N 2 physisorption, temperature-programmed reduction (TPR-TGA), UV–Vis diffuse reflectance and Mössbauer spectroscopy. Formation of finely dispersed ferrite and cobalt-oxide species was observed on MCM-41 and SBA-15 supports. It was found that the surface properties of the mesoporous support and the temperature of precursor decomposition determine the type of formed metal oxides, their dispersion, reducibility and the catalytic activity in total oxidation of toluene.

Effect of the pretreatment conditions on the physico-chemical and catalytic properties of cobalt- and iron-containing Ti-MCM-41 materials

Cobalt and/оr iron modified Ti-MCM-41 materials, prepared by an incipient wetness impregnation technique, were investigated using X-ray diffraction (XRD), N 2 physisorption, temperature-programmed reduction (TPR-TGA), FT-IR spectroscopy, EPR and Mössbauer spectroscopy. Formation of finely dispersed metal oxide species could be observed for the cobalt and/or iron modified Ti-MCM-41 samples. The surface properties of the mesoporous support and the pretreatment procedure (media and temperature) predetermine the types of the formed metal oxides, their dispersion, reducibility and the catalytic activity in total oxidation of toluene. It was also found that incorporation of lower amount of titanium into the mesoporous support favors the formation of finely dispersed iron or/and cobalt ions on Fe/Ti-MCM-41 and CoFe/Ti-MCM-41 samples. The high and stable catalytic activity of Co/Ti-MCM-41 samples was due to the formation of finely dispersed Co 3O 4 nanoparticles. Cobalt oxide with optimal dispersion could be obtained by pretreatment in air and subsequently in hydrogen at 773 K. This effect was more pronounced for Co/Ti-MCM-41 catalyst with higher titanium content (Si/Ti = 10). Formation of finely dispersed cobalt ferrite particles in CoFe/Ti-MCM-41 samples following pretreatment in air and subsequently in hydrogen at 773 K had an additional positive effect on the catalytic performance.

Lanthanum based high surface area perovskite-type oxide and application in CO and propane combustion

The perovskite-type oxides using transition metals present a promising potential as catalysts in total oxidation reaction. The present work investigates the effect of synthesis by oxidant co-precipitation on the catalytic activity of perovskite-type oxides LaBO3 (B= Co, Ni, Mn) in total oxidation of propane and CO. The perovskite-type oxides were characterized by means of X-ray diffraction, nitrogen adsorption (BET method), thermo gravimetric and differential thermal analysis (ATG-DTA) and X-ray photoelectron spectroscopy (XPS). Through a method involving the oxidant co-precipitation it’s possible to obtain catalysts with different BET surface areas, of 33-44 m2/g, according the salts of metal used. The characterization results proved that catalysts have a perovskite phase as well as lanthanum oxide, except LaMnO3, that presents a cationic vacancies and generation for known oxygen excess. The results of catalytic test showed that all oxides have a specific catalytic activity for total oxidation of CO and propane even though the temperatures for total conversion change for each transition metal and substance to be oxidized.

Lanthanum based high surface area perovskite-type oxide and application in CO and propane combustion

The perovskite-type oxides using transition metals present a promising potential as catalysts in total oxidation reaction. The present work investigates the effect of synthesis by oxidant co-precipitation on the catalytic activity of perovskite-type oxides LaBO3 (B= Co, Ni, Mn) in total oxidation of propane and CO. The perovskite-type oxides were characterized by means of X-ray diffraction, nitrogen adsorption (BET method), thermo gravimetric and differential thermal analysis (ATG-DTA) and X-ray photoelectron spectroscopy (XPS). Through a method involving the oxidant co-precipitation it's possible to obtain catalysts with different BET surface areas, of 33-44 m2/g, according the salts of metal used. The characterization results proved that catalysts have a perovskite phase as well as lanthanum oxide, except LaMnO3, that presents a cationic vacancies and generation for known oxygen excess. The results of catalytic test showed that all oxides have a specific catalytic activity for total oxidation of CO and propane even though the temperatures for total conversion change for each transition metal and substance to be oxidized.

Estudo da oxidação total do etanol usando óxidos tipo perovskita LaBO3 (B= Mn, Ni, Fe)

The present work investigated the effect of coprecipitation-oxidant synthesis on the specific surface area of perovskite-type oxides LaBO3 (B= Mn, Ni, Fe) for total oxidation of ethanol. The perovskite-type oxides were characterized by X-ray diffraction, nitrogen adsorption (BET method), thermogravimetric analysis (TGA-DTA), TPR and X-ray photoelectron spectroscopy (XPS). Through method involving the coprecipitation-oxidant was possible to obtain catalysts with different BET specific surface areas, of 33-51 m2/g. The results of the catalytic test confirmed that all oxides investigated in this work have specific catalytic activity for total oxidation of ethanol, though the temperatures for total conversion change for each transition metal.

Temperature programmed desorption study of hydrogen adsorption on LaMO 3 oxides

Temperature programmed desorption spectra of H 2 adsorbed on LaMO 3 (M = Cr, Fe, Co and Ni) perovskite oxides were obtained as a function of the adsorption temperature and the reduction temperature of the oxide. In the systems H 2-LaCrO 3 and H 2-LaNiO 3, activated adsorption is observed when the adsorption is effected above room temperature. After adsorption of H 2 at room temperature on reduced LaMO 3, the spectra present a desorption peak between 340 and 380 K. LaNiO 3 presents, in addition, a second desorption peak at 610–615 K. These peaks increase in intensity with the reduction temperature of the oxide. The TPD peaks observed for H 2-LaCoO 3 (red) and H 2-LaNiO 3 (red) are assigned to hydrogen adsorbed on metallic cobalt and nickel. On LaCrO 3 (red) and LaFeO 3 (red) more oxidized metal centers (M n+ ; n < 3) should be involved in hydrogen adsorption. After reduction of the LaMO 3 oxides in several zones of temperature and adsorption of hydrogen at room temperature, LaFeO 3 (red) exhibited the lowest desorption of H 2. This result is similar to the minima for O 2 adsorption and catalytic activity for total oxidation observed for this oxide.

ChemInform Abstract: Physicochemical Properties of LaFeO3. Kinetics of Reduction and of Oxygen Adsorption.

AbstractDie Ergebnisse der Temp.‐programmierten Reduktion zeigen, daß LaFeO3‐,g zuerst zu fast stöchiometrischem LaFeO3 (600‐850 K) reduziert wird und dann zu α‐Fe und La2O3 (850‐ 1250 K).

Physicochemical properties of LaFeO3. Kinetics of reduction and of oxygen adsorption

The reduction with hydrogen of LaFeO3 and the kinetics of oxygen adsorption on this perovskite have been studied. The results of temperature-programmed reduction suggest that the starting sample was reduced first to nearly stoichiometric LaFeO3(600–850 K) and then to α-Fe and La2O3(850–1250 K). The reduction process at 1063–1163 K is controlled by formation and growth of nuclei of metallic iron. The kinetic data for reduction fit the Avrami–Erofeev equation. The kinetic data for oxygen adsorption fit the Elovich equation using t0 values as calculated by the method of Aharoni and Ungarish. Activation energies for reduction and for oxygen adsorption were 194 and 16 kJ mol–1, respectively. Oxygen adsorption was very low in comparison with other LaMO3 oxides, as would be expected from its low catalytic activity for total oxidation.