Acrolein coupling on reduced TiO2(110): The effect of surface oxidation and the role of subsurface defects

作者：Benz Lauren; Haubrich Jan; Quiller Ryan G; Friend Cynthia M^*

来源：Surface Science, 2009, 603(7): 1010-1017.

DOI：10.1016/j.susc.2009.02.016

• Temperature programmed reaction
• Titanium dioxide
• Acrolein
• Coupling reaction
• Interstitials
• Point defects
• Subsurface defects
• Oxygen vacancies

Reactions of acrolein, water, and oxygen with the vacuum-reduced surface of TiO2(110) are reported in a temperature programmed reaction study of the interaction of an aldehydic pollutant with a reducible metal oxide. A total of 25% of the acrolein that binds to the surface is converted to products. Notably, carbon-carbon coupling occurs with 86% selectivity for formation of C-6 products: C6H8, identified as 1,3-cyclohexadiene, in a peak at 500 K and benzene immediately thereafter at 530 K. Acrolein is evolved from the surface in three peaks: a peak independent of coverage at 495 K, attributed to decomposition of an intermediate that is partly converted to C6H8; a coverage-dependent peak that shifts from 370 K (low coverage) to 260 K (high coverage), which is attributed to adsorption at 5-fold coordinated Ti sites; and a multilayer state at 160 K. Water and acrolein compete for 5-fold coordinated titanium sites when dosed sequentially. The addition of water also opens a new reaction pathway, leading to the hydrogenation of acrolein to form propanal. Water has no effect on the yield of 1,3-cyclohexadiene. Exposure of the surface to oxygen prior to acrolein dosing quenches the evolution of acrolein at 495 K and concurrently eliminates the coupling. From these results, we propose that reduced subsurface defects such as titanium ion interstitials play a role in the reactions observed here. The notion that subsurface defects may contribute to the reactivity of organic molecules over reducible oxide substrates may prove to be general.

• 出版日期2009-4-1