The Synthesis Of LDH/ Kaolin And The Catalytic Performance Of Their Supported Gold Catalysts For The Esterification Of Alcohols With Aldehydes

Hydrotalcite-like compounds called layered double hydroxide(LDH),are part of anionic clays that are often used in the catalytic field because of their unique structure and properties.However,conventional methods for LDH preparation give poor control over the morphology,particle size,and surface area and are unable to prevent aggregation of powder samples which significantly limits the applications of the resulting materials as catalysts and adsorbents.From this view of point,hierarchical structures with controllable morphology,orientation,and dimensionality have evoked considerable interest.The esterification of aldehydes and alcohols has been a hot topic in the field of catalysis because of its wide range of application and atom economy.In this paper,a series of catalysts based on LDH/kaolin were prepared.Furthermore,the supported Au/LDH/kaolin catalysts were prepared and used in esterification of aldehydes and alcohols.Firstly,we used an abundant kaolin clay in Inner Mongolia as raw material and synthesized the composite of LDH/ kaolin by different methods to optimize the synthesis conditions with optimum synthesis method.The catalysts were characterized by XRD?FT-IR?TEM?Zeta potential.The results showed that the sixteen alkyl methyl ammonium bromide(CTAB)plays an important role in the synthesis process.The addition of a small amount of CTAB by coprecipitation method can affect the morphology of LDH,which has impact on the recombination between LDH and kaolin.Secondly,a series of Au/LDH/kaolin catalysts with different ions,different molar ratios of magnesium with aluminum and different LDH loading were prepared by liquid phase reduction method using LDH / kaolinas support.And the catalysts were characterized by XRD ? TEM ? N2Adsorption-desorption?UV-vis?TEM?XPS?AAS?ICP.The results revealed that the product of ethyl benzoate was obtained in good to excellent yield when the loading of nano-gold was 2% and the LDH synthesis ion in the composite carrier was magnesium ion and aluminum ion,the molar ratio of Mg/Al was 4: 1 and the loading was 15%.Finally,the influence of reaction time,temperature and base on performance of catalysts was investigated.With the addition of K2CO3,the yield of ethyl benzoate could reach 93.9% under the reaction temperature of25 oC and the reaction time of 3 h.It is a green synthesis due to the realization of the reaction under ambient temperature and the recycling use of the catalyst.