NiMo/MCM-41 Catalysts for the Hydrotreatment of Polychlorinated Biphenyls

MCM-41 type mesoporous materials of pure silicon and aluminosilicates (with Si/Al atomic ratios of 20 and 40) were prepared by a facile synthesis method and used to support NiMo catalysts. Characterization by XRD showed typical patterns of this type of mesoporous solids with a partial collapse of the structure on increasing Al content. In addition, signals attributed to the formation of MoO3, NiO and Al2(MoO4)3 in the transition-metal containing catalysts were observed. The 29Si-NMR-MAS spectra showed that local arrangement of the Si–O–Si bonds was regular, independently of the solid being pure or modified with Al, while the 27Al-MAS-NMR spectra of the aluminosilicates showed both structural and non-reticular species. The N2 adsorption–desorption curves showed type IV isotherms, with considerable diminution in the BET areas once the metals were incorporated. The catalytic results in thiophene hydrodesulfurization (HDS) and polychlorinated biphenyl hydrodechlorination (HDCl) revealed a considerable catalytic activity for all prepared catalysts as compared with a commercial NiMo/Al2O3 one, being highest in the case of the NiMo/Al-MCM-41(40) one for HDS, and for NiMo/Al-MCM-41(20) in HDCl. The excellent properties for HDCl can be attributed to good dispersion of Ni and Mo active phases and to the bifunctional character of the catalysts, namely, to the participation of both coordinatively unsaturated sites of the NiMoS active phase and Brønsted acid sites of the support.