Papers by Keyword: CO Oxidation

Abstract: Platinum and iridium are known to belong to a family of partly miscible metals. On the other hand, these metals are high demanded as active components of the catalysts for a variety of industrially important processes. In the present work, a series of bimetallic Pt-Ir catalysts supported on alumina were prepared using a “single source precursor” concept. The ratio of metals in the alloy was varied from 1:3 to 3:1. The thermal stability and catalytic activity in CO oxidation of the samples were studied in a prompt thermal aging regime. Monometallic Pt/γ-Al₂O₃ and Ir/γ-Al₂O₃ samples were used as references. All the studied catalysts were characterized by UV-vis spectroscopy in initial state and after the aging treatment. It was found that the bimetallic nanoparticles being subjected to the high temperature aging at 600 and 800 °C undergo redistribution with further stabilization in a noticeably more active state. The observed increase in the catalytic activity is explained by an enrichment of the particles’ surface with platinum.

Abstract: In the present work, the impact of the rhodium deposition on the thermal stability of ceria-based catalysts was studied. The samples were prepared by an incipient wetness impregnation of the support with aqueous solution of rhodium nitrate. The loading of Rh was 0.1 and 1 wt.%. The textural characteristics of the samples were examined by a low-temperature nitrogen adsorption. It was shown that the addition of rhodium intensifies the process of ceria agglomeration, which leads to the lower values of specific surface area along with increased average pore diameter after the aging at 1000 °C. Stability of the catalysts was investigated by means of a prompt thermal aging procedure. The high-loaded catalyst (1 wt.% Rh/CeO₂) was more active than the 0.1 wt.% Rh/CeO₂ sample, while the stability of both the catalysts was excellent. It should be emphasized that the alumina-based reference samples with the similar rhodium loading were significantly less active and poorly stable.

Abstract: New data on the structure of silicon-containing oxide layers SiO₂+TiO₂ on titanium formed by the method of plasma electrolytic oxidation (PEO) as well as on the structure and catalytic activity in CO oxidation of MnO_x+SiO₂+TiO₂/Ti composites formed on their basis using impregnation and annealing methods have been obtained. It has been demonstrated that silicon and titanium are rather homogeneously distributed over the SiO₂+TiO₂ coating bulk. The coating outer part is silicon-enriched titanium-depleted. The MnO_x+SiO₂+TiO₂/Ti composites catalyze the CO conversion at temperatures above 100°C. Nanowhiskers consisting predominantly of manganese oxides have been found on the surface of the MnO_x+SiO₂+TiO₂/Ti composites.

Abstract: In recent years, with the aggravating of environmental pollution, the purification of carbon monoxide is currently a subject of interest. The catalytic oxidation method is an effective way. Manganese oxide nanoparticles were prepared by emulsion self-assembly method and then, synthetic and commercial manganese oxide-supported gold nanoparticle catalysts were successfully synthesized by the deposition-precipitation (DP) method. The catalysts were characterized by XRD, Raman, BET, ICP and HRTEM. The activity of the oxide and oxide-supported gold nanoparticle catalysts were evaluated on the fixed bed microreactor and Au/MnO_x had the highest activity. The intrinsic activity of Au/MnO_x at 35 °C is 0.81 mol_CO·mol^-1_Au·min^-1. Compared with O₂, CO concentration has bigger effect on the reaction activity.

Abstract: Mesoporous ceria catalysts were prepared by nanocasting of a mesoporous carbon and KIT-6. The prepared mesoporous ceria catalysts were used to catalyze CO oxidation. The various characterization techniques were employed to study the relationship between catalyst nature and catalytic properties. The results indicate that ceria prepared by using mesoporous carbon as template possess an ordered mesoporous architecture and exhibit much better catalytic activity compared with those prepared by using KIT-6 as template. The residual SiO₂ from KIT-6 was demonstrated to be the main reason for the much worse catalytic activities by the characterization results of X-ray Fluorescence Spectrometer and FTIR spectra.

Abstract: Atmospheric-pressure dielectric barrier discharge (DBD) cold plasma was used to prepare high performance Au/P25 catalysts (Au/P25-P). XRD and UV-Vis DRS spectra for Au/P25 catalysts were performed. The results indicated that the size of Au nanoparticles in Au/P25-P was smaller than that prepared by conventional thermal impregnation method (Au/P25-H). The temperature-dependent CO oxidation was performed to investigate the activity of Au/P25 catalysts. Au/P25-P gave excellent catalytic activity for CO oxidation than that of Au/P25-H. This may be attributed to the smaller size of Au nanoparticles in Au/P25-P.

Abstract: The catalytic activity of Ni-Al (Ni25Al) nanoparticles fabricated by thermal plasma evaporation was examined for methanol decomposition and CO oxidation. The nanoparticles exhibited high activity for both reactions. Characterization of the nanoparticles revealed that the fabricated nanoparticles were mainly comprised of Ni and Ni₃Al phases. During CO oxidation, the Ni phase was oxidized to NiO, while the Ni₃Al phase remained unchanged. The NiO phase is supposed to serve as the active sites for CO oxidation. In contrast, during methanol decomposition, no obvious oxidation was observed for both Ni and Ni₃Al phases. The Ni and Ni₃Al phases are supposed to contribute to the high activity for methanol decomposition.

Abstract: Silicon-containing oxide layers deposited on titanium using the plasma electrolytic oxidation (PEO) method were modified with manganese and cobalt compound through impregnation followed by annealing. The obtained manganese composites are catalytically active in the process of oxidation of CO at 100 оС, while cobalt-containing structures demonstrate this type of activity at temperatures above 200оС. The composition and surface structure of the obtained systems were investigated by means of X-ray phase and energy dispersive analyses and by high resolution scanning electron microscopy (SEM). Granule-like particles with diameters of a few dozens of nanometers were observed on the surface of oxide-cobalt layers on titanium, whereas the surface of oxide-manganese layers was coated by nano-whiskers of diameters <50 nm and length <1 μm. The presence of manganese-containing nano-whiskers substantially increases the catalyst specific surface, thus facilitating the attainment of higher degree of transformation of initial gaseous substances.

Abstract: A series of mesoporous TiO2 supports were synthesized by the sol-gel template method by using different surfactant and Au/TiO2 catalysts were prepared by the solution reduction method. The catalytic oxidation of CO was taken as the probe reaction for comparing the catalyst activity. Wide-angle XRD patterns and N2 adsorption–desorption isotherms revealed that the TiO2 with crystallized anatase and mesoporous structure can be synthesized after an optimized sol-gel template method. The results indicated that the pore size of TiO2 plays a key role in the catalyst activity. Among them the activity of Au/TiO2-F1 catalyst synthesized by using the F127 surfactant demonstrated superior activity to other catalysts. CO could be converted at 70 °C.

Abstract: Mesoporous CeO2 was first synthesized by hydrothermal method, and then used to synthesize different content of (Co3O4)x/CeO2 (x was the molar ratio of Cu and Co) by deposition-precipitation method. The fresh and doped catalysts were characterized by X-ray diffraction (XRD), N2 adsorption and desorption, H2 temperature programmed reduction (H2-TPR) and O2 temperature programmed desorption (O2-TPD) to study the crystal structure, surface area, and the mechanism of CO oxidation. The results show that: In XRD pattems, the doped cobalt amounts of samples from x=20% to x=100% have Co3O4 crystal structure. The N2 adsorption and desorption indicated the samples were mesoporous structure. Compared with other samples, the better reducibility and activity oxygen species of (Co3O4)50%/CeO2 coincided with its better catalytic activity.