All regular ground coffees are acceptable for Passover use when bearing an OU.
Decaffeinated coffee:
Coffee is often decaffeinated by means of ethyl acetate, which is derived from either kitniyot or chometz. Therefore, decaffeinated coffees are not acceptable for Passover unless specifically listed in the gray pages of our Passover guide (section which contains items that to not require Passover certification).
Instant coffees often contain maltodextrin, which is derived from either corn (kitniyot) or wheat (chometz). Therefore, all instant coffees require special Passover certification unless explicitly mentioned in the grey pages (section in our Passover Guide that lists items that do not require Passover certification).