Synthesis Of γ-Al₂O₃ By Precipitation-supercritical CO₂ Drying And Its Catalytic Activity

Since the 21st century, social development, the economic revitalization and national defense construction put forward new requirements to the material, and component miniaturization, high integration of the material requirements the size more and more small and high performance. The ultrafine particles which have peculiar properties, especially for nano-materials will play an important role in the key materials. Nano-materials have many interfaces and the grain boundary atoms as much as 15% 50%. The special structure makes these nano-materials having unique volume effect, surface effect, quantum size effect, macroscopic quantum tunneling effect, thus it has a singular mechanical, electrical, magnetic, thermal, optical, chemical activity, catalytic and superconducting performance characteristics, so that the nano-materials have an important application in the national defense, electronics, chemical industry, metallurgy, light industry, aerospace, ceramics, nuclear technology, catalysts, pharmaceutical and other areas.Because of the crystal structure, good mechanical strength and high chemical stability, The nano-alumina such as powder, thin films, porous templates, have a wide range of applications. For example the production of heat-resistant materials, catalyst and catalyst carrier, vehicle exhaust purifier catalyst. In the current, Nano-alumina's usage is the largest and most important in the world, and its market prospect is very broad.CO is one of the most important air pollutants, the study of catalytic oxidation of CO has a very important theoretical and practical significance. The noble metal catalyst ,such as Au, Pt, Pd ,is the main active component in CO low-temperature oxidation. But its price is more higher. The price of Cu is much lower, and it reserves well. Therefore, if the Cu catalyst used in the catalytic oxidation of CO, its application prospects will be very broadIn this paper, we use aluminum nitrate (Al(NO3)3) and ammonium carbonate ((NH4)2CO3) as raw material, then we use chemical precipitation combined with supercritical CO₂ fluid drying to prepare the nano-alumina, and then use lanthanum and cerium to modifying. Then we load copper to prepare a series of catalysts to study their catalytic properties of CO oxidation.The main content of this thesis are listed as follows:1. Using precipitation method combined with supercritical CO₂ drying, which with different initial concentration of Al (NO3)3·9H2O, to prepareγ-Al₂O₃. The powders are characterized by TG-DTA, SEM, TEM, BET, XRD and FTIR.The obtained powders prepared by supercritical CO₂ drying, were composed of small grains.The grains have approximately spherical shape, uniformity size, and no apparent reunion. The surface area and particle size change with different initial concentration of Al (NO3)3·9H2O. The decrease or increase of the concentration will make the surface area decreasing and make particle size becoming larger. We discover theγ-Al₂O₃ samples have the smallest particle size when the concentration of Al (NO3)3·H2O is 0.3 mol/L and its calcining temperature is 600℃.The surface area ofγ-Al₂O₃ prepared under this condition is 286.25 m2/g.2. The CO catalyze tests of theγ-Al₂O₃ catalyst had been put up. From their catalytic results, we know: the effect of CO oxidation catalyze of theγ-Al₂O₃ samples which prepared by the 0.3 mol/L Al (NO3)3·9H2O is best.The oxidation begin from 400℃, and end of 670℃, when CO conversion rate is approach to 100%. But CO conversion temperature of the other samples prepared by the 0.1 mol/L, 0.2 mo/L, 0.4 mol/L Al (NO3)3·9H2O were begin from 500℃, and end of 700℃when the conversion rate only up to 95 %.3. Using the lanthanon to modify theγ-Al₂O₃, then characterize theγ-Al2O by XRD, BET, TEM to analysis their structure. Then put up CO oxidation catalytic tests. Its catalytic effects were compared withγ-Al₂O₃ samples. Ce/γ-Al₂O₃ greatly improves the catalyze activity, and the improvement of catalytic activity of lanthanum/γ-Al₂O₃ is smaller.4. Using impregnation method to loading in Cu withγ-Al₂O₃ samples and modifiedγ-Al₂O₃ samples, and putting up CO oxidation catalytic tests. Compared the CO oxidation catalytic tests result withγ-Al₂O₃ samples and modifiedγ-Al₂O₃ samples we know that the Cu supported catalyst use of lanthanon modified is better for CO oxidation catalytic. Compare catalytic properties with different lanthanon modifiedγ-Al₂O₃ supported catalyst samples. The catalytic activity of lanthanum and cerium modified catalyst regard to significantly improve: Cu/Ce/γ-Al₂O₃ react from 200℃, and end of 450℃; Cu/La/γ-Al₂O₃ start before 200℃,to 450℃when the conversion rate up to 100 %. The effect of lanthanum and cerium modified together catalyst is the best.