Intercalation of Molybdate Ions into Ni/Zn Layered Double Hydroxide Salts: Synthesis, Characterization, and Preliminary Catalytic Activity in Methyl Transesterification of Soybean Oil

Abstract

This study reports the synthesis and characterization of a Ni/Zn layered double hydroxide salt intercalated with acetate ions and the subsequent replacement of the acetate ions with molybdate ions via an ion exchange reaction, conducted at two different pH values. Regardless of the pH employed during the synthesis, the basal spacing in the Ni/Zn layered double hydroxide salt decreased from 13.08 A to approximately 9.5 A, which agreed with intercalation of hydrated molybdate anions. The non-calcined material and the material submitted to heat treatment at 250 °C (basal spacing reduced to 7.35 A, due to dehydration) were tested as catalyst for the methyl transesterification of soybean oil. Like sodium molybdate in homogeneous media, the solid materials were active catalysts. After reaction at 120 °C for 4 h, the materials afforded high conversions at an alcohol/soybean oil molar ratio of 35:1 and preserved the structure after three consecutive uses. In conclusion, intercalation of molybdate anion into the layered double hydroxide salt proved to be an efficient alternative to support the active species and transform a soluble catalyst into a solid with application in heterogeneous catalysis.