Subnanometer platinum clusters in zeolite NaEMT via stoichiometric carbonyl clusters

Abstract The direct carbonylation of [Pt(NH 3 ) 4 ] 2+ -exchanged zeolite NaEMT generates [Pt 3 (CO) 3 (μ-CO) 3 ] 2− 3 complexes nearly exclusively. The preferential formation of triplane complexes is attributed to the perfect matching of the complex with a nearly threefold symmetry axis to the hosting hypercage exhibiting a threefold symmetry as well. The complexes are formed by a reductive carbonylation, where (i) the reducing hydrogen is produced via the low-temperature water–gas shift reaction and (ii) the formed protons are stored in charge compensating ammonium ions. Small subnanometer platinum clusters of zero (Pt 0 x ) and partial positive (Pt δ + x ) charge are found during the decarbonylation of the anionic platinum carbonyl clusters, generated by reoxidation with the aid of the stored protons. The smallest clusters are assumed to exhibit a size-quantization (metal–insulator transition) effect. All transient states of the processes are monitored by UV–vis and IR spectroscopy in situ.