Metal-Free Himalayan Cone-Derived Activated Carbon with a Competitive Catalytic Performance for a CO₂-Assisted Soft Oxidative Dehydrogenation of Ethylbenzene to Styrene

Himalayan cone, an organic mulch, was pyrolyzed to synthesize a bioderived carbon to study the vapor-phase CO2-assisted soft oxidative dehydrogenation of ethylbenzene to styrene. The impact of biomass-derived activated carbon was compared with commercially available carbon materials, namely commercial activated carbon, carbon granules, and multiwalled carbon nanotubes. Herein, the biochar-activated carbon showed an amorphous nature with an anthracite coal-like structure, containing 90.31% carbon content as analyzed by CHNS analysis. The initial effect of temperature on the synthesized biochar-activated carbon showed optimum catalytic activity at 550 °C, with a conversion of 53% and selectivity of 70%, and a feed flow of 0.5 mL h–1, a catalyst amount of 0.5 g, and a CO2 gas flow. The rate of ethylbenzene’s disappearance varied between zero and first order, and the rate of reaction increased with an increase in temperature, while the highest energy of activation was obtained to be 51.48 kJ mol–1 for carbon granules, followed by a value of 37.18 kJ mol–1 for biochar-activated carbon. Additionally, the thermodynamic study depicted a positive value for the change in enthalpy, explaining the endothermic nature of the reaction. Theoretical DFT studies for activated carbon with carbonyl oxygen species depicted a lower adsorption energy for ethylbenzene and a higher desorption energy for styrene, indicating favorable conditions for the soft oxidative dehydrogenation of ethylbenzene to styrene. The biomass-derived, cost-effective biochar-activated carbon showed a good time-on-stream study value with stable catalytic activity for up to 30 h, and the results suggest that it has the potential to be used in industrial applications.