Catalonian government is a region body government under the Spanish rule. It can't pass laws that are not under their competence and overpass the Spanish Constitution. It doesn't have control of territory, frontiers, taxes and things like that.
It's not a persecuted group under a dictatorship persecution, so it can't ask for international recognition and support.
On the worst case politicians going against Spanish laws can be treated as traitors (see Manning or Snowden in USA).
So, only with the agreement of all Spain, Catalonia can become independent. What would be a reasonable path for Catalonian independence?