The chemistry of diiodomethane is explored in ultrahigh vacuum on a MoAl alloy film grown on planar, dehydroxylated alumina by reaction with molybdenum hexacarbonyl. The majority of the diiodomethane forms methylene species below similar to 250 K, although a small proportion forms CH2I(ads), which hydrogenates to form iodomethane. The majority (similar to 90%) of the adsorbed methylene species thermally decomposes to carbon and hydrogen. The remainder undergoes several reactions, including partial hydrogenation to form adsorbed methyl species or total hydrogenation to form methane. The methyl species can couple forming ethane or undergo methylene insertion reactions to form alkyl species UP to C-4. These form alkenes via a beta-hydride elimination reaction. This chemistry is relatively unique, only having been found previously for Ni(110) surfaces. No such chemistry is found on Ni(100) and Ni(111).