Microwave plasma assisted preparation of Pd-nanoparticles with controlled dispersion on woven activated carbon fibres

The low-pressure cold microwave (MW) plasma is shown as an efficient method to increase acidity of the ACF within less than 1 min treatment without affecting the fibre morphology and strength. The ion-exchange capacity was 1.6 times higher compared to the non-treated ACF sample. Selective removal of the carboxylic groups from the ACF surface by the air-MW-plasma allows to keep the phenolic groups intact. Palladium was deposited on ACF from [Pd(NH3)4]Cl2 solution via ion-exchange with the protons of the phenolic surface groups. Surface phenolic groups were able to chemically anchor Pd in cationic form, leading after reduction in H2 to small Pd° nanoparticles (<3 nm). The Pd dispersion was measured by CO pulse adsorption and confirmed by the TEM analysis. Heating of the Pd/ACF catalysts in H2 at 573-773 K is necessary to reduce Pd(II) to Pd°. This reduction can be also achieved by the H2-MW-plasma treatment in less than 1 min with the corresponding saving of energy.