Catalytic Properties of Unsupported Catalysts Based on Transition Metal Phosphides in Hydrotreating of Pyrolysis Products of Chlorinated Polymer Wastes

Nickel, cobalt, molybdenum, tungsten, and iron phosphides were prepared in situ from oil-soluble precursors and red phosphorus in the presence of a chlorinated substrate, 1,4-dichlorobenzene. Their catalytic activity was studied in competing processes of the hydrogenolysis of model feedstock containing a chlorinated derivative (1,4-dichlorobenzene) and heteroatomic compounds (benzothiophene, guaiacol, terephthalic acid, quinoline). Analysis of the phase composition of the catalysts by X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) confirmed the formation of the phases of the metal phosphides, chlorides, and phosphates. The activity of the phosphides in the 1,4-dichlorobenzene hydrodechlorination increases in the order Mo < Fe < W < Co < Ni, and that in the joint process of 1,4-dichlorobenzene hydrodechlorination and benzothiophene hydrodesulfurization, in the order Co < W < Fe ≈ Ni < Mo. In the hydrodechlorination of 1,4-dichlorobenzene in a mixture with guaiacol, the activity of all the phosphides except iron phosphide decreases as compared to the 1,4-dichlorobenzene hydrodechlorination in the single-component system. Iron phosphide shows promise as a protective bed catalyst in the hydrotreating of polymer waste pyrolysis products, and nickel phosphide, as a catalyst for the hydrotreating of products formed by pyrolysis of polyvinyl chloride in polymer waste mixtures.