Catalytic Degradation of Acrylonitrile−Butadiene−Styrene into Fuel Oil 2. Changes in the Structure and Catalytic Activity of Iron Oxides

The changes in the structure and catalytic activity of three iron oxides (α-FeOOH, γ-Fe2O3, and an Fe3O4−C composite) were studied by temperature-programmed desorption/degradation (TPD) and XRD analysis. Thermal desorption analysis was performed for the fresh iron oxide catalysts. Thermal degradation experiments were performed for 4-phenylbutyronitrile as nitrogen-containing model compound adsorbed over α-FeOOH, fresh or prepared by heating at 280, 350, and 400 °C. TPD was also performed for acrylonitrile−butadiene−styrene copolymer (ABS) mixed with α-FeOOH. XRD analysis was performed after each TPD experiment. Catalytic degradation of 4-phenylbutyronitrile over α-FeOOH leads to formation of light aliphatic nitriles and styrene derivatives. Increasing the temperature, α-FeOOH catalyst gradually changes its composition and crystalline structure, with decreasing the catalytic activity. The changes are accompanied by elimination of water and oxygen and can be schematically represented as follows: α-FeOOH → α-Fe2O3 → Fe3O4. Iron oxide catalysts act mainly on the primary products of ABS thermal degradation, but they can also degrade the chain end or branched styrene units in the polymer.