Au/Co ₃O ₄-TiO ₂ catalysts for preferential oxidation of CO in H ₂ stream

A series of Au catalysts supported on Co ₃O ₄-TiO ₂ with various Co contents were prepared. Co ₃O ₄-TiO ₂ support was prepared by incipient-wetness impregnation with aqueous solution of Co(NO ₃) ₃ on TiO ₂. Gold catalyst was prepared by deposition-precipitation at pH 7 and 65 °C. The catalysts were characterized by ICP-MS, XRD, TEM, HRTEM and XPS. The catalytic performance of these catalysts was investigated by preferential oxidation of carbon monoxide in hydrogen stream (PROX). The reaction was carried out in a fixed bed reactor with feed of CO:O ₂:H ₂:He = 1.33:1.33:65.33:32.01 (volume ratios). Au/TiO ₂ catalyst had both high CO oxidation activity and high H ₂ oxidation activity. Adding suitable amount of Co ₃O ₄ on Au/TiO ₂ could enhance CO conversion to a higher extent and suppress H ₂ oxidation. On Au/TiO ₂ catalysts, gold nucleates at oxygen defect sites of anatase TiO ₂ and remains highly dispersed and in good contact with the support. The gold atoms directly in contact with TiO ₂ are positively charged and highly stable. Doping with cobalt oxide increases the number of oxygen defects on TiO ₂, thus leading to a higher concentration of strongly bound gold atoms. The amorphous nature of Co ₃O ₄ along with TiO ₂ not only enhances electronic interaction between Au and Co ₃O ₄-TiO ₂, but also stabilizes the nano-size gold particles, thereby enhancing the catalytic activity of CO towards higher extent.