Hydrogen-assisted dechlorination of 1,2-dichloroethane on active carbon supported palladium-copper catalysts

摘要

A series of active carbon supported palladium-copper catalysts with varying amounts of both metal components and overall metal loading 2 wt.%, prepared by incipient wetness impregnation were characterized by temperature programmed reduction (TPR), hydrogen chemisorption, temperature programmed (palladium) hydride decomposition (TPHD), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). TPHD and XRD studies indicated that the bimetallic Pd-Cu/C catalysts exhibited a considerable degree of alloying. Pd/C, Cu/C and Pd-Cu/C catalysts were investigated in the hydrodechlorination (HdCl) of 1,2-dichloroethane in the gas phase at a relatively low reaction temperature (210-230℃). All catalysts showed fair stability with time on stream (up to ~15 h). The Pd/C and Pd-rich Pd-Cu catalysts essentially retained their initial activity while the bimetallic samples with higher Cu content exhibited some deactivation at the initial stage of reaction. Cu-rich bimetallic samples exhibited the highest selectivities toward ethene (desired reaction product), >90%. For all bimetallic Pd-Cu/C samples, this selectivity gradually increased with time on stream. XPS studies of freshly reduced and post-reaction catalysts did not support the hypothesis that during hydrodechlorination the surface of Pd-Cu is being gradually enriched in copper, as could be expected of a higher affinity of copper to chlorine. Post-reaction deposits investigated by the temperature programmed hydrogenation (TPH) showed substantial amounts of chlorine on the copper catalyst, whereas all palladium-containing Pd-Cu/C samples exhibited only carbon-containing deposit, with C2-hydrocarbons desorbing at a relatively low temperature (300℃). Suggested interpretation of catalytic data includes both the role of C2H_x species building up on catalyst's surface during hydrodechlorination as well as the role of Pd-Cu mixed sites in the mechanism of hydrogen-assisted dechlorination of 1,2-dichloroethane.