Catalytic Total Oxidation Research Articles

Restrictive nanoreactor for growth of transition metal oxides (MnO2, Co3O4, NiO) nanocrystal with enhanced catalytic oxidation activity

Metal oxides like MnO2, Co3O4 and NiO were fabricated by controlling decomposition of metal salt precursor in the presence and absence of restrictive nanoreactor. The growth of oxide crystals was inhibited in restrictive space provided by hard template (nanocasting), which made the catalysts possess smaller crystal size, higher surface area and better low-temperature reducibility. Significantly, nanocasting-derived oxides (MnO2, Co3O4 and NiO) performed much better for catalytic total oxidation of benzene with T90% at 289, 253 and 355°C, which are 125, 41 and 61°C lower than that over the general oxides prepared by direct calcination.

Catalytic Total Oxidation of SOFC Exhaust Gas on Cu-Mn Catalysts

SOFC exhaust gases, such as methane and carbon monoxide, cause environmental problems. However, extra energy can be realized from oxidizing these out-gases into CO 2 and H 2 O. This extra energy can be recycled in an SOFC system and increase the thermal efficiency. Thus the development of new catalysts that lower the oxidation temperature will make the SOFC system more efficient. CULLEN et. al.[1] reported high conversion rate of SOFC exhaust gas using a La-Cu-Mn impregnated alumina catalyst and a Pt-Pd catalyst in series. In this work, Cu-Mn catalysts that are used in the oxidation of methane or carbon monoxide were tested for SOFC exhaust gas oxidation. For determining the best ratio of Cu-Mn in catalysts, different ratios of La2O3-MnO-CuO/γ-Al2O3catalysts were prepared. The result shows approximtely 0.5 to 2 Cu/Mn ratio is the best composition for SOFC exhaust gas oxidation[Fig. 1]. Fig. 1. Conversion of CO(160℃), H2(240℃), CH4(460℃) with various Cu-Mn ratio. Cu-Mn perovskite and spinel supported catalysts were also tested. The perovskite supported catalysts showed much higher activity than the spinel supported. This was especially so for the case of methane conversion; the perovskite supported catalysts showed similar performance to alumina supported. The methane conversion of reference, CP and MP were 53.1%, 55.1% and 56.3% at 500℃, respectively.

Catalytic Total Oxidation of SOFC Exhaust Gas on Cu-Mn Catalysts

SOFC exhaust gas oxidation technology will contribute to reducing the pollutants and providing economically feasible SOFC systems. The Cu-Mn based materials, known as CO and H2 oxidation catalysts, were tested as novel metal-free SOFC exhaust gas oxidation catalysts. Catalysts are prepared with incipient wetness impregnation method using metal nitrate precursors on γ-Al2O3. Various Cu-Mn catalysts are also prepared to study the effect of CuO-MnO ratio on catalytic activity. The feed gas was synthesized as similar composition of SOFC exhaust gas. The optimized conversion was obtained when CuO and MnO had the same weight ratio(CuO/MnO wt. ratio = 1). The conversion of CO, H2 and CH4 is 43.4, 36.1 and 58.0, repectively.

Total Oxidation of Formaldehyde over MnOx-CeO2 Catalysts: The Effect of Acid Treatment

The effect of acid treatment in mixed MnOx–CeO2 samples has been investigated in the catalytic total oxidation of formaldehyde. The acid treatment has no effect on the textural and redox properties of the materials when Mn is stabilized in a MnOx–CeO2 solid solution (Mn content below 50%). However, these properties were found to be highly altered by acid treatment when the solubility limit of Mn in the ceria was exceeded (Mn content above 50%). This enabled access to the primary porosity and oxidized the manganese species to a higher oxidation state via a Mn dismutation reaction. As a result, the catalytic activity of pure manganese oxide, after chemical activation, in the oxidation of formaldehyde is greatly improved—at 100 °C, the conversion of formaldehyde is increased by a factor of 5 and the corresponding intrinsic reaction rate by 1.4. Combined in situ surface analysis unambiguously identified formate species as a result of formaldehyde oxidation at room temperature on the chemically activated pure MnOx. The evolution of various surface species was monitored by increasing the temperature and in situ FTIR, and XPS results provided direct evidence of the desorption of monodentate formate species into formaldehyde and the oxidation of bidentate-bridging formate species. Changes in the average oxidation state of surface manganese confirmed the participation of oxygen from MnOx in the formation of formate species at room temperature and their transformation into CO2 and H2O when increasing the temperature.

