Pressboard is bonded with urea formaldehyde resin. Ammonia probably was not the best thing for that resin bond. I don't think sophisticated chemistry is going to get the job done. Remove the panel and seal it with a urethane or alkyd primer (oil base paint). The odor will be sealed, and the panel can be cleaned in the future as needed. If neutraliztion is attempted you would need an acid to react with ammonaia, but I am concerned it would weaken the board. The coating should help matters anyway and prevent further deterioration.