(621aw) Surface Chemistry of Cellulosic Aldoses on Transition Metals

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.^1,2 Conventional density functional theory (DFT) calculations with the Perdew, Burke and Ernzerhof (PBE) functional³ predicted η₂(C,O) as the most stable structure; whereas, experiments could only detect the η₁(O) configuration. Our calculations reveal that the Revised PBE (RPBE) functional⁴ can correctly predict the most stable adsorption configuration of aldoses on transition metals. Additionally, for C₆ 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 η₁(O) structure; thus explaining why the η₁(O) configuration was detected in experiments. Entropy calculations also demonstrate that the transformation from η₁(O) to η₂(C,O) is thermodynamically not favorable even at higher temperatures. Finally, based on the most stable η₁(O) adsorbed configuration, the catalytic activity of Pd and Pt surfaces towards the decomposition, oxidation and hydrogenation reactions is evaluated.

References:

1. McManus, J. R.; Salciccioli, M.; Yu, W.; Vlachos, D. G.; Chen, J. G.; Vohs, J. M., Correlating the Surface Chemistry of C2 and C3 Aldoses with a C6 Sugar: Reaction of Glucose, Glyceraldehyde, and Glycolaldehyde on Pd(111). The Journal of Physical Chemistry C 2012, 116, 18891-18898
2. McManus, J. R.; Yu, W.; Salciccioli, M.; Vlachos, D. G.; Chen, J. G.; Vohs, J. M., Biomass-Derived Oxygenate Reforming on Pt(111): A Demonstration of Surface Science Using D-Glucose and Its Model Surrogate Glycolaldehyde. Surface Science 2012, 606, L91-L94.
3. Perdew, J. P.; Burke, K.; Ernzerhof, M., Generalized Gradient Approximation Made Simple. Physical Review Letters 1996, 77, 3865-3868.
4. Hammer, B.; Hansen, L. B.; Nørskov, J. K., Improved Adsorption Energetics within Density-Functional Theory Using Revised Perdew-Burke-Ernzerhof Functionals. Physical Review B 1999, 59, 7413-7421.