Zirconyl and hafnium hydrogen tellurates as catalysts for esterification

Abstract

Catalytic performance of zirconyl hydrogen tellurate (ZrOHTe) and hafnium hydrogen tellurate (HfHTe) was studied for the first time. A process of butyl acetate synthesis was used as a test reaction. A number of physicochemical techniques (XRD, SEM, TGA/DSC and XPS) was applied for catalyst characterization. Using molecular electrostatic potential and net atomic charges, both the electronic structure and the chemical reactivity of ZrOHTe and HfHTe were considered. Kinetic (activation energy, pre-exponential factor) and thermodynamic (enthalpy, entropy, Gibbs free energy barrier) parameters were calculated. A plausible reaction mechanism for esterification was offered. Particles of a low crystallinity degree or small-sized crystallites were found to form ZrOHTe and HfHTe. The fragments in ZrOHTe/HfHTe are prismatic/layered in shape with an average size around 160 μm. XPS exposed that \({\text{HTeO}}_{4}^{-}\) managed the surface phenomena for ZrOHTe and HfHTe. A higher butyl acetate yield using ZrOHTe than HfHTe due to higher surface acidity of the former was generated.