Functionalization And Application Of Alumina Aerogel

Alumina supports usually possess better properties than siliceous counterparts such as higher acidity/basicity and are more favorable for achieving high dispersion of catalytic nanoparticles.In addition,the interaction between the supported transition metal and alumina is usually stronger than that with silica.Therefore alumina supports are most often commercially applied.This research is mainly investigated from two aspects:?i?the regulation of surface chemistry such as specific surface area and pore size of alumina aerogels and exploring the relationship between pore size distribution and catalytic activity.?ii?tailoring the chemistry of aerogel toward the particular catalytic reactions through the addition of different components,i.e.dispersion of the various oxides or metals in an aerogel matrix.In this thesis,we demonstrate a simple and effective method to synthesis alumina aerogels with adjustable particle and pore sizes by adding polyethylene glycol?PEG?with different molecular mass and different amount for the same molecular mass and the mechanism of pore size regulation was investigated.The alumina with different pore structure was used as the carrier supporting active component for formaldehyde degradation,and the relationship between catalytic activity and pore size distribution was explored.The main results were as follows:In the process of sol–gel,PEG is used as not only complexing agent but also phase separation agent,tunable pore size can be easily achieved by changing the molecular mass of PEG and the amount of PEG of the same molecular mass.Owing to their high surface area and the three-dimensional network structure for promoting the transport of material into mesoporous where reactions took place,Al₂O₃ with centered pore size distribution was demonstrated to have excellent catalytic performance.Compared with time-consuming and complicated traditional preparation methods,catalyst prepared by one step method can promise the uniform dispersion of iron oxide nanoparticles and mitigate the metal leaching and sintering effectively compared to the metal impregnated catalysts.In this thesis,we also report one-pot synthesis strategies to add transition metallic ion into the sol-gel-derived alumina matrix as the heterogeneous catalyst and evaluate the catalytic activity of bimetallic catalyst supported on alumina aerogel.The research includes the following aspects:?i?the existence form of bimetallic nanocomposites in alumina aerogel matrixes using the novel synthesis method was investigated.?ii?The synergic association between bimetallic ions was further confirmed by XPS,H₂-TPR.?iii?The catalytic mechanism and RhB degradation pathway were proposed based on a series of tests.To identify the reactive species generated and the roles of three radicals in the degradation system of organic pollutants,an in situ EPR test and radical competition experiment were performed.Confocal Raman shows the generation of oxide groups with the sulfur compound,and the XPS result implies a transformation in the valence state of different metal ions and oxygen on bimetallic catalyst surface.The RhB degradation intermediates were confirmed by the liquid chromatography-mass spectrometry?LC-MS?.?iv?effects of some parameters,including reaction temperature,pH values and RhB concentrations on RhB degradation were also investigated.The main results were as follows:The catalyst exhibits low iron leaching,good structural stability and high catalytic efficiency being maintained after reuse.The bimetallic catalyst supported on alumina aerogel showed a higher catalytic performance than monometallic catalysts.High active radicals containing oxygen were the main radical species responsible for the organic pollutant elimination.Whether in acidic or alkaline conditions,the alumina aerogels even possess excellent catalytic activity.