Simple alcohols such as methanol and ethanol have been employed to probe catalytic activities of the surface of perovskites (ABO3) which are typically composed of alkaline or lanthanide cations (A) and transition metal cations (B). The catalytic properties of perovskites could be tuned by altering the A and B cations. The current talk will focus on the adsorption and surface reactivity of SrTiO3(100) towards methanol and ethanol, which was investigated using in situ synchrotron-based, ambient pressure X-ray photoelectron spectroscopy (APXPS) and temperature-programmed desorption (TPD). At high pressure (~10-1 Torr) of methanol, APXPS experiments suggests that a methoxy is the major surface intermediate with formation of formate and acetate. In addition, the Ti 2p spectra indicats that the Ti4+ is partically reduced due to methanol adsorption. When a small amount of O2 (0.02 Torr) is added, methoxy converts to gas-phase CO and CO2. While in the presence of 0.1 Torr O2, all surface methoxy reacts to form formate, acetate and CO2. Operando experiments with a mass spectrometer (MS) show that H2, CO2 and H2O are the major gas-phase products and CO is the minor product. In the case of ethanol reacting with the SrTiO3(100) surface, the surface species are primarily ethoxy and acetate, whereas the gas-phase products are mostly H2, CO2 and H2O with a small amount of CO in the presence of various amount of O2. Temperature dependent experiments with APXPS shows that elevated surface temperature (300 °C compared to 250 °C) resulted in the increase in the production of gas-phase CO2, which suggest that the reaction is more likely following Langmuir-Hinshelwood mechanism, although this surface temperature effect was more significant on methanol reaction than on ethanol reaction. However, in a UHV chamber, TPD spectra monitoring hydrogen (m/z=2), water (m/z=18), carbon monoxide (m/z=28), formaldehyde (m/z=30), methanol (m/z=31), carbon dioxide (m/z=44), and dimethyl ether (m/z=46) following adsorption of 7 L of methanol/ethanol at 190 K showed a simple desorption of methanol from the surface at ~220 K with a small amount of production of CO and aldehydes ~300 K. TPR of the alcohols on the same STO surface exhibits little-to-no reaction with the flux equivalent to ~10-7 Torr at the surface. This work was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Chemical Sciences, Geosciences, and Biosciences Division.

Adsorption and reaction of alcohols on SrTiO3(100) by ambient pressure XPS

253rd National Meeting (2017)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.