Tang Mingjin, Larish Whitney A, Fang Yuan, Gankanda Aruni, Grassian Vicki H
Department of Chemistry, University of Iowa , Iowa City, Iowa 52242, United States.
Departments of Chemistry and Biochemistry, University of California, San Diego , La Jolla, California 92093, United States.
J Phys Chem A. 2016 Jul 21;120(28):5609-16. doi: 10.1021/acs.jpca.6b05395. Epub 2016 Jul 7.
We have investigated the heterogeneous uptake of gaseous acetic acid on different oxides including γ-Al2O3, SiO2, and CaO under a range of relative humidity conditions. Under dry conditions, the uptake of acetic acid leads to the formation of both acetate and molecularly adsorbed acetic acid on γ-Al2O3 and CaO and only molecularly adsorbed acetic acid on SiO2. More importantly, under the conditions of this study, dimers are the major form for molecularly adsorbed acetic acid on all three particle surfaces investigated, even at low acetic acid pressures under which monomers are the dominant species in the gas phase. We have also determined saturation surface coverages for acetic acid adsorption on these three oxides under dry conditions as well as Langmuir adsorption constants in some cases. Kinetic analysis shows that the reaction rate of acetic acid increases by a factor of 3-5 for γ-Al2O3 when relative humidity increases from 0% to 15%, whereas for SiO2 particles, acetic acid and water are found to compete for surface adsorption sites.
