Preparation of AuCu/TiO₂ catalysts by different methodologies for preferential carbon monoxide oxidation

The preferential oxidation of CO in H₂-rich mixtures (CO-PROX reaction) has been considered very promising for H2 purification, reducing CO level below 50 ppm and allowing its use in Proton Exchange Membrane Fuel Cell (PEMFC). Au nanoparticles supported on TiO₂ (Au/TiO₂ catalysts) have been shown good activity and selectivity for CO-PROX reaction in the temperature range between 20 °C and 80 °C; however, the catalytic activity strongly depends on the preparation method. In addition, the addition of Cu to Au/TiO₂ catalyst could increase the activity and selectivity for CO-PROX reaction. In this work, AuCu/TiO₂ catalysts were prepared by two methodologies using borohydride as reducing agent and electron beam irradiation. Using the borohydride reduction method AuCu/TiO₂ catalysts with different compositions of Au and Cu were prepared in one-step synthesis where Au³⁺ and Cu²⁺ ions were dissolved in water and reduced using sodium borohydride in the presence of TiO₂ support. In a similar way, using electron beam irradiation, Au³⁺ and Cu²⁺ ions were dissolved in a water/2-propanol solution and irradiated in the presence of TiO₂ support at room temperature using different dose rates (kGy s^-1) and irradiation time (s). The catalysts prepared by borohydride reduction showed Au nanoparticles with sizes in the range of 3-5 nm and a good dispersion onTiO₂ support, resulting in a good catalytic activity. The addition of Cu to Au/TiO₂ catalyst in certain proportions increased CO conversion and CO₂ selectivity, proving that the addition of a second metal had a promoting effect for CO-PROX reaction. The catalysts prepared by electron beam irradiation showed large Au nanoparticles sizes (> 10 nm) and low dispersion on TiO₂ support resulting in low CO conversions and CO₂ selectivity. (author)