The influence of acidity of carbon nanofibre-supported palladium catalysts in the hydrogenolysis of hydroxymatairesinol

Abstract

The lignan hydroxymatairesinol (HMR, extracted from Norway spruce knots) was hydrogenolysed to matairesinol (MAT) over palladium supported by carbon nanofibres (Pd/CNF) in 2-propanol at 70°C under hydrogen flow. The influence of support acidity on the activity and the selectivity to MAT was studied. The acidity of the Pd/CNF catalyst was varied by heat-treatment at different temperatures in nitrogen flow. The catalysts were characterized by transmission electron microscopy (TEM), inductively coupled plasma emission mass-spectrometry (ICP-MS, metal content), H 2 -chemisorption (dispersion, metal particle size), and titration using NaOH. A more acidic support material was more active and selective to the desired product MAT. The major byproduct was 7-iso-propoxymatairesinol resulting from a reaction of the solvent with HMR over the acid sites on the support. The hydrogenolysis of HMR to MAT requires both the presence of metal and acidity.

Influence of Reaction Parameters on the Hydrogenolysis of Hydroxymatairesinol Over Carbon Nanofibre Supported Palladium Catalysts

“…For growing of the CNF, a Ni/SiO 2 catalyst was used. The synthesis of the Ni/SiO 2 growth catalyst and the growing of CNF are described in detail in [9]. The CNF were grown in a quartz vessel inside a tubular furnace at 550°C for 24 h in a flow of N 2 (480 mL/min), H 2 (96 mL/min), and CO (266 mL/min).…”

“…The samples were silylated prior to analysis using N,O-bis(trimethylsilyl)trifluoro-acetamide. The silylation procedure and the analysis are described more in detail in [9].…”

“…In our previous studies related to HMR hydrogenolysis, we have investigated the influence of support acidity for palladium catalysts supported on carbon [7], zeolites [8] and carbon nanofibres (CNF) [9]. For both carbon [7] as well as CNF [9] supported palladium catalysts, it was concluded that the activity increased when the amount of acid sites was increased.…”

“…For both carbon [7] as well as CNF [9] supported palladium catalysts, it was concluded that the activity increased when the amount of acid sites was increased. For Pd/CNF also the selectivity to MAT increased with acidity.…”

“…On the other hand, in the case of palladium catalysts on supports with much stronger acid sites, i.e., H-Beta zeolites [8], the activity decreased as the concentration of acid sites increased. Palladium is required for the hydrogenolysis reaction, since the support itself without palladium did not give any MAT [8,9]. It was concluded that Brønsted acid sites are needed for the hydrogenolysis reaction; Pd/SiO 2 and Pd/Al 2 O 3 showed low activity in comparison to the zeolites used (alumina, in comparison to zeolites, has small amounts of Brønsted and high amount of Lewis acid sites, and silica has even lower amount of acid sites than alumina) [8].…”