Carbon nanofibre-supported palladium catalysts as model hydrodechlorination catalysts

摘要

Different carbon nanofibre-supported palladium catalysts (Pd/CNF) were prepared and tested for tetrachloroethylene hydrodechlorination. Catalyst properties were varied by changing metal loading (0.5% and 1% wt.), preparation procedure (aqueous or organic solutions), and support chemistry (parent or HNO_3-oxidised CNFs). Fresh and used (during 108,000 s at 0.5 MPa, 523 K, 24 g s mmol~(-1) space time) catalysts were characterised by TEM, XRD, TPD, TPO-MS, nitrogen physisorption, and XPS. Results obtained indicate that the preparation method (using aqueous or organic precursor) plays a key role both in the intrinsic activity of the catalysts (higher for aqueous solutions), and catalyst deactivation (also faster for aqueous solutions).The surface chemistry of the support, influenced by the surface activation and the preparation procedure, markedly affects the Pd~(2+)/Pd~0 ratio (found to be optimal at about 0.3-0.6) and chlorine concentration, these parameters determining the catalysts performance. In general terms, aqueous precursors lead to the highest initial activity (maximum initial TOF of 18 s~(-1), whereas the maximum initial TOF for catalysts prepared from organic precursor is of 5.6 s~(-1)) and faster deactivation (minimum TOF_(108,000s)/TOF_0 of 0.06 and 0.38, respectively). Deactivation causes were observed to be different in both cases: coke formation for the aqueous precursor and chlorine poisoning for the organic-phase precursor.