Hydrogen-rich syngas production from steam reforming of toluene using highly active and stable Ni@SiO2 yolk-shell catalysts

Catalytic reforming technology holds significant potential for treating biomass gasification tar. However, the design of catalysts that offer high activity, low carbon deposition, and long-term stability remains a challenge. In this study, Ni@SiO₂ yolk-shell catalysts were synthesized and evaluated for their activity and stability in toluene steam reforming. The Ni@SiO₂-10 catalyst demonstrated excellent stability and activity, maintaining a 100 % toluene conversion rate over a 120-h test period with virtually no carbon deposition after reforming. In contrast, Ni/SiO₂ and Ni/Al₂O₃ catalysts, synthesized by incipient wetness impregnation, showed significant sintering and carbon deposition after use. Under identical support conditions, Ni@SiO₂ reduced the initial reaction temperature for toluene steam reforming from 462 °C to 418 °C. Increasing the Ni loading significantly enhanced the number of active sites, decreased the size of the SiO₂ microspheres, and thinned the SiO₂ shell layer, thereby elevating the toluene conversion from 72 % to 100 %. Both temperature and the GHSV (gas hourly space velocity) had a significant impact on catalytic performance, with conversion rates stabilizing at 700 °C and an GHSV = 24500 h⁻¹. The yolk-shell structure of Ni@SiO₂ promoted high Ni dispersion, reducing aggregation and carbon deposition, which were key to its high activity and stability. These findings are crucial for the development of catalysts for biomass tar reforming.