Produced at the multi-million-metric-ton level, propylene ranks as one of the main building blocks in petrochemistry. Refineries produce the light olefin, which is then converted to polypropylene and other compounds, primarily by cracking naphtha and other petroleum starting materials.
Low-cost supplies of propane from shale gas have prompted some manufacturers to make propylene, instead, via propane dehydrogenation (PDH), a process commonly mediated by platinum and chromium catalysts. Vanadium-based catalysts, which would bypass the high cost and toxicity concerns associated with the other metals, look like promising alternatives. But mechanistic details of vanadium PDH catalysts remain unknown, limiting scientists’ ability to improve them.
To address that shortcoming, a research team led by Jinlong Gong of Tianjin University prepared alumina-supported vanadium oxide catalysts and probed their PDH activity with vibrational spectroscopy, computations, and other methods.
The team found that pretreating the catalysts with hydrogen forms V-OH groups, which promote the PDH reaction and improve catalyst stability. They also found that V3+ surface sites demonstrate more PDH activity than V4+ and V5+ sites. Omitting the hydrogen pretreatment and exposing the catalysts directly to propane forms the active V3+ sites without the OH caps. This OH-less form of the catalyst shows high PDH activity initially, but it quickly becomes inactive because of a buildup of carbon gunk called coke, which blocks catalyst sites (Angew. Chem. Int. Ed. 2018, DOI: 10.1002/anie.201800123).