Impregnation vs. coprecipitation dispersion of Cr over TiO2 and ZrO2 used as active and stable nanocatalysts in oxidative dehydrogenation of ethane to ethylene by carbon dioxide

Abstract

The catalytic performance of Cr/ZrO₂ and Cr/TiO₂ nanocatalysts, prepared by coprecipitation and impregnation methods, was examined in oxidative dehydrogenation of ethane to ethylene using CO₂ as an oxidant. Physicochemical characterization techniques such as XRD, FESEM, EDX, BET and FTIR were performed to explore the correlation of catalytic performance with properties of the nanocatalysts. The XRD analysis confirmed the formation of crystalline TiO₂ and/or ZrO₂ in the synthesized samples. The FESEM and EDX images revealed the formation of homogeneous spherical agglomerates within the nanometer range and with a uniform dispersion over the surface of all samples, especially Cr/ZrO₂ (P). The BET results proved the high surface area of Cr/ZrO₂ (P) and Cr/TiO₂ (P) nanocatalysts. Among all the samples, the Cr/ZrO₂ (P) nanocatalyst had the highest specific surface area. Catalytic tests showed that Cr-based catalysts prepared by coprecipitation, had higher ethane conversion and ethylene yield in comparison to those prepared by impregnation method. Among all the samples, Cr/ZrO₂ (P) had the highest ethane conversion (48% at 700 °C) and ethylene yield (43% at 700 °C). This could be attributed to the smaller particles, higher surface area, better dispersion of the active phase and uniform morphology of the Cr/ZrO₂ (P) nanocatalyst.