Catalysts For Total Oxidation Research Articles

Coprecipitated Co–Al and Cu–Al oxide catalysts for toluene total oxidation

Highly crystalline mixed cobalt– and copper–aluminium oxides were obtained from coprecipitated precursors. These Co–Al and Cu–Al oxide systems appeared to be active catalysts of the total oxidation of toluene in the temperature range of 250–450 °C. The study on chemical and phase composition, thermal stability, texture and reducibility of the synthesized samples allowed to identify their active phases in toluene combustion.

Application of industrial waste based catalysts for total oxidation of propane

High metal containing wastes from the aluminium industry, the tannery industry and the electroplating industry were tested as precursors for catalysts. These waste materials were processed using various treatments and tested for the total oxidation of volatile organic compounds employing propane as a model gas. Comparisons were made with unprocessed counterparts in certain cases. Investigations were made in the temperature range of 100–500°C with a GHSV of 5000h−1. Characterization of fresh and used catalysts was performed using techniques like BET analysis, X-ray diffraction (XRD), X-ray fluorescence (XRF), inductively coupled plasma optical emission spectrometry (ICP-OES) and thermal analyses (DTA/TG). The results showed that the catalyst obtained from combination of red mud with tannery shavings mixed in high ratio followed by thermal treatment and the unprocessed red mud were the most active. A 50% conversion in the range of 320–380°C was achieved. In comparison, the other wastes showed lower activity, requiring much higher temperatures for the same conversion.In view of the low cost involved and easy availability of such materials, their utilization as a source of catalyst can be of interest.

Iron-modified ceria and Au/ceria catalysts for Total and Preferential Oxidation of CO (TOX and PROX)

Iron-modified ceria supports containing different molar percentages of Fe (0%, 10%, 25%, and 50%) were synthesized by thermal decomposition of the metal propionates. The formation of a Ce–Fe oxide solid solution is evidenced through XRF, XRD, BET and Raman spectroscopy. For iron contents above 25% the formation of α-Fe 2O 3 was detected, pointing out the formation of the isolated oxides. The catalytic activity of the Fe-modified catalysts in the Total Oxidation of CO reaction (TOX) is higher than for the bare CeO 2 material. The synergy between Ce and Fe shows a maximum for 10% Fe content (CeFe10), catalyst that shows the highest CO conversion per atom of Fe incorporated. Gold catalyst was also prepared on CeFe10 and its catalytic activity compared with Au/CeO 2 catalyst. The addition of iron to the gold catalyst resulted in an enhancement of the catalytic activity for CO oxidation especially at low temperature. This Au/CeFe10 catalyst was also active and selective with excellent stability in the Preferential Oxidation of CO (PROX) showing a higher CO conversion than the Au/CeO 2 catalyst at temperatures below 150 °C being hardly affected by the presence of CO 2 and H 2O in the gas stream.

One-step non-hydrolytic sol–gel preparation of efficient V2O5-TiO2 catalysts for VOC total oxidation

Vanadia-titania catalysts are highly regarded for the control of industrial and domestic gas effluents. They are particularly used for the abatement of volatile organic compounds and for the removal of aromatic, polyaromatic and polychlorinated air pollutants like furans and dioxins. Here, mixed oxide catalysts are formed by non-hydrolytic condensation of chloride precursors with diisopropyl ether in non-aqueous medium. Calcination was applied to provoke the migration of the vanadium oxide toward the surface of the anatase particles, leading to well-spread vanadia species. The materials are made of mesoporous spherical particles of a few microns, themselves constituted by the aggregation of 10–25nm sized particles. Their chemical composition is precisely controlled. The samples are characterized by ICP-AES, N2-physisorption, XRD, XPS, SEM and TOF-SIMS. Their performances as total oxidation catalyst are evaluated in the deep oxidation of benzene, chosen as a model atmospheric pollutant. The activity of the materials compares well with that of catalysts prepared by classical wet impregnation. Along with the V surface concentration, the environment in which V surface species are located is identified as a key parameter. The superior activity of polymeric species as compared to isolated ones is shown.

