Governing effect of catalyst acidity on the selectivity of guaiacol hydroconversion to fuel additives over supported Ni-catalysts

Abstract

Ni catalysts with ∼5 wt% Ni content were prepared using SiO2, γ-Al2O3, zeolite H-Beta, and SAPO-11 as supports and studied in the hydroconversion of guaiacol (GUA) in a solvent-free, continuous flow-through catalytic system. The acidity of the catalyst was found to direct the reaction towards different dominant reaction pathways. Over the virtually non-acidic Ni/SiO2 catalyst, the reaction was initiated by the hydrogenation of the aromatic ring, followed by hydrogenolysis reactions giving cyclohexane, methane and methanol as main products. Over γ-Al2O3 and zeolite catalysts with Lewis and/or Brønsted acidity, the reaction was initiated by facile acid-catalyzed transmethylation reactions followed by metal-catalysed hydrogenation and hydrodeoxygenation (HDO) reactions. An O-free liquid product was obtained containing substantially all of the GUA carbon in methyl-substituted 6-membered carbocyclic moieties. The Brønsted acid catalysts are unfavorable due to their high activity in aromatic condensation reactions leading to coke deposition and rapid loss of activity.