Influence of metal coating methods on the activity of bimetal-containing zeolite catalysts of Co,Pd-ZSM-5 in carbon monoxide oxidation

It has been established that catalytic activity in the CO oxidation of bimetal-containing zeolite Co,Pd-systems based on ZSM-5 and obtained via ion exchange and impregnation at different orders of the introduction of metal cations is higher than that of monometal-containing systems Co-ZSM-5 and Pd—ZSM-5. Through TPD of NH₃, it was determined that coordination-unsaturated bicationic associates are formed in Co,Pd/ZSM-5 zeolites obtained by ion exchange. It was found that the activity of bimetal-containing systems depends on the relation of the active components.     

Catalytic activity of Co/SiO2 and Co/TiO2 nanosized systems in the oxidation of carbon monoxide

The effects of the preparation procedure, active component concentration, and conditions of formation of nanosized cobalt-containing systems based on TiO₂ and SiO₂ mesoporous powders on their catalytic activity in the oxidation of carbon monoxide were studied. The active phase in the systems was cobalt spinel CoCo₂O₄ found in all samples. High catalytic activity was found in the samples characterized by relatively high contents of surface active centers (cobalt cations with octahedral surroundings).     

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^?1. 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 Cu²⁺ and Fe³⁺, respectively.     

Self-assembly of manganese oxide nanoparticles and hollow spheres. Catalytic activity in carbon monoxide oxidation

Reactions between MnSO(4) and KMnO(4) in the presence of carboxylic acids provide a facile, one-pot route to nanostructured manganese oxides with high surface areas. Acetic and propionic acid induce formation of hierarchical nanosphere morphologies whereas butyric acid promotes assembly of hollow spheres. The materials are active catalysts for CO oxidation.     

Copper-cerium oxide catalysts for the selective oxidation of carbon monoxide in hydrogen-containing mixtures: I. Catalytic activity

A series of copper-cerium oxide catalysts were prepared, and their properties toward the reaction of CO oxidation in hydrogen-containing gas mixtures were studied. It was found that the copper-cerium oxide catalysts are stable, active, and selective in this reaction. The conditions under which these catalysts decreased the concentration of CO from 1 to <10^?3 vol % in hydrogen containing water vapor and carbon dioxide were determined.     

Effect of preparation of Ag/Co composite oxide on characteristic and activity for carbon monoxide oxidation

We report our results on the development of 1:1 in molar Ag/Co composite oxide prepared by co-precipitation, and the effect of different rates of precipitation and heat treatment on the surface area, pore size and also catalytic activity for CO oxidation. It was observed that slow precipitation of the catalysts gave small pore sizes, high surface area and high activity for CO oxidation at low calcination temperatures. This revised version was published online in June 2006 with corrections to the Cover Date.     

Low-temperature oxidation of carbon monoxide over (Mn1 − x M x )O2 (M = Co, Pd) catalysts

(Mn_{1 ? x} M _x )O₂ (M = Co, Pd) materials synthesized under hydrothermal conditions and dried at 80°C have been characterized by X-ray diffraction, diffuse reflectance spectroscopy, electron microscopy, X-ray photoelectron spectroscopy, and adsorption and have been tested in CO oxidation under CO + O₂ TPR conditions and under isothermal conditions at room temperature in the absence and presence of water vapor. The synthesized materials have the tunnel structure of cryptomelane irrespective of the promoter nature and content. Their specific surface area is 110–120 m²/g. MnO₂ is morphologically uniform, and the introduction of cobalt or palladium into this oxide disrupts its uniformity and causes the formation of more or less crystallized aggregates varying in size. The (Mn,Pd)O₂ composition contains Pd metal, which is in contact with the MnO₂-based oxide phase. The average size of the palladium particles is no larger than 12 nm. The initial activity of the materials in CO oxidation, which was estimated in terms of the 10% CO conversion temperature, increases in the following order: MnO₂ (100°C) < (Mn,Co)O₂ (98°C) < (Mn,Co,Pd)O₂ (23°C) < (Mn,Pd)O₂ (?12°C). The high activity of (Mn,Pd)O₂ is due to its surface containing palladium in two states, namely, oxidized palladium (interaction phase) palladium metal (clusters). The latter are mainly dispersed in the MnO₂ matrix. This catalyst is effective in CO oxidation even at room temperature when there is no water vapor in the reaction mixture, but it is inactive in the presence of water vapor. Water vapor causes partial reduction of Mn⁴⁺ ions and an increase in the proportion of palladium metal clusters.     

