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On the large Pd surface segregation and reactivity of Pd1Fe99 and Pd5Fe95 dilute alloys
A388 Surface Science 287/288 (1993) 346-349 North-Holland
On the large Pd surface segregation and reactivity of Pd~Fe99 and PdsFe95 dilute alloys J.C. Bertolini, J.L. Rousset, P. Miegge, J. Massardier and B. Tardy Institut de Recherches sur la Catalyse, 2 avenue Albert Einstein, 69626 l~lleurbanne Cedex, France Received 17 August 1992; accepted for publication 19 November 1992 The surface composition of PdlFe99 and PdsFe95 was determined using low energy ion spectroscopy (LEIS). After stabilization by annealing of the samples at 870 K, the Pd enrichment at the surface was found to be very important, since it reaches values as large as 55 and 65 at% respectively for the Pd1Fe99 and PdsFe95 alloys. The performances in catalysis of such alloy surfaces were measured for the 1,3-butadiene hydrogenation reaction (at 300 K and 35 Torr for the hydrogen pressure). The activity ((2.1-9.3) × 1015 molecules cm -2 s -1) and selectivity into butenes ( ~ 1) of such Pd-rich surfaces were found to be of the same order of magnitude as for (111) and (110) Pd single crystal faces.
Surface Science 287/288 (1993) 350-354 North-Holland
Investigation of Pt25Ni75( 11 1): preferential sputtering and surface segregation P. Weigand, W. Hofer and P. Varga lnstitut fiir AUgemeine Physik, TU Wien, Wtedner Hauptstrasse 8-10, A-1040 l/'tenna, Austria Received 3 September 1992; accepted for publication 19 November 1992 The surface composition of Pt25NiTs(lll) has been determined by ion scattering spectroscopy and Auger electron spectroscopy. The surface layers are found to be enriched in Pt due to preferential sputtering. Thermal treatment induces further segregation of Pt at the topmost atomic layer, From the different sampling depths of ISS and AES composition profiles are deduced, which show a strong dependence on the temperature during thermal treatment. At an annealing temperature of 770 K the thermally induced Pt segregation is determined by the composition of the sputter induced altered layer being enriched in Pt. However, at an annealing temperature of 970 K the sputter induced altered layer has disappeared and the Pt segregation at the topmost atomic layer is determined by the bulk composition.
Surface Science 287/288 (1993) 355-360 North-Holland
LEED and EELS studies on vanadium (110) and (111) single crystal surfaces K. Nakayama and S. Usami Applied Physics, Faculty of Engineering, Yokohama National University, Tokiwadai 156, Hodogaya-ku, Yokohama 240, Japan Received 1 September 1992; accepted for publication 19 November 1992 The surface atomic arrangements and the electronic states of vanadium (110) and (111) single crystals have been investigated at room temperature with low energy electron diffraction (LEED) and electron spectroscopic techniques. LEED was observed with a CCD camera. The LEED pattern of the most densely packed (110) plane showed no extra features beyond those expected for the bulk, while the (111) surface was observed to reconstruct into a (vr3 × ¢'3)R30 ° superstructure. Electron energy loss spectra for both specimens were also measured with primary electrons in the low energy range from 100 to 300 eV. The loss peaks observed for the (110) and (111) surfaces could be attributed to such common energy losses as bulk and surface plasmons, interband transitions and inner-shell excitations. However, the magnitudes of the observed plasmon loss energy with low energy incidence for the (11I) surface differ from values calculated on the basis of Ritchie's formula [Phys. Rev. 106 (1957) 874].
On the large Pd surface segregation and reactivity of Pd~Fe99 and PdsFe95 dilute alloys J.C. Bertolini, J.L. Rousset, P. Miegge, J. Massardier and B. Tardy Institut de Recherches sur la Catalyse, 2 avenue Albert Einstein, 69626 l~lleurbanne Cedex, France Received 17 August 1992; accepted for publication 19 November 1992 The surface composition of PdlFe99 and PdsFe95 was determined using low energy ion spectroscopy (LEIS). After stabilization by annealing of the samples at 870 K, the Pd enrichment at the surface was found to be very important, since it reaches values as large as 55 and 65 at% respectively for the Pd1Fe99 and PdsFe95 alloys. The performances in catalysis of such alloy surfaces were measured for the 1,3-butadiene hydrogenation reaction (at 300 K and 35 Torr for the hydrogen pressure). The activity ((2.1-9.3) × 1015 molecules cm -2 s -1) and selectivity into butenes ( ~ 1) of such Pd-rich surfaces were found to be of the same order of magnitude as for (111) and (110) Pd single crystal faces.
Surface Science 287/288 (1993) 350-354 North-Holland
Investigation of Pt25Ni75( 11 1): preferential sputtering and surface segregation P. Weigand, W. Hofer and P. Varga lnstitut fiir AUgemeine Physik, TU Wien, Wtedner Hauptstrasse 8-10, A-1040 l/'tenna, Austria Received 3 September 1992; accepted for publication 19 November 1992 The surface composition of Pt25NiTs(lll) has been determined by ion scattering spectroscopy and Auger electron spectroscopy. The surface layers are found to be enriched in Pt due to preferential sputtering. Thermal treatment induces further segregation of Pt at the topmost atomic layer, From the different sampling depths of ISS and AES composition profiles are deduced, which show a strong dependence on the temperature during thermal treatment. At an annealing temperature of 770 K the thermally induced Pt segregation is determined by the composition of the sputter induced altered layer being enriched in Pt. However, at an annealing temperature of 970 K the sputter induced altered layer has disappeared and the Pt segregation at the topmost atomic layer is determined by the bulk composition.
Surface Science 287/288 (1993) 355-360 North-Holland
LEED and EELS studies on vanadium (110) and (111) single crystal surfaces K. Nakayama and S. Usami Applied Physics, Faculty of Engineering, Yokohama National University, Tokiwadai 156, Hodogaya-ku, Yokohama 240, Japan Received 1 September 1992; accepted for publication 19 November 1992 The surface atomic arrangements and the electronic states of vanadium (110) and (111) single crystals have been investigated at room temperature with low energy electron diffraction (LEED) and electron spectroscopic techniques. LEED was observed with a CCD camera. The LEED pattern of the most densely packed (110) plane showed no extra features beyond those expected for the bulk, while the (111) surface was observed to reconstruct into a (vr3 × ¢'3)R30 ° superstructure. Electron energy loss spectra for both specimens were also measured with primary electrons in the low energy range from 100 to 300 eV. The loss peaks observed for the (110) and (111) surfaces could be attributed to such common energy losses as bulk and surface plasmons, interband transitions and inner-shell excitations. However, the magnitudes of the observed plasmon loss energy with low energy incidence for the (11I) surface differ from values calculated on the basis of Ritchie's formula [Phys. Rev. 106 (1957) 874].