Acid–base properties of γ-Al2O3 and MgO–Al2O3 supported gold nanoparticles

Gold nanoparticles supported on γ-alumina and magnesia-doped γ-alumina were synthesized by co-precipitation via a modified sol–gel method. The syntheses were found to produce catalysts with controllable acidity; the presence of either gold or magnesia produced catalyst possessing unbalanced density of acidic and basic sites, while the addition of both gold and magnesia produced catalyst possessing balanced density of relatively stronger acidic and basic sites. The variation of the acid–base strengths of the synthesized catalysts was assessed by using NH3-TPD, CO2-TPD, and infrared analysis of adsorbed CO2 and correlated to their catalytic activity in 2-propanol decomposition probe reaction. Catalysts containing magnesia and gold were found to exhibit base catalytic properties through their greater selectivity for acetone formation, while plane γ-alumina and γ-alumina doped with magnesia or gold exhibited acid catalytic properties through their selectivity for propene formation.

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► Au/MgO–Al2O3 catalysts were prepared by co-precipitation via alumina sol–gel chemistry.
► Reduced Au nanoparticle size increased with increasing magnesia content.
► Au/8%MgO–Al2O3 exhibited base catalytic properties in 2-propanol decomposition reaction.
► Au/MgO–Al2O3 exhibited balanced acidic and basic site densities as measured by NH3 and CO2-TPD.
► IR of adsorbed CO2 revealed that Au/MgO–Al2O3 possessed stronger base sites strength than Au/γ-alumina.