Dispersed Ni-Doped Aegirine Nanocatalysts for the Selective Hydrogenation of Olefinic Molecules

A mild hydrothermal route was employed for the first time to prepare pure synthetic aegirine nanocatalysts with high dispersion of the nickel species, different Ni contents, low-temperature reducibility of the Ni2+ species, and two average nanocrystalline domain sizes of 12 and 25 nm. The developed method allowed the formation of a novel nanocarrier for nickel that induced a well dispersion of the metal and its protection from sulfur poisoning. The nanocrystalline aegirine materials were fully characterized by XRD, BET, SEM-EDX, HRTEM, FT-IR, ICP, TGA, and TPR in order to confirm the aegirine structure and particle morphology. In this study, the synthetic Ni-nanoaegirine materials were tested as a nanocatalyst for the selective hydrogenation of aromatics (toluene) and olefins (1-octene) at low H2 pressures (70 psig) and moderate temperatures (140–200 °C). The hydrogenation activity of the synthesized materials was assessed and it was found that the 12 nm Ni-aegirine materials were more active than the 25 nm catalysts at the same Ni loading. The difference in catalytic activity might be attributed to the difference in crystalline domain sizes and the number of small active centers created on the surface because of the high dispersion obtained for the nickel during the hydrothermal crystallization. Furthermore, Ni-aegirine nanocatalysts were very selective toward the hydrogenation of 1-octene in a 50 wt % 1-octene/toluene mixture with almost no toluene saturation indicating the importance of having developed small nickel sites on the surface. The 2.5Ni-AEG-25 nanocatalysts could be selected as a catalyst of choice to replace expensive noble metal catalysts for 1-octene hydrogenation with minimal toluene saturation. It also seems that the hydrogenation activity was enhanced by increasing the surface area of the catalyst and promoted by the high metallic dispersion of the Ni clusters on the surface of the carrier. The catalyst in this study is proposed as a candidate for olefins elimination from light hydrocarbon streams to prevent the formation of gums and deposits with no significant aromatics hydrogenation, as was demonstrated when using a real naphtha feedstock.