With the Bachelor's thesis at the end of your studies, you show that you can work independently on a problem at the interface of Mathematics and sustainable Chemistry.
The Bachelor's project is usually carried out in the last semester of the degree course; the exact conditions for registration can be found in the examination regulations.
Your project can be both theoretical and practical in nature, and collaboration with a company is also possible - as a student, you can propose a topic yourself.
It is best to find out early on (i.e. a few months in advance) in your desired subject areas on which topic and at what time a Bachelor's project can be carried out and supervised so that nothing stands in the way of a smooth process. As soon as everything has been clarified and your (laboratory) workstation is ready, the project can be registered with the examination board.
Good luck! :)