We recommended him as chairman.
推薦 is not the right word. It should be replaced with 推挙（すいきょ）.
推薦する means "to recommend A (usually products) to B (someone else). Therefore, 私達は彼を議長に推薦した means “We recommended him to the sitting Chairman”. The sitting Chairman was looking for a secretary, so we referred him to the Chairman. “He” is not the successor of the sitting Chairman.
推挙する means "to recommend A (person) as B (job position).
For more information about the difference, please refer to the definition by a reliable dictionary.