Preparation of Layered Double Hydroxide (LDHs)<i>-</i>Supported Gold Catalysts and its Activity and Stability for Low-Temperature CO Oxidation

Abstract

A new type of gold catalysts have been prepared by supporting gold colloids on layered double hydroxide (MgAl-LDHs) carrier at different pH values. CO oxidation reaction at room temperature was used as probe reaction to test the oxidation activity of the gold catalysts, and X-ray diffraction (XRD), X-ray fluorescence (XRF) and high resolution transmission election microscopy (HRTEM) techniques were used to characterize the physical phase, gold loading, morphology as well as mean diameter of gold particles and particle distribution of the represented gold catalyst samples. Influence of pH value during synthesis of the catalysts on the gold loading and oxidation activity of the gold catalysts was studied. Besides these, the stability of the gold catalysts was investigated by thermal treatment and exposure to air and natural light for a long time. The results indicated that gold colloids can be attached on the carrier easily when pH value was controlled between 6-7, and gold loading in the gold catalysts prepared in this condition was above 1.3wt.%. 100% conversion of CO at room temperature can be obtained when the fresh prepared catalysts had been calcined in the air for 2 h at 473 K. The HRTEM images of the gold catalyst showed that the gold particles were highly dispersed on the surface of the carrier, and the average size of the gold particles was 3.2 nm. After thermal treatment at 723 K or storage 4 weeks in air, gold particle size was still kept less than 5nm and the conversion of CO at room temperature over the aged catalysts achieved 100%.