Effects of Li Promoter on the Catalytic Performance of Fe-Li/AC for Ethylbenzene Dehydrogenation in the Presence of CO2

Dehydrogenation of ethylbenzene (EB) to styrene (ST) under CO2 was investigated over the activated carbon (AC)-supported iron catalyst with a Li promoter (Fe-Li/AC). N2 physical adsorption and X-ray diffraction showed that the Li promoter can increase the catalyst surface area and the dispersion of iron active species. CO2 temperature-programmed desorption suggested that Li can enhance the basicity of Fe/AC and CO2 adsorption on the catalyst. The addition of Li as promoter greatly improves the catalytic activity of Fe/AC and the coupling effect of CO2 and suppresses the catalyst deactivation for EB dehydrogenation under CO2. The ST selectivity and yield reach 96.2% and 62.9%, respectively, during EB dehydrogenation over the catalyst Fe(3.0)-Li(0.6)/AC (the loadings of Fe and Li being 3.0 and 0.6 mmol/g, respectively) at 550 °C, contact time of 3.57 (g·h)/mol, and CO2/EB mole ratio of 20. Higher ST yield can be obtained for EB dehydrogenation under CO2 than that under N2, which is attributed to that CO2 serves as a weak oxidant for keeping the high valence state of iron species in the catalyst and eliminating the hydrogen produced by EB dehydrogenation.