Acetylene coupling with ethylene dichloride, which uses both coal and oil resources, is attractive for sustainable PVC manufacturing. Herein, highly active and stable carbon nitride-based catalysts were developed by a novel pre-oxidation-pyrolysis process, affording unprecedented dehydrochlorination activity with good durability. The best-performing system was further modified with different precious metals (Au, Pt, and Ru) to promote the hydrochlorination chemistry between the in-situ formed hydrogen chloride and acetylene co-feed. The presence of metal centers intensifies the hydrochlorination activity but weakens the dehydrochlorination ability due to competitive adsorption between the two reactants at the metal sites. Superior coupling performance was achieved over C₃N₄/AC and single-atom Au/C₃N₄/AC catalysts in cascade reactors. Our results strongly suggest that dehydrochlorination is an essential step in the coupling reaction, and the activation of acetylene and ethylene dichloride molecules requires different active sites that should be engineered in future work.