Anime

But also how did he make that platinum coil? It has a melting point of 1772°C, so that can't possibly be fused together with the tools he had.

If you have the pure metals, then you can join pieces by getting them hot. In the case of platinum, it's highly ductile so you can cold work the pieces together. For the purposes of a catalyst, you don't even need to join them together; the key is to expose as much surface area as possible. It would actually better to shave it into smaller pieces. However, the Ostwald process reacts gaseous ammonia at a specific temperature so it makes sense that the platinum is suspended as a coil; to allow even air flow and to only catalyze the reaction with the gaseous form.

The documentation calls for 10% rhodium, but that is apparently to prevent the degradation of the catalyst.