Catalytic oxidative dehydrogenation of 1-butene to 1,3-butadiene with CO₂ over Fe₂O₃/γ-Al₂O₃ catalysts: the effect of acid or alkali modification

Fe₂O₃/γ-Al₂O₃ catalysts were modified by acid and alkali (H₂SO₄, LiOH, NaOH and KOH) and were investigated for 1,3-butadiene (BD) synthesis through the oxidative dehydrogenation of 1-butene with CO₂. Nitrogen sorption and XRD results revealed that physical and original crystalline structure of Fe₂O₃/γ-Al₂O₃ catalysts remained intact after the modification. The acidity and alkalinity of the catalysts were determined quantitatively and qualitatively by NH₃-TPD and CO₂-TPD, respectively. The sequence of catalyst activity for these five catalysts was: Li–Fe₂O₃/γ-Al₂O₃ > S–Fe₂O₃/γ-Al₂O₃ > Fe₂O₃/γ-Al₂O₃ > K–Fe₂O₃/γ-Al₂O₃ > Na–Fe₂O₃/γ-Al₂O₃. The catalytic activity (BD rate) of Fe₂O₃/γ-Al₂O₃ catalysts was improved ~41% after the modification of LiOH. Results indicated that too little amount of acid sites as well as the strong basic sites over catalyst surface were not facilitate to the formation of BD. TG characterization results illustrated that the coke resistant ability of the catalysts was enhanced with the catalyst alkalinity.