Systematic Enumeration of Elementary Reaction Steps in Surface Catalysis

The direct synthesis of complex chemicals
from simple precursors (such as syngas) is one of the main objectives
of current research in heterogeneous catalysis. To rationally design
catalytic materials for this purpose, it is essential to identify
the critical elementary reaction steps that ultimately determine a
catalyst’s activity and selectivity with respect to a desired
product. Unfortunately, the number of potentially relevant elementary
steps is in the thousands, even for relatively simple target species
like ethanol. The challenge of identifying the critical steps is thus
akin to finding the proverbial needle in a haystack. Recently, a model-reduction
scheme has been proposed, which tackles this problem by prescreening
the barriers of all potential reactions with computationally inexpensive
approximations. Although this route appears highly promising, it raises
the question of how the starting point of the model-reduction process
can be determined. In this contribution, we present a systematic method
for enumerating all intermediates and elementary reactions relevant
to a chemical process of interest. Using this approach, we construct
reaction networks for C,H,O-containing systems consisting of up to
four non-hydrogen atoms (more than 1 million reactions). Importantly,
the scheme goes beyond simple bond-breaking reactions and allows considering
rearrangement and transfer reactions as well. The presented reaction
networks thus cover the chemistry of syngas-based processes (and beyond)
to an unprecedented scale.