Au/Co3O4–TiO2 catalysts for preferential oxidation of CO in H2 stream

Abstract

A series of Au catalysts supported on Co3O4–TiO2 with various Co contents were prepared. Co3O4–TiO2 support was prepared by incipient-wetness impregnation with aqueous solution of Co(NO3)3 on TiO2. 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:O2:H2:He=1.33:1.33:65.33:32.01 (volume ratios). Au/TiO2 catalyst had both high CO oxidation activity and high H2 oxidation activity. Adding suitable amount of Co3O4 on Au/TiO2 could enhance CO conversion to a higher extent and suppress H2 oxidation. On Au/TiO2 catalysts, gold nucleates at oxygen defect sites of anatase TiO2 and remains highly dispersed and in good contact with the support. The gold atoms directly in contact with TiO2 are positively charged and highly stable. Doping with cobalt oxide increases the number of oxygen defects on TiO2, thus leading to a higher concentration of strongly bound gold atoms. The amorphous nature of Co3O4 along with TiO2 not only enhances electronic interaction between Au and Co3O4–TiO2, but also stabilizes the nano-size gold particles, thereby enhancing the catalytic activity of CO towards higher extent.