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Synthesis And Catalytic Application In Selective Aerobic Alcohols Oxidation Of Hydrotalcite-like Compounds

Posted on:2004-07-06Degree:MasterType:Thesis
Country:ChinaCandidate:P LiuFull Text:PDF
GTID:2121360122466518Subject:Analytical Chemistry
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The Selective oxidation of alcohols to the corresponding carbonyl compounds is a key process in organic synthesis and plays a central role in the fine chemicals industry. Traditional methods for performing such transformation generally involve the use of stoichiometric quantities of Cr(Vl), Mn(VII) or other inorganic oxidants and copious amounts of organic solvents, which have caused serious environmental pollution. From the standpoint of the so-called green and sustainable chemistry, another approach to construct the cleaner catalytic system for this reaction has been demanded urgently.From an economical and environmental point of view the use of molecular oxygen as a sole oxidant has attracted considerable attention, and recently there have been great efforts in the development of alcohols' selective aerobic oxidation protocols. Research emphasis is placed on the designing of efficient catalysts that can increase the reaction activity and selectivity of molecular oxygen and catalyze the selective reaction under mild conditions. For industrial use heterogeneous catalysts are probably preferred, therefore, an important challenge for present is to develop heterogeneous catalysts that are not only versatile, active and selective but also stable and recyclable.On the basis of previous literatures, this paper reviews the new developments in selective oxidation of alcohols by using molecular oxygen, and selects the promising hydrotalcite-like compounds (HTIcs) as research object. HTIcs consist of Brucite-like layers with positive charge and anionic compounds in the interlayer to form neutral materials. The main properties of HTIcs are as follows: (i) basicity due to their surface hydroxyl functions, (ii) cation exchange ability in the Brucite-like layer, and (iii) anion exchange ability in the interlayer. These properties make it possible for HTIcs to being base catalysts, redox catalysts and support of catalysts.HTIcs were first applied in aerobic alcohols oxidation in 1998 by Kaneda, and the advantage of high selectivity and recyclable of HTIcs has attracted attention. At present, the application research of HTIcs in aerobic alcohols oxidation is in early stage. The train of thought of this paper was to improve the catalytic activity by making use of structural properties of HTIcs. First, we prepared a series of HTIcs and tried to select some active and selective catalysts. Then we modified these catalysts by change the cation in the layer or pillar other anion in the interlayer in order to achieve higher activity. The main results are summarized as follows:1. HTIcs with different cations in the layer were synthesized by coprecipitation. Various preparative factors such as precipitation method, operational temperature, pH value, aging time and In/Mg/AI molar ratio, which affect the purity and crystal form of lnMgAI-CO3 HTIcs were studied. The results of product characterization by XRD and IRmethods show that high supersaturation coprecipitation at constant pH, which handing precepitation temperature and aging temperature at 65℃, washing temperature at room temperature, pH ranging from 10 to 11.5, aging for 8 hours and In3+/M3+ molar ratio ranging from 0.1 to 0.8, give rise to high purity and better crystal form of lnMgAI-CO3 hydrotalcite-like compounds. The preparation law of cation collocated HTIcs was summed up, which successfully applied in synthesis of 22 kinds of hydrotalcite-like compounds.2. The oxidation of benzyl alcohol with O2 in toluene was chosed to evaluate the performance of the different synthesized HTIcs. We found that noble metal Ru3+ collocated HTIcs have much higher activity for the selective reaction than non-noble metal collocated HTIcs. RUC0AI-CO3 and RuCoMgAI-CO3 are two better catalysts, however, the catalytic selectivity of RuCoAI-CO3 calcined sample decrease obviously. The study also shows that RuCoAI-CO3 can keep highly catalytic selectivity if reaction is under 80℃ and less than 8 hour. The solvent effect was investigated, and we found that HTIcs have higher catalyt...
Keywords/Search Tags:Hydrotalcite-like compounds, Synthesize, Molecular oxygen, Alcohols, Selective oxidation, Ruthenium, Polyoxometallate, Catalytic activity
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