Surface Chemistry of Acetone on Metal Oxides:  IR Observation of Acetone Adsorption and Consequent Surface Reactions on Silica−Alumina versus Silica and Alumina

Pathways and generated surface species of adsorption and consequent surface reactions of acetone vapor on characterized silica, alumina, and ∼5 wt % silica−alumina were examined by in-situ infrared (IR) spectroscopy, following degassing at room (RT) and higher temperatures (100−400 °C). For reference and confirmatory purposes, adsorptives of mesityl oxide and acetic acid, and adsorbents of K-modified and pyridine-covered silica−alumina, were employed. In the absence of Lewis and Bronsted acid sites, as well as of basic sites (i.e., on silica), acetone molecules are weakly hydrogen-bonded to surface OHδ+ groups to desorb completely at 100 °C, without involvement in any further surface reactions. The availability of such acid−base sites on alumina and silica−alumina facilitates acetone chemisorption and activation for aldol condensation type surface reactions, leading to formation of surface species of mesityl oxide at RT to 200 °C and their oxidative conversion into acetate species at 300−400 °C. A more obvious availability of Bronsted acid sites on silica−alumina enhances progression of the surface reactions involved.