Low-temperature Carbon Monoxide Oxidation Research Articles

Low-temperature oxidation of carbon monoxide on Pd(Pt)/CeO2 catalysts prepared from complex salts

Catalysts containing cerium oxide as a support and platinum and palladium as active components for the low-temperature oxidation of carbon monoxide were studied. The catalysts were synthesized in accordance with original procedures with the use of palladium and platinum complex salts. Regardless of preparation procedure, the samples prepared with the use of only platinum precursors did not exhibit activity at a low temperature because only metal and oxide (PtO, PtO2) nanoparticles were formed on the surface of CeO2. Unlike platinum, palladium can be dispersed on the surface of CeO2 to a maximum extent up to an almost an ionic (atomic) state, and it forms mixed surface phases with cerium oxide. In a mixed palladium-platinum catalyst, the ability of platinum to undergo dispersion under the action of palladium also increased; as a result, a combined surface phase with the formula PdxPtyCeO2 − δ, which exhibits catalytic activity at low temperatures, was formed.

Base Metal Oxides Active for Low Temperature CO Oxidation

Among base metal oxides, Co3O4, MnO2, and NiO, which have p-type semiconducting properties, hold potential catalytic capability for the oxidation of carbon monoxide (CO) at temperatures below 0oC. Either of the following requirements should be fulfilled; low moisture content in reaction feed, optimum temperature and atmosphere for catalyst pretreatments, and the control of metal oxide morphology. Surface oxygen vacancies are assumed to play a key role in low temperature CO oxidation.

The role of hydroxyl groups in low temperature carbon monoxide oxidation

Using the unique ability of inelastic neutron scattering spectroscopy to quantify surface hydroxyls, it is shown that two hydroxyls are essential for the low temperature oxidation of CO over a model palladium catalyst.

Preparation of nickel nanoparticles for catalytic applications

Spherical oxidized nickel particles 15 to 200 nm in average size have been produced by a crucibleless aerosol method involving metal vapor condensation in an inert gas flow and oxidation processes. The particles have been characterized by scanning electron microscopy, X-ray microanalysis, X-ray diffraction, BET surface area measurements, and vibrating-sample magnetometry. The process parameters have been optimized for the preparation of particles with tailored size, specific surface area, and saturation magnetization. A dc electric field applied to the condensation zone during the oxidation process reduces the size and increases the extent of oxidation of the particles. We have studied low-temperature oxidation of carbon monoxide and propane on nickel nanopowders differing in particle size and extent of oxidation. The nanoparticles with optimized characteristics have been shown to have a marked catalytic effect on these processes.

Supported gold nanocatalyst for low temperature CO oxidation and combustion of volatile organic compounds (VOC)

Carbon monoxide (CO) and volatile organic compounds (VOC), such as butadiene and isoprene, are air pollutants emitted by many industrial sources, such as burning of wood and fuel with poor ventilation, and by natural sources including forest fires or volcanic eruptions. It was found that these compounds are also significantly abundant in many industrial processes. Therefore, low-temperature catalytic oxidation of CO and combustion of VOC is one of the most important problems in catalysis, since even small exposures to CO or VOC (ppm) can be lethal. Catalytic oxidation is one effective method of removing CO. Nanoparticle catalysts are characterized by a large surface area, high dispersion and strong metal-support interaction. It is therefore expected that nanoparticle catalysts would show high catalytic activity for the low temperature oxidation of CO. Our results demonstrate the application of the vapor phase synthesis to synthesize supported and unsupported nanoparticle catalysts for CO oxidation. The method is based on the laser vaporization/controlled condensation (LVCC) technique of gold (Au) and copper (Cu) nanoparticles supported on a variety of oxide supports such as CeO2, TiO2, CuO and MgO. Our results indicate that Au nanoparticles supported on CeO2 exhibit higher catalytic activity than Au supported on other oxides. This high activity is attributed to the strong interaction of Au with CeO2. The results also indicate that 5 % Au loading on CeO2 has higher activity than 2% Au or 10% Au. The effect of preparation method on the catalytic activity is investigated. It was found that the catalytic activity for 5%Au/CeO2 prepared by the chemical (deposition-precipitation) method is higher than the catalytic activity of Au/CeO2 prepared by physical (LVCC). In any combustion system, there are significant amounts of other toxic gases,besides CO, such as nitric oxide, butadiene, and isoprene. We investigated the catalytic activity of the Au/CeO2 nanoparticle catalyst in the presence of 1000 ppm of butadiene and in the presence of 1000 ppm of isoprene. Our results indicate the combustion of butadiene and isoprene to CO2 and H2O, as supported by the mass spectrum and the CO conversion curve. Finally, the Au/CeO2 nanoparticle catalyst can be an active catalyst for selective CO oxidation at temperatures below 300oC even in the presence of VOC. Furthermore, this catalyst shows great promise for the low temperature combustion of VOC such as butadiene and isoprene.

