If I understand what you're trying to say, none of your options makes complete sense, at least to me. Corporate patronage typically refers companies or corporations that make a decision to support financially a non-revenue associated cause or organization. For that reason, corporate patrons aren't typically appointed or named, per se, because it is the patron corporation itself that is making the decision to offer support.
So here's my suggestion:
"The XXX non-profit foundation welcomed (or announced) YYY, Inc., as a corporate patron"
There are some subtle but important things in here:
1. Corporate patrons are announced or welcomed, not appointed or even named (unless somehow the patronage is competitive and selective, which would be highly unusual, as most non-profits need all of the corporate patronage they can get).
2. Their is a plural possessive pronoun and so can't be used to refer back to a singular antecedent noun (XXX non-profit in this case). You wouldn't even want to use the gramatically correct alternative its, because this would suggest that XXX non-profit only has one corporate patron ... YYY, Inc.
Named isn't wrong here and you might see it used in this context from time to time. It's only a matter of what is MOST appropriate. So, if I'm being asked, I'd recommend announced or welcomed over named. Conversely, I'd very strongly advise against chosen or selected for the logical reasons I stated. MOST patronage deals aren't selective on the part of the target of the support, making those words illogical.