skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Dark- and photoreactions of ethanol and acetaldehyde over TiO{sub 2}/carbon molecular sieve fibers

Abstract

TiO{sub 2} has been synthesized within the pores of carbon molecular sieve fibers (CMSF) in order to grow particles of quantum size. TiO{sub 2}/CMSF characteristics were followed by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and UV-vis diffuse reflectance. XPS showed that all Ti cations are in a +4 oxidation state. The reduction profile of Ti cations (made by preferential O anion removal due to Ar{sup +} sputtering), as evidenced by Ti{sup +x}/Ti{sup +4} cations, is very similar to that already observed for well-defined TiO{sub 2} surfaces. The absence of XRD pattern indicated that TiO{sub 2} particles are in an amorphous form. UV-vis diffuse reflectance showed a considerably blue shift ({Delta}E = 0.6--0.7 eV) of the band gap of TiO{sub 2}/CMSF when compared to TiO{sub 2} (anatase). This shift translates an average particle radius of 15 {+-} 2 {angstrom}. Larger TiO{sub 2} particles, outside the CMSF nanopores, are, however, observed by TEM. Dark- and photoreactions of ethanol and acetaldehyde have been investigated over TiO{sub 2}/CMSF by steady state kinetics and temperature programmed desorption in UHV conditions, as well as in batch conditions at atmospheric pressure. UHV-steady state ethanol reactions have shown eightfold increase in the reaction rate at 573 Kmore » in the presence of UV when compared to dark reactions at the same temperatures. The rate constants ratio k{sub 2}K{sub 2}/k{sub 1}K{sub 1}, for the photoreactions of ethanol, is ca. 40 times higher for TiO{sub 2}/CMSF than for TiO{sub 2} (powder) indicating the high selectivity of the former toward total conversion of ethanol to CO{sub 2} with minor accumulation of acetaldehyde (k{sub 1}K{sub 1} and k{sub 2}K{sub 2} are the rate constants for ethanol to acetaldehyde and acetaldehyde to CO{sub 2}, respectively). Evidence of C-C bond dissociation is given by formaldehyde desorption during UV-acetaldehyde-TPD over TiO{sub 2}/CMSF under UHV conditions. Moreover, UV-acetaldehyde-TPD indicated a twofold increase of the reductive coupling product (butadiene). The latter requiring Ti{sup +x} (x < 4) to be formed translates an increase of Ti{sup +x} populations under UV illumination.« less

Authors:
; ;  [1];  [2]
  1. Univ. of Auckland (New Zealand)
  2. Nuclear Research Center, Beer Sheva (Israel)
Publication Date:
OSTI Identifier:
684577
Resource Type:
Journal Article
Journal Name:
Journal of Catalysis
Additional Journal Information:
Journal Volume: 185; Journal Issue: 1; Other Information: PBD: 1 Jul 1999
Country of Publication:
United States
Language:
English
Subject:
14 SOLAR ENERGY; ETHANOL; ACETALDEHYDE; PHOTOLYSIS; TITANIUM OXIDES; CATALYTIC EFFECTS; MOLECULAR SIEVES; ULTRAVIOLET RADIATION

Citation Formats

Reztsova, T, Chang, C H, Idriss, H, and Koresh, J. Dark- and photoreactions of ethanol and acetaldehyde over TiO{sub 2}/carbon molecular sieve fibers. United States: N. p., 1999. Web. doi:10.1006/jcat.1999.2520.
Reztsova, T, Chang, C H, Idriss, H, & Koresh, J. Dark- and photoreactions of ethanol and acetaldehyde over TiO{sub 2}/carbon molecular sieve fibers. United States. doi:10.1006/jcat.1999.2520.
Reztsova, T, Chang, C H, Idriss, H, and Koresh, J. Thu . "Dark- and photoreactions of ethanol and acetaldehyde over TiO{sub 2}/carbon molecular sieve fibers". United States. doi:10.1006/jcat.1999.2520.
@article{osti_684577,
title = {Dark- and photoreactions of ethanol and acetaldehyde over TiO{sub 2}/carbon molecular sieve fibers},
author = {Reztsova, T and Chang, C H and Idriss, H and Koresh, J},
abstractNote = {TiO{sub 2} has been synthesized within the pores of carbon molecular sieve fibers (CMSF) in order to grow particles of quantum size. TiO{sub 2}/CMSF characteristics were followed by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and UV-vis diffuse reflectance. XPS showed that all Ti cations are in a +4 oxidation state. The reduction profile of Ti cations (made by preferential O anion removal due to Ar{sup +} sputtering), as evidenced by Ti{sup +x}/Ti{sup +4} cations, is very similar to that already observed for well-defined TiO{sub 2} surfaces. The absence of XRD pattern indicated that TiO{sub 2} particles are in an amorphous form. UV-vis diffuse reflectance showed a considerably blue shift ({Delta}E = 0.6--0.7 eV) of the band gap of TiO{sub 2}/CMSF when compared to TiO{sub 2} (anatase). This shift translates an average particle radius of 15 {+-} 2 {angstrom}. Larger TiO{sub 2} particles, outside the CMSF nanopores, are, however, observed by TEM. Dark- and photoreactions of ethanol and acetaldehyde have been investigated over TiO{sub 2}/CMSF by steady state kinetics and temperature programmed desorption in UHV conditions, as well as in batch conditions at atmospheric pressure. UHV-steady state ethanol reactions have shown eightfold increase in the reaction rate at 573 K in the presence of UV when compared to dark reactions at the same temperatures. The rate constants ratio k{sub 2}K{sub 2}/k{sub 1}K{sub 1}, for the photoreactions of ethanol, is ca. 40 times higher for TiO{sub 2}/CMSF than for TiO{sub 2} (powder) indicating the high selectivity of the former toward total conversion of ethanol to CO{sub 2} with minor accumulation of acetaldehyde (k{sub 1}K{sub 1} and k{sub 2}K{sub 2} are the rate constants for ethanol to acetaldehyde and acetaldehyde to CO{sub 2}, respectively). Evidence of C-C bond dissociation is given by formaldehyde desorption during UV-acetaldehyde-TPD over TiO{sub 2}/CMSF under UHV conditions. Moreover, UV-acetaldehyde-TPD indicated a twofold increase of the reductive coupling product (butadiene). The latter requiring Ti{sup +x} (x < 4) to be formed translates an increase of Ti{sup +x} populations under UV illumination.},
doi = {10.1006/jcat.1999.2520},
journal = {Journal of Catalysis},
number = 1,
volume = 185,
place = {United States},
year = {1999},
month = {7}
}