Surface dynamics of the intermetallic catalyst Pd2Ga, Part I – Structural stability in UHV and different gas atmospheres

• Stability of bulk and surface of intermetallic Pd2Ga were investigated.
• The bulk was found to be stable under moderate conditions relevant for catalysis.
• The surface is highly sensitive towards a passivating oxidative decomposition.
• Different surface states of the catalyst can be easily controlled by pre-treatments.

The structural and electronic properties of unsupported Pd2Ga were investigated after different pre-treatments. Pd2Ga provides with respect to elemental Pd a significantly modified electronic structure with its d-band center being shifted away from the Fermi level. It was found that the electronic structure of the surface depends strongly on its pre-treatment and on the chemical environment. We report a detailed bulk and surface characterization of the intermetallic compound by means of XRD, DTA/TG/MS, SEM, XPS, and HR-TEM. At moderate temperatures, the bulk of Pd2Ga is chemically resistant against H2 or O2 atmosphere and against mechanical load. Contrariwise its surface is highly sensitive against even traces of oxidizing agents, leading quickly to a disparity between bulk and surface structure and composition. The reversibility of this dynamic effect depends on the degree of decomposition and on the sample history. An almost pure intermetallic surface can only be achieved in highly reducing atmospheres.

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