and confirmed in this work by catalytic experiments of the CO-exposed X-HCP-Ru (Fig. ). CO could neither be detected in the gas phase (Fig. ), nor observed in the ATR-IR spectrum (Fig. ), which can also be caused by the low density of metal sites. Regarding topological changes, nitrogen physisorption reveals the loss of pore volume under the catalytic conditions (from 0.18 to 0.046 cm 3 g -1 ), which can affect the accessibility of catalytically active sites (Fig.