Investigation of the deactivation of iron nanocomposites by coking in the dehydrogenation of ethylbenzene

Iron-containing composites were prepared and characterised by X-ray diffraction (XRD), thermoprogrammed reduction analyses (TPR), basicity measurements, textural properties, Raman spectroscopy, scanning electron microscopy coupled to EDX (SEM-EDX), thermoprogrammed oxidation analysis (TPO) and evaluated in the dehydrogenation of ethylbenzene with CO2. The presence of either Ce or Co promoters greatly enhanced the catalytic activity of the solids in the dehydrogenation of ethylbenzene with CO2, when compared to Sn and Mn analogues, due to their easy reducibility. The cobalt species (FeCo2O4 and CoOx) in the CoFeSi catalyst determined the activity. Severe reaction conditions provoked the formation of amorphous carbon, and also graphitic species were observed. In addition, the reducibility of Co species may play a role in favouring the formation of hard carbonaceous deposits, as the redox process involved the Co and Fe species in the ethylbenzene and CO2 environments. The investigation of temperature, CO2/EB ratio, W/F and space velocity for the most active solid showed that 550 °C, P = 1 atm, a CO2/EB ratio of 30, W/F = 2.5 gcat h molEB−1 and a space velocity of 3.4 h−1 provided an EB conversion and styrene selectivity of about 15.3% and 99.6%, respectively.

Graphical abstractFigure optionsDownload full-size imageDownload high-quality image (207 K)Download as PowerPoint slideHighlights► Iron-based nanocomposites were tested in the ethylbenzene dehydrogenation with CO2. ► Characterised by BET measurements, XRD, SEM-EDX, H2-TPR, CO2-TPR and Raman spectroscopy. ► FeCo and FeCe nanocomposites active in ethylbenzene dehydrogenation to styrene. ► Physical degradation and carbonaceous deposition on the nanocomposites. ► Graphitic and filaments of carbon.