Methane partial oxidation to synthesis gas over bimetallic cobalt/tungsten carbide catalysts and integration with a Mn substituted hexaaluminate combustion catalyst

Co0.2W0.8Cx and supported Co0.2W0.8Cx catalysts are shown to be active for the partial oxidation of methane to synthesis gas. The catalyst stability is improved by operating at elevated pressure, or in the presence of excess methane. At atmospheric pressure the Co0.2W0.8Cx catalysts deactivate by oxidation, as seen by X-ray diffraction. Manganese substituted hexaaluminate catalysts with different Mn contents have been tested as catalysts for the total combustion of methane. In particular BaMn2Al10O19 is active and stable for the combustion reaction. The temperature rise observed in the reactor was up to 300K, depending on the reaction conditions, and complete conversion of oxygen in the feed was achieved. A process for stabilising the carbide catalysts is demonstrated, combining the manganese substituted hexaaluminate total oxidation catalyst, in series before the carbide reforming catalyst: this process leads to stable operation, with no carbon formation in the reactor and no carbide catalyst oxidation observed.

Co and Ni ferrospinels as catalysts for propane total oxidation

Co and Ni ferrospinels were prepared by coprecipitation and by mechano-chemical method, characterized using XRD, N 2 adsorption, EDX and H 2 -TPR techniques and tested in the catalytic total oxidation of propane within the temperature range of 250–600 °C. Depending on the ferrospinel composition, the method of preparing it and the reaction conditions, total conversion to CO 2 was observed at temperatures between 400 °C and 500 °C. The best results were obtained with the Co ferrite catalyst prepared by coprecipitation, which gives total conversion at temperatures as low as 400 °C. The ferrospinel catalysts showed a good stability during the catalytic test.

New Cu-based mixed oxides obtained from LDH precursors, catalysts for methane total oxidation

The methane total oxidation was studied over high surface area mesoporous Cu–Mg–Al mixed oxide catalysts obtained from layered double hydroxides (LDHs) precursors. XRD and H 2-TPR revealed that both CuO and CuAl 2O 4 phases were present in the calcined catalysts. The best results were obtained with the catalysts containing 10 and 20 at.% Cu, total conversion being achieved at temperatures lower than 525 °C in these cases. The catalyst containing 10% Cu showed the best specific activity per unit mass of copper. The influences of the contact time and of the methane concentration in the feed gas on the catalytic performances have also been investigated. The stability of the copper-based catalysts during the catalytic test was evidenced.

Dry citrate-precursor synthesized nanocrystalline cobalt oxide as highly active catalyst for total oxidation of propane

A set of nanocrystalline cobalt oxide (Co 3O 4)-based catalysts have been prepared by means of an innovative soft reactive grinding (SRG) procedure. The catalysts exhibited excellent activities and high stabilities for propane catalytic combustion. Complete conversion has been achieved at reaction temperatures as low as 240 °C. Comparing with the highly active Co 3O 4 catalysts in the current literature, the catalysts in this work show exceptionally high specific rate for propane total oxidation (ca. 91.3 mmol C 3 m − 2 h − 1 at 200 °C). A correlation between the O 2-TPD results and the activity for Co 3O 4 reveals that a high concentration of superficial electrophilic oxygen (O −) species is important for achieving a high activity. The prominent lattice distortion induced by prolonged citrate-precursor grinding is suggested to play a key role in creating and maintaining a high density of surface defects, which leads to highly activity and stability of the cobalt spinel catalyst.

Thermal degradation of iron chelate complexes adsorbed on mesoporous silica and alumina

Nanometric Fe2O3 particles could be inserted inside the internal pore volume of SBA-15 mesoporous silica and mesoporous alumina supports, when Fe(III) chelates (EDTA, gluconate or citrate) were used as impregnating precursors. The oxidative degradation of the chelating anions was followed by combined TG-DTA. Strong chelate-SiOH interactions (case of bulky EDTA), favored by the mesopore curvature, yield sub-nanometric extremely well dispersed Fe2O3 particles preferentially located at the micropore mouths (confinement effect). Fe2O3 even more strongly interacts with alumina walls, generating either (Fe,Al)2O3 mixed phases or Fe-aluminate micro domains. These iron-based mesoporous alumina composites proved very active catalysts in total oxidation of phenol at ambient conditions, with extremely low iron leaching (0.2%).

