Your tank is too small for angelfish. For a single Angelfish you need 120 litres minimum, and the tank has to be a minimum of 18" tall. For a pair you need 200 litres plus.
What kind of catfish? There are thousands of species. Do you mean a pleco (700 species), cory (around 100 species or so), a syno, maybe something else entirely?
http://www.planetcatfish.com