Low-temperature oxidation of carbon monoxide and methane over alumina and ceria supported platinum catalysts

The ignition and extinction processes for total oxidation of CO, CH4 and CO+CH4 mixture in oxygen excess over Pt/Al2O3 and Pt/CeO2 catalysts with the platinum phase distributed either homogeneously or heterogeneously (i.e., locally high platinum concentration) in the support have been studied by temperature programmed oxidation experiments. Following the preparation methods by Arnby et al. [42], the samples have the same Pt load and dispersion. Generally the catalytic activity follows the order: Pt/CeO2 (heterogeneous)>Pt/CeO2 (homogeneous)>Pt/Al2O3 (heterogeneous)>Pt/Al2O3 (homogeneous) as indicated by lower ignition and/or extinction temperatures. For Pt/Al2O3, the addition of NO2 to the reactant stream increases the rate of oxidation of CO in the pre-ignition regime although the light-off temperature T50 is shifted towards higher temperatures (except for low CO concentrations). In the case of the Pt/CeO2, the CO conversion generally decreases. For CH4 oxidation in the presence of NO2, the conversion increases for Pt/Al2O3 and decreases for Pt/CeO2. The addition of CO2 in the reactant stream has minor influence on CO oxidation over Pt/Al2O3 while for Pt/CeO2, T50 is shifted towards higher temperatures. For the simultaneous oxidation of CO and CH4, a reverse hysteresis for methane oxidation is observed, i.e., the extinction process occurs at higher temperature than the corresponding ignition process. The improved activity for CO oxidation over samples with heterogeneous Pt distribution is likely due to less tendency towards CO self-poisoning through the development of steeper concentration gradients in the Pt containing regions in the porous support material. The significant increase of activity for both reactions over ceria-supported Pt is here assigned to highly active sites at the platinum–ceria boundary but also, to some extent, the oxygen storage and release function and dynamics of the transport of oxygen in the Pt/CeO2 system.

Preparation, Characterization, and Catalytic Behavior of Nanostructured Mesoporous CuO/ZrO2 Catalysts for Low-Temperature CO Oxidation

High-surface area mesoporous 20 mol% CuO/ZrO2 catalyst was prepared by a surfactant-assisted method of nanocrystalline particle assembly, and characterized by x-ray powder diffraction (XRD), N2 adsorption, transmission electron microscopy (TEM), H2-TPR, TG-DTA, and x-ray photoelectron spectra (XPS) techniques. The catalytic properties of the CuO/ZrO2 nanocatalysts calcined at different temperature were evaluated by low-temperature carbon monoxide oxidation using a CATLAB system. The results showed that these mesoporous nanostructured CuO/ZrO2 catalysts were very active for low-temperature CO oxidation and the CuO/ZrO2 catalyst calcined at 400°C exhibited the highest catalytic activity.

Low temperature carbon monoxide oxidation over nanosized silver doped manganese dioxide catalysts

Nanosized silver doped manganese dioxide catalysts have been prepared and tested for CO oxidation reaction at lower temperature. Silver doped manganese dioxide catalysts show higher CO conversion as compared to undoped manganese dioxide. Under the influence of excess oxygen catalysts are stable and show good activity. From time on stream experiments it is clear that the catalysts are highly stable for CO oxidation for a longer period in absence of moisture as well as in presence of moisture in the feed gas. The catalysts show higher activity for CO conversion in presence of moisture, indicating that moisture facilitates CO oxidation reaction on the catalyst surface.

Characterization of Hydrous Palladium Oxide: Implications for Low-Temperature Carbon Monoxide Oxidation

The structure of hydrous palladium oxide has been investigated by powder diffraction with both X-rays and neutrons, transmission electron microscopy, inelastic neutron scattering spectroscopy, infrared spectroscopy, and periodic-DFT calculations. The results clearly show the formulation as PdO·H2O is correct rather than as Pd(OH)2 as has been proposed previously. The material is best described as ∼18 A diameter particles of nanocrystalline PdO with a monolayer or so of hydroxyls capped by 4−7 layers of water. The very small nanocrystallites are agglomerated into larger clusters which reduces the effective surface area. This structure is very similar to that proposed for hydrous ruthenium oxide, RuO2·xH2O, x = 2, and for water on anatase and rutile. This model provides a quantitative explanation for why hydrous palladium oxide deactivates three times faster at 25 °C than at 100 °C in the low-temperature oxidation of CO to CO2.

