Effect of aluminum source on the structure and performance of Ni/Al₂O₃ catalysts in CO₂-CH₄ reforming

Three Ni/Al₂O₃ catalysts were prepared with different aluminum sources by the solution combustion method and characterized by XRD, H₂-TPR, NH₃-TPD, N₂ sorption, TG-DTG and TPH. The effect of aluminum source on the structure and performance of Ni/Al₂O₃ catalysts in CO₂-CH₄ reforming was then investigated. The results show that the NiNO-AlNO catalyst with Al(NO₃)₃·9H₂O as aluminum source owns a large surface area of 102 m²/g and a wide and intense high-temperature reduction peak; besides, the Al₂O₃ support displays certain crystallinity. In contrast, the NiNO-AlSO and NiNO-AlCl catalysts, prepared with Al₂(SO₄)₃·18H₂O and AlCl₃·6H₂O sources, respectively, are composed of amorphous Al₂O₃ as support and crystal Ni as active component; the Ni species is poorly dispersed and present as large grains, with a small reduction peak and weak interaction with the support. In particular, because of the high stability of Al₂(SO₄)₃ and difficulty in converting Al₂(SO₄)₃ to active Al₂O₃ at high temperature, certain sulfur-containing substances are preserved and the resultant NiNO-AlSO catalyst shows strong surface acidity. The catalytic evaluation results indicate that the NiNO-AlNO catalyst exhibits high activity and stability in the CO₂-CH₄ reforming; the conversions of CH₄ and CO₂ are 31.21% and 48.97%, respectively. The carbon deposition analysis illustrates that the content of deposited carbon (present mainly in the amorphous form) on the NiNO-AlNO catalyst is rather low, suggesting a high resistance against carbon deposition.