One-pot lower olefins production from CO2 hydrogenation

In this work the one-pot conversion of CO2 into lower olefins is investigated over a physical mixture of a methanol synthesis catalyst and a methanol-to-olefins (MTO) zeolite. First, the feasibility of the single reactions is tested at CO2 to olefins conditions, i.e., high temperature and high H2/CO2 pressure, providing insights on the reaction mechanism and catalyst stability. The effects of the operating conditions are then analyzed over the individual samples, starting from CO2/H2 mixtures in the case of the methanol synthesis catalyst and from methanol in CO2/H2 in the case of the zeolite. The In2O3-ZrO2 catalyst exhibits very good selectivity to methanol and high activity, reaching thermodynamic equilibrium above 380 degrees C. The zeolite sample showed high activity as well and the presence of high H2 partial pressure consistently increases the zeolite lifetime at high temper-atures, but also the paraffin selectivity at the expense of the olefins, especially at low space velocity. It is therefore clear that a trade-off should be identified when testing the bi-functional catalytic samples in order to guarantee high methanol formation and good olefins production in the one-pot process. Finally, a comparison between methanol-mediated and modified Fischer-Tropsch (MFT) routes is presented, highlighting strengths and weaknesses of each reaction pathway. In particular, CO must be reduced in the methanol-mediated route, while methane and C5+ hydrocarbons formation is the main issue for the MFT reaction.