Robust nickel cluster@Mes-HZSM-5 composite nanostructure with enhanced catalytic activity in the DTG reaction

Abstract

Isoparaffin-rich gasoline plays an essential role in the global energy consumption. In this regard, there have been extensive studies to prepare catalysts for efficient synthesis of isoparaffin-rich gasoline. In this paper, we report a protocol to incorporate Ni nanoclusters (NiNC) into mesoporous Mes-HZSM-5 zeolite for the synthesis of NiNC@Mes-HZ catalysts. The catalysts are prepared via impregnation of Ni6(PET)12 clusters into Mes-HZSM-5 zeolite, followed by annealing at 550 °C in air. The NiNC@Mes-HZ catalysts are characterized by TEM, XRD, H2-TPR, NH3-TPD, ICP-MS, as well as N2-physical adsorption method. The Ni clusters (average diameter: ca. 1.2–2.7 nm) are found to locate at mesoporous area of the zeolite and interact with Brønsted acid sites of the HZSM-5 zeolite, evidenced by the pyridine adsorption Fourier-transform infrared spectrum analysis. The NiNC@Mes-HZ catalysts (Ni cluster loading = 0.11 wt%) exhibit 100% conversion of dimethyl ether (DME) with 66.4C% selectivity towards C5-11. Results show 53.5C% of C5-11 product contains isoparaffin. This is considerably higher than that for Mes-HZSM-5 zeolite (27.5C% isoparaffin selectivity) and xNiNP@Mes-HZ (73.4% DME conversion) catalysts in the DTG process at 350 °C. The higher selectivity of the 0.11NiNC@Mes-HZ catalysts towards isoparaffin production is deemed to associate with the ease of DTG reaction to take place at the interface of the Ni nanoclusters and acidic sites of the zeolite. Further, it is shown that the nickel nanoclusters largely improve the durability of Mes-HZSM-5 zeolite (over 205 h), which is mainly due to the inhibition of carbon deposition production during the DTG process, evidenced by TPO-MS analysis of the used NiNC@Mes-HZ. The Ni nanoclusters in the zeolite show good hydrogenation capacity and cracking performance, enhancing the olefin methylation pathway on the acidic sites of Mes-HZSM-5 and attenuating the aromatic methylation cycle during the DTG reaction.