Simultaneous production of hydrogen and carbon nanotubes from biogas over mono-and bimetallic catalyst

Abstract

In this study, simultaneous production of hydrogen and carbon nanotubes from direct conversion of biogas is experimentally investigated. A series of monometallic Fe, Co, and Ni and bimetallic CoMo, NiMo, and FeMo supported on MgO was prepared and tested for catalytic conversion of biogas in a fixed-bed reactor at 900 °C and 1 atm. Among the monometallic catalysts, Co/MgO shows the highest production yields of H2 and CNTs with excellent catalyst stability. Ni/MgO has a steadily deactivation with time on stream, while Fe/MgO exhibits the lowest catalytic performance due to the oxidation of iron species by CO2, resulting in a severe catalyst deactivation. For the bimetallic catalysts, the addition of Mo would greatly increase the production yields of H2 and CNTs due to the higher metal dispersion and SMSI effects. NiMo/MgO can achieve a remarkable 100%CO2 conversion, and 95%CH4 conversion, producing gas products comprising of H2 up to 74%v/v with H2/CO=3.1. NiMo/MgO and CoMo/MgO catalysts provided the higher yields of H2 and CNTs than FeMo/MgO catalyst, while FeMo/MgO produced the high graphitic CNTs due to the high solubility of carbon in Fe. The stability test under an extremely high GHSV of 600,000ml/g-h reveals that NiMo/MgO shows the excellent stability. CoMo/MgO is rapidly deactivated due to a large carbon deposition, while FeMo/MgO still suffers from CO2 oxidation, resulting in a severe deactivation. The long-term stability for 10h confirms that NiMo/MgO can perform the excellent catalytic performance. The process shows a high potential for simultaneous production of H2 and CNTs from abundant and renewable biogas.