Site versus solid species

Suzy

As explained a few posts earlier, I am working on a catalytic combustion problem. The only tutorials on surface reaction I can find, however, are for CVD.

In the Fluent sponsored tutorial 15 (on CVD). They use both solid, site, and gaseous forms of Ga and As.

Since I am not interested in deposition on the surface do I need solid species?

Any explanation on the differences between solid and site species in relation to surface reaction would be appreciated.