Journal of Catalysis, Vol.330, 145-153, 2015
Selectivity and mechanism of thermal decomposition of beta-diketones on ZnO powder
The thermal chemistry of beta-diketones underlies a number of catalytic processes related both to the catalytic reactions yielding commodity chemicals and to the production of supported transition metal catalysts themselves. The mechanisms of decomposition during thermal transformation of three beta-diketones, acetylacetone (acacH), 1,1,1-trifluoroacetylacetone (tfacH), and 1,1,1,5,5,5-hexafluoroacetylacetone (hfacH), were studied on ZnO powder surface using Fourier-transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), and density functional theory (DFT) computational investigation. The initial O-H dissociation leads to the formation of corresponding beta-diketonates in all the cases investigated. These diketonates are important surface intermediates that can be generated in a controlled manner in these experiments. The presence on the C-CF3 entity determines the preferred thermal decomposition pathways, as the C-C bond in this group starts to react with a surface of ZnO around 400 K, followed by immediate decomposition of the resulting CF3 group. Above 600 K, the presence of the CF3-substituent leads to the formation of ketene-like structures observed by vibrational spectroscopy. The reaction mechanisms examined with the help of DFT calculations are correlated with the vibrational signatures of the species produced and with the F-containing species recorded by XPS. (C) 2015 Elsevier Inc. All rights reserved.