Pt-Re small cluster interaction with H2

Abstract

The interaction of small Pt-Re clusters with H2 is reported here through ab initio multicon-figuration self-consistent field (MC-SCF) calculations, plus extensive multireference configuration interaction (MR-CI), variational and perturbative calculations. These calculations provide a cluster model for the activation of hydrogen by Pt-Re bimetallic catalysts. It was found that the 6S(5d56s2) Re atom ground state needs an important activation to induce very weak capture of separated hydrogen atoms, whereas in the lowest excited states the activation energies are small or zero, with a very reasonable depth of well. The four lowest states of Pt-Re were found to be 4 Σ+, 6Πyz, Σ + and 6Πxz. Pt-Re interaction with H2 has been studied from both metal ‘sides’. It was established that Pt-Re with the platinum side in the ground electronic 4Σ+ state and in the lowest 6Π+ excited states is able to capture H2 molecules without activation, whereas in the 6Πyz and 6Πxz excited states there is no capture. The rhenium side of Pt-Re in its four lowest states considered cannot capture the H2 molecule. The interaction of Pt2-Re with H2 was studied also. For the ground 2B2 electronic state and the low lying 2A1 electronic state the platinum moiety can spontaneously capture and break H2. The rhenium side of Pt2-Re(B2), however, can capture H2 only after surmounting a small barrier, and the excited Pt2-Re(2A1) can spontaneously capture H2. For Pt2-Re in its low lying 4A1 electronic state both metal sides capture and break H2 after surmounting a small barrier.