The explosive payload is 18,700 pounds of H6, a mixture of RDX, TNT, and aluminum. H6 is an Australian produced explosive composition, widely used for underwater blast weapons such as mines, depth charges, torpedoes and mine disposal charges. HBX compositions (HBX-1, HBX-3, and H6) explosives contain powdered aluminum; HBX-3 and H-6 having lower sensitivity to impact and much higher explosion test temperatures than previous aircraft bomb and naval underwater weapons explosive filler compounds.
The powdered aluminum(aluminum oxide) is the oxydizer. On further research I found that the MOAB is RDX based and not a true Fuel Air/Thermobaric weapon but has some characteristics of one.