Supported Co-oxidants

Liu et al. used GGA calculations with the PBE functional to probe adsorption and reaction of 02 and CO on Au supported on defect-free TiO2(110).185 These calculations used a bilayer of Au forming a continuous strip across the support surface. 02 adsorption was found to be favorable only for adsorption on Au adjacent to the support surface. An analysis of the bonding character of these states indicated that the support enhances charge transfer from Au to 02 for Au atoms in close proximity to the support. CO oxidation via a reaction between adsorbed CO and adsorbed 02 at the Au/support interface was found to have a small activation barrier (0.1 eV). CO oxidation pathways involving adsorbed atomic oxygen were not examined, although adsorbed O is created by the pathway mentioned above. Also, dissociation of adsorbed 02 was found to occur with a barrier of 0.5 eV. 

Role of cationic gold in supported CO oxidation catalysts, J. C. Fierro-Gonzalez, J. Guzman, and B. C. Gates, Topics Catal., 2001, 44, 103. 

Fig. XVIII-27. Specific rates of CO oxidation on single crystal and supported catalysts as a function of temperature. (From Ref 308. Reprinted with permission from American Chemical Society, copyright 1988.)...

Figure A3.10.25 Arrhenius plots of CO oxidation by O2 over Rli single crystals and supported Rli/Al203 at PCO = PO2 = 0.01 atm [43]. The dashed line in the figure is the predicted behaviour based on the rate constants for CO and O2 adsorption and desorption on Rli under UHV conditions.

Wei-Ping won the bet. A series of rapid kinetic experiments provided strong support for the concept of two independent active sites. CODH/ACS was reacted with CO and the rate of development of each of the enzyme s characteristic EPR signals was compared with the rates of CO oxidation and acetyl-CoA synthesis. On the basis of these... 

In the copresence of H2O, gold NPs supported on insulating metal oxides such as AI2O3 and Si02 can also exhibit catalytic activity at room temperature for CO oxidation. 

A 5 wt.% CoOx/Ti02 catalyst was prepared via an incipient wetness technique in which an aqueous solution of Co(N03)2 6H20 (Aldrich, 99.999%) was impregnated onto a shaped Ti02 (Milleimium Chemicals, commercially designated as DT51D, 30/40 mesh), as described in detail elsewhere [6]. Other supported metal oxide catalysts, such as FeOx, CuO, and NiOx, were obtained in a fashion similar to that used for preparing the CoO, catalyst. 

CO conversions over Au/Ce02 catalyst were measured in the dry and wet condition as shown in Fig. 1. Similar to other supported gold catalysts, Au/Ce02 catalyst showed higher CO conversions in the presence of water vapor than in the absence of it at the same temperature. Catalytic activities for CO oxidation over Au/Ce02 catalysts prepared at different calcinations temperature were compared in the dry and wet condition as shown in Fig. 2. Au/Ce02 catalyst calcined at 473 K showed the highest initial CO conversion in the absence of water vapor. However, the CO conversion decreased steadily and reached a steady-state value over this catalyst. 

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. 

The catalysts were tested for their CO oxidation activity in an automated microreactor apparatus. The catalysts were tested at space velocities of 7,000 -60,000 hr . A small quantity of catalyst (typically 0.1 - 0.5 g.) was supported on a frit in a quartz microreactor. The composition of the gases to the inlet of the reactor was controlled by mass flow controllers and was CO = 50 ppm, CO2 = 0, or 7,000 ppm, HjO = 40% relative humidity (at 25°C), balance air. These conditions are typical of conditions found in spacecraft cabin atmospheres. The temperature of the catalyst bed was measured with a thermocouple placed half way into the catalyst bed, and controlled using a temperature controller. The inlet and outlet CO/CO2 concentrations were measured by non-dispersive infrared (NDIR) monitors. 

CO oxidation tests on Au supported on various metal oxides were undertaken at low CO concentrations, where the adiabatic temperature rise in the bed is negligible. Since CO oxidation is highly exothermic, when high CO concentrations are present in the feed 1%), and at high conversions, the adiabatic temperature rise in the catalyst bed due to the heat of reaction may be as high as 100 C. Therefore, it is important to monitor the catalyst bed temperature when high CO concentrations are present in the feed. 

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. 

Broqvist, P., Molina, L.M., Gronbecka, H. and Hammer, B. (2004) Promoting and poisoning effects of Na and Cl coadsorption on CO oxidation over MgO-supported Au nanopartides. Journal of Catalysis, 227, 217-226. 

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