Catalytic steam reforming of acetic acid from aqueous bio-oil for efficient hydrogen production over high stable Co/(NixMgy)Al2O4 catalyst

Acetic acid is one of the major components of the aqueous bio-oil. Steam reforming of medium-low temperature acetic acid to produce H2 is important for addressing the energy crisis and challenges of global climate change. However, catalysts for steam reforming still suffer from low H2 selectivity, low conversion and poor long-term stability. Spinel supports with varying Ni/Mg molar ratios were synthesized via co-precipitation, followed by the loading of cobalt via wet impregnation. The effects of reaction temperature, steam-to-carbon ratio (S/C), and carrier gas dilution level on acetic acid steam reforming were systematically evaluated. Stability tests were conducted at 550 °C, S/C = 3, and a N2 flow rate of 35 mL/min to investigate the catalyst's resistance to coking and long-term stability. The 5Co/(Ni0.8Mg0.2)Al2O4 catalyst exhibits 99.8 % conversion under the conditions of T = 550 °C, N2 flow rate = 35 mL/min, LHSV = 11.25 h−1, and S/C = 5, along with 85.9 % H2 selectivity and 72.1 % conversion at S/C = 7 and N2 flow rate = 65 mL/min while maintaining other parameters unchanged. This superior performance is a well-balanced distribution of acidic and basic sites, leading to more active sites. The 5Co/(Ni0.5Mg0.5)Al2O4 catalyst exhibits‌ a high activity and enhanced long-term stability: the conversion of acetic acid reaches 86.0 % and H2 yield remains stable near 2.43 molH2/molAcOH over a 50-h reaction period under the conditions of T = 550 °C, N2 flow rate = 35 mL/min, LHSV = 11.25 h−1, and S/C = 3 due to precisely controlled metal particle size and optimized oxygen vacancy concentration. The catalytic mechanism and the formation pathways of methanol and acetone in steam reforming are investigated and discussed. The present work provides extensive information about the acetic acid steam reforming process for producing hydrogen, and offers a significant contribution to valorisation of aqueous phase bio-oil.