CO oxidation catalyzed by gold nanoparticles confined in mesoporous aluminosilicate Al-SBA-15: Pretreatment methods

Gold nanoparticles with an average size of ∼3 nm confined in the mesoporous aluminosilicates Al-SBA-15 were synthesized by a procedure of successive aminosilane grafting and gold adsorption-reduction. The aluminosilicate, while traditionally regarded as an inert support for gold nanoparticles giving low activity for CO oxidation, was activated by a high-temperature hydrogen reduction pretreatment process and showed good catalytic activities in CO oxidation. We have made two different kinds of SBA-15, one templated by pluronic 123 with the normal method of synthesis (denoted as Al-SBA-15(N)) and the other templated by a ternary mixture of P123-CTAB-SDS (denoted as Al-SBA-15(F)) giving film morphology. It turns out the two support, although both can strongly confine the Au nanoparticles (NP) to ∼3 nm, require different ways of pretreatments. Al-SBA-15(N) needs first calcination and then hydrogen reduction, but Al-SBA-15(F) needs a direct hydrogen reduction to give good catalytic activity. Electron paramagnetic resonance (EPR) measurements were performed for the catalyst at various stages of their treatments to identify the superoxide anion formation. The high-temperature hydrogen reduction of the aluminosilicate materials produces defect sites for oxygen adsorption to give the superoxide species which facilitates the CO oxidation.