Nickel encapsulated in silicalite-1 zeolite catalysts for steam reforming of glycerol (SRG) towards renewable hydrogen production

Valorisation of crude glycerol via steam reforming, i.e., SRG, is a promising method to produce sustainable hydrogen. However, catalyst deactivation under harsh SRG conditions is still a main challenge which hinders the further development of practical SRG. In this work, the encapsulated Ni catalyst in siliceous silicalite-1 zeolite (Ni@Si-1) were developed to show the improved performance and enhanced anti-deactivation potentials in catalytic SRG as compared with the conventional impregnated Ni catalysts (i.e., Ni/Si-1). Importantly, the post-synthetic treatment of Ni@Si-1 using TPAOH solution formed the encapsulated Ni catalyst with the mesoporous hollow structure (i.e., Ni@HolSi-1), which demonstrate even better performance in SRG with glycerol conversion of >95%, H₂ yield of ~70%, H₂/CO₂ molar ratio of >2.33 and CO/CO₂ molar ratio of <1 at 750 °C. Specifically, highly dispersed ultrasmall encapsulated Ni particles were retained within the hollow crystals of siliceous silicalite-1, as confirmed by XPS and HRTEM characterisation. The activation energy for glycerol conversion over Ni@HolSi-1 (i.e., Ea = ~ 19 kJ mol⁻¹) was much lower than that of Ni/Si-1 and Ni@Si-1. 100-h longevity tests over the three catalysts were investigated at 750 °C, and the Ni@HolSi-1 catalyst exhibited an excellent stability and activity, as well as insignificant coke deposition, which could be due to the enhancement of highly dispersed yet accessible Ni NPs within the hollow Si-1 crystals. The findings of the work show the promise of the encapsulation strategy and mesoporous zeolites for developing the future reforming catalysts.