Single-layer hexagonal boron nitride (h-BN), nominally an insulator with a band gap of about 6 eV, has recently been the subject of two entirely disconnected applications, thanks to its propensity for harboring defects. It has been touted as a source of single photon emission (not the subject of this talk) and as a promising hydrogenation catalyst [1]. In this talk, we will present results of a closely coupled computational and experimental effort, that shows that vacancies induced in defect-laden hexagonal boron nitride (dh-BN) can effectively convert alkenes to alkanes and activate the CO2 molecule for hydrogenation. Our density functional theory (DFT) based determination of reaction pathways and activation energy barriers will trace the reactivity to the nature of the mid gap state (introduced by the defect). In particular, we will show that activation occurs through back-donation to the π* orbitals of CO2 from frontier orbitals (defect state) of the dh-BN sheet localized near a nitrogen vacancy (VN). Subsequent hydrogenation to formic acid (HCOOH) and methanol (CH3OH) proceeds through vacancy-facilitated co-adsorption of hydrogen and CO2. These results were experimentally confirmed in a reactor designed to continuously produce defects in h-BN by the application of mechanical force. Equimolar batches of CO2 and hydrogen at 583 kPa were processed for 12 hours. Gas sampling and GC-MS analysis confirmed the temperature-dependent switchable catalysis with formic acid formation observed at reaction temperatures above 160 degrees Centigrade and methanol formation observed at lower temperatures (as low as 20 degrees Centigrade), which are in great agreement with the thermodynamics and kinetics of our calculated reaction pathways.

Predictive modeling and experimental validation of defect induced CO2 hydrogenation on single-layer h-BN

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

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