Studies On Synthesis And Control Of Particle Size Of Hydrotalcite-Like-Compounds Under Ultrasonic Radiation

Hydrotalcite, also named anionic clay, consists of stacks of mixed hydroxides layers which are positively charged and interlayer anions. It can make various technical applications because of its properties of exchangeable anion and adjustable ion in layer. Many researches have showed that it is necessary to study on control of particle size of HTLcs because the application in many areas was affected by its particle size and particle size distribution. In this paper, NiAl-HTLcs with different particle size distribution were prepared by methods of ultrosonic radiation. The effect of many factors on particle size distribution was systematically studied. Particle size of HTLcs was analyzed by particle size analyzer made in Japan and their physic-chemical properties were characterized by XRD,FT-IR,DTA-TG,TPD and chemical analysis measurements. The catalytic activity of catalysts NiAl-HTLcs with same composition and construction but different particle size was studied through catalysis of phenyl aldehyde and ethanol.Ultrasound wave is a kind of sound wave with frequency bigger than 20kHz and has been used in many areas because of its distinctive properties. In this paper ultrasonic wave was introduced to the process of preparation of HTLcs and the titration curves of different molar ratio nitrate solutions of Ni-Al using NaOH as precipitator were considered, and feasible pH value was confirmed. the effect of such as composition of nitrate solutions,reaction time,salinity,titration method,stir manner and dispersant agent on particle size of NiAl-HTLcs was studied in detail, the composition of HTLcs was detected by chemical analysis. The construction of samples was detected by XRD and FT-IR. TG-DTA analysis was performed to characterize their thermal behaviour and thermal decomposition. TPD analysis was performed to characterize their acid-base. It was concluded that : under ultrasonic co-precipitation and general co-precipitation, the optimal pH value to NiAl-HTLcs preparation was 5.1～5.7 and 5.0～6.0, median particle size of composition was 0.38μm and 8.06μm, particle size distribution is 0.26μm～1.15μm～1.15μm～2.60μm,2.98μm～44.94μm where composition percentage was 90.04%,9.96%,0% and 0%,3.75%,96.25%.Experimental findings indicated:Hydrotalcite with very small particle size,short and homogeneous particle size distribution was synthesized under Ultrasonic radiation condition. Under ultrasonic radiation, using constant pH method, particle size of NiAl-HTLcs is reduced with longer reaction time and larger salinity, the particle size of products were reduced gradually with the rising of Ni²⁺/Al³⁺ molar ratio of material solutions. It was showed that concentration of Ni(NO₃)₂ and Al(NO₃)₃ is 3.5 mol/L and 3.0 mol/L, reaction time is 2～3h, medium particle size is 0.38μm and specific area is 1.7072E+5 cm² /c³m for NiAl-HTLcs. Samples was characteriated that was synthesized under ultrasonic co-precipitation and general co-precipitation, XRD indicated that sample was hydrotalcite under ultrasonic, TG-DTA indicated that they have better thermal stability, TPD indicated that sample has many basic center and strong base, so, they have better catalysis acticity.Catalysis of phenyl aldehyde to benz-ether by ethanol hydroproxide under free-solvent was performed in order to study the effect of particle size of NiAl-HTLcs under Ultrasonic radiation on reaction activity and selectivity of aimed products. The NiAl-HTLcs was prepared under general precipitation and Ultrasonic radiation with Ni²⁺/Al³⁺=5 material solution with particle size being 8.79μm,0.38μm, were used as catalysts. It is showed that 58.43% percent conversion, b catalyst demand 30min, but a catalyst demand 80min and not reached that conversion, the reaction time is shorten largely, so, b catalyst has larger reacting acticity than a catalyst. This dates instructed that the small particle size was fit for catalization of catalyst in this reaction.