An egg-shell type Ni/Al2O3 catalyst derived from layered double hydroxides precursor for selective hydrogenation of pyrolysis gasoline

Authors: Xin Wen, Rushi Li, Yixuan Yang, Jiali Chen, Fazhi Zhang

Abstract:
Egg-shell type catalysts, in which a thin layer of catalytically active component is distributed on the outer surface of the support particle, have been theoretically and experimentally proved to be useful in processes where the reaction has a very high rate and the intraparticle diffusion becomes the limiting step. Herein we report the preparation of an egg-shell Al₂O₃-supported nickel (Ni/Al₂O₃ catalyst derived from layered double hydroxides (LDHs) precursor, and its catalytic performance for selective hydrogenation of pyrolysis gasoline (PyGas), an important by-product of ethylene industry from thermal decomposition of heavier oil fractions, which was carried out in the liquid phase. Firstly, a Ni²⁺Al³⁺-containing LDHs (NiAl-LDHs) precursor was in situ grown on the surface of γ-Al₂O₃ spheres by using a diluted ammonia solution as precipitator. Then, egg-shell Al₂O₃-supported nickel oxide (NiO/Al₂O₃) sample with NiO crystallites highly dispersed on the external edge of the Al₂O₃ support was obtained after calcination at 450 ^◦C. The experimental study of selective hydrogenation of styrene (PyGas model 1) for revealing the intrinsic hydrogenation kinetics was carried out in a batch reactor at 60 ^◦C using the egg-shell Ni/Al2O3 catalyst (denoted LP-Ni/Al₂O₃; LP is expressed as layered precursor) fabricated by subsequent ex situ presufidation and final H₂ reduction at 500 ^◦C of the NiO/Al₂O₃ sample. In addition, an Ni/Al₂O₃ catalyst with uniform distribution of Ni in the catalyst was prepared by a conventional wet impregnation method (denoted IM-Ni/Al₂O₃; IM is expressed as impregnation method) with the consistent Ni loading amounts and given into the consideration for comparison. The estimated effectiveness factor (ŋ) of the LP-Ni/Al₂O₃ catalyst was higher than that of the IM-Ni/Al₂O₃ one, demonstrating the catalyst with eggshell structure has a lower intraparticule mass transfer resistance. The catalytic hydrogenation activities of both Ni-based catalysts were further evaluated by selective hydrogenation of diolefins (PyGas model 2), along with selective hydrogenation of PyGas model 1, in a micro-flow reactor. The egg-shell Ni/Al₂O₃ catalyst derived from LDHs precursor exhibited a superior catalytic hydrogenation performance, which mainly be due to Ni metal being deposited on the Al2O3 support in a much thinner outer layer, as well as a smaller average size of nickel particles with stronger interaction between the nickel species and support. Several characterization techniques including powder X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), low temperature N₂ adsorption–desorption, X-ray photoelectron spectroscopy (XPS), and temperature programmed reduction of hydrogen (TPR)/temperature programmed desorption of hydrogen (H₂-TPD) were adopted to investigate the physical–chemical properties of the two supported Ni catalysts in detail.

Keywords:
Ethylene industry
Pyrolysis gasoline
Selective hydrogenation
Egg-shell catalyst
Layered double hydroxide

Published in: Applied catalysis A: General   (Volume 468, Pages 1-474, 5 November 2013)

Publisher: Elsevier  

ISSN Information: 0926-860X

An egg-shell type Ni/Al2O3 catalyst derived from layered double hydroxides precursor for selective hydrogenation of pyrolysis gasoline

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