TiO2 , faceting

Methanol decomposition has also been studied on sputtered, Oil -, and 114 -faceted crystal faces of TiO2(001). Chemisorbed methanol formed surface methoxide species about half of the methoxides formed recombined with surface hydroxyl species to form methanol at 365 K. The remainder of the methoxide species decomposed at higher temperatures to form some combination of methanol, methane, dimethyl ether, formaldehyde, and CO depending on the preparation of the crystal surface [74]. 

Methanol decomposition on 114 -faceted TiO2(001) was accompanied by the formation of dimethyl ether attributed to the presence of four-coordinate Ti surface cations, yet no ether was formed on the vacuum annealed SnO2(110) surface, which also contains four-coordinate metal cations. However, the tin cations present on the surface are present as Sn SnO has a bulk four-coordinate structure, hence there is only one coordination vacancy, again precluding bimolecul lr coupling reactions [79]. 

Decomposition reactions of larger aliphatic alcohols have been examined in detail on the (Oil [-faceted TiO2(001) surface [80]. Ethanol adsorbed at 300 K exhibited a low temperature desorption peaks for ethanol and water at 365 K and a high temperature desorption state for decomposition products at 588 - 595 K. Half of the ethanol adsorbed on the surface desorbed as ethanol at 365 K. Half of the remaining surface ethoxide groups desorbed as ethanol at 588 K. The... 

Qualitatively similar results were obtained for reaction and desorption of normal and iso-propanol on the 011 [-faceted TiO2(001) surface. In the case of normal propanol, almost half of the molecules initially adsorbed desorbed as the parent molecule at 370 K, while half of the remaining surface species reacted to form propanol at 580 K. The ratio of propene to propionaldehyde generated at 580 K was 10 1. Desorption of isopropanol quantitatively mirrored the desorption of normal propanol in two desorption states at 365 and 512 K. Isopropanol did not generate any dehydrogenation products (e.g., acetone), and the surface did not generate any bimolecular coupling products for any of the probe alcohol molecules. The absence of ether formation on the (Oil [-faceted surface is consistent with the need for double-coordination vacancies to facilitate that reaction, and the absence of such sites on this surface of titanium dioxide [80]. 

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