It appears Riot has updated the catalog.bin files, or they were updated; they come from their WebGL comics. I'll attach the catalog.bin file so you can take a look and, if possible, add support for converting it to .json.
https://assetcdn.rgpub.io/public/live/bundle-offload/09648726-b12b-45db-94b8-2af261880ea4/6971658d997a6a000800d969/comics-pipeline-1/WebGLBuild/StreamingAssets/aa/catalog.bin