1 research outputs found
Following Molecules through Reactive Networks: Surface Catalyzed Decomposition of Methanol on Pd(111), Pt(111), and Ni(111)
We
present a model of the surface kinetics of the dehydrogenation reaction
of methanol on the Pd(111), Pt(111), and Ni(111) metal surfaces. The
mechanism consists of 10 reversible dehydrogenation reactions that
lead to the final products of CO and H<sub>2</sub>. The rate coefficients
for each step are calculated using <i>ab initio</i> transition
state theory that employs a new approach to obtain the symmetry factors.
The potential energies and frequencies of the reagents and transition
states are computed using plane wave DFT with the PW91 exchange correlation
functional. The mechanism is investigated for low coverages using
a global sensitivity analysis that monitors the response of a target
function of the kinetics to the value of the rate coefficients. On
Pd(111) and Ni(111), the reaction COH → CO + H is found to
be rate limiting, and overall rates are highly dependent upon the
decomposition time of the COH intermediate. Reactions at branches
in the reaction network are also particularly important in the kinetics.
A stochastic atom-following approach to pathway analysis is used to
elucidate both the pathway probabilities in the kinetics and the dependence
of the pathways on the values of the key rate coefficients of the
mechanisms. On Pd(111) and Ni(111) there exists significant competition
between the pathway containing the slow step and faster pathways that
bypass the slow step. A discussion is given of the dependence of the
model target’s probability density function on the chemical
pathways