Adsorption and Reactivity of Cellulosic Aldoses on Transition Metals

The adsorption of cellulosic biomass derived aldoses on heterogeneous catalysts is the first and governing step in their conversion to platform chemicals. However, there is a discrepancy between theoretical and experimental observations in determining the most stable configuration of adsorbed aldoses on transition metal surfaces:,conventional density functional theory (DFT) calculations with the Perdew, Burke, and Ernzerhof (PBE) functional (Perdew et al. Phys. Rev. Lett. 1996, 77, 3865) predicted eta(2)(C,O) as the most stable structure, whereas experiments could only detect the eta(1)(O) configuration. Our calculations reveal that the revised PBE (Hammer,et al. Phys. Rev. B 1999, 59, 7134) functional can correctly predict the most stable adsorption configuration of aldoses on transition metals. Additionally, for C-6, aldoses like glucose, which exist mostly in the ring form, the open-chain adsorption configuration is a result of the transition-metal-catalyzed ring-opening process. Adsorbed glucose in the cyclic form undergoes deprotonation and ring opening, and the resultant open-chain configuration closely resembles the eta(1)(O) structure, thus explaining why the eta(1)(O) configuration was detected in experiments. Entropy calculations also demonstrate that the transformation from eta(1)(O) to eta(2)(C,O) is thermodynamically not favorable even at higher temperatures. Finally, based on the most stable eta(1)(O) adsorbed configuration, the catalytic activity of Pd and Pt surfaces toward the decomposition, oxidation, and hydrogenation reactions is evaluated.