My son got into Purdue 3 years ago and merit came with the offer - but honestly we were surprised it came at all given most everything we read said for engineering at least, the merit awards were minimal in quantity.
My daughter goes to another public and got merit with admission. She then got more merit via the Honors College - after she accepted -but this was in the form of endowed scholarships and she had to participate in an interview weekend to get them.
Congrats on your admission to Purdue - assume you are full pay (but they’re a wonderful “value” - and enjoy your four years) - and as others say, keep an eye open each year for what is offered to returning students via academic and other departments.