Graphene-supported metal nanoparticles as novel catalysts for syngas production using supercritical water gasification of microalgae

In this study, biomass conversion of chlorella sp. microalgae was investigated in the catalytic supercritical water gasification (SCWG) process. The catalytic effect of five different graphene-supported metal nanoparticle catalysts (Ni/rGO, Cu/rGO, Co/rGO, Mn/rGO and Cr/rGO) were evaluated on the composition of syngas. The impact of main process factors including catalyst loading (40, 70, and 100wt%), and temperature (355-405 degrees C) was studied on the SCWG process over Ni/rGO catalyst as the most efficient catalyst among the selected metal nanoparticles. The findings showed that at the optimum Ni/rGO loading of 70wt% (at temperature of 380 degrees C), the hydrogen yield increased by a factor of 5.8 in comparison to absence of Ni/rGO catalyst. At the optimum temperature of 405 degrees C (Ni/rGO loading of 40wt%), hydrogen selectivity of 31.9% was obtained. The results revealed that increment of Ni/rGO catalyst loading extremely reduced the solid residue and tar formation, which is desired in the SCWG process. Moreover, Characterizations proved the stability of prepared catalysts at supercritical condition.