Ethanol steam reforming under engine exhaust-like conditions: energy recovery of reformate and coke-to-power integrated approach

Abstract

Ethanol steam reforming (ESR) was evaluated as an on-board energy recovery strategy for internal combustion engines under engine exhaust-like conditions using a bench-scale reactor and two catalysts: a commercial Ni/Al₂O₃ catalyst promoted with CaO and K₂O, and a Co catalyst supported on sepiolite. Experiments were conducted between 300 and 600 °C, selected according to exhaust temperature ranges experimentally obtained in a medium-duty compression ignition (CI) engine, and at steam-to-ethanol (S/E) ratios from 3:1 to 13:1. The nickel catalyst showed the broadest and most robust operating window, achieving complete conversion above 400 °C and positive energy recovery over a wide temperature range, although with significant coke formation at intermediate temperatures (400–500 °C), especially at low S/E ratios. The cobalt catalyst exhibited lower activity but higher hydrogen selectivity and lower methane formation, with optimal performance concentrated above 500 °C and negligible coke under high steam conditions. Considering the additional energy recovered from coke gasification, overall energy recovery reached values of 1.17–1.20 under optimal conditions, confirming the viability of ESR coupled with exhaust waste heat. This integrated reforming–regeneration analysis highlights that moderate coke formation does not necessarily penalize the overall energy balance, provided that effective regeneration strategies are implemented. However, bench-scale operation also revealed progressive mechanical degradation of the catalyst bed, including erosion, fragmentation, and pulverization caused by repeated coke formation–regeneration cycles, leading to increased pressure drop and operability limitations.