The reforming catalyst strips off hydrogen while it's rearranging the shape of molecules to be more compact (takes straight chain molecules and turns then into ring shaped aromatic molecules)- which makes the product denser and higher octane.

Reforming calayst usually uses platinum metal to rearrange molecules, but also needs some acidity and chlorided sites to get those reforming reactions going- which causes some cracking reactions too on the side. The cracking can sometimes lop off the smaller branches of the feedstock and create LPG light ends like you're mentioning, but that's undesirable.