Solar-driven pyrolysis of microalgae in molten salt with Ni/Ce-based catalyst for hydrogen production

Solar-driven pyrolysis of microalgae in molten hydroxides is a promising technology for hydrogen production, yet it faces challenges due to the high content of methane, C₂—C₅ hydrocarbons, and tar in the gas products. To achieve clean and efficient hydrogen production, this study proposes a solar-driven pyrolysis in molten salt coupled with Ni/Ce-based catalysts of microalgae to produce hydrogen. First, the effects of four different Ni/Ce-based catalysts on microalgae pyrolysis characteristics were investigated in a molten NaOH-Na₂CO₃ system. It was observed that the basic sites present on the ZrO₂ support within the Ni-ZrO₂ catalyst facilitated the adsorption of water vapor, whereas the Ni component effectively promoted the scission of C—H bonds. The results showed that the synergistic action of the Ni and ZrO₂ catalyst promote C—H bond cleavage in volatiles and oxygen adsorption and migration, achieving the highest conversion rates for small hydrocarbons and tar reforming. On the one hand, optimal catalytic performance was achieved with Ni/ZrO₂ at a Ni loading of 10%. Further increasing Ni loading led to decreased catalytic activity due to Ni particle agglomeration. On the other hand, the catalyst exhibited the best tar reforming performance at a catalyst-to-feedstock mass ratio of 1. Excessively high catalyst-to-feedstock ratios increased bed pressure drop and reduced volatile reforming efficiency. Compared with no catalyst, the aromatic hydrocarbon content in the tar was reduced to 0.020 mmol/g, corresponding to a 26% increase in hydrogen yield, which reached a maximum of 93 mmol/g. This solar-driven pyrolysis of microalgae in molten salt with the Ni-based catalyst effectively promotes the steam reforming of methane and tar, simultaneously achieving a marked enhancement in hydrogen yield and product quality. Thus, it provides a new pathway for the synergistic conversion of solar energy and biomass.