Performance of alumina supported Ni catalyst with core-shell and supported structures in dry reforming of methane

Dry reforming of methane is one the interesting processes in which CH4 and CO2 are consumed at the same time and valuable syngas is produced. In this research, Ni@Al2O3 core shell structure catalyst is compared with the Ni/Al2O3 supported catalysts in terms of their catalytic stability, activity and carbon formation in dry reforming of methane. The core-shell structure catalysts were prepared by microemulsion method and impregnation technique was used for the supported catalysts. The Ni loadings were 5- 20 wt. % for the both types of catalysts. The prepared catalysts were analyzed with BET, XRD, TPR, XPS, TEM, XAS, and ICP analysis. BET analyses, TEM, and SEM-EDS images showed that core- shell structure catalysts were successfully prepared with smaller particle size and higher surface area (≥ 200 m2/ g) than the supported catalysts ( ˂ 200 m2/ g). Furthermore, TPR and XPS analysis revealed that NiAl2O4 species was the main Ni phase in all the catalysts, making strong interaction between Ni and Al2O3. XANES analysis revealed that all the catalysts were almost reduced completely. The catalytic test reaction was carried out at 750 ºC, GHSV= 144 L. g-1 .h-1 and CH4:CO2: N2= 1:1:1. The results demonstrated that core- shell catalysts had better catalytic activity than the supported catalysts due to encapsulation of Ni with shell, preventing Ni particle from agglomeration and sintering in comparison with the supported catalysts. The highest CH4 and CO2 conversions belonged to 20%Ni@Al2O3 catalyst with around 55% and 57%, respectively. Further, H2/CO ratio was almost 1 for the core-shell catalyst whereas this amount was around 0.9 for the supported catalysts. The lower amount of carbon was also deposited in the core- shell catalysts due to smaller particle size and Ni covered with the shell. The lowest amount (~2wt.%) of coke deposited on the 12% Ni@Al2O3 catalysts while this amount was about 5 wt. % for the supported catalysts with the same loading. The long term thermal stability test (24 h) showed great stability for the core-shell structure catalyst while it was gradually deactivated after 120 h in reaction due to carbon formation