Catalytic total oxidation of 1,2-dichloroethane over highly dispersed vanadia supported on CeO2 nanobelts

CeO2 nanobelts were synthesized via a facile aqueous-phase precipitation route under mild conditions (template-free and non-hydrothermal), and then the highly dispersed vanadia catalysts with a wide range of VOx loadings were prepared by a conventional incipient-wetness impregnation method. The target VOx/CeO2 catalysts were characterized in detail and used in catalytic combustion of 1,2-dichloroethane (DCE). The results revealed that the monolayer dispersed VOx (6.0%VOx/CeO2) exhibited the most outstanding initial and stable activities, however, the main product containing carbon was CO, not desired CO2. A reaction mechanism of DCE total oxidation was proposed based on the study of TPSR and in situ FTIR. The first step of this mechanism was considered to be a dissociative adsorption of CCl bonds on Lewis acid sites (such as Ce4+/3+, V5+/4+ or Ce3+–O2−–V5+) via Cl abstraction, and then the dissociated DCE can be oxidized directly to CO2 by surface active oxygen species over pure CeO2. Whereas, over VOx/CeO2 catalysts, the formation of intermediate acetaldehyde was a key step via CH bond activation and hydrogen transfer on VOx species, subsequently, partially oxidized to CO by the lattice oxygen of VOx.

Study and modelling of kinetics of the oxidation of VOC catalyzed by nanosized Cu–Mn spinels prepared via an alginate route

The catalytic total oxidation of toluene at low concentrations in air over Cu1.5Mn1.5O4 catalysts synthesized via the alginate route has been investigated. Several kinetic models have been selected and tested to describe the kinetics of the total oxidation of toluene. Results showed that the power law model and Langmuir model were not enough to represent the kinetics of toluene combustion over the catalyst. On the contrary, the model based on the Mars–van Krevelen mechanism provided a good fit (R2=0.94) towards the experimental data and allowed to determine the kinetic parameters.

Thermal multicomponent lattice Boltzmann model for catalytic reactive flows.

Catalytic reactions are of great interest in many applications related to power generation, fuel reforming and pollutant abatement, as well as in various biochemical processes. A recently proposed lattice Boltzmann model for thermal binary-mixture gas flows [J. Kang, N. I. Prasianakis, and J. Mantzaras, Phys. Rev. E. 87, 053304 (2013)] is revisited and extended for the simulation of multispecies flows with catalytic reactions. The resulting model can handle flows with large temperature and concentration gradients. The developed model is presented in detail and validated against a finite volume Navier-Stokes solver in the case of channel-flow methane catalytic combustion. The surface chemistry is treated with a one-step global reaction for the catalytic total oxidation of methane on platinum. In order to take into account thermal effects, the catalytic boundary condition of S. Arcidiacono, J. Mantzaras, and I. V. Karlin [Phys. Rev. E 78, 046711 (2008)] is adapted to account for temperature variations. Speed of sound simulations further demonstrate the physical integrity and unique features of the model.

Microkinetic Modeling of Ethane Total Oxidation on Pt

Catalytic total oxidation is important in several applications. However, associated models are rather empirical. In this study, a microkinetic model is developed for ethane total oxidation, under f...

Evidence of A–B site cooperation in the EuFeO3 perovskite from 151Eu and 57Fe Mössbauer spectroscopy, EXAFS, and toluene catalytic oxidation

