10.1002/anie.202007790
Angewandte Chemie International Edition
RESEARCH ARTICLE
as 170 kJ mol−1 (Fig. 9; Si:Al=6.2). These shifts in barriers are
nearly symmetric, such that the average barrier decreases slightly
to 107 kJ mol−1 at the highest Al content (Fig. 9). If Al are assumed
to be distributed thermodynamically (i.e., based on a Boltzmann
average), then the effective barrier can be computed for each
Si:Al ratio. This Boltzmann-averaged barrier decreases nearly
monotonically as Al content increases, to a minimum of 108 kJ
mol−1 at Si:Al of 8 and 114 kJ mol−1 at Si:Al of 6.2 (Fig. 9). These
spectating Al are not directly involved in the methylation transition
state; rather, they modify the solvation environment provided by
the zeolite by altering its polarity and providing H-bonding sites
that interact with the transition state or conjugate base of the
reacting site, in a manner sensitive to the specific positions of the
Al centers, resulting in dramatic effects (both increases and
decreases) in activation barriers.
Acknowledgements
A.H., S.N., and D.H. acknowledge financial support from the ACS
Petroleum Research Fund New Doctoral Investigation Award
(57079DNI5) and the National Science Foundation CAREER
program (1942684-CBET). This work used the Extreme Science
and Engineering Discovery Environment (XSEDE),[63] which is
supported by the National Science Foundation grant number ACI-
1548562 through allocation CTS160041. J.B, J.D.I., C.N, and R.G.
acknowledge financial support by the National Science
Foundation DMREF program (1922173-CBET) for the
experimental work at Purdue.
Keywords: alkanol dehydration • DFT calculations •
heterogeneous catalysis • solvation • zeolites
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