Potential catalysts for the production of NaClO3 in the decomposition of HOCl

By pursuing the aim of identifying new types of catalysts in the electrolytic production of NaClO3 from NaCl (chlorate process), we report a detailed study on the decomposition of hypochlorous acid accelerated by yttrium(III) chloride (YCl3), yttrium(III) oxide (Y2O3) and telluric acid (Te(OH)(6)) at 80 degrees C. The results were compared with those obtained in the uncatalyzed and chromium(VI) catalyzed reactions. In general, the decomposition of HOCl occurs via two competing paths toward the formation of ClO3- or O-2. In the case of YCl3, the decomposition proceeds via the oxygen path over the entire studied pH range. Y2O3 slightly catalyzes the chlorate path under acidic conditions, however the noted catalytic effect is probably due to the self-buffering of the reaction mixture (Y2O3 suspension). Although, a real catalytic process takes place in the presence of Te(OH)(6), a significant pH-effect is also observed which is most likely associated with the acid-base equilibria of telluric acid. pH dependent studies demonstrate that the optimum pH of decomposition is at around 6.7-6.9 in this case. The comparison of the results obtained in the presence of chromium(VI) and Te(OH)(6) reveals that the former is a more active catalyst. On the basis of kinetic and stoichiometric results, it is reasonable to assume that Te(OH)(6) may be utilized as an alternative catalyst in the chlorate process. (C) 2021 The Author(s). Published by Elsevier B.V. on behalf of Institution of Chemical Engineers.

Automated summary

This study investigates the decomposition of hypochlorous acid accelerated by various catalysts in the electrolytic production of NaClO3. It is found that Y2O3 and Te(OH)(6) might serve as alternative catalysts in the chlorate process, with chromium(VI) being more active. The decomposition of HOCl occurs via chlorate or oxygen pathways, with an optimum pH of around 6.7-6.9.