Research On Synthesis And Catalytic Properties Of Magenetic Hydrotalcite-Containing Rare Earth

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 have some defects, 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 rare earth with Layered double hydrotalcites to solve the above problem.In this dissertation, in view of the idea of the application of rare earth catalyst, at first we let the rare earth Ce incorparate into the layer lattice of the Mg-Al hydrotalcites, then we assembled it with magnetic substrates obtaining nickel, so we get magnitic Mg-Al-Ce hydrotalcites of which the grain is even. This dissertation discuss the influence of rare earth Ce on structure and catalytic property of magnitic Mg-Al-Ce hydrotalcites by the measurement of XRD, VSM(Vibrating-sample Magnetometer), TG-DTA, IR ,and so on. We applied calcited products of magnitic Mg-Al-Ce hydrotalcites(calcited at 450~500癈 ) in Knoevenagel condensation of benzaldehyde with diethyl malonate, and compared the results with magnitic Mg-Al hydrotalcites ,then we find the magnitic Mg-Al-Ce hydrotalcites have some advance in catalytic property.(1) We synthesize magnetic substrates with different Fe(III): Ni(II): Fe( II) molar ratio by the method of co-precipitation. Research on magnetic substrates of XRD and VSM shows the bigger influernce of Fe(III): Ni( II): Fe( II) molar ratio, temperature,and pH to grain size and magnetical propertyes. Under the condition of Fe(III): Ni( II): Fe( II) molar ratio being 1:1:4, temperature of 40 C, pH 10, magnetical properties of magnetic substracts are optimum.(2) We synthesize magnitic Mg-Al-Ce hydrotalcites by the method of co-precipitation and study construction, FT-IR, thermal property, magnetical property and basicity. Results of XRD and FT-IR show that the addition of rare earth Ce to hydrotalcites does not change the typical layerer-structure, and we also find when Mg2+ / (Al3++Ce3+) molar ratio being 3, Al3+ / Ce2+ molar ratio being 7, Mg2+/(Fe2++Ni2+)molar ratio being 50, pH 9-10, reaction temperature of70 5C, aging temperature of 80 5 C, aging time of 8 h, the construction of magnitic Mg-Al-Ce hydrotalcites is the best. So we think it practicable that the rare earth Ce incorporated into the layer lattice of the layered materials. Results of VSM show the addition of Ni improve the magnetical properties of magnetic substracts,so the magnetization of samples increase lineally with the content of magnetic substrates,which is same to magnitic Mg-Al hydrotalcites. The analysis of basicity of magnetic solid bases show the addition of rare earth Ce does not influence basicity of solid bases of magnitic Mg-Al-Ce hydrotalcites, and their basicity (Ho) is still between 9.3 and 15.0.(3) We applied calcited products of magnitic Mg-Al-Ce hydrotalcites(calcited at 450-500 C ) in Knoevenagel condensation of benzaldehyde with diethyl malonate, and compared the results with magnitic Mg-Al hydrotalcites ,then we find the addition of rare earth Ce does change the optimized reaction conditions of Knoevenagel condensation(without solvent): without changing the content of catalyst, l~2wt% and reactant ratio(benzaldeehyde/diethyl malonate molar ratio), 1 - 1.2, reaction time reduced 2 hours and reaction temperature decreased to 120 C.In the same time, conversation of diethyl malonate and selectivity of the product is increased 10 persent in general. It showed the addition of rare earth Ce to improve the catalytic property of layered hydrotalcites is practicable again. In addition, because the magnetic substracts contained Ni increase the magnetization of samples, we can separate and recover catalyst of magnetic solid bases from reaction system more easlier.