RuO2, model catalyst

Fig. 5.16. Time evolution of the site occupation by O and CO of the two prominent adsorption sites at the RuO2(110) model catalyst surface shown in Fig. 5.14. The temperature and pressure conditions chosen (T = 600K, pco = 20atm., P02 = 1 atm.) correspond to optimum catalytic performance, cf. Fig. 5.15. Under these conditions, kinetics builds up a steady state surface population in which O and CO compete for either site type at the surface, as reflected by the strong fluctuations in the site occupations (from [53])...

In order to address both fundamental and application aspects of electrochemical promotion in this Chapter, the combustion of ethylene over Ir02 or RUO2 catalysts and the reduction of NO with propylene over Rh catalysts —all deposited on yttria-stabilized zirconia (YSZ) solid electrolyte— have been chosen as model catalytic systems. While the literature of electrochemical promotion deals mainly with metal catalysts, our laboratory has a long experience with promotion of metal oxide catalysts, such as Ir02 and RUO2. In fact, ethylene combustion with Ir02/YSZ film catalyst was the first catalytic system found to exhibit the phenomenon of permanent electrochemical promotion, which manifests itself as a shift in the steady-state open-circuit activity due to polarization, and is attributed to a change in... 

Figure 13-14. A model reaction for photochemical O2 evolution with a sacrificial electron acceptor and colloidal RUO2 catalyst.

Fig. 7.7 Core-sheU model for RuOj powder catalysts. The degree of surface oxidation is determined by the CO/O2 reactant feed ratio and the temperature. The inactive RuO2(100)-c(2 x 2) (light blue) surface facets are formed under oxidizing conditions (C0/02<2), whereas the low-activity metallic ruthenium surfaces (Ru(OOOl)-O) (dark blue) are exposed under net reducing conditions (C0/02>2). The most active state is an ultrathin RUO2 (light and dark green thickness 1-2 mn) layer supported on a metallic ruthenium core. This state is achieved by complete reduction of the RUO2 particle followed by mild re-oxidation below 500 K...

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