Preparation and characteristics of solid base hydrotalcite

Abstract

In this report, we announce the fabrication of hydrotalcite compounds (HTs) with different molar ratios of Mg/Al by constant pH at low supersaturation method. The obtained compounds could serve as solid base catalysts. The crystal structure and phase composition were investigated by X-Ray Diffraction technique. The increase in Mg/Al molar ratio led to the expansion of the interlayer spacings of brucite-like layers in HTs because of the substitution of small ions (Al³⁺) by larger ions (Mg²⁺) in the octahedra of hydroxide layers. The elemental analysis proved the compatibility of experimental Mg/Al molar ratios and theoretical values. The presence of function groups was elucidated by FT-IR method. The results of thermo-analysis exhibited that the structure of HTs collapsed at temperatures higher than 400 ^oC due to the dissociation of HTs to MgO and Al₂O₃. The base site density determined by titration method was found to be directly related with Mg/Al molar ratio. The catalytic activity was tested on the glucose to fructose isomerization reaction. In all tested samples, HT5 gave the highest activity with fructose yield of 16.3%. Alongside HT1-HT5 chain, the catalytic activity increased versus Mg/Al molar ratio, as well as the density of base site.

Keywords. Hydrotalcite, solid base catalyst, glucose, fructose, isomerization reaction.