Ultrasmall gold nanoclusters selectively-confined within extra-large pore zeolite GTM-4 as active oxidation catalysts

Preformed gold nanoclusters of size below 1 nm have been selectively confined within the germanosilicate zeolite GTM-4, displaying the extra-large pore chiral -ITV framework. The synergy between the method of preparation of the Au nanoclusters, through the use of a historical recipe involving essential oils that stabilize very small clusters, and the dimensions of the -ITV extra-large pores as well as the singular 3D-arrangement of the anchoring Ge-OH groups associated with the framework-interrupted positions, enables the efficient confinement of Au₈-Au₁₃ nanoclusters, as suggested by fluorescence spectroscopy, inside the extra-large pores of the -ITV framework, as suggested by the similar Au content determined in bulk (by elemental XRF analysis) and in the surface (by XPS). These clusters seem to display the appropriate dimensions as to be stabilized within the -ITV channels through a simultaneous interaction with several Ge-OH groups present in closeby d4r units. Indeed, the interaction with such structural Ge-OH groups promotes an increase of the electron density in the Au nanoentities that result in a very high oxidation catalytic activity intrinsic to Au for the aerobic oxidation of cyclohexene. This work opens the way to the development of metal@zeolite catalysts with extra-large pores in frameworks with singular chemical features and catalytic performances.