| In this paper,a nickel-iron,nickel-aluminum hydrotalcite material was prepared by coprecipitation method using divalent metal nickel salt and trivalent metal iron salt or aluminum salt as raw materials,and the obtained material was calcined in an ammonia atmosphere to obtain nickel so that to obtain derivatives of iron and nickel aluminum hydrotalcite.The prepared materials were characterized by XRD,FT-IR,SEM,XPS,N2 adsorption-desorption and so on.The results show that the nickel-aluminum hydrotalcite-derived material is composed of crystals of metallic nickel and Al2O3,and the ferronic-iron-hydrotalcite-derived material is composed of crystals of metallic nickel and Ni-Fe alloy.The results of vibrating sample magnetometer test(VSM)show that the nickel-aluminum hydrotalcite-derived material has strong magnetic properties,and the ratio of saturation magnetization of the derivative materials prepared under Ni/Al = 4:1 and ammonia atmosphere is 35.28 emu/g,the coercive force is 5.01 Oe,and the remanence is 5.02 emu/g.Similarly,the ferronickel-based hydrotalcite-derived material obtained under Ni/Fe = 1:1 and ammonia atmosphere is very strong.The magnetic properties have a specific saturation magnetization of 79.99 emu/g,a coercive force of 4.13 Oe,and a remanence of 4.14 emu/g.In this paper,a nickel-aluminum hydrotalcite material was prepared by coprecipitation method through a divalent metal nickel salt and a trivalent metal aluminum salt.The molar ratio of Ni-Al was(1:1,2:1,3:1,4:1,5:1),and then was calcined in an ammonia gas atmosphere to obtain a nickel-aluminum-based hydrotalcite-derived material.The structure,morphology and particle size were characterized by XRD,SEM,VSM,FT-IR,SEM and BET.The XRD test results show that the diffraction peak is sharp and symmetrical and the hydrotalcite-like crystallinity is high when the Ni/Al molar ratio is 4:1.This paper also objectively evaluated the catalytic properties of the two materials.The effects of calcination temperature,reaction temperature and molar ratio of synthetic nickel-aluminum hydrotalcite materials on the catalytic effect were discussed.The optimal synthesis conditions were as follows: calcination temperature 500 ℃,molar ratio 3:1,optimal reaction conditions were: reaction temperature was 180 ℃,reaction time was 6 h,the amount of nickel-aluminum hydrotalcite-derived material(calcination at 500 ℃ under ammonia gas)was 0.3g.Under the optimum process conditions,the urea conversion was 82% and the MC selectivity was 99%.The catalytic performance of the nickel-aluminum and ferronic-hydrotalcite-derived materials with different Ni/Al and Ni/Fe molar ratios prepared under ammonia gas for the alcoholysis reaction between methanol and urea was evaluated.The results show that the nickel-aluminum hydrotalcite-derived material with a molar ratio of Ni/Al of 3:1 has good catalytic activity,the conversion of urea reaches 82%,the selectivity of methyl carbamate reaches 99%,and the molar ratio of 1:1 Ni/Fe ferronickel hydrotalcite-derived material has good catalytic activity,the urea conversion rate is 64%,and the selectivity of methyl carbamate is 99%.The effects of catalyst preparation conditions and reaction conditions on the catalytic performance were discussed.The optimum reaction conditions were as follows: nickel-aluminum molar ratio of 3:1,calcination temperature of 500 ℃ reaction temperature of 180 ℃,reaction time of 6 h,the amount of catalyst dosage was 0.3 g and methanol and urea were 40 ml and 2 g,respectively.The molar ratio of nickel to iron is 1:1,the calcination temperature is 500 ℃,the reaction temperature is 180 ℃,the reaction time is 6h,the amount of catalyst is 0.3g,and the amounts of methanol and urea are 40ml and 2g,respectively. |
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