Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
5423924 | Surface Science | 2009 | 8 Pages |
Abstract
Reactions of acrolein, water, and oxygen with the vacuum-reduced surface of TiO2(1Â 1Â 0) 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 C6 products: C6H8, identified as 1,3-cyclohexadiene, in a peak at 500Â K and benzene immediately thereafter at 530Â K. Acrolein is evolved from the surface in three peaks: a peak independent of coverage at 495Â K, attributed to decomposition of an intermediate that is partly converted to C6H8; a coverage-dependent peak that shifts from 370Â K (low coverage) to 260Â K (high coverage), which is attributed to adsorption at 5-fold coordinated Ti sites; and a multilayer state at 160Â 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 495Â 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.
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Physical Sciences and Engineering
Chemistry
Physical and Theoretical Chemistry
Authors
Lauren Benz, Jan Haubrich, Ryan G. Quiller, Cynthia M. Friend,