Heterogeneous catalysis

Kolesov G, Vinichenko D, Tritsaris GA, Friend CM, Kaxiras E. Anatomy of the Photochemical Reaction: Excited-State Dynamics Reveals the C−H Acidity Mechanism of Methoxy Photo-oxidation on Titania. Journal of Physical Chemistry Letters. 2015;6 :1624-1627.Abstract

Light-driven chemical reactions on semiconductor surfaces have potential for
addressing energy and pollution needs through efficient chemical synthesis; however, little is known about the time evolution of excited states that determine reaction pathways. Here, we study the photo-oxidation of methoxy (CH3O) derived from methanol on the rutile TiO2(110) surface using ab initio simulations to create a molecular movie of the process. The movie sequence reveals a wealth of information on the reaction intermediates, time scales, and energetics. The reaction is broken in three stages, described by Lewis structures directly derived from the “hole” wave functions that lead to the concept of “photoinduced C−H acidity”. The insights gained from this work can be generalized to a set of simple rules that can predict the efficiency of photo-oxidation reactions in reactant−catalyst pairs.

Matthew M. Montemore

Matthew M. Montemore

Matthew earned his BA in Physics from Grinnell College in 2009 and his PhD in Mechanical Engineering from the University of Colorado Boulder in 2014.

Tritsaris GA, Vinichenko D, Kolesov G, Friend CM, Kaxiras E. Dynamics of the Photogenerated Hole at the Rutile TiO2(110)/Water Interface: A Nonadiabatic Simulation Study. Journal of Physical Chemistry C . 2014;118 :27393-27401.Abstract

Hydrogen production in photoelectrochemical cells constitutes an important avenue toward carbon-free fuel. The most convenient process for hydrogen production is the splitting of water molecules, which necessitates a catalytic
reaction involving a semiconductor. Here, we introduce a framework for the study of photocatalyzed reactions on semiconductor surfaces based on time-dependent density functional theory that explicitly accounts for the evolution of electronically excited states. Within this framework, we investigate the possibility of hole-mediated splitting of molecularly adsorbed water on a representative metal oxide surface the rutile TiO2(110). We find that oxidative dehydrogenation of water is possible in synergy with thermal effects at temperatures between 60 and 100 K only when defects like Ti interstitials are present in the subsurface region. This study presents a general computational strategy for describing photoexcited semiconductor/adsorbate interfaces and also demonstrates that the occurrence of water dissociation on the rutile TiO2(110) surface depends sensitively on the local atomic environment and external parameters such as temperature.