(738g) Elucidating Structure-Function Relationships of Molybdenum Oxides for Catalytic Alkane Dehydrogenation

Ethylene, propylene, and isobutylene are critical building blocks in the chemical industry for a vast array of applications such as paints, adhesives, and fuel additives. Traditionally, these olefin feedstocks are produced via naphtha cracking. Recent technological advances in natural gas production, though, have resulted in an abundance of light alkanes. Coupled with a growing demand for light olefins, this shift has led to renewed interest in catalytic dehydrogenation as a way to selectively convert alkanes into their corresponding olefins. Although industrial light alkane dehydrogenation processes are typically catalyzed by supported Pt or CrO_x materials, the high cost of Pt and adverse health effects associated with Cr⁶⁺ motivate research into alternative catalysts, particularly in the metal oxide space.

Previous studies on bulk MoO₃ have shown that molybdenum oxides exhibit catalytic alkane dehydrogenation activity but deactivate quickly as the Mo reduces to lower oxidation states. However, as metal loading decreases, the Mo species transitions from crystalline nanoparticles to isolated sites and becomes increasingly more difficult to reduce. Using isobutane as a probe molecule, this study explores different morphologies of supported MoO_x species and their alkane dehydrogenation activities. Our preliminary results show that all MoO_x catalysts exhibit similar initial activities. However, while high Mo loading catalysts are easily reduced and follow similar deactivation trends as those observed with bulk MoO_x, low Mo loading catalysts exhibit very little reduction or deactivation even after several hours under non-oxidative reaction conditions. Highlighting the importance of catalyst structure on its activity and stability, sub-monolayer metal oxides may warrant further investigation as alternative light alkane dehydrogenation catalysts even if their bulk oxide counterparts may not.