EuFeO3 perovskite was considered as a case study of the cooperative effects of the rare earth and transition metal elements in the total catalytic oxidation of aromatic hydrocarbons. For this purpose, a EuFeO3 perovskite was prepared using the citrate route. Extensive characterization was performed via ex situ and in situ methods. EXAFS revealed that oxygen vacancies are formed in the nearest neighborhood of Fe and next-nearest neighborhood of Eu. Combining 151Eu and 57Fe Mössbauer experiments also suggested local oxygen defects in the proximity of the Eu cations during the reaction, as well as cooperative electron delocalization effects between Eu and Fe. XPS has shown the +3 oxidation state of both Eu and Fe cations and the relatively strong ionicity of the Fe–O chemical bonds, as suggested by the weakened 2p3/2 satellite in the Fe2p spectrum. A systematic change of this satellite with the A cation in AFeO3 perovskites was also discussed. The thermal treatment of the catalyst at 623K, in air or toluene, was accompanied by a partial reduction of Fe and a partial oxidation of Eu, respectively. The interaction between the two elements appeared to be influenced mainly by the temperature and only slightly by the sample environment during further treatments. Catalytic oxidation of toluene on this perovskite led only to the production of carbon dioxide and water with no side-product formation from partial oxidation reactions. All the characterization and catalytic results preferably agree with a Volkenstein mechanism.

Mesoporous CexZr1−xO2 solid solutions supported CuO nanocatalysts for toluene total oxidation

Mesoporous CexZr1−xO2 solid solutions were prepared by the surfactant-assisted method and used as support of CuO nanocatalysts for catalytic total oxidation of toluene. The prepared CuO/CexZr1−xO2 catalysts have a wormhole-like mesoporous structure with high surface area and uniform pore size distribution, and the CuO nanoparticles were highly dispersed on the surface of CexZr1−xO2. The doping of ZrO2 in CeO2 promotes the dispersion of active copper species and enhances the reducibility of copper species. The effect of Ce/Zr ratio, calcination temperature and CuO loading amount on the catalytic performance of CuO/CexZr1−xO2 was investigated in detail. The 400°C-calcined 8%CuO/Ce0.8Zr0.2O2 catalyst exhibits the highest activity with the complete toluene conversion temperature of 275°C at the condition of GHSH=33,000h−1 and the toluene concentration of 4400ppm. The interfacial interaction between CuO and the CexZr1−xO2 support, highly dispersed CuO nanoparticles and the nature of the support contribute to the high catalytic activity of mesoporous CuO/CexZr1−xO2 nanocatalysts.

Synthesis of a catalyst of Mn–Fe–O by mechano-chemical reaction

In this work, the Fe–Mn–O system was mechanically processed in a high-energy ball-milling. The as milled powders were characterized by X-ray diffraction (XRD), temperature programmed reduction (TPR), X-ray photoelectron spectroscopy (XPS) and specific surface area measurement. Catalytic total oxidation of n-hexane was studied to find out the suitability of the material for VOC decomposition reaction. The route of the solid state transformation of Mn–Fe–O system has been established as a function of the cumulated energy from mechanical milling. Complex multicomponent catalysts, which may be difficult to prepare by conventional high temperature treatment, have been successfully prepared by milling.

Mesoporous Ce1−x Mn x O2 mixed oxides with CuO loading for the catalytic total oxidation of propane

High-surface-area mesoporous Ce1−x Mn x O2 mixed oxides were prepared by a surfactant-assisted method of nanocrystalline particle assembly, and their catalytic properties for the total oxidation of propane were evaluated using a microreactor–GC system. The prepared Ce1−x Mn x O2 particles were nanoscaled with fluorite structure, possessing a mesoporous structure with uniform pore-size distribution, which demonstrated very high activity for the propane total oxidation. The promoting effect of CuO on the catalytic activity of Ce1−x Mn x O2 was also investigated, indicating that the addition of copper could improve the catalytic activity for propane conversion. The catalytic behavior depended on the Ce/Mn ratio, the surface area and the mesoporosity of the catalysts. The catalyst with the Ce/Mn ratio of 1.5 exhibited the highest catalytic activity, suggesting a good candidate for replacing noble metal catalysts in the propane total oxidation.

Influence of hierarchically porous niobium doped TiO2 supports in the total catalytic oxidation of model VOCs over noble metal nanoparticles

An Nb doped, hierarchically micro(meso)macroporous TiO2 (anatase phase) was synthesised via a facile self-formation procedure and employed as a catalytic support, combining the advantages of a promoter with improved diffusion through the intrinsic macroporous network. The efficiency of the catalytic systems in the total oxidation of butan-1-ol and toluene was determined. Niobium was found to promote catalytic activity, with minimal secondary products. Indications suggest that reduction of the catalyst occurs at lower temperatures with an Nb dopant owing to stronger support–metal interactions, which boosts efficiency. This study found that noble metals, Pd and Pt, behave differently when deposited on Nb–TiO2 with Pt benefiting most from Nb doping, with a marked increase in activity and CO2 selectivity whereas Pd catalysts have improved low temperature activities. This work highlights the feasibility of economic and energetic reductions by minimising catalyst loading in favour of cheaper catalytic promoters and a reduction in operational temperature during VOC remediation.

