A. Cruz

Pt-Re small cluster interaction with H2

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.

Theoretical study of the reaction of H2 with a Cu2Pt2 cluster

The study of the interaction of a pyramidal tetramer of Cu2Pt2 with the H2 is reported here through ab initio multiconfigurational self-consistent field (MC-SCF) calculations, plus extensive multireference configuration interaction (MR-CI), variational and perturbative calculations. The lowest three electronic states X 1A′, a 3A′ and a 1A′ of the bare cluster were considered in order to study this interaction. For the H2 Cs approaching a Pt vertex, results show that the Cu2Pt2 pyramid cluster in its X 1A′ and a 1A′ states can spontaneously capture and dissociate the H2. For the H2 Cs approaching a Cu vertex, where H2 is located in the Cs reflecting plane, the Cu2Pt2 cluster in its X 1A′ electronic state shows capture of the hydrogen molecule after surmounting an energy barrier; moreover, in this approach the Cu2Pt2 cluster in its a 1A′ electronic state shows spontaneous capture of the hydrogen molecule. For the H2 approaching a Cu vertex, where the Cs reflecting plane bisects the H2 molecule, the Cu2Pt2 cluster in its three lowest-lying states is able to capture the hydrogen molecule after surmounting a small barrier. The Cu2Pt2+H2 Cs face-on interactions show a lower H2 activation than that which was obtained in the equivalent Pt4+H2 interactions.