Controlled Prepapation Of Diffierent Morphological Perovskite, ZnO Nanomaterials And Their Catalytic And Sensing Properties

Perovskite oxides, due to its good redox properties, high temperature stability, etc., have wide applications in catalysis, solar cells, environmental gas detection and other areas. However, perovskites synthesized by conventional method usually have low surface area (< 10 m2/g) and low activity, which limits its application. In this thesis, in order to enhance their surface area and performance, perovskites with different morphology were synthetized and Pd-doped catalysts can improve the performance of catalytic oxidation. The relationship of composition, structure and performance of products were clarified. The catalytic activities of the as-prepared catalysts were evaluated by the oxidation of methane and CO and the gas sensing response to n-hexanol, and the relationships between physicochemical properties and catalytic performance of the materials were established. The main contents were as follows:1. LaNiO3 nanoparticles were prepared using sol-gel method with lysine, citric acid, stearic acid, palmitic acid, glycine and lauric as complexing agent. The LaNiO3 by different complexing agent possess different structure. Using lysine as complexing agent, the obtained LaNiO3 had the highest specific surface area (17.3 m2/g) and the most excellent CO catalytic oxidation activity (T50%of 221 ℃, T90% of 260 ℃). Lysine was crystal growth orientation agent which could combine with metal cation, and increased surface area of perovskite. With the increasing of carbon chain in complexing agent, specific surface area of LaNiO3 decreased, which resulted the decreasing of catalytic activity of CO gradually. Using lysine-assisted sol-gel method, Cu and Sr were used to substitute the A, B sites of LaNiO3. The catalytic oxidation activity of CO was improved and the Lao.9Sr0.1Ni0.9Cu0.1O3 had the highest adsorbed oxygen concentration and best catalytic activity with T50% and T90% of 211 ℃ and 247 ℃. It is concluded that the excellent catalytic performance of these materials might be associated with its high specific surface area and the concentration of adsorbed oxygen species.2. As a new material, hollow spheres have larger surface area. In this thesis, multi-shell hollow spheres LaMnO3 catalysts were synthesized using hard template with glucose carbon spheres. Under a relatively slow heating rates (1 ℃/min), when the ratio of La/Mn was 1:5, relatively pure phase multi-shell hollow spheres LaMnO3 could be synthesized with a range diameter of from 180 to 250 nm and the highest specific surface area (42.7 m2/g). When the ratio of La/Mn was less than or greater than 1:5, La2O3 or MnO2 would appeared, which indicated that the adsorption capacity of surface carbon microspheres for different metal cations was different. Compared with the bulk perovskite, hollow spheres LM-5 catalyst possessed the maximum ratio of surface Oaas/Olatt, a higher Mn4+ content and more excellent low-temperature reduction, which led to the best catalytic methane combustion performance (T50%= 480 ℃ and T90%= 570 ℃) and low apparent activation energy (50.6 kJ/mol).3. In recent years, it was discovered that combining Pd with perovskite catalyst occurs regeneration phenomenon in catalytic reaction. In this paper, three-dimensional macroporous LaMnO3 and LaMno.97Pd0.03O3 were successfully prepared using the PMMA hard template method. The hydrogen treatment had been taken in these as-prepared catalysts from 300 ℃ to 700 ℃. The catalytic methane combustion activity of all reduced samples had been improved. After hydrogen reduction treatment at 500 ℃, the 500-LMP had excellent catalytic activity (the T50%= 412 ℃ and T90% 504 ℃) with the apparent activation energy of 51.5 kJ/mol. Moreover, after 100 h on-stream reaction, there was no remarkable change in catalytic activity of 500-LMP. In addition, Pd doped high specific surface area perovskite can improve the dispersion and stability of Pd. The macroporous structure helps to improve the efficiency of gas treatment. After the hydrogen treatment Pd catalyst segregated from the substrate, which results in a strong metal support interaction (SIMI) between Pd and perovskite. This enhances the catalytic activity and thermal stability.4. The three-dimensional macroporous ZnO, Au/ZnO and Pt/ZnO were successfully prepared using the PMMA hard template method and their gas sensing peroperties to n-hexyl alcohol were investigated. The ZnO had well-ordered pores with an average diameter of 180 ± 10 nm and wall thickness of 25 ± 5 nm. The SEM showed there wasn’t obvious change after introduction of Au or Pt. The results of gas-sensing showed that compared with the usual one-dimensional and two-dimensional structure of ZnO,3DOM ZnO with macroporous structure had a faster response time (6 s) to n-hexyl alcohol, which was due to its unique macroporous structure and free diffusion of gas molecules. After doping Au or Pt, the band gap of material became smaller, and the contents of surface adsorption oxygen and donor defect increased, which resulted in the improvement of gas sensing response to n-hexyl alcohol. Moreover, the Au/ZnO had a high response of 95 at 240 ℃ to 10 ppm of n-hexanol and a good selectivity.