Effects of preparation conditions on gold/Y-type zeolite for CO oxidation

The effects of preparation conditions (i.e. chloroauric acid concentration, pH of gold solution, solution temperature, and mixing time) on gold supported on Y-type zeolite (Au/Y) for CO oxidation were studied. The catalysts were characterized by AA, temperature-programmed reduction (TPR), XRD, TEM and XPS, in order to understand the correlation of the gold precursors in the solution and the gold particles in Y-type zeolite to the catalytic activity. It was found that more gold species prepared in the supercage of Y-type zeolite would enhance Au/Y with higher catalytic activity. However, higher pH, higher gold concentration and lower temperature would generate more and larger gold species in the solution, which caused large gold particles prepared on the exterior surface of Au/Y. Due to the limited surface area, these large particles provided little activity for the reaction. Moreover, lower pH and lower gold concentration would generate more gold monomers in the solution at higher solution temperature, which caused more gold species prepared in the sodalite cage of Au/Y. Due to molecular sieving effect, they were not available for CO oxidation. It can be concluded from this study that Au/Y prepared from a gold solution with surface acidity modified Y-type zeolite (1 g of zeolite per 125 ml solution), with initial gold concentration around 1.46×10−3 M, solution pH at 6, solution temperature around 80 °C, and mixing time for 1 h would possess an optimum catalytic activity for CO oxidation.