A green chemistry approach to styrene from ethylbenzene and air on MnxTi1−xO2 catalyst

Abstract

Styrene (ST) is an industrially important commodity chemical, and design of a suitable catalyst, which provides high ethyl benzene (EB) conversion and styrene selectivity at lower temperature with sustainable activity, is one of the major challenges in the field of heterogeneous catalysis. Manganese incorporated in titania (Mn_xTi_1−xO₂) anatase lattice, prepared via the solution combustion method, was evaluated for oxidative dehydrogenation (ODH) of EB with O₂ or air. Mn_xTi_1−xO₂ catalysts were characterized by different physiochemical methods. Up to 15% Mn could be introduced into the TiO₂ lattice. TEM and XRD indicate disordered mesoporosity, further confirmed by adsorption isotherm analysis. Mn_xTi_1−xO₂ catalysts were evaluated for ST synthesis from EB using air or oxygen as oxidant between 440 and 570 °C. Reaction conditions have been varied systematically, such as catalyst composition, and EB/air/O₂ flow. Mn_xTi_1−xO₂ shows sustainable 55% styrene yield for 45 h without deactivation under optimum conditions. A thorough analysis of spent catalysts demonstrates the conversion of initial anatase phase Mn_xTi_1−xO₂ to Mn₃O₄ supported on the rutile (R) phase of TiO₂. The above change occurs in the first few hours of reaction and the Mn₃O₄ on R-TiO₂ phase is the active phase of the catalyst and responsible for sustainable activity for longer duration.