Catalytic oxidative steam reforming of tar using Ni-Re alloy catalysts supported by hydrothermal carbon derived from lignin

Tar contamination in product gas from biomass gasification remains a critical challenge. This study developed and evaluated Ni-Re bimetallic catalysts supported on hydrothermal carbon (HTC) derived from lignin for catalytic oxidative steam reforming of tar. The HTC support was synthesized via hydrothermal carbonization, and a series of Ni-Re/HTC catalysts with varying Ni-to-Re weight ratios were prepared using incipient wetness impregnation. Naphthalene was employed as a tar model to systematically assess catalytic performance under three reaction modes: thermal cracking, steam reforming, and oxidative steam reforming. Among the catalysts tested, Ni-Re/HTC with a 7:3 Ni-to-Re weight ratio exhibited the best performance, attributed to the synergistic roles of Ni as the primary active phase and Re as a dispersion promoter that suppresses Ni sintering and coke formation. Optimal operating conditions were identified at 800 °C, a steam-to-carbon molar ratio (H 2 O/C) of 1.5, and an oxygen-to-carbon molar ratio (O 2 /C) of 0.3. Under these conditions, near-complete naphthalene conversion (98.9%), high H 2 yield (91.6%), and negligible carbon deposition were achieved. Validation using real biomass tar confirmed that the optimized catalyst maintained tar conversion above 97% and H 2 yield above 86% over 18 h operation, demonstrating excellent catalytic stability and strong potential for practical tar reforming applications.