We used direct-rate measurements and reflection absorption infrared spectroscopy (RAIRS) to investigate CO oxidation on a PdO(101) film at 450 K and focused on characterizing how the gas-phase composition (O 2 + CO) influences the reaction kinetics and the coupling between the reaction and the surface phases that develop. We find that chemisorbed O atoms on Pd(111) are intrinsically more reactive than PdO(101) and that CO oxidation rates can be as much as 2−3 times higher on Pd(111) compared with PdO(101) for the conditions studied. Using RAIRS, we show that reduction of PdO( 101) by CO produces metallic Pd(111) domains at 450 K and identified several rate processes that couple the PdO(101) and Pd(111) phases during reaction, including the formation of Pd( 111) domains from O vacancies on PdO(101), oxygen transfer from the oxide to the metal to generate chemisorbed O atoms, and the healing of surface oxygen vacancies on PdO(101) via O atom migration from the bulk oxide as well as O 2 dissociative adsorption. We show that the CO oxidation rates increase autocatalytically as the surface fraction of metallic Pd initially increases during reaction because Pd( 111) is more reactive than PdO(101) over the range of conditions studied. Our results further demonstrate that the oxide and gaseous O 2 can act cooperatively to supply metallic Pd(111) domains with chemisorbed O atoms, resulting in higher CO oxidation rates achieved on mixtures of PdO(101) and Pd(111) compared with pure Pd(111). The present study clarifies key rate processes and the resulting kinetic couplings among the gas-phase and solid phases during CO oxidation on partially reduced PdO(101). We expect that our findings will provide useful guidance for advancing first-principles kinetic modeling of CO oxidation promoted by transition-metal catalysts.

BackgroundSeveral studies have used functional magnetic resonance imaging (fMRI) to show that neural activity is associated with driving. fMRI studies have also elucidated the brain responses associated with driving while performing sub-tasks. It is important to note that these studies used computer mouses, trackballs, or joysticks to simulate driving and, thus, were not comparable to real driving situations. In order to overcome these limitations, we used a driving wheel and pedal equipped with an MR-compatible driving simulator (80 km/h). The subjects drove while performing sub-tasks, and we attempted to observe differences in neuronal activation.MethodsThe experiments consisted of three blocks and each block consisted of both a control phase (1 min) and a driving phase (2 min). During the control phase, the drivers were instructed to look at the stop screen and to not perform driving tasks. During the driving phase, the drivers either drove (driving only condition) or drove while performing an additional sub-task (driving with sub-task condition) at 80 km/h.ResultsCompared to when the drivers were focused only on driving, when the drivers drove while performing a sub-task, the number of activation voxels greatly decreased in the parietal area, which is responsible for spatial perception. Task-performing areas, such as the inferior frontal gyrus and the superior temporal gyrus, showed increased activation. Performing a sub-task simultaneously while driving had affected the driver’s driving. The cingulate gyrus and the sub-lobar region (lentiform nucleus, caudate, insula, and thalamus), which are responsible for error monitoring and control of unnecessary movements (e.g., wheel and pedal movements), showed increased activation during driving with sub-task condition compared to driving only condition.ConclusionsUnlike simple driving simulators (joysticks, computer mouses, or trackballs) used in previous research, the addition of a driving wheel and pedals (accelerator and brake) to the driving simulator used in this study closely represents real driving. Thus, the number of processed movements was increased, which led to an increased number of unnecessary movements that needed to be controlled. This in turn increased activation in the corresponding brain regions.

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