PURPOSE:To accomplish effective removal of tree chlorine in hydrochloric acid. CONSTITUTION:Firstly, a coating liquid is prepared by mixing (A) a solution formed by dissolving a platinum salt in an organic solvent and (B) a dispersion medium containing fluororesin powder, and a fluororesin substrate is then coated with this liquid followed by drying and heating, thus obtaining a reductive catalyst where platinum main particles are deposited, through fluororesin subordinate particles, onto the substrate. Thence, a fixed bed 6 is formed in a treatment column 5 using this catalyst, and fed with a hydrochloric acid solution 51 from above along with a hydrogen gas 8 from below. The catalyst, with the numerous fluororesin subordinate particles attached to the surface of the platinum main particles, is broad in reactive region, and since the main particles are deposited onto the substrate, free chlorine in the hydrochloric acid can be removed effectively for a long period of time.
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