How Well Does Pt(211) Represent Pt[n(111) × (100)] Surfaces in Adsorption/Desorption?

We have investigated to what extent Pt(211) is representative for Pt[n(111) × (100)] surfaces in adsorption/desorption behavior of water, hydrogen, and oxygen through temperature-programmed desorption. In contrast to surfaces with n > 3, H2O adsorbs to Pt(211) in a crystalline fashion far below the usual crystallization temperature of amorphous solid water. For D2, we find that desorption from (100) steps is independent of terrace length for n ≥ 3, but desorption from the neighboring (111) terraces varies. Larger terraces result in larger variations in binding energies as a consequence of decreasing proximity of adsorption sites to the step edge. For O2, we observe enhanced dissociation on Pt(211) resulting in a much larger maximum O coverage than surfaces with n > 3. The TPD characteristics suggest formation of 1D PtO2 structures, which are only formed for n = 3 with this (100) step type. Hence, Pt(211) can by no means be considered representative of Pt(111) terraces truncated by (100) steps. Our results stress that great caution is required when extrapolating results from theoretical studies based on this smallest unit cell containing the (100) step edge to catalysis by actual particles.