I'm reading a lot about hydrogenation reactions and a lot of papers describe homolytic dissociation of hydrogen into two neutral radicals from interaction with Pd. That's fine, but some papers then say the hydrogen atom sits in octahedral sites on the palladium surface (and can also become sub-surface hydrides) while other papers say the dissociated hydrogen atom becomes a Pd-H hydride. Which is it? Or are they one and the same?
Diagrams sometimes show a hydrogen atom sitting in-between Pd atoms (in the lattice) while others show the hydrogen atoms sticking up out of the surface as a Pd-H. I cant find an answer as to what the differences are and what causes the different types of hydrogen interactions. Any help appreciated.