Manuscrits lul·lians de la Biblioteca de Catalunya. I

Abstract not availabl

Phosphonic Acid SAM Modification of Metal Oxides Toward The Creation of Better Dehydration Catalysts

In this Thesis, the synthesis and performance of new catalysts tailored specifically for dehydration reactions is investigated. Due to their inexpensiveness and bifunctionality, metal oxides have been successfully used to catalyze elimination reactions. However, as is habitual over heterogeneous catalysts, selectivity toward desired products is low for the system at hand: materials that can perform dehydration reactions also catalyze dehydrogenation and condensation reactions. Self-assembling monolayers (SAMs) have been used in this contribution as an approach to improve performance of some already existent catalysts. Previous results showed that over TiO2 Anatase, the dipole moment of phosphonic acid SAMs affected the near-surface electrostatics, enabling regulation of the dehydration activity of primary alcohols by changing the elongation of the C&beta;&nbsp;- H bond, whose scission limits the reaction. Activities and selectivities of the coated catalysts exceeded those of the native, uncoated materials. The same approach has been tested on several metal oxides. Out of the different oxides that have been screened, an overall beneficial effect on dehydration was only observed for a group of them. These materials (TiO2, CeO2, SnO2) have a common descriptor: their moderate metal &ndash; oxygen bond strength (~4 eV). These results indicate that the response of dehydration activity and functionalization with phosphonic acids appears to be correlated with the electron mobility and energetics of the material. Similarly, the effects of PA deposition have been tested with different alcohols, over TiO2: 1-butanol, 2-butanol and tert-butanol. Due to their different inherent ability to stabilize charges, the inductive effects generated as a result of the C&beta;&nbsp;- H bond elongation were more ineffective for the higher substituted reactants. Several additional effects caused by the presence of SAMs such as changes in water mobility as a surface species and steric impediments caused by the interruption of the catalytic surface were observed. These interconnected phenomena collectively could explain the observed rates and provided experimental insight on the mechanism behind PAs effects on metal oxide surfaces and dehydration reactions.</p