All perfect praise be to Allah the Lord of the Worlds. May His peace and blessings be upon our Prophet Mohammad and upon all his family and companions.
It is no secret that a university grants a reward for the research paper which hasn`t been published in another journal. Thus, an already published research doesn`t entitle the researcher to receive another reward. Accordingly, you (Asker) aren`t entitled to receive a reward for your research from the university where you work. Moreover, as an honest Muslim, you are expected to tell the university where you work that the publication fees have already been covered by another academic organization. Therefore, it is unlawful for you to take for yourself the money, which the university has paid to cover publication expenses. You should remember that Nawwas bin Sam'an (May Allah be pleased with him) reported: I asked Messenger of Allah (PBUH) about virtue and sin, and he said: "Virtue is noble behaviour, and sin is that which creates doubt and you do not like people to know about it." [Related by Muslim]. And Allah The Almighty Knows Best.