The structure of NaY zeolite is known to break down at pH less than 2.8 [26]. In this study, even when the initial pH was 1.7, the solution pH reached a stable acidic value of 3 in less than 5 min after the addition of the NZVI/NaY catalyst. The NaY zeolite was still stable under such a pH condition. We did not observe any structural breakdown of zeolite in the catalytic reaction.