Electron withdrawing ligands inhibit oxygen transport by Al⁺: temperature-dependent kinetics of AlO⁺/(O₂)AlO⁺ + H₂/CH₄

Abstract

Al⁺ has been shown to enable the oxygen atom transfer (OAT) to convert methane to methanol at thermal energies through a unique, barrierless mechanism. Quantum chemical calculations suggested that the efficacy of methanol formation relative to other product channels could be tuned by the presence of electron-withdrawing or -donating groups. Here, the kinetics of AlO⁺, which has no electron-withdrawing group, and of (O₂)AlO⁺, which includes an electron-withdrawing group, reacting with CH₄ or with H₂ are studied using a selected-ion flow tube apparatus. In all cases, AlO⁺ yields the OAT product (CH₃OH or H₂O) in addition to the hydrogen atom transfer (HAT) product, while (O₂)AlO⁺ yields only the HAT product; the electron-withdrawing O₂ group has inhibited oxidation as predicted.

GRAPHICAL ABSTRACT

KEYWORDS:

• Ion-molecule kinetics
• catalysis
• selected-ion flow tube

Acknowledgements

The views expressed are those of the authors and do not reflect the official guidance or position of the United States Government, the Department of Defense, or of the United States Air Force. This work was supported by the Air Force Office of Scientific Research under AFOSR-19RVCOR042 and 22RVCOR009 (AFRL). BCS was supported through the Institute for Scientific Research of Boston College under contract FA9453-10-C-0206.

We are grateful for the extraordinary impact of Dieter Gerlich on, amongst other fields, the study of kinetics of ion-molecule reactions. His brilliance reverberates in our lab and in others throughout the world.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by the Air Force Office of Scientific Research under AFOSR-19RVCOR042 and 22RVCOR009 (AFRL). BCS was supported through the Institute for Scientific Research of Boston College under contract FA9453-20-C-0048.