Abstract
Highly dispersed Pd/SiO2/cordierite monolith catalysts (PSC) were prepared to investigate the influence of support alkalinity on 2-ethyl-anthraquinone (eAQ) hydrogenation. The support alkalinity was adjusted by the MgO content in SiO2 washcoat. The behavior of the PSC catalysts was tested by liquid phase hydrogenation of eAQ in a continuous trickle bed reactor. PSC catalyst with 2wt.% MgO (Mg-2 sample) exhibited excellent for hydrogenation of eAQ. The support alkalinity directly influenced the electronic properties of the Pd nanoparticles as proved by Fourier transformed infrared spectroscopy with CO probe molecule and X-ray photoelectron spectroscopy. The electron density at lower binding energy of the supported Pd particles increased with the increasing alkalinity. PSC catalysts with alkali modifiers exhibited higher hydrogenation efficiency for benefiting the activation of CO group in eAQ and the adsorption of eAQ via the enhanced interaction of lone pair of CO electrons. However, increased support alkalinity contributed to higher Pd loss due to the weak coating strength. Besides, the active quinone selectivity decreased with the progressive MgO addition due to the tautomerization of 2-ethylanthrahydroquinone to 2-ethyloxoanthrone, which is the precursor of other degradations. Consequently, a volcano shape curve between hydrogenation efficiency (H2O2 yield) and MgO content was obtained.
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