Ru supported on Mg/Al hydrotalcites for phenol hydrogenation.

Abstract

Cyclohexanone and cyclohexanol are high value-added products widely used in polymer and chemical industry as organic solvents in oil paints or varnishes [1] or as intermediates in nylon, oxalic acid, caprolactam and adipic acid syntheses [2]. These compounds have been traditionally obtained from cyclohexane oxidation, a tedious and energy consuming process with low selectivity for the desired cyclohexanone and cyclohexanol. Thus, hydrogenation of phenol has emerged as a promising alternative to the former process with greater selectivity and, considering that phenol could be obtained from the degradation of lignin, which is a widespread, sustainable, carbon neutral precursor, this synthetic route has gained the attention of the scientific community. It has been reported that in phenol hydrogenation, hydrogen is added to the aromatic ring by a spill-over mechanism in which both phenol and hydrogen are adsorbed on metal sites, and that the adsorption configuration is strongly related to the number of acid and basic sites around metal sites [3]. In addition, it is known that supports with acid-base properties and moderate specific surface area improve both thermal stability and metallic phase dispersion. With respect to metallic sites, noble metals like Pd or Ru are benchmark hydrogenating agents [4]. In this work, catalysts containing 2 wt.% Ru supported on non-commercial hydrotalcites with different Mg/Al molar ratios were tested in the hydrogenation of phenol in a batch reactor with semiautomatic sample collection working at 200 ºC and 30 bar. The catalysts were fully characterized by means of XRD, N2 adsorption-desorption at -196 ºC, XPS and HR-TEM.