Real-Time Facile Detection of the WO3 Catalyst Oxidation State under Microwaves Using a Resonance Frequency

Shuntaro Tsubaki; Tomoki Higuchi; Tomoki Matsuzawa; Satoshi Fujii; Masateru Nishioka; Yuji Wada

doi:10.1021/acsomega.0c04862

Real-Time Facile Detection of the WO₃ Catalyst Oxidation State under Microwaves Using a Resonance Frequency

ACS Omega. 2020 Dec 1;5(49):31957-31962. doi: 10.1021/acsomega.0c04862. eCollection 2020 Dec 15.

Authors

Shuntaro Tsubaki^{1

2}, Tomoki Higuchi¹, Tomoki Matsuzawa¹, Satoshi Fujii^{1

3}, Masateru Nishioka⁴, Yuji Wada^{1

5}

Affiliations

¹ School of Materials and Chemical Technology, Tokyo Institute of Technology, E4-3, 2-12-1, Ookayama, Meguro-ku, Tokyo 152-8552, Japan.
² PRESTO, Japan Science and Technology Agency (JST), 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan.
³ Department of Information and Communication Systems Engineering, National Institute of Technology Okinawa College, 905 Henoko, Nago-shi, Okinawa 905-2192, Japan.
⁴ National Institute of Advanced Industrial Science and Technology, 4-2-1, Nigatake, Miyagino-ku, Sendai 983-8551, Japan.
⁵ Institute of Innovative Research, Tokyo Institute of Technology, 4259 Nagatsuta-cho, Midori-ku, Yokohama, Kanagawa 226-8503 Japan.

Abstract

Microwaves (MWs) are often used to enhance various heterogeneous catalytic reactions. Here, we demonstrate real-time monitoring of a catalyst's oxidation state in a microwave catalytic reaction using a resonance frequency. The changes in the catalyst's oxidation state during the reaction induced changes in the resonance frequency in the cavity resonator. The resonance frequency was not affected by 2-propanol adsorption, while the frequency decreased with the reduction of WO₃ → WO_3-x. That is, the redox state of the WO₃ catalyst could be detected using the resonance frequency. The oxidation state of the WO₃ catalyst was then directly observed by the resonance frequency during the dehydration reaction of 2-propanol by microwaves as a model reaction. Resonance frequency monitoring revealed that the enhanced dehydration of 2-propanol by microwaves was attributable to the reduction of the WO₃ catalyst. Moreover, the temporal changes in the oxidation state of the WO₃ catalyst detected by the resonance frequency coincided with that observed by operando Raman spectroscopy. Therefore, real-time resonance frequency monitoring allowed facile detection of the bulk catalyst oxidation state under microwaves without using any spectroscopic apparatus.