Can I sell my half of a duplex?

If your side is deeded separately than the other side -- then you should be able to sell your 1/2. Maybe contact the real estate agent that originally sold the unit to verify. I would strongly suggest letting your attached neighbor know you plan on selling -- maybe they would be interested in buying the other side for an income property or for a friend/family member.

How did you purchase it? Do you own both units? If they are deeded separately you should be able to sell your unit however you should verify this with the city and your title officer. You want to make sure they are in fact separate and their in no in lieu fee to convert to separate units. I would definitely let the neighbor know as they may be interested or know someone who is interested.