CO oxidation over gold nanoparticles on Mg(OH)₂ and MgO subjected to different redox treatments

CO oxidation over gold nanoparticles (Au NPs) supported on magnesium oxide and magnesium hydroxide was studied at 30°C during 15 h. Gold (∼2.6 wt.%) was supported by deposition precipitation on commercial magnesia followed by thermal treatment of selected samples in hydrogen or in oxygen at different temperatures: 350 or 500°C. The formation of Au NPs during the phase transition of Mg(OH)₂ to MgO under either reduction or oxidation was monitored by in situ UV-Visible spectroscopy, online mass analysis and X-ray diffraction (XRD). The Mg(OH)₂ to MgO phase transition led to the decapsulation of ∼30% of the gold that had been encapsulated by the Mg(OH)₂ species during gold deposition from aqueous solution on MgO. The initial activity on CO oxidation was similar for Au NPs supported either on Mg(OH)₂ or on MgO, and was practically independent the type of redox pretreatment. In turn, the catalytic activity decay with reaction time strongly depended on the type of redox pre-treatment, pre-oxidised catalysts being more stable than pre-reduced ones. It was suggested that sample pre-treatment affects activity decay via change of the CO₂-catalyst interaction.