Support induced effects on the activity and stability of Ga2O3 based catalysts for the CO2-assisted oxidative dehydrogenation of propane

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The influence of the support nature (Al2O3, TiO2, SiO2) on the activity and stability of supported Ga2O3 (10 wt%) catalysts was investigated for the production of propylene through the CO2-assisted oxidative dehydrogenation of propane (CO2-ODP). Catalytic activity was found to be higher when gallium oxide was dispersed on alumina support which was characterized by the highest acid site density and moderate surface basicity. Below 650 °C propylene yield increased in the order Ga2O3-TiO2<Ga2O3-SiO2<Ga2O3-Al2O3, which was modified as Ga2O3-Al2O3<Ga2O3-TiO2<Ga2O3-SiO2 for higher reaction temperatures. Propylene selectivity decreased with increasing reaction temperature followed by an increase of ethylene and methane selectivity implying that the side reactions of propane hydrogenolysis and propane/propylene decomposition were facilitated at higher temperatures hindering the CO2-ODP reaction. Gallium oxide catalysts supported on TiO2 and SiO2 exhibited sufficient stability for 30-35 hours on stream at 660 and 710 οC, contrary to Ga2O3-Al2O3 which although was stable at 710 οC it was gradually deactivated when the reaction was taking place at 600 °C. Temperature programmed oxidation experiments showed that carbon deposition was favored over Ga2O3-Al2O3 catalyst when the reaction was conducted at low temperature, which may be related to the higher surface acidity of this sample and be responsible for its deactivation with time. SEM images and elemental mapping obtained from both the freshly prepared and used Ga2O3-MxOy samples showed that Ga and M (M: Si, Ti, Al) were uniformly present even after prolonged catalyst interaction with the reaction mixture. EDS analysis indicated that carbon formation was accelerated with increasing reaction temperature.