| Layered double metal oxides(LDOs) with certain constitute have ideal catalytic activity to such reaction as alkalization, and they could availably perform function of formation by controlling the grain size of the precursors ?layered double hydrotalcites( LDHs) and by changing their constructional distribute of pores. But we find that the LDO particles are in nanometer scale before formation, and though they have higher catalytic activity and better selectivity, their recovery is extremely difficult; and after formation, their catalytic activity decreases with the increasing of mass transmittion resistance, and their selectivity is influenced to some degree as well. We bourgeon the speculation of assembling magnetism with catalytic property to solve the problems of separation and recovery of nanometer catalysts.In this dissertation, in view of the idea of magnetical separation techniques in the field of biology, for the first time we synthesized nano-sized magnetic Mg-Al hydrotalcites by the method of co-precipitation. The grain size is even and between 20nm and 50nm. This dissertation discuss the influence of Fe(II)/Mg molar ratio on structure and magnetic property of magnetic Mg-Al hydrotalcites by the measurements of XRD, TEM, VSM(Vibrating-sample Magnetometer), TG-DTA, FT-IR. We apply calcited products of magnetic Mg-Al hydrotalcites ( calcited at 450 - 50CTC) in Knoevenagel condensation of benzaldehyde with diethyl malonate, and study the influence of reaction condition on catalytic activity, and find the optimum reaction conditions of Knoevenagel condensations of benzaldehyde with diethyl malonate catalyzed by magnetic solid bases, and investigate life span and recovery of magnetic solid bases.(1) We synthesize magnetic substrates of which the grain size is about 10nm and magnetism is 50.76emu/g with the method of precipitate by ferric salt. Research on magnetic substrates of XRD, TEM and VSM shows the bigger influence of types of ferric salt, temperature, and pH to grain size and magnetical properties. On the condition of Fe(II)/Fe(III) molar ratio being 1:2, temperature of65 癈, pH^10, magnetical properties of magnetic substrates synthesized by ferric sulfate and ferrous sulfate are optimum.(2) We study construction, facial surface. FT-IR, thermal property, magnetical property and basicity of magnetic Mg-Al hydrotalcites. Results of XRD, TEM and DTA show that the addition of magnetsm to hydrotalcites does not change the typical layered-structure, but make it more stable, so we think it practicable that magnetic substrates are assembled with layered-materials; results of VSM show specific saturation magnetization of samples increase lineally with the content of magnetic substrates; the analysis of basicity of magnetic solid bases show the addition of magnetic substrates does not influence basicity of solid bases of magnetic Mg-Al hydrotalcites, and their basicity (Ho) is between 9.3 and 15.0.(3) We apply the calcited magnetic Mg-Al hydrotalcites in Knoevenagel condensation of benzaldehyde with diethyl malonate. The optimized reaction conditions of Knoevenagel condensation(without solvent) catalyzed by magnetic solid bases are: reaction time, 8h; reaction temperature, 140癈; content of catalyst. l~2wt%; reactant ratio(benzaldehyde/diethyl malonate molar ratio), 1~-1.2. On these conditions, conversation of diethyl malonate is above 80% and selectivity of the product of C6H5CH桟(CO2C2H5)2 is above 50%. Catalysts of solid bases could be used repeatedly, and regenerated easily, so they are promising catalysts.(4) We separate and recover catalyst of magnetic solid bases from reaction system by making use of additional magnetic field. Results show that compared to the un-magnetic solid bases, during 30 minutes recovery of magnetic solid bases could attain 90% or so, which exalt to extra degree.
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