A photolithographic method was developed for micropatterning of catalyst (ferroin) for the Belousov-Zhabotinsky (BZ) reaction on a cation-exchange membrane. The propagation of chemical waves through microgaps on a catalyst line was quantitatively investigated. When a periodic train of: chemical waves entered a microgap, the frequency of the chemical waves was converted into lower frequencies such as 1/2, 1/3, and 1/4 of the original frequency depending on the gap width. The firing number depended on the gap width and the original frequency of the chemical waves. The frequency conversion is explained in terms of the recovery time of the BZ reaction media.