Temperature CO Oxidation

The oxidation of CO is the simplest reaction and has been the most intensively studied since Langmuir first presented a theory of adsorption and catalysis for this reaction [13]. Supported Au NPs such as Au/Ti02, Au/Fe203 and Au/Co304 are extraordinarily active in CO oxidation, even at 200 K, and are much more active than the other noble metals catalysts at temperatures below 400 K [14—16]. Gold clusters composed of several atoms can promote the reaction between CO and 02 to form C02 at as low as 40 K [17]. Most recently, Lahr and Ceyer [18] have extended the temperature range at which the activity for CO oxidation is observed to as low as 70 K by using an Au/Ni surface alloy. 

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Effect of ozone pretreatment on low temperature CO oxidation catalysts... 

Titanium dioxide supported gold catalysts exhibit excellent activity for CO oxidation even at temperatures as low as 90 K [1]. The key is the high dispersion of the nanostructured gold particles over the semiconducting Ti02 support. The potential applications of ambient temperature CO oxidation catalysts include air purifier, gas sensor and fuel cell [2]. This work investigates the effects of ozone pretreatment on the performance of Au/Ti02 for CO oxidation. 

Room temperature CO oxidation has been investigated on a series of Au/metal oxide catalysts at conditions typical of spacecraft atmospheres CO = 50 ppm, COj = 7,000 ppm, H2O = 40% (RH) at 25 C, balance = air, and gas hourly space velocities of 7,000- 60,000 hr . The addition of Au increases the room temperature CO oxidation activity of the metal oxides dramatically. All the Au/metal oxides deactivate during the CO oxidation reaction, especially in the presence of CO in the feed. The stability of the Au/metal oxide catalysts decreases in the following order TiOj > FejO, > NiO > CO3O4. The stability appears to decrease with an increase in the basicity of the metal oxides. In situ FTIR of CO adsorption on Au/Ti02 at 25 C indicates the formation of adsorbed CO, carboxylate, and carbonate species on the catalyst surface. 

The objective of this study was to develop a low temperature CO oxidation catalyst that continually removes low concentrations of CO from the atmospheres of space stations. CO is a major contaminant in spacecraft environments. Since... 

The activity of the Au/metal oxide catalysts is extremely sensitive to the method of preparation. The Au/metal oxide catalysts were prepared by the co-precipitating method [1]. During the course of this study, we have determined that the activity and the stability of the catalyst for room temperature CO oxidation were a function of Ph of the solution, temperature of precipitation, aging temperature and time, catalyst wash procedure, and calcination. 

CO oxidation on 1%Au supported on various metal oxide catalysts was carried out to determine the effect of metal oxide on the activity and stability of the catalysts during room temperature CO oxidation. Figure 4 shows the CO conversion as a function of time on stream on 1%Au supported on various metal oxides such as CO3O4, Fe Oj, NiO, ZrOj, and TiO. All the catalysts showed high initial CO conversions. The stability of the catalysts decreased in the following order TiO > ZrOj > NiO > FejOj > CO3O4. The stability of the catalysts appears to decrease with increasing basicity of the metal. 

Au/metal oxides are active for low temperature CO oxidation. The activity of the catalysts is very sensitive to catalyst preparation. All the Au/metal oxides tested for room temperature CO oxidation deactivated substantially with time. The deactivation... 

Tian, F. and Ding, Y. (2006) Low temperature CO oxidation over unsupported nanoporous gold. 

Grunwaldt J-D, Maciejewski M, Becker OS, et al. 1999. Comparative Study of Au/Ti02 and AU/Z1O2 catalysts for low-temperature CO oxidation. J Catal 186 458-469. 

Lopez N, Janssens TVW, Clausen BS, et al. 2004a. On the origin of the catal3dic activity of gold nanoparticles for low-temperature CO oxidation. J Catal 223 232-235. 

Au-Pd alloys with compositions close to that of the bulk components and that particle sizes were ca. 25 to 50 nm in diameter. The catalysts that were effective for H2O2 synthesis were found to be wholly inactive for CO oxidation at ambient temperature, and catalysts that were effective for low temperature CO oxidation were inactive for H2O2 synthesis. This shows that selective oxidation reactions active may utilize very different sites than those for the oxidation of CO. 

Y. Z. Yuan, A. P. Kozlova, K. Asakura, H. L. Wan, K. Tsai, and Y. Iwasawa, Supported Au catalysts prepared from Au phosphine complexes and As-precipitated metal hydroxides Characterization and low-temperature CO oxidation, J. Catal. 170(1), 191-199 (1997). 

J. D. Grunwaldt, C. Kiener, C. Wogerbauer, and A. Baiker, Preparation of supported gold catalysts for low-temperature CO oxidation via size-controlled gold colloids, J. Catal. 181(2), 223—232 (1999). 

Supported Au catalysts have been extensively studied because of their unique activities for the low temperature oxidation of CO and epoxidation of propylene (1-5). The activity and selectivity of Au catalysts have been found to be very sensitive to the methods of catalyst preparation (i.e., choice of precursors and support materials, impregnation versus precipitation, calcination temperature, and reduction conditions) as well as reaction conditions (temperature, reactant concentration, pressure). (6-8) High CO oxidation activity was observed on Au crystallites with 2-4 nm in diameter supported on oxides prepared from precipitation-deposition. (9) A number of studies have revealed that Au° and Au" play an important role in the low temperature CO oxidation. (3,10) While Au° is essential for the catalyst activity, the Au° alone is not active for the reaction. The mechanism of CO oxidation on supported Au continues to be a subject of extensive interest to the catalysis community. 

Currently, low-temperature CO oxidation over Au catalysts is practically important in connection with air quality control (CO removal from air) and the purification of hydrogen produced by steam reforming of methanol or hydrocarbons for polymer electrolyte fuel cells (CO removal from H2). Moreover, reaction mechanisms for CO oxidation have been studied most extensively and intensively throughout the history of catalysis research. Many reviews [4,19-28] and highlight articles [12, 29, 30] have been published on CO oxidation over catalysts. This chapter summarizes of the state of art of low temperature CO oxidation in air and in H2 over supported Au NPs. The objective is also to overview of mechanisms of CO oxidation catalyzed by Au. 

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