Abstract: The supported catalyst LaCoO3/γ-Al2O3 was prepared by ultrasound during the impregnating preparation steps and the effects of ultrasound with various frequencies on the properties of catalyst were investigated in this paper. 　　For the preparation of LaCoO3/γ-Al2O3, 5 g ofγ-Al2O3 ( 20 mesh) was added to 20 mL of molar ratio 1:1 mixture of aqueous solution of La(NO3)3 and Co(NO3)2. Ultrasonic irradiation was performed with direct immersion horn (with various frequencies i.e. 33, 40, 50 and 70 kHz) at 20 ℃. The precursors were filtered off, washed with water, dried for 2 h at 120 ℃ and were calcined for 5 h at 850 ℃. The formation of LaCoO3 was determined by XRD. Another sample (O＃ sample) for comparision LaCoO3/γ-Al2O3 was prepared under the same experimental conditions and steps except ultrasonic irradiation was replaced by mechanical stirring for 2 h in impregnating step. 　　The effects of ultrasonic irradiation frequencies and irradiation time in impregnating step on loading of LaCoO3 were studied. The results showed that ultrasonic irradiation could decrease impregnating time and increase loading of LaCoO3. And ultrasonic irradiation with 50 kHz frequencies showed the best experimental result. The loading of LaCoO3 of LaCoO3/γ-Al2O3 ( 1＃ sample ), prepared by ultrasonic irradiation ( with 50 kHz for 5 min), was 25％ more than that of 0＃ sample. Transmission electron micrograph showed that on the support surface of 1＃ sample, the average particle size of LaCoO3 was 8 nm. The scanning electron micrographs and electron microprobe analyzer scans showed that on the support surface of 1＃ sample, distribution of LaCoO3 particles was better compared with that on the support surface of 0＃ sample. Using the BET method, surface area and pore distribution were determined. They were 133.17 m2•g－1(1＃ sample) and 114.71 m2•g－1 (0＃ sample )respectirely. 1＃ sample have more micropores than 0＃ sample. According to the results of activities evaluation of decomposition of NO, the catalytic activity of 1＃ sample was higher than that of 0＃ sample. Therefore, using ultrasonic irradiation in the impregnating step of catalyst preparation is an effective method for enhancing catalytic activity of the catalyst.

Key words: Ultrasound, Provskitetype oxide, Supported catalyst, Preparation