  Gas-phase chemistry at extreme conditions (low densities and temperatures) is
difficult, so the presence of interstellar grains is especially important for
the synthesis of molecules that cannot form in the gas phase. Interstellar
grains are advocated to enhance the encounter rate of the reactive species on
their surfaces and to dissipate the energy excess of largely exothermic
reactions, but less is known of their role as chemical catalysts that provide
low activation energy pathways with enhanced reaction rates. Different
materials with catalytic properties are present in interstellar environments,
like refractory grains containing space-abundant (d)block transition metals.
Quantum chemical calculations considering extended periodic surfaces were
carried out in order to search for the stationary points and transitions states
to finally construct the reaction potential energy surfaces. Binding energy and
kinetic calculations based on the Rice Ramsperger Kassel Marcus (RRKM) scheme
were also performed to evaluate the catalytical capacity of the grain and to
allocate those reaction processes within the astrochemical framework. Our
mechanistic studies demonstrate that astrocatalysis is feasible in
astrophysical environments. Thermodynamically the proposed process is largely
exergonic, but kinetically it shows energy barriers that would need from an
energy input in order to go through. The present results can explain the
presence of CH3OH in diverse regions where current models fail to reproduce its
observational quantity. The evidence of astrocatalysis opens a completely new
spectrum of synthetic routes triggering chemical evolution in space. From the
mechanistic point of view the formation of methanol catalysed by a single atom
of Fe0 is feasible; however, its dependency on the temperature makes the
energetics a key issue in this scenario.
