Acetic Acid decomposition on a CeO2(111) model catalyst

CALAZA, FLORENCIA C.; CHEN, TSUNG-LIANG; MULLINS, DAVID R.; OVERBURY, STEVEN H.

Asheville, NC

Simposio; Southeastern Catalysis Society 9th Annual Fall Symposium; 2010

North American Catalysis Society

(Poster - Presenter) The chemical reactivity of Acetic Acid molecules on CeO2(111) thin films was studied on fully oxidized surfaces as well as on reduced surfaces of ceria (CeOx) where a fair amount of vacancies are present.  The acid molecule readily chemisorbed in UHV on both of these surfaces by breaking its OH bond and leaving acetate adsorbed on the surface of the catalyst.  By TPD, the decomposition of acetic acid on CeO2(111) at temperatures above 500 K resulted on liberation of CO, CO2, H2O and ketene (CH2CO). It is interesting to compare the chemistry seen in this case with other C2 oxygenates like ethanol and acetaldehyde where no C-C cleavage was detected. On the reduced surface less selective decomposition occurs with only H2 and small amounts acetaldehyde and acetylene desorbed but a substantial amount of C left on the surface. The surface intermediates were determined by soft x-ray photoelectron spectroscopy (sXPS) and near edge x-ray absorption fine structure (NEXAFS) as a function of temperature and ceria reduction. It was found that on both oxidized and reduced surfaces the adsorption of acetic acid produced acetate below 200 K.  The decomposition pathway is different on the two surfaces however. On CeO2, the acetate signal intensity decreases between 500 K and 600 K as water, ketene, CO and CO2 desorb. A small amount of a C2-carbanion (OCHCH2Ce) is produced which leads to additional CO and CO2 above 600 K. In the case of reduced CeOx more of the acetate converts to carbanion above 500 K.  Some of this species desorbs as acetaldehyde and acetylene, but most of the C remains on the surface as a poorly characterized CHx species even after heating the sample to 900 K.  The C can be removed by heating the sample in 10-7 torr of O2 at 700 K. Research sponsored by the Division of Chemical Sciences, Geosciences, and Biosciences, Office of Basic Energy Sciences, US Department of Energy, under contract DE-AC05-00OR22725 with Oak Ridge National Laboratory, managed and operated by UT-Battelle, LLC. Use of the National Synchrotron Light Source, Brookhaven National Laboratory, was supported by the US Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-98CH10886.