Catalytic activity of electrodeposited copper-containing compounds in conversion of carbon monoxide by steam

Possibility of using an ultradisperse copper-containing powder produced by the electrolytic method as an efficient catalyst for conversion of carbon monoxide by steam was studied.     

The effects of the conditions of formation of Ag-Co zeolite supported systems on their activity in the oxidation of carbon monoxide

The activity of Ag-Co zeolite catalysts in the oxidation of CO was studied. The peculiarities of the formation of Ag-Co-NaX systems with different active metal ratios were studied. The temperatures of hydrogen absorption maxima in the H₂ temperature-programmed reduction spectra of Ag-Co-NaX systems with different Ag/Co ratios correlated with the catalytic activity in the oxidation of CO. Different valence states of silver (Ag⁺, Ag⁰) and cobalt (Co³⁺, Co²⁺) were observed by X-ray photoelectron spectroscopy. It was found that the mutual influence of these states in the surface layer of Ag-Co zeolite catalysts affected their activity.     

Catalytic activity and regeneration property of a Pd nanoparticle encapsulated in a hollow porous carbon sphere for aerobic alcohol oxidation

A core-shell composite consisting of a palladium (Pd) nanoparticle and a hollow carbon shell (Pd@hmC) was employed as a catalyst for aerobic oxidation of various alcohols. The core-shell structure was synthesized by consecutive coatings of Pd nanoparticles with siliceous and carbon layers followed by removal of the intermediate siliceous layer. Structural characterizations using TEM and N(2) adsorption-desorption measurements revealed that Pd@hmC thus-obtained was composed of a Pd nanoparticle core of 3-6 nm in diameter and a hollow carbon shell with well-developed mesopore (ca. 2.5 nm in diameter) and micropore (ca. 0.4-0.8 nm in diameter) systems. When compared to some Pd-supported carbons, Pd@hmC showed a high level of catalytic activity for oxidation of benzyl alcohol into benzaldehyde using atmospheric pressure of O(2) as an oxidant. The Pd@hmC composite also exhibited a high level of catalytic activity for aerobic oxidations of other primary benzylic and allylic alcohols into corresponding aldehydes. The presence of a well-developed pore system in the lateral carbon shell enabled efficient diffusion of both substrates and products to reach the central Pd nanoparticles, leading to such high catalytic activities. This core-shell structure also provided high thermal stability of Pd nanoparticles toward coalescence and/or aggregation due to the physical isolation of each Pd nanoparticle from neighboring particles by the carbon shell: this specific property of Pd@hmC resulted in possible regeneration of catalytic activity for these aerobic oxidations by a high-temperature heat treatment of the sample recovered after catalytic reactions.     

The mercury-sensitized oxidation of carbon monoxide

The mercury-photosensitized oxidation of CO was studied at 275°C over a wide range of [O₂]/[CO] ratios in the absence and presence of the oxygen atom scavenger 2-trifluoromethylpropene (TMP) and at 25°C at low [O₂]/[CO] ratios in the presence of TMP. By following the quantum yield of CO₂ production, Φ {CO₂}, as a function of the [O₂]/[CO] ratio, the reactions of vibrationally excited CO (v υ 9) and electronically excited O₂, probably in the c¹Σ^?_u state, were studied. At low [O₂]/[CO] ratios the predominant reactions are of vibrationally excited CO (v υ 9). Relative rate constants for chemical reaction versus deactivation of CO (v υ 9) were obtained. At higher [O₂]/[CO] ratios, the principal reactions are of electronically excited O₂. Relative rate constants for chemical reactions and deactivation of this electronically excited O₂ with CO, O₂, and TMP were obtained. From the effect of total pressure on Φ {CO₂}, it is proposed that an intermediate CO₃ is formed in the reaction of electronically excited O₂ with CO.     

Catalytic activity of Pd/CN systems in hydrogenation of styrene

Hydrogenation of styrene was applied as a test reaction to study the catalytic activity of Pd deposited on the surface of carbonaceous materials enriched with nitrogen (C_N). The nitrogen content in the support material was found to have a great influence on the degree of styrene conversion to ethylbenzene. In addition, the reaction was carried out in the presence of modified carbonaceous materials acting as catalysts.