  We present a first-principles based multiscale modeling approach to
heterogeneous catalysis that integrates first-principles kinetic Monte Carlo
simulations of the surface reaction chemistry into a fluid dynamical treatment
of the macro-scale flow structures in the reactor. The approach is applied to a
stagnation flow field in front of a single-crystal model catalyst, using the CO
oxidation at RuO2(110) as representative example. Our simulations show how heat
and mass transfer effects can readily mask the intrinsic reactivity at
gas-phase conditions typical for modern in situ experiments. For a range of
gas-phase conditions we furthermore obtain multiple steady-states that arise
solely from the coupling of gas-phase transport and surface kinetics. This
additional complexity needs to be accounted for when aiming to use dedicated in
situ experiments to establish an atomic-scale understanding of the function of
heterogeneous catalysts at technologically relevant gas-phase conditions.