The effect of the use of lanthanum-doped mesoporous SBA-15 on the performance of Pt/SBA-15 and Pd/SBA-15 catalysts for total oxidation of toluene

Abstract Platinum and palladium were supported on a mesoporous SBA-15 for total oxidation of toluene. The effects of the use of lanthanum-doped SBA-15 on the performance of Pt/SBA-15 and Pd/SBA-15 catalysts and on the total oxidation of toluene were evaluated. Lanthanum-substituted mesoporous SBA-15 molecular sieve has been prepared by direct synthesis and post-synthesis procedures using lanthanum nitrate as source. By post-synthesis procedure, La was ion-exchanged on calcined silica. Characterizations by atomic absorption, X-ray diffraction, nitrogen adsorption, 29Si MAS NMR and FT-IR spectroscopy have been carried out to evaluate the efficiency of the incorporation of lanthanum by these procedures. Lanthanum was well incorporated into the SBA-15 structure only by post-synthesis procedure. Structural and textural evolutions of LaSBA-PS (post-synthesis) material were studied according to the Si/La ratio. These LaSBA-15 mesoporous molecular sieves retain the hexagonal order and physical properties of siliceous SBA-15 material. After removing the surfactant molecules by calcinations, 1 wt% of platinum or 0.5 wt% of palladium was impregnated on SBA-15 or LaSBA-PS (Si/La = 20) via incipient wetness technique using respectively hexachloroplatinic acid and palladium nitrate as the Pt and Pd sources. The activity for toluene total oxidation of the pre-reduced samples follows this order: 0.5 wt% Pd/SBA-15 > 1 wt% Pt/SBA-15 > 0.5 wt% Pd/LaSBA-PS > 1 wt% Pt/LaSBA-PS. 0.5 wt% Pd/SBA-15 was found to be a very interesting catalyst for VOC oxidation. However, the lower activity of the lanthanum catalysts could be explained by patches of LaOX residing on the surface of the metal particles (particularly on Pd) and/or to the interaction between the metal and LaSBA-PS which modifies the electron density of the metal. For the Pt-based catalyst the observed higher dispersion of platinum species for Pt/LaSBA-PS and thus to the increase of the Pt–O bond strength with the decrease of the Pt crystallite size could also inhibit the reaction.

Effect of the preparation method on Au/Ce-Ti-O catalysts activity for VOCs oxidation

Studies concerning the preparation of gold phases dispersed on binary Ce-Ti oxide (Ce 0.3Ti 0.7O 2) were performed in order to elaborate catalysts for total oxidation of VOCs. Solids containing gold, cerium and titanium were synthesized by impregnation and deposition precipitation (DP) method using NaOH, Na 2CO 3 or urea as precipitant agent. These catalysts have been characterized by means of total surface area (BET), X-ray diffraction (XRD), diffuse reflectance ultra-violet–visible spectroscopy (DR/UV–vis) and temperature programmed reduction (TPR) and their reactivity towards the oxidation of propene was studied. Thus, it was revealed that the gold-based material prepared by DP method using urea as precipitant agent was the most efficient catalyst towards the total oxidation of propene. Based on the characterisation data, it has been shown that the preparation method has an effect on the catalytic activity.

Evaluation and characterization of Mn–Cu mixed oxide catalysts for ethanol total oxidation: Influence of copper content

Mixed oxides of manganese and copper with different wt% of copper have been prepared and evaluated in ethanol combustion. The co-precipitation method used for the synthesis of Mn xCu y mixed oxides is adequate to obtain catalysts with excellent catalytic performance in combustion reactions. Catalysts were characterized by means of XRD, FT-IR, TPR and O 2-TPD. A small amount of copper prevents manganese oxide reaching a crystalline structure. This poor crystalline structure of manganese oxide may improve the existence of oxygen vacancies giving a best performance in ethanol combustion to CO 2. When the copper content increases, an extent of solid state reaction between Cu and Mn is favored and the partial oxidation of ethanol becomes more important. The incorporation of manganese into incomplete spinel structure diminishes CO 2 yield.

