Hydrodechlorination of PCDDs, PCDFs and dl-PCBs in fly ashes from a Colombian incinerator over mono and multimetallic (Mo, Ni, Pd) alumina-supported catalysts

Mono, bi and trimetallic catalysts of Mo, Ni and Pd supported on γ-Al2O3 were synhesized and tested for hydrodechlorination of PCDD/Fs and dl-PCBs of fly ashes from a Colombian solid waste incinerator. Catalysts were characterized by elemental analysis, BET, XRD, NH3-TPD, pyridine FTIR, H2-TPR, UV–vis, CO chemisorption and TEM. BET surface area and total pore volume decreased slightly after metal incorporation. All the synthesized materials showed type IV isotherm with H1 hysteresis. No metal oxides were detected by XRD, suggesting a high dispersion of metals that was confirmed with CO analysis. UV–vis spectra showed a band associated with the charge transfer of O2− → Mz+ and catalysts displayed media and strong acidity; only Lewis acid sites were identified by pyridine FTIR. The reduction of the metals in the catalysts was not complete under the used conditions; then no all the material was available for reaction. Bimetallic and trimetallic supported catalysts containing Pd showed a greater catalytic activity towards hydrodechlorination than the corresponding monometallic catalysts. The best activity was obtained over MoPdA catalyst that showed the highest medium acidity content (59%) with 0.32 and 0.64% wt of Pd and Mo, respectively. Conversion and reduction in toxicity was 99.9% for PCDD/Fs; and 97.1% conversion and 99.5% reduction in toxicity for dl-PCBs. Rate of disappearance of chlorinated compounds was favored by bimetallic catalysts that contained Pd.