New Au/FeOx/SiO2 catalysts using deposition–precipitation for low-temperature carbon monoxide oxidation

Abstract An easy and efficient method for the preparation of the new Au/FeOx/SiO 2 catalysts towards low-temperature CO oxidation has been developed. FeO x promoted SiO 2 calcined at different temperatures were used as novel carriers and supported Au catalysts were prepared by precipitation–deposition technique. It was found that the carrier only dried at 383 K supported Au catalyst exhibited better catalytic activity, over which CO conversion reached 100% at a temperature as low as 350 K. Higher dispersion of FeO x and Au, more active sites and stronger interaction between Au and FeO x could be responsible for its higher activity.

Role of Au−C Interactions on the Catalytic Activity of Au Nanoparticles Supported on TiC(001) toward Molecular Oxygen Dissociation

High-resolution photoemission and density functional calculations on realistic slab surface models were used to study the interaction and subsequent dissociation of O(2) with Au nanoparticles supported on TiC(001). The photoemission results indicate that at 150 K O(2) adsorbs molecularly on the supported gold nanoparticles, and upon heating to temperatures above 200 K the O(2) --> 2O reaction takes place with migration of atomic oxygen to the TiC(001) substrate. The addition of Au to TiC(001) substantially enhances the rate of O(2) dissociation at room temperature. The reactivity of Au nanoparticles supported on TiC(001) toward O(2) dissociation is much larger than that of similar nanoparticles supported either on TiO(2)(110) or MgO(001) surfaces, where the cleavage of O-O bonds is very difficult. Density functional calculations carried out on large supercells show that the contact of Au with TiC(001) is essential for charge polarization and an enhancement in the chemical activity of Au. Small two-dimensional particles which expose Au atoms in contact with TiC(001) are the most reactive. While O(2) prefers binding to Au sites, the O atoms interact more strongly with the TiC(001) surface. The oxygen species active during the low-temperature (<200 K) oxidation of carbon monoxide on Au/TiC(001) is chemisorbed O(2). Once atomic O binds to TiC(001), the chemisorption bond is so strong that temperatures well above 400 K are necessary to remove the O adatoms from the TiC(001) substrate by direct reaction with CO. The high reactivity of Au/TiC(001) toward O(2) at low-temperature opens the route for the transformation of alcohols and amines on the supported Au nanoparticles.

Effective platinum catalysts for low-temperature oxidation of CO

A number of platinum-based catalysts bonded on carbon fiber karbopon were prepared using alcohol solutions of H2PtCl6. The catalytic activity of the samples was determined in the low-temperature oxidation of carbon monoxide by oxygen. The effect of the solvent nature of the precursor on the activity of the catalysts was determined. The best results were obtained in the presence of 1.5% Pt/karbopon catalyst prepared using isobutyl alcohol; 100% CO conversion was achieved in respiratory treatment (12000 h−1, room temperature).

Catalytic systems based on carbon fiber materials for the low-temperature oxidation of carbon monoxide

New heterogenized catalytic systems for the low-temperature oxidation of CO were synthesized by supporting solutions of Pd, Cu, and Fe salts on carbon fibrous materials (carbopon and busofit). The carbon supports were studied by elemental analysis, SEM, TGA, and TPD. The effects of the nature of the support, the concentration and composition of the active component, and the conditions of preparation on the efficiency of the catalytic system were studied. It was ascertained that attenuation of hydrophilic properties of the support led to the decrease in system activity. The investigation of the catalysts by XPS showed that sample treatment in the reaction medium results in redistribution of the components of the active phase in the near-surface layer of the catalyst. The catalytic system based on carbon fibrous material carbopon prepared by supporting active components (Pd, Cu, and Fe salts) in three stages with intermediate activation in the reaction medium ensures 95% conversion of CO under respiratory conditions, and is promising for the design of the main element of breathing masks on its basis.

Mesoporous Ce0.8Zr0.2O2 solid solutions-supported CuO nanocatalysts for CO oxidation: a comparative study of preparation methods

Ce0.8Zr0.2O2 solid solutions were prepared by three different methods, namely, surfactant-assisted, co-precipitation, and sol–gel methods, and were used as supports of CuO nanocatalysts by the deposition-precipitation (DP) method. The prepared supports and catalysts were characterized by using XRD, N2 adsorption, TEM, and H2-TPR techniques. The influence of preparation methods on the low-temperature carbon monoxide oxidation activity of these CuO/Ce0.8Zr0.2O2 catalysts was investigated comparatively by using a microreactor-GC system. The catalyst prepared by surfactant-assisted method is more active for low-temperature CO oxidation than the ones prepared by the co-precipitation and sol–gel methods. The support and catalysts prepared by surfactant-assisted method possess mesoporous framework, nanoscale particle size, and high surface area, improving the synergistic effect between CuO species and support, which is beneficial for enhancing the catalytic performance of low-temperature CO oxidation.

