Catalonia has had a republican government during the following times:
- In 1641, during a insurrection (called The Reaper's War) against King Philip IV, the Catalan Courts proclaimed a republic that would rely on French Protection to keep its independence. A week later, the very same courts proclaimed the French King (Louis XIII) as Count of Barcelona (the title of the sovereign of Catalonia) - thus, ending the independent republic.
- In 1873, the first Spanish Republic was proclaimed, and Catalonia - as the rest of Spain - would be under republican government until the end of this Republic, in 1874.
- In 1931, the Second Spanish Republic was proclaimed, and Catalonia, again, had a republican government. With the partially failed coup-of-state of June 1936, Spain went to suffer a civil war that the Republican government lost. Catalonia was fully lost to the republicans by Feb 1939.
- Also, during the Second Spanish Republic, powers were devolved to some of the regions/nationalities/lands (the use of any word in this context is loaded with bias towards one side or the other) of Spain. As such, there was a government in Catalonia. The president of that government proclaimed the Catalan State in the form of a republic in 6 Oct 1934. He military govern of the region sent troops that ended this republic by 7 Oct 1934.
Also, although a republic was not formally proclaimed, you have the War of Spanish Succession, where Catalonia supported the candidate of the House of Austria, Leopold, against King Philip V. Once that it was clear that no more support could be expected from Leopold, the rebels against Philip V agitated for an independent republic - and England put such a clause in its peace proposal, although it was quickly dropped.
So as you can see, there has been at least two official proclamations of a independent republic (1641, 1934) that lasted for a few days (7 days, 1 day) and two longer republics (1 year, 8 years) in common with the rest of Spain.
Now, without the source, I can't really understand to which republic that comment was referring to.
Note: I have not mentioned the proclamation of a Catalan Republic in 2017. Speaking of that would break the 20-years rule of this subredit.