The Growth and Properties of Pd and Pt on Al₂O₃/NiAl(110)

Abstract

Small metal particles have strongly size-dependent properties, which -in the case of supported particles -are also influenced by the particle substrate interaction. We have investigated such effects for Pd deposited on a thin alumina film grown on NiAl(11 0) by probing the adsorption behaviour of CO. Structure and size of the metal islands were varied by employing different substrate temperatures during evaporation. We found that at 90 K small, disordered aggregates are formed, whereas deposition at 300 K results in larger crystallites with (111) facets. The CO thermal desorption spectra show a size-dependent behaviour which can be attributed to a higher degree of CO coordination with decreasing particle size. The results are compared with the corresponding behaviour of Pt. In contrast to Pd, Pt leads to a strong interaction with the substrate at 300 K. This gives rise to a desorption feature of CO in a temperature range which is typical for transition metal oxides.

Determination of surface OH acidity from the formation of acid/base complexes on ultrathin films of γ-Al2O3 on NiAl(100)

“…Additionally, Heemeier et al have also shown that increasing the concentration of surface hydroxyl groups increases metal dispersion on metallic supported catalysts [17], presumably due to the addition of more nucleation sites for the initiation of metal particle growth. Recently, a number of research groups have developed the use of ultrathin films of Al 2 O 3 that can be grown on the surfaces of single crystals of the intermetallic compounds of Ni and Al as models for Al 2 O 3 catalyst supports [1,15,16,[18][19][20][21][22][23][24][25]. Such ultrathin films have a number of advantages for fundamental studies utilizing modern surface spectroscopies.…”

Finite size effects on supported Pd nanoparticles: Interaction of hydrogen with CO and C2H4

“…A knowledge of the morphology of supported metal nanoparticles is of tremendous importance in heterogeneous catalysis because the catalytic properties of nanoparticles strongly depend on their exact surface structure ( [1][2][3][4][5][6][7][8][9] and references therein). Metal nanoparticles often exhibit low Miller-index facets and single crystal surfaces have therefore frequently been used as model systems.…”

Photochemistry of Methane on Pd/Al2O3 Model Catalysts: Control of Photochemistry on Transition Metal Surfaces

“…[4,5] The size of clusters and, hence, their geometrical and electronic structures can be controlled by changing formation conditions such as metal deposition rates and surface temperature. [6] Thus, it is of great interest to know if surface (photo)reactions can be controlled by manipulating the electronic and geometrical structures of the metal clusters.…”