I was fooling around with string diagrams in a monoidal category and I was thinking about them in terms of chemical reactions. I wondered about bending a wire around and attaching it to the input of the box it came out of. I realized that what I was looking at was a catalyst. I then drew a box with many inputs but only one output and saew that this was an autocatalytic reaction. In this reaction, the product is something necessary for the input. I know that closed loops in the string diagrams are traces. Has anyone seen a paper where traces are seen as catalysts? Has anyone seen work on chemistry using string diagrams in amonoidal category?