Synthesis of CeO 2–MnO x mixed oxides and catalytic performance under oxygen-rich condition

Ce 0.5Zr 0.5O 2, Ce 0.5Zr 0.2Mn 0.3O 2 and Ce 0.5Mn 0.5O 2 were prepared by citric acid sol–gel method. The effect of manganese on the structural and redox properties of ceria-based mixed oxides was investigated by means of powder X-ray diffraction, X-ray photoelectron spectroscopy, Brunauer–Emmett–Teller analyses, temperature-programmed reduction and catalytic activity evaluation in the presence of excess O 2. The results showed that some Mn cations could enter into the ceria lattice to form solid solutions. Mn 3O 4 appeared due to the instability of the mixed oxides with increment of the Mn doping ratio while another oxide Mn 2O 3 is detected in the physical mixture of ceria and manganese oxide. These Mn-doped mixed oxides, especially Ce 0.5Mn 0.5O 2, presented better catalytic activities than Ce 0.5Zr 0.5O 2 and even Pt-loaded catalyst for total oxidation of C 3H 8 and oxidative sorption of NO in the presence of excess oxygen. The oxidation ability of Mn and the strong interaction between Mn and Ce were suggested to promote the oxygen storage/transport capacity of the mixed oxides as well as reactive adsorption of nitric oxide and hydrocarbons.

Environmental green chemistry as defined by photocatalysis

Photocatalysis is efficient in several fields. Firstly, in selective mild oxidation: oxidation of gas and liquid hydrocarbons (alkanes, alkenes, cyclo-alkanes, aromatics) into aldehydes and ketons. Primary and secondary alcohols are also oxidized into their corresponding aldehydes or ketones. The high selectivity was ascribed to a photoactive neutral, atomic oxygen species. Once platinized (only 0.5 wt.% Pt) titania may catalyze reactions involving hydrogen (deuterium-alkane isotopic exchange and alcohol dehydrogenation). For fine chemicals, high initial selectivities enable titania to address most of the twelve principles of “green chemistry”, such as the synthesis of 4- tert-butyl-benzaldehyde, an important intermediate in perfume industry by direct selective oxidation of 4- tert-butyl-toluene with air. A new field recently appeared: thio-photocatalysis. Oxygen was replaced by sulfur, using H 2S as a convenient and reactive source. For instance, the conversion of propene in 1-propanthiol was successfully obtained. The reaction was performed using either CdS or TiO 2. The latter was much more active than CdS. In environmental photocatalysis, titania becomes a total oxidation catalyst once in presence of water because of the photogeneration of OH radicals by neutralization of OH − surface groups by positive holes. Many toxic inorganic ions are oxidized in their harmless upper oxidized state. The total degradation of organic pollutants (pesticides, herbicides, insecticides, fungicides, dyes, etc. …) is the main field of water photocatalytic decontamination. The UVA solar spectrum can de advantageously used as demonstrated by many campaigns performed in the solar pilot plant at the “Plataforma Solar de Almeria” (Spain).

Influence of cobalt precursor and fuels on the performance of combustion synthesized Co3O4/γ-Al2O3 catalysts for total oxidation of methane

A series of nanosized Co3O4/γ-Al2O3 catalysts have been prepared using a combination of wetness impregnation and subsequent combustion synthesis (CS) in self-propagating mode. Alumina impregnated with various cobalt precursors and fuels, and respective as-burnt combustion-synthesized catalysts were characterised by TGA-DTA, IR-spectroscopy, N2 adsorption–desorption, XRD, SEM/EDX and TEM, and tested in the total oxidation of methane. The observed influence of the initial precursors cobalt acetate, mixtures of cobalt acetate/cobalt nitrate, and mixtures of cobalt nitrate wit fuels such as urea, citric acid, glycine, and glycerine on the catalytic performance correlates well with their combustion behaviour. Catalysts obtained with the combustion method at the highest velocities and the lowest temperatures during the synthesis were found to have the highest activity (complete conversion of methane at 400–425 °C). After two days of catalytic performance in the reaction, no considerable deactivation of combustion-synthesized catalysts was observed and their particle size remained about twice less in comparison with the sample prepared by cobalt nitrate thermal decomposition.