Synthesis and physicochemical characterization of palladium-cerium oxide catalysts for the low-temperature oxidation of carbon monoxide

The effect of CeO2 preparation procedure on the electronic and structural states of the active component of Pd/CeO2 catalysts and their activity in the low-temperature reaction of CO oxidation was studied. The following two nonequivalent states of palladium were detected in the catalysts having low-temperature activity using XPS and IR spectroscopy: Pd0(Pdδ+) as the constituent of a palladium-reduced interaction phase and Pd2+ as the constituent of a palladium-oxidized interaction phase Pd x CeO2 −δ. It was found that the procedure used for preparing a CeO2 support considerably affected the formation of these phases and quantitative ratios between them. It was demonstrated that the palladium-oxidized interaction phase was responsible for low-temperature activity, whereas the palladium-reduced interaction phase was responsible for activity in the region of medium and high temperatures.

Robust Gold-Decorated Silica−Titania Pebbles for Low-Temperature CO Catalytic Oxidation

A deposition-precipitation (DP) process was used to prepare silica-titania core-shell pebbles decorated with nanocrystalline gold suitable for low-temperature catalytic oxidation of carbon monoxide (CO). The microstructure, phase content, crystallography, and catalytic activity were correlated with the pH (3-8), aging time (15, 30, 60 min), and heat treatment employed for gold crystallization (200-400 degrees C). A homogeneous metal distribution, high gold loading (3.7-4.4 wt %), and superior interfacial adhesion between gold and titania were obtained when the support pebbles were prepared at 600 degrees C, a temperature lower than that required for the anatase-to-rutile transformation. Nucleation and growth of {111} faceted gold was favored at mid-pH (6.4-8), while smaller crystals (<7.5 nm) were obtained at short aging times (<or=60 min) and low growth temperatures (<or=300 degrees C). Catalytic activity was optimized by homogeneously dispersing gold nanocrystals (3 nm) using pH 6.4 and an aging time of 30 min. These robust materials may offer superior activity and lifetimes when deployed in fluidized bed catalytic cracking units.

Palladium doped manganese dioxide catalysts for low temperature carbon monoxide oxidation

Nano-sized palladium doped manganese dioxide catalysts with varying compositions were prepared by the co-precipitation method. Palladium doped manganese dioxide catalysts show markedly enhanced CO oxidation activity, and CO conversion even at 35 °C. Strong interaction occurs between palladium and manganese dioxide which results in high catalytic activity and total CO conversion occurs at a lower temperature. Activity test carried out at fixed temperature indicate that the catalysts retain their activity with increasing time. The moisture influenced the catalytic activities considerably. The SEM study shows that particles are nano-sized and almost spherical in shape.

Supported metal catalysts based on fibrous carbon material for low-temperature CO oxidation

A number of supported-metal (Pt, Pd) catalysts based on Karbopon nonwoven carbon fibers were prepared by deposition from hydrosols and by ion exchange. The catalytic activity of the catalysts in low-temperature oxidation of carbon monoxide by atmospheric oxygen was determined. Catalyst samples were studied by transmission electron microscopy.

Corrigendum to “The preparation and catalytic behavior of CuO/Ti Sn1−O2 catalysts for low-temperature carbon monoxide oxidation” [Catal. Comm. 9 (2008) 2131–2135

Corrigendum to “The preparation and catalytic behavior of CuO/Ti Sn1−O2 catalysts for low-temperature carbon monoxide oxidation” [Catal. Comm. 9 (2008) 2131–2135

Catalytic systems based on carbon supports for the low-temperature oxidation of carbon monoxide

Catalytic systems containing palladium, copper, and iron compounds on carbon supports-kernel activated carbon and fibrous carbon materials (Karbopon and Busofit)-for the low-temperature oxidation of CO were synthesized. The effects of the nature of the support, the concentration and composition of the active component, and the conditions of preparation on the efficiency of the catalytic system were studied. The catalytic system based on Karbopon exhibited the highest activity: the conversion of carbon monoxide was 90% at room temperature and a reaction mixture (0.03% CO in air) space velocity of 10 000 h. It was found that the metals occurred in oxidized states in the course of operation: palladium mainly occurred as Pd, whereas copper and iron occurred as Cu and Fe, respectively. © 2008 MAIK Nauka.