Non-toxic Fe-based catalysts for styrene synthesis: The effect of salt precursors and aluminum promoter on the catalytic properties

The catalytic dehydrogenation of ethylbenzene to produce styrene is an important industrial process because it is used in the manufacture of resins, synthetic rubber and plastics. The most used catalysts for this process are iron oxides containing potassium and chromium oxides. These catalysts show high activity and selectivity but deactivate with time on-stream in the industrial units, mainly due to the loss of potassium. On the other hand, the storage of the exhausted catalytic materials causes environmental damage because of the toxicity of chromium compounds. In order to find non-toxic and potassium-free catalysts, the effect of aluminum and the salt precursor on the properties of iron oxides was investigated in this work. The catalysts showed high specific area, were resistant to reduction and were potassium-free; these features can prevent their deactivation. Also, they showed higher activity and selectivity than hematite and were no harmful for the environment. In these catalysts aluminum acts both as textural and structural promoter. Among the starting salt precursors studied (nitrate, sulfate and chloride), the iron chloride was the most efficient one, producing active and selective catalysts with high resistance against deactivation.