Calcined Ni—Al layered double hydroxide as a catalyst for total oxidation of volatile organic compounds: Effect of precursor crystallinity

AbstractThe effect of hydrothermal treatment on properties (crystallinity, porous structure, reducibility, acidity, basicity, and catalytic activity and selectivity in toluene and ethanol total oxidation) of Ni—Al layered double hydroxide precursors and related mixed oxides was examined. The hydrothermal treatment increased considerably both the content of crystalline phase and LDH crystallite size. On the other hand, only a slight effect of the precursor hydrothermal treatment on crystallinity of the related Ni—Al mixed oxides obtained by calcination at 450°C was observed. The reducibility of NiO particles appeared to be hindered considerably compared to the reducibility of pure NiO. Catalytic activity of the Ni—Al mixed oxides prepared from the precursors hydrothermally treated for a short time (4 h) was the highest. The highest amount of acetaldehyde formed during the total oxidation of ethanol, i.e. the worst selectivity was found for the calcined Ni—Al LDH without hydrothermal treatment.

Implementation of the Multi-Channel Monolith Reactor in an Optimisation Procedure for Heterogeneous Oxidation Catalysts Based on Genetic Algorithms

A multi-criteria optimisation procedure based on genetic algorithms is carried out in search of advanced heterogeneous catalysts for total oxidation. Simple but flexible software routines have been created to be applied within a search space of more then 150,000 individuals. The general catalyst design includes mono-, bi- and trimetallic compositions assembled out of 49 different metals and depleted on an Al2O3 support in up to nine amount levels. As an efficient tool for high-throughput screening and perfectly matched to the requirements of heterogeneous gas phase catalysis - especially for applications technically run in honeycomb structures - the multi-channel monolith reactor is implemented to evaluate the catalyst performances. Out of a multi-component feed-gas, the conversion rates of carbon monoxide (CO) and a model hydrocarbon (HC) are monitored in parallel. In combination with further restrictions to preparation and pre-treatment a primary screening can be conducted, promising to provide results close to technically applied catalysts. Presented are the resulting performances of the optimisation process for the first catalyst generations and the prospect of its auto-adaptation to specified optimisation goals.

Influence of the support in selective CO oxidation on Pt catalysts for fuel cell applications

One crucial requirement for the proton exchange membrane fuel cells (PEMFC) is to feed clean hydrogen to the anode, which is rapidly poisoned by traces of CO present from the upstream hydrocarbon reforming and water–gas shift processes. The removal of CO can be achieved by using catalysts able to selectively oxidize CO in the presence of excess hydrogen. Herein we report the effect of the support on Pt catalysts for total and selective oxidation (SELOX) of CO. The catalysts supported on ceria and zirconia presented higher activity than alumina and silica supported catalysts in SELOX reaction at low temperatures, but with lower CO conversions.

Manganese oxide OMS-2 as an effective catalyst for total oxidation of ethyl acetate

This investigation focuses mainly on the use of a synthetic cryptomelane type manganese octahedral molecular sieve, OMS-2, as a catalyst for the total oxidation of ethyl acetate. OMS-2 was found to be a highly efficient catalyst giving 100% conversion and selectivity to CO2, the final oxidation product. In addition, it was stable with time on stream and resistant to coking. A mechanism is proposed to explain the high selectivity. Presence of Mn4+-O2− Lewis acid–base pairs, ability of Mn to exist as a redox couple, viz. Mn4+/Mn3+ and availability of facile lattice oxygen, seem to facilitate the oxidation process.

Catalytic activity of copper and palladium based catalysts for toluene total oxidation

In this study, catalysts containing 0.5 wt.% of palladium or 5 wt.% of copper were compared towards toluene total oxidation using FAU Zeolite and ZrO 2 supports. A 0.5%Pd/NaFAU and 5%Cu/ZrO 2 were found to be promising catalysts for this reaction. Palladium presented then a better affinity for FAU zeolite and copper oxide had a better affinity for zirconia. The performances of Pd based catalysts were correlated to interaction between the active phase and the support whereas the activity of copper oxide was related to oxygen mobility property of the support leading to copper oxide particles easily reducible. Support modifications, yttrium addition for ZrO 2 and cation exchange for the zeolite FAU, still enhanced the catalytic activity. Therefore, 0.5%Pd/CsFAU and 5%Cu/Zr 95Y 5 samples were found to be interesting catalysts for total VOC oxidation.