Atomic-layer by atomic-layer compositional depth profiling: Surface segregation and impurity cosegregation of Pt-Rh and Pt-Ru alloys

3D atom probe study of gas adsorption and reaction on alloy catalyst surfaces I: Instrumentation

“…Thermal treatments alone at the temperatures employed here are not sufficient to cause chemical changes to the surfaces. This is in agreement with earlier atom probe studies of heating Pt-Rh in vacuo, which demonstrate that temperatures of at least 873 K are required to induce significant segregation [7,18]. FIM observations also confirmed little interaction between any surface and the gases N 2 , C 2 H 2 and CO, at least within the temperatures of interest in this work.…”

“…A final operating temperature of 60 K was selected, which when combined with a pulse fraction of 20% yielded alloy compositions that agreed within 1% of the stated values. This pulse fraction was identical to that used by other atom probe groups to study Pt-Rh [17][18][19].…”

3D atom probe study of gaseous adsorption on alloy catalyst surfaces III: Ternary alloys – NO on Pt–Rh–Ru and Pt–Rh–Ir

“…On platinum-ruthenium alloys, slight platinum surface segregation was noted on heating under vacuum [23,24], while platinum also segregated to the surface in a Pt-20%Ir alloy under vacuum heating and with sulphur contaminated surfaces [25,26]. Similar surface enrichment of platinum has also been observed in Pt-Rh [27], although for this alloy the presence of sulphur causes rhodium enrichment instead [28].…”

Surface segregation in ternary Pt–Pd–Rh alloys studied with Monte Carlo simulations and the modified embedded atom method

“…The experimentally observed Rh segregation can presumably be attributed to the presence of small impurities. Indeed, it has experimentally already been observed that for binary Pt-Rh alloys, traces of C make Rh segregate to the surface [21,22]. The simulations show further that the influence of the surface is clearly restricted to just one single atomic layer only.…”