Investigation of Ethane Dehydrogenation and Hydrogenolysis on Pt(111), Pt(211), and Pt(100): Bayesian Quantification and Correction of DFT-Based Enthalpic and Entropic Uncertainties

Computational investigations of heterogeneously catalyzed
reactions
using density functional theory (DFT) are often inaccurate, largely
due to uncertainties in the choice of DFT functional (enthalpic uncertainty)
and approximations for modeling adsorbate movement along the catalyst
surface (entropic uncertainty). This work illustrates that both uncertainties
are significant in the investigation of ethane dehydrogenation (EDH)
and hydrogenolysis on Pt catalysts by considering the complete deconstruction
of ethane on Pt(111), Pt(211), and Pt(100) using microkinetic modeling
(MKM). Hence, this work uses both noncalibrated and Bayesian-calibrated
MKMs to quantify and correct inaccuracies in macroscopic properties
due to both uncertainties. A Bayesian approach to the correction of
entropic errors was introduced using a “Modified Fermi Function
(MFF)” to calibrate between the two bounds of entropy represented
by the harmonic oscillator (HO) and free translator (FT) approximations.
Regardless of enthalpic and entropic uncertainties, all three surfaces
are capable of ethane activation; however, Pt(211) was found to be
the most active and is largely responsible for methane production.
Next, Pt(111) is largely responsible for acetylene production, and
Pt(100) has the highest ethylene selectivity but is most susceptible
to coking. By comparison of different calibrated models, the FT entropy
approximation was found to better describe EDH under typical experimental
conditions. Statistical evidence was found to support Pt(111) as the
active site for EDH, assuming that one single site is responsible
for the chemistry. On the three surfaces, competing second dehydrogenations
to CH2CH2 and CH3CH were observed
as well as isomerization of CH3CH back to CH2CH2 and deeper dehydrogenation of CH3CH. C–C
cleavage was found to largely proceed via the CH3C intermediate
on Pt(100) and Pt(111), while on Pt(211), it was via both CHC and
CH3C.