Effects of surface species and homogeneous reactions on rates and selectivity in ethane oxidation on oxide catalysts
Name
1976257.pdf
Description
Accepted version
Size
2.45 MB
Format
Adobe PDF
Checksum (MD5)
1da549c40270c548cec5aabca357be0f
Author(s)
Liu, Yilang
McGill, Charles J
Green, William H
Deshlahra, Prashant
Date Issued
December 2021
Journal
AIChE Journal
Publisher
Wiley
Citation
Liu, Yilang, McGill, Charles J, Green, William H and Deshlahra, Prashant. 2021. "Effects of surface species and homogeneous reactions on rates and selectivity in ethane oxidation on oxide catalysts." AIChE Journal, 67 (12).
Version
Author's final manuscript
Abstract
Selective alkane oxidations on metal oxide catalysts involve complex mechanisms with multiple reactions in series and parallel, different types of reduced and oxidized surface species, and potential contributions from gas-phase reactions. Here, kinetics and thermodynamics of elementary steps involved in C2H6-O2 reactions on SiO2-supported small vanadium oxide domains are determined using density functional theory. These surface reactions together with gas-phase mechanisms are incorporated in kinetic simulations to determine how surface and gaseous reactions interact and contribute to rates and selectivity. The results show that gas-phase reactions within pore volumes in contact with the catalyst contribute significantly to C2H6 activation rates, even at conditions where gas-phase reactions in empty volumes without catalyst are negligible. The majority of C2H6 activations occur on the surface, via H abstraction by vanadium oxo species present at terminal lattice oxygens. The gas-phase activations via H-abstraction by OH radicals also exhibit significant contributions. The reduced centers formed by reactions at vanadium oxo species are re-oxidized rapidly and, therefore, are present in very small concentrations at reaction conditions. The re-oxidation steps lead to the formation of HO2 radicals and surface peroxo species that are also rapidly consumed and are present in small concentrations. The peroxo species preferentially convert C2H4 to its epoxide product and influence selectivity even at low concentrations. The gas-phase reactions decrease the concentrations of peroxo species and improve selectivity slightly. The effects of reaction conditions and catalyst site density provide further insights into how factors beyond conversions at lattice oxygens influence rates and selectivity in alkane oxidation reactions of significant industrial importance.
MIT Department
Massachusetts Institute of Technology. Department of Chemical Engineering
Terms of Use
Creative Commons Attribution-Noncommercial-ShareAlike
Persistent DSpace Link
DOI of Published Version
https://doi.org/10.1002/aic.17483
