The word "than" always involves a comparison form -- either an "er" on a word or the words "more" or "less." It can only compare.
...larger than that...
...louder than I thought...
...wiser than I...
...more comfortable than that one...
...more appropriate than what he said...
...more suitable than what she chose...
Since "different" has no comparison form, it has to be "different from."
Happy punctuating!
Margie