Pd8Ni92(1Â 1Â 0) surface structure from surface X-ray diffraction. Surface evolution under hydrogen and butadiene reactants at elevated pressure

The (N × 1) reconstruction (N = 5-6) of the clean Pd8Ni92(1 1 0) surface has been investigated by surface X-ray diffraction. A good fit with experimental data collected under UHV conditions is obtained when introducing undulations in the outer dense rows, constituted mainly of Pd atoms which strongly segregate to the surface. This reconstruction can be regarded as a way to relax the strains induced on the bigger Pd surface atoms, at least partially. The modifications of the surface were studied under butadiene then hydrogen as well as during butadiene hydrogenation at elevated pressure at 300 K and the (N × 1) reconstruction was found to be still present. The main changes are observed under pure hydrogen and during butadiene hydrogenation.