Influence of the zeolite support on the catalytic properties of confined metal clusters: a periodic DFT study of O2 dissociation on Cun clusters in CHA

Functionalization of zeolite-encapsulated Cu5 clusters as visible-light photoactive sub-nanomaterials

The unique structural properties of zeolites make them ideal environments for encapsulating subnanometric metal clusters on their microporous channels and cavities, showing an enhanced catalytic performance. As a first step towards the functionalization of these clusters as photocatalysts as well, this work addresses the optical properties of zeolite-encapsulated Cu5-TiO2 nanoparticles as well as their application in the photo-induced activation of CO2 by sunlight. Model density functional theory (DFT) calculations indicate the stability of the Cu5 cluster adsorbed on the TiO2 nanoparticles filling the pores of a model zeolite structure. Second, it is shown that while TiO2 nanoparticles absorb in the UV, the photo-absorption spectrum of the Cu5-TiO2 nanoparticle composite is peaked at the visible region, where the sun has its maximum energy input, also allowing for the photo-induced activation of CO2 adsorbed onto the Cu5 cluster.

An alternative catalytic cycle for selective methane oxidation to methanol with Cu clusters in zeolites

The partial oxidation of methane to methanol catalyzed by Cu-exchanged zeolites involves at present a three-step procedure that requires changing reaction conditions along the catalytic cycle. In this work we present an alternative catalytic cycle for selective methane conversion to methanol using as active species small Cu5 clusters supported on CHA zeolite. Periodic DFT calculations show that molecular O2 is easily activated on Cu5 clusters producing bi-coordinated O atoms able to dissociate homolytically a CH bond from CH4 and to react with the radical-like non-adsorbed methyl intermediate formed producing methanol, while competitive overoxidation to CO2 is energetically disfavored. The present mechanistic study opens a new avenue to design catalytic materials based on their ability to stabilize radical species.