Parallel pathways for photocatalytic decomposition of acetic acid on TiO{sub 2}

Journal Article · Fri Oct 01 04:00:00 EDT 1999 · Journal of Catalysis

DOI:https://doi.org/10.1006/jcat.1999.2594· OSTI ID:20000969

Muggli, D S; Falconer, J L

Acetic acid decomposes photocatalytically on TiO{sub 2} at room temperature in an inert atmosphere through two parallel pathways. In one pathway, acetic acid decomposed to gas-phase CO{sub 2} and apparently forms hydrogen and methyl groups, which combine on the surface to form CH{sub 4}. In the other pathway, acetic acid extracts oxygen from the TiO{sub 2} lattice to form adsorbed H{sub 2}O and gas-phase CO{sub 2} and C{sub 2}H{sub 6}. The extracted oxygen is replenished by diffusion from the bulk in an inert atmosphere or by gas-phase O{sub 2}. The formation of CH{sub 4} and CO{sub 2} in the first pathway does not consume lattice oxygen. The first step in photocatalytic decomposition (PCD) of acetic acid appears to be dissociation of the O-H bond, producing surface acetates. However, molecularly adsorbed acetic acid reacts at the same rate and with the same selectivity as surface acetates. Only the {alpha}-carbon forms CO{sub 2} during PCD. When gas-phase O{sub 2} is present, adsorbed methyl groups oxidize before they are hydrogenated to CH{sub 4}. The oxidizing agent during photocatalytic oxidation (PCO) is different from that during PCD and is most likely adsorbed oxygen. Adsorbed oxygen reacts with acetic acid in a different pathway from the two reactions observed for PCD, so a Mars Van Krevlen mechanism for PCO appears unlikely. The TiO{sub 2} surface is not homogeneous and some surface sites are more active during both PCD and PCO. Co-adsorbed water increases the rate of CH{sub 4} formation, apparently by reacting with CH{sub 3(ads)} to form CH{sub 4}, but in contrast to adsorbed O{sub 2}, water does not react with acetic acid in a separate pathway that is different from those observed for PCD without water.

• Research Organization: Univ. of Colorado, Boulder, CO (US)
• OSTI ID: 20000969
• Journal Information: Journal of Catalysis, Journal Name: Journal of Catalysis Journal Issue: 1 Vol. 187; ISSN 0021-9517; ISSN JCTLA5
• Country of Publication: United States
• Language: English

Related Subjects

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATION
ACETIC ACID
CARBON DIOXIDE
CATALYTIC EFFECTS
CHEMICAL REACTION KINETICS
ETHANE
METHANE
PHOTOLYSIS
SYNTHESIS
TITANIUM OXIDES
WASTE WATER
WATER TREATMENT