Compositional Tuning of Y–Zr Oxides as Lewis Acid–Base Catalysts for Dehydrogenation Reactions

Oxide surfaces that expose low-coordination metal–oxygen Lewis acid–base (LAB) pairs are very effective at heterolytic C–H activation steps in alkane dehydrogenation catalysis. This study reports the synthesis of Y2O3–ZrO2 (YZO) materials with high surface areas across a broad range of Y/Zr ratios via hydrothermal treatment in the presence of lauric acid. These materials retain small crystallites that expose high densities of low-coordination LAB pair sites in the temperature range required for high alkene yields in dehydrogenation reactions compared with monoclinic ZrO2. Catalysts with Y/Zr atomic ratios below 0.21 show stable gravimetric and areal alkane dehydrogenation rates that are comparable with those on dispersed noble metal catalysts and exceed those on Cr- or Ga-based catalysts in current practice, and also high dehydrogenation selectivities. Y/Zr ratios above 0.5 lead to the formation of a separate Y2O3 phase that appears to be responsible for higher cracking selectivities and for the formation of deactivating organic residues. This compositional window and the reported synthesis protocols provide a strategy for the synthesis of small-crystal oxides with high surface areas and exposed low-coordination Zr–O LAB pairs as earth-abundant catalysts for a broad range of dehydrogenation reactions and their (reverse) hydrogenation counterparts.