The natural lignan hydroxymatairesinol was hydrogenolysed to a potential anticarcinogenic substance matairesinol over different carbon-supported palladium catalysts. The reaction was conducted in 2-propanol at 70°C under hydrogen flow in a stirred glass reactor. The catalysts were characterised by N 2 -physisorption, CO pulse chemisorption and pH measurement of aqueous catalyst slurries. The most active catalyst (Degussa-Hu¨ls) gave yields of matairesinol over 90% in 4 h. It was concluded that the acidity of the catalyst had a profound influence on the reaction rate.
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.
Liquid-phase lactose oxidation was investigated over supported Pd/C and Pd-carbon nanofibre catalysts, which were characterized by several methods. A complex relationship between catalyst activity and catalyst acidity was established, i.e. optimum catalyst acidity resulted in the highest activity in lactose oxidation. In-situ catalyst potential measurements during lactose oxidation gave information about the extent of accumulation of oxygen on the metal surface. These results could be correlated with catalyst deactivation, which was extensive over the most acidic catalysts at low reaction temperatures. Selectivity for the desired product, lactobionic acid, was a maximum of approximately 83% at 93% conversion. The main side-product was lactulose formed via isomerisation of lactose. Lower selectivity toward lactobionic acid was obtained when the rate of oxidation of lactose was low.
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