Dimethyl carbonate synthesis from carbon dioxide using ceria–zirconia catalysts prepared using a templating method: characterization, parametric optimization and chemical equilibrium modeling

Abstract

In this paper, a series of Ce_xZr_1−xO₂ solid solution spheres were synthesized by exo- and endo-templating methods and tested for dimethyl carbonate (DMC) synthesis using direct conversion of CO₂. The synthesized catalysts were characterized by X-ray diffraction (XRD), N₂-physisorption, scanning electron microscopy (SEM), and CO₂/NH₃-temperature-programmed desorption (TPD). Formation of Ce_xZr_1−xO₂ solid solutions with tetragonal and cubic crystal structures depending on cerium/zirconium compositions was confirmed by XRD analysis. The specific surface area of the mixed oxide decreased and the average pore diameter increased with an increase in the ceria content, with the exception of the mixed oxides with x = 0.4–0.5 i.e. Ce_0.4Zr_0.6O₂ and Ce_0.5Zr_0.5O₂. The basic and acidic site density of the synthesized catalysts was in the order: ZrO₂ < CeO₂ < Ce_0.5Zr_0.5O₂, and the basic and acidic site density per unit area followed the same order. The best Ce_0.5Zr_0.5O₂ catalyst was further used for the optimization of reaction conditions such as reaction time, reaction temperature, catalyst dose and reusability for DMC synthesis. Furthermore, study of chemical equilibrium modeling was done using the Peng–Robinson–Stryjek–Vera equation of state (PRSV-EoS) along with the van der Waals one-fluid reaction condition so as to calculate change of Gibbs free energy (ΔG°) and heat of reaction (ΔH°).