Non-oxidative decomposition of propane: Ni-Cu/Al2O3 catalyst for the production of CO2-free hydrogen and high-value carbon nanofibers

Abstract

A Ni-Cu/Al2O3 catalyst was tested in the thermal decomposition of propane to produce CO2-free hydrogen and high value-added carbon nanofibers (CNF), the quantity and quality of which are key to making the process economically viable. The effect of temperatures in the range 550–750°C and space velocities from 24 to 240 l gCat−1h−1 on the product distribution, conversion, H2 selectivity and carbon formation rate (CFR) was evaluated. In addition to H2, CH4 and C2H4 together with small amounts of C2H6 were detected in the reaction gases. While propane conversion overpassed 90% at 700°C and higher temperatures, H2 selectivity reached 40% for low space velocities (24 l gCat−1h−1). Likewise, the CFR increased with temperature to 50 gC gCat−1h−1 at 700°C, doubling the rates reported for methane or ethane as the feedstock and same reaction conditions. The CNF, thoroughly characterized by XRD, N2 physisorption, SEM and TEM, exhibited bimodal and wide diameter distribution (6–120 nm) and fishbone morphology with high graphitic order (interplanar distance: 0.339–0.347 nm, and crystal sizes around 5 nm) and good textural properties (specific surface area: 100–190 m2 g−1 and total pore volume: 0.23–0.45 cm3 g−1).