AFAIK a marriage certificate is not a mandatory document for a Tier 4 Study visa application. It is essential to demonstrate that you have:
an unconditional offer of a place on a course with a licensed Tier 4 sponsor
enough money to support yourself and pay for your course – the amount will vary depending on your circumstances
knowledge of English
tuberculosis test results, if you’re from a country where this is required
The guidance states that you may also need to provide additional documents depending on your circumstances. UKVI may therefore ask for your marriage certificate if they deem it to be relevant and you don’t provide it with the application. If you’re not applying to bring your spouse with you as a dependent, they may not ask for it.