| dc.description.abstract | The methanol decomposition on the iridium oxide prepared under ambient pressure hasn’t been studied fully. In our previous studies [1], the crystal and surface structure of iridium oxide prepared under ambient pressure varied with pressures. Therefore, the desorption property and reaction pathway of methanol on the iridium oxide prepared under different conditions might be affected by the oxide structure. In this studies, 5 structures of Ir oxides prepared under 1 × 10-6 Torr, 1 × 10-2 Torr, 1 × 10-1 Torr, 1 and 5 Torr O2 at 775 K are selected for the methanol decomposition investigation by the temperature programmed desorption (TPD), the infrared reflection adsorption spectroscopy (IRAS), near ambient X ray photoelectron spectroscopy (NAP-PES) and the near ambient pressure- mass spectroscopy (NAP-MS).
The clear reaction pathway of CD3OD on Ir oxide grown under 10-6 Torr oxygen (2 × 1 oxygen adsorbed Ir(100)) demonstrates the CD3OD dehydrogenation from CD2O at 180 K and CO at 220 K, oxidation to DCOO at 300 K CO2, to then CO2 from total dehydrogenation at 370 K. The Langmuir dose CD3OD is difficult to combine with surface oxygen and form CO2 on Ir oxide grown under 10-2 and 10-1 Torr oxygen (Ir(100)-(2 × 1)-O + IrO2(100) and IrO2(100)), compared to TPD results on 2 × 1 oxygen adsorbed Ir. Since oxide growth condition up to 1 × 10-2 Torr, carbon species is more facile to desorb from the oxide. The reaction mechanisms of methanol on Ir(100)-(2 × 1)-O + IrO2(100) and IrO2(100) are simply decomposing to CO and D2, as that on single crystal Ir [2]. In ambient methanol experiments, the main mechanism of CH3OH is decomposition to CHxO at 300 K, and then main product CO and the minor product CHx (x = 1 ~ 3) on the Ir oxide grown under below 1 × 10-1 Torr. It is consistent with the Langmuir doses experiment. The reactions of CD3OD are preferential to oxidation with facile desorption at low temperature on Ir oxides grown under 1 and 5 Torr oxygen (IrO2(102) & (10-2) and IrO2(110)). The CD2O formation and CO desorption occur at lower temperature on IrO2(102) & (10-2) and IrO2(110), compared to 2 × 1 oxygen adsorbed Ir(100). In ambient pressure experiment, the CO and CHx products is further reduced on higher oxygen-covered oxide at 300 K, but CHxO (x = 1 ~ 3) and C* still slightly increases on Ir oxides grown under above 1 Torr oxygen. Gaseous productions on the Ir oxides grown above 10-2 Torr O2 have higher selectivity to CD2O at 400 K, rather than CO. | en_US |