(688h) Tuning the Dehydration Activity of Alcohols Using Phosphonic Acid Self-Assembled Monolayers
One of the biggest problems in heterogeneous catalysis is that of poor selectivity. Often dopants are utilized to tune the properties of various catalysts to improve selectivity or activity. Over the last decade self-assembled monolayers (SAMs) have been developed as a means to control the selectivity of reactions on supported metal catalysts. We sought to utilize a similar approach for metal oxide catalysts. We developed a simple and rapid approach to functionalize anatase titania and other oxides with phosphonic acid SAMs. These SAMs are exceptionally robust, resisting thermal degradation up to 400°C. We investigated the selectivity of these catalysts for reactions of alcohols on titania. When 1-propanol is reacted over titania three main pathways are possible: dehydration, dehydrogenation, and condensation. At low temperatures (~250°C), dehydrogenation is favored on the native catalyst, closely followed by condensation. However, upon functionalization of titania with phosphonic acids with various alkyl tails (methyl, octadecyl, benzyl, etc), dehydration becomes the dominant pathway. More importantly, depending on the functionality of the alkyl tail acid (e.g. 4-aminobenzylphosphonic vs 3-fluorobenzylphosphonic acid), the activity of dehydration can be tuned over a wide range, allowing far higher dehydration activities than on the uncoated catalysts. Using reactor and surface studies, we will demonstrate in this presentation how the selectivity and activity of metal oxide catalysts (i.e. anatase titania) can be tuned for certain constituents.