Surface Chemistry of 2-Propanol on Clean and Oxygen Precovered Ir(111)

The decomposition and oxidation of 2-propanol oil clean and O-precovered Ir(111) were studied using temperature-programmed desorption and molecular beam reactive scattering. On the clean surface, 2-propanol reacts via a 2-propoxide intermediate, followed by beta-hydride elimination (the reaction-limiting step), producing acetone and adsorbed hydrogen at 225 K. Reactive scattering measurements show that the acetone production from the reaction of 2-propanol reduces with increasing Surface temperature from 333 to 600 K. At 600 K, 2-propanol reacts mainly via nonselective decomposition, producing CO, H-2, and adsorbed C. No acetone production was observed when a beam of 2-propanol was impinged oil the sample at 600 K. We speculate that at high surface temperature (600 K) the formation of acetone in the eta(1) (O) binding configuration is inhibited, leaving only eta(2) (C, O) acetone species, which tend to nonselectively decompose to CO, H-2, and C-ad. On the O-covered Ir(111) surface, the thermal-induced reaction of 2-propanol also occurs via a 2-propoxide intermediate with beta-C-H bond activation. The reaction mechanism changes with surface concentration of oxygen, causing changes in the kinetics of acetone and water evolution. Interestingly, acetone is formed upon impinging a 2-propanol beam oil O-Ir(111) at 600 K. We propose that the role of surface oxygen includes (1) acting as a Bronsted base, (2) acting as a precursor of a nucleophilic attacker in the beta-C-H cleavage step, and (3) altering the surface interaction with the produced acetone.