Synthesis of Ni(ii)-phosphotungstic acid/nanocrystalline HZSM-5 catalyst for ultra clean gasoline in a single-stage reactor

Abstract

Although considerable progress has been made in FCC gasoline hydrorefining, it is still a great challenge to develop new catalysts and single-stage reactors to realize deep refining whilst retaining octane number. The core of one-pot hydrogenation is to develop a deep desulfurization catalyst and maintain the high aromatization activity of C–H compounds in the corresponding oil at low temperatures. In this paper, a bifunctional nanocrystalline HZSM-5 zeolite supported Keggin-type phosphotungstic acid (HPW) and a Ni salt catalyst (NiPW-Nano-Z) are designed and applied for hydrorefining of FCC gasoline in order to obtain high quality fuel. The catalysts have been characterized using inductively coupled plasma, N₂-physisorption, Fourier transform infrared spectroscopy, X-ray diffraction, ultraviolet-visible spectroscopy, in situ electron spin resonance, UV-Raman spectroscopy, ³¹P magic angle spinning-nuclear magnetic resonance, X-ray photoelectron spectroscopy, IR spectra of in situ adsorbed pyridine, H₂-temperature programmed reduction. The role of calcination temperature, the type of raw material and the rare earth metal oxide on the framework structures of polyoxometalate on the nanocrystalline HZSM-5 zeolite, are discussed in detail. The Keggin structure of HPW and the scaffold structure of nanocrystalline HZSM-5 zeolite on NiPW-Nano-Z calcined at 350 °C have been maintained. The NiPW-Nano-Z catalyst has shown excellent catalytic performance for the hydrodesulfurization, aromatization with hydrogenation of olefins activity of FCC gasoline by single-stage reactor. The distribution of the products is measured and calculated. The contents of sulfur, total aromatics and olefins are 8.4 μg g⁻¹, 24.4 vol% and 10.0 vol%, respectively, which demonstrates that the quality of products has met the National standard VI of vehicle gasoline in China. The improved catalytic performance of the NiPW-Nano-Z catalyst can be due to the synergistic effect between Ni(II) and HPW(III) on the nanocrystalline HZSM-5 zeolite. The effect of the polyoxometalate structure and acidity of nanocrystalline HZSM-5 zeolite on the hydrorefining of FCC gasoline is also investigated in detail.