Study On Preparation,characterization And Application Of Macroporous Pseudo-boehmite

The purpose of this paper is to study the preparation of pseudo-boehmite with industrial grade aluminum sulfate and sodium meta-aluminate coming from industrial wastes,and to explore the effects of preparation process,pore expansion and modification on the crystal form,pore structure,surface acidity and morphology of pseudo-boehmite.Then,the self-made pseudo-boehmite was extruded and roasted to get the corresponding catalyst support,which was loaded with Pd active component.The activity and selectivity of isophorone C=C hydrogenation on Pd/Al₂O₃ catalysts prepared by the silicon-modified Al₂O₃ support and Pd（acac）₂ as well as Pd Cl₂ as precursors were studied in order to develop excellent preparation methods of pseudo-boehmite and high performance Pd/Al₂O₃ catalysts.Firstly,the effects of gelling conditions,such as gelling temperature,p H value,reactant concentration and dropping acceleration,on the crystal phase and pore structure of pseudo-boehmite were studied.The study found that gelling conditions have the biggest impact on crystal phase and pore structure of pseudo-boehmite.With the increase of gelling temperature and p H value,the pseudo-boehmite products showed higher crystallinity,the volume and aperture of the pore first increased and then decreased.Too high temperature or too high p H value will lead to the formation of bauxite.The best gelatinization temperature is 60℃,gelatinization p H value is 10-11.The smaller the reactant concentration,the better the crystal form and pore structure of the product.The slower the droplet acceleration,the higher the crystallinity of the product,the larger the pore volume and aperture.Then the effects of aging and washing conditions on the morphology and pore structure of pseudo-boehmite were studied.The results show that aging time have no significant effect on the crystal type and pore structure of pseudo-boehmite.With the increase of aging temperature and p H value,the crystallinity,pore volume and pore size of pseudo-boehmite increase.The most suitable aging temperature is 90℃,and the aging p H value is 10.5.Ethanol washing is helpful to increase the pore volume and specific surface of pseudo-boehmite.The removal effect of SO₄^2-and Na⁺in beaming washing is better than that in leaching washing,and increasing the temperature of washing water is helpful to improve the washing effect.The effects of modifiers on the crystallinity,pore structure and morphology of pseudo-boehmite were further studied.It was found that the addition of ammonium carbonate significantly changed the crystallinity,pore structure and morphology of pseudo-boehmite.With the increase of ammonium carbonate,the crystallinity of pseudo-boehmite decreased,the pore volume and pore size increased first and then decreased,and the morphology gradually changed from sheet to rod shape.The maximum pore size was obtained when the addition amount of ammonium carbonate was 5%.The addition of sodium silicate significantly also changed the crystallinity,pore structure,acidity and morphology of pseudo-boehmite.With the increase of sodium silicate,the crystallinity of pseudo-boehmite decreased,the pore volume and pore diameter increased first and then decreased,and the morphology gradually changed from sheet to rod.When the Si O₂ content is 8%,the pore volume is up to 1.53 cm³/g,and the pore diameter is 12.34 nm.On this basis,the effects of preparation methods on the C=C selective hydrogenation activity and stability of isophorone over Pd/Al₂O₃ catalysts were studied.It was found that the support of Pd/Al₂O₃ catalyst and the active component precursors had a significant effect on the activity and stability of the C=C selective hydrogenation of isophorone.The activity and activity stability of the Pd/Al₂O₃ catalyst prepared with Pd Cl₂ as the precursor are much higher than that prepared with Pd（acac）₂ as the precursor.The results reveal that the selective hydrogenation of isophorone by the C=C bond on Pd/Al₂O₃ catalysts is a structure-sensitive reaction.When the average particle size of active component Pd nanoparticles is less than 5nm,the selective hydrogenation activity of isophorone reaches 100%and the selective hydrogenation activity of TMCH is more than 99%,indicating high activity stability.