Zeolite MCM-22 Modified with Au and Cu for Catalytic Total Oxidation of Methanol and Carbon Monoxide

The goal of this work was to use MCM-22 zeolites for preparation of monometallic (Cu or Au) and bimetallic (Cu and Au) catalysts for oxidation reactions. The focus was on precise determination of the nature of gold and copper species and their activity in the oxidation processes. For that purpose several characterization techniques were applied (XRD, N2 adsorption/desorption, TEM, SEM, UV–vis, H2-TPR, 27Al MAS NMR, FT-IR with the adsorption of pyridine, NO, and CO, ESR spectroscopy). They allowed us to define the following species formed on MCM-22 surface: metallic gold particles (XRD, UV–vis), isolated Cu2+ with octahedral coordination (UV–vis, ESR), square planar Cu2+ cations (ESR, IR), Cu+ species (ESR+NO, FTIR+CO, and FTIR+NO), and oligonuclear clusters (UV–vis) as well as CuO-like species (H2-TPR). The presence of gold on the MCM-22 surface modified further by copper species caused the interaction between two modifiers leading to much easier reduction of CuO-like species and higher mobility of oxygen...

Removal of BTX Compounds in Air by Total Catalytic Oxidation Promoted by Catalysts Based on SiO2(1-x)Cux

The aim of this study was to reduce the emissions of organic compounds, such as BTX (benzene, toluene and xylenes), due to their toxicity and adverse effects on the environment. In this regard, catalysts (SiO2(1-x)Cux) were developed which exhibit high catalytic activity for converting BTX compounds to CO2 and H2O, and which do not require the use of solvents and materials detrimental to the environment, with low production cost and good reproducibility. Cu (from copper(II) nitrate) was loaded (2.99; 5.01; 10.01 and 19.97 wt.%) onto supports (SiO2) by wet impregnation. The study was carried out within the temperature range of 50-350 oC. The catalysts described in this paper have high catalytic activity in the total oxidation of BTX. The conversion of benzene in this study exceeded 85% at 150 oC.

Mesoporous manganese oxide nanoparticles for the catalytic total oxidation of toluene

Mesoporous manganese oxide nanoparticles with the phases of tetragonal hausmannite, mixture of hausmannite Mn3O4 and monoclinic Mn5O8, and bixbyite Mn2O3 have been prepared by calcination of manganese acetate hydrate precursor at 200, 300, 400 and 700 °C, all of which were found to be active for the catalytic total oxidation of toluene. Their catalytic behavior depended on the oxidation state of manganese, the oxygen mobility and the amount of surface adsorbed oxygen species. The mesoporous nanoparticles calcined at 400 °C exhibited the highest catalytic performance with the complete toluene conversion temperature of 275 °C, suggesting that incorporating Mn5O8 into Mn3O4 could promote oxygen mobility, increase the amount of surface adsorbed oxygen and facilitate the activation of surface oxygen for the oxidation of toluene.

Synthesis and physicochemical characterization of nanostructured CeO2/clinoptilolite for catalytic total oxidation of xylene at low temperature

A series of nanostructured CeO2/Clinoptilolite catalysts with different loadings of ceria were prepared by redox reaction followed by wet impregnation method and tested for oxidation of xylene. The catalysts were characterized by XRD, FESEM, BET, FTIR, and TG‐DTG analysis. XRD data confirmed the formation of CeO2 as the crystalline phase with an average crystallite size of about 11.6 nm for three ceria loading of 10, 20, and 30%. FESEM and size distribution analyses showed that nanocatalysts have nanometric particles with an average size of 37.46 nm. Specific surface analysis revealed that the synthesized nanocatalysts had large enough surface area for catalytic oxidation of p‐xylene. Furthermore, the results showed that the catalytic performance of the supported CeO2 catalysts was much higher than that of treated clinoptilolite, in particular, CeO2 (30%)/Clinoptilolite exhibited the highest conversion, 98% at 350°C. It is observed that increasing both the xylene concentration and GHSV results in decreasing of the xylene conversion; however, even at higher concentrations of xylene (3000 ppm), the nanostructured catalyst has still enough destruction ability to reduce the pollutant. A simplified reaction mechanism was proposed with respect to the behavior of adsorbed species on the catalyst surface to clarify the path through which the reaction components interact with each other. © 2012 American Institute of Chemical Engineers Environ Prog, 32: 587–597, 2013

