Strain in Silica-Supported Ga (III) Sites: Neither Too Much nor Too Little for Propane Dehydrogenation Catalytic Activity
<p>Well-defined Ga(III) sites on SiO<sub>2</sub> are highly active, selective, and stable catalysts in the propane dehydrogenation reaction. In this contribution, we evaluate the catalytic activity towards propane dehydrogenation of tri-coordinated and tetra-coordinated Ga(III) sites on SiO<sub>2</sub> by means of first principles calculations using realistic amorphous periodic SiO<sub>2</sub>models. We evaluated the three reaction steps in propane dehydrogenation, namely the C-H activation of propane to form propyl, the beta-hydride elimination transfer to form propene, and a Ga-hydride, and the H-H coupling to release H<sub>2</sub>, regenerating the initial Ga-O bond and closing the catalytic cycle. Our work shows how Brønsted-Evans-Polanyi relationships are followed for these three reaction steps on Ga(III) sites on SiO<sub>2</sub> and highlights the role of the strain of the reactive Ga-O pairs on such sites of realistic amorphous SiO<sub>2</sub> models. While highly strained sites are very reactive sites for the initial C-H activation, they are more difficult to regenerate. The corresponding less strained sites are not reactive enough, pointing to the need of a right balance in strain to be an effective site for propane dehydrogenation. Overall, our work provides an understanding of the intrinsic activity of acidic Ga single sites towards the propane dehydrogenation reaction and paves the road towards the design and prediction of better single-site catalysts on SiO<sub>2 </sub>for the propane dehydrogenation reaction.</p>
