(179b) Synthesis, Characterization and Evaluation of (Ce, Y, Zn)-Ion-Exchanged Silicalite-1 Supported Ni Catalyst Structures for CO2 Capturing By Methane Dry Reforming

Recent developments in nano-catalysis helped to re-design catalytic structures that can overcome conventional catalyst deactivation challenges, and hence, give rise to industrial reactions that are more environmentally friendly. The methane dry reforming reaction (MDR) is a useful way to produce H₂ and synthesis gas, and at the same time capture two main greenhouse gases; CO₂ and CH₄. However, through the last decades the reaction was not feasible due the rapid deactivation of the Ni based catalyst by fouling and sintering. In this study a microwave-assisted hydrothermal synthesis method was used to synthesize a Ni based catalyst, in which Ni at different loadings (10, 15 and 20 wt%) was deposited by incipient wet-impregnation on a MFI type silicalite-1 zeolite support. The catalyst performance was further improved by the introduction of metals; Ce, Y and Zn through an ion-exchange procedure. The alkalinity of the support was further enhanced by the introduction of Mg and Ca. These catalyst systems were evaluated at different temperatures and feed ratios in a packed bed reactor experimental setup. Different catalyst structural properties were characterized by XRD, FESEM, TEM, N₂-physisorption, XPS, FTIR and H₂-TPR. Time-on-stream evaluation experiments showed that the Ce ion-exchanged silicalite-1 supported Ni catalyst had the highest activity and stability. The catalyst maintained a CH₄ conversion of 90%, a CO₂ conversion of 85% and a H₂/CO ratio that ranged from 1.7 to 2.9. Ce improved the oxygen storage capacity of the catalyst which facilitated the oxidation of carbon depositions. In addition, the unique MFI structure that is composed of 10 straight membered channels of silicate-rings and 10 zigzag sinusoidal membered ring channels reduced diffusion limitations and offered a fast gas flow reaction environment. Carbon depositions from CH₄ cracking were also reduced due to the absence of alumina in the silicalite-1 support framework. Moreover, the high internal surface area of the support facilitated high Ni dispersion which prevented sintering of the catalyst. Raman spectroscopy, TGA and TEM images revealed that carbon deposits on most spent catalyst structures were predominantly multi-walled carbon nanotubes (MWCNTs) with defects.