Comparative synthesis and physicochemical characterization of CeO2 nanopowder via redox reaction, precipitation and sol–gel methods used for total oxidation of toluene

ABSTRACTNanostructured CeO2 was successfully prepared using three different methods of redox reaction, precipitation and sol–gel methods. Their catalytic activities were studied toward total catalytic oxidation of toluene. The nanostructured CeO2 physicochemical properties were assessed by XRD, FESEM, BET, TPR‐H2, TPD‐CO2 and FTIR analyses. The XRD patterns showed that the synthesized catalysts had small crystalite size between 8.7 and 15.8 nm. The FESEM images reflected that the synthesized samples had nanoparticles less than 100 nm. BET analysis revealed that the synthesized CeO2 had large surface area in the order of redox reaction > precipitation > sol–gel. TPR patterns indicated that nano CeO2 had high reducibility. TPD‐CO2 showed the presence of weak and medium basic sites. Among synthesized samples, cerium oxide prepared from redox reaction was the most active in total oxidation of toluene. This feature was due to the smallest particle size, largest BET surface area and high reducibility of the nanocatalyst.The synthesized nano CeO2 had high activity and stability, which presents it as a suitable catalyst in catalytic applications. © 2011 Curtin University of Technology and John Wiley & Sons, Ltd.

Total catalytic oxidation of toluene using Pd impregnated on hierarchically porous Nb2O5 and Ta2O5 supports

A series of supported Pd catalysts were elaborated using hierarchically porous Nb2O5 and Ta2O5 materials, synthesised with and without a non-ionic surfactant. The deposition of Pd nanoparticles was achieved using the wet impregnation method on calcined supports. The catalytic systems were pre-reduced in hydrogen and investigated for their efficiency in the total oxidation of toluene and found to have increased activity in comparison to a series of reference catalysts based on hierarchically porous TiO2 and ZrO2, with minimal benzene formation. Results have shown how activities are dependent on the support material, synthesis conditions and chemical composition.

Synergy between tungsten and palladium supported on titania for the catalytic total oxidation of propane

Titania-supported palladium catalysts modified by tungsten have been tested for the total oxidation of propane. The addition of tungsten significantly enhanced the catalytic activity. Highly active catalysts were prepared containing a low loading of 0.5wt.% palladium, and activity increased as the tungsten loading was increased up to 6wt.%. Catalysts were characterised using a variety of techniques, including powder X-ray diffraction, laser Raman spectroscopy, X-ray photoelectron spectroscopy, temperature-programmed reduction and aberration-corrected scanning transmission electron microscopy. Highly dispersed palladium nanoparticles were present on the catalyst with and without the addition of WOx. However, the addition of WOx slightly increases the average palladium particle size, and there was some evidence for the Pd forming epitaxial islands on the support in the tungsten-doped samples. Surface analysis identified a combination of Pd0 and Pd2+ on a Pd/TiO2 catalyst, whereas all of the Pd loading was found in the form of Pd2+ with the addition of tungsten into the catalysts. At low tungsten loadings, isolated monotungstate and some polytungstate species were highly dispersed over the titania support. The concentration of polytungstate species increased as the loading was increased, and it was also promoted by the presence of palladium. The coverage of the highly dispersed tungstate species over the titania also increased as the tungsten loading increased. Some tungstate species were also found to be associated with the palladium oxide particles, and there was an enrichment of oxidised tungsten species at the peripheral interface of the palladium oxide nanoparticles and the titania. Sub-ambient temperature–programmed reduction experiments identified an increased concentration of highly reactive species on catalysts with palladium and tungsten present together, and we propose that the new WOx-decorated interface between PdOx and TiO2 particles may be responsible for the enhanced catalytic activity in the co-impregnated catalysts.