Heat capacity and thermodynamic functions of silica-doped γ-Al2O3

Abstract

Abstract Alumina can exist in a variety of structural phases, including the more common alpha and gamma phases. The gamma phase is particularly useful as a support material for catalysts, but compared to the alpha phase there is little thermodynamic data reported for it. Even less data are available for alumina prepared with dopants such as silica. These materials have improved thermal stability over their un-doped counterparts. This makes them especially useful in high temperature catalytic applications, and while they have been, in many regards, well characterized, gaps still exist in the available thermodynamic data. Additionally, water from synthesis conditions or catalytic preparation tends to bind to gamma phase alumina, further complicating thermodynamic data collection and analysis. We collected heat capacity data for a set of silica-doped alumina samples calcined at 300 °C (chemical formula Al2O3 0.089 SiO2 1.190 H2O), 600 °C (Al2O3 0.089 SiO2 1.027 H2O), 900 °C (Al2O3 0.089 SiO2 0.321 H2O), and 1100 °C (Al2O3 0.089 SiO2 0.187 H2O) using a Quantum Design Physical Properties Measurement System (PPMS). The data were fit to mathematical functions, and from these fits entropy, enthalpy, and Gibbs energy functions were calculated. The standard molar entropies for silica-doped alumina calcined at 300 °C, 600 °C, 900 °C, and 1100 °C are 101.69 J K−1 mol−1, 90.206 J·K−1·mol−1, 73.758 J·K−1·mol−1, and 66.444 J·K−1·mol−1 respectively.