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Activating 2D materials for CO2 and CO hydrogenation to higher alcohols: predictive modeling meets experiments

  • Talat Rahman (University of Central Florida, USA)
Date
Tuesday 31 March 2020
Time
Address
Hotel NH Noordwijk Conference Centre Leeuwenhorst

Talat S. Rahman1, Duy Le1, Tao Jiang1 and Richard Blair2
1Department of Physics, University of Central Florida, Orlando, FL 32816, USA    
2Florida Space Institute, University of Central Florida, Orlando, FL 32816, USA

e-mail: talat.rahman@ucf.edu

There is an on-going quest for cheap and abundant catalysts that would facilitate hydrogenation of CO2, an abundant greenhouse gas in the Earth’s atmosphere, and CO, a poisonous exhaust, into fuels and chemicals that are traditionally derived from petroleum. Interestingly, the recent high attention paid to two dimensional (2D) materials has also resulted in their consideration as promising catalysts for a variety of reactions. This is not surprising because of the high surface to volume ratio, structural stability and flexibility.

In this talk I will first present results of our joint computational and experimental examination of the hydrogenation of CO and CO2 to methanol, ethanol and methane on a popular transition metal dichalcogenide: molybdenum disulfide (MoS2). I will highlight the important role that defects [1] (S vacancy) and transition metal nanoparticles [2] play without which the basal planes of these materials would remain inert. It will be shown that while S vacancies facilitate CO hydrogenation on single-layer MoS2, our density functional theory (DFT) based kinetic Monte Carlo simulations show that the reactivity and product selectivity is further improved by both a Cu substrate or adsorbed Au nanoparticles. On yet another 2D material, hexagonal boron nitride (h-BN), I will show that vacancies can effectively help convert alkenes to alkanes and activate the basal plane for CO2 hydrogenation. Our DFT based determination of reaction pathways and activation energy barriers will trace the reactivity to the nature of the mid gap state (defect introduced) and that  activation occurs through back-donation to the π* orbitals of CO2 from frontier orbitals (defect state) of the h-BN sheet localized near a nitrogen vacancy. 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 ˚C and methanol formation observed at lower temperatures (as low as 20 ˚C), which are in great agreement with the thermodynamics and kinetics of our calculated reaction pathways. The relative importance thermodynamics and kinetics in predicting activity and reaction selectivity and turn over frequencies will also be discussed.      

Acknowledgements

This work has been partially funded by DOE through grant DE-FG02-07ER15842.

References

  1. D. Le, T. B. Rawal, and T. S. Rahman, J. Phys. Chem. C 118, 5346 (2014).
  2. T.B. Rawal, D. Le, and T.S. Rahman, J. Phys.: Condens. Matter 29 415201 (2017).
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