Sol–gel synthesis of Ni–Co/Al2O3–MgO–ZrO2 nanocatalyst used in hydrogen production via reforming of CH4/CO2 greenhouse gases

Abstract

Ni–Co/Al2O3–MgO–ZrO2 nanocatalysts with various amounts of Mg (5, 10 and 25 wt %) were synthesized via sol–gel method. The physiochemical properties of nanocatalysts were characterized by XRD, FESEM, EDX, BET and FTIR analysis. The samples were employed for CH4/CO2 reforming in atmospheric pressure, temperature range from 550 to 850 °C, under various mixtures of CH4/CO2 and different GHSVs. Raising the MgO content leads to the lower crystallinity and intensifying of amorphous behaviour. Also, this trend promotes dispersion of active phase which probably is related to the strong metal-support interaction FESEM images confirm that the synthesized samples have nanometric particles. In addition, comparing the FESEM images of all prepared nanocatalysts presents that narrower particle size distribution and more uniform dispersion without agglomeration are found for MgO rich nanocatalyst. EDX results, besides verifying the declared claim about the dispersion of samples in XRD and FESEM analysis, reveal the presence of the utilized elements. Moreover, higher surface area was observed for Ni–Co/Al2O3–ZrO2 promoted with 25 wt% MgO compared to the other ones. The noted superior characterization of MgO rich nanocatalyst establishes its best products yield. Also, this nanocatalyst represents the stable yield with H2:CO ratio of 1 during the 1440 min stability test. H2:CO ratio of 1 was acquired at 750 °C which would be very useful from an energy saving point of view. In the case of the most active, MgO rich nanocatalyst, the effect of other operational variables such as, GHSV and feed gas composition on the catalytic performance has been evaluated. The yield of H2 and CO descends at higher GHSVs, owing to the low residence time and mass transport limitations. Equimolar ratio of CH4/CO2 was obtained as the best ratio of reactants. Also, a simplified reaction mechanism was proposed with respect to the behaviour of adsorbed species on the catalyst surface.