Dr. Keenan joined the faculty of the university’s Department of Chemistry in 1949. He was a visiting scholar at Oak Ridge National Laboratory (1950–51) and a National Science Foundation Fellow at Cambridge University (1957–58, 1964–65). He served as associate dean of the College of Liberal Arts (1973–75) and as the first president of the reconstituted Faculty Senate in 1972–73. He was an expert in liquid ammonia chemistry, on which he published a number of papers; in the origins of the discipline of the philosophy of science, on which he conducted many years of research; and in innovative approaches to the teaching of chemistry. He was the coauthor of two textbooks: General College Chemistry (6th ed., 1980) and Fundamentals of College Chemistry (3rd ed., 1972), which made significant changes in the teaching of beginning chemistry. The textbooks were adopted in more than one thousand colleges and universities in the United States and abroad.
In 1969 he won an Alumni Outstanding Teaching Award and in 1979 received the Phi Eta Sigma Award for excellence in teaching. His intellectual contributions to the life of the university have been recognized by placement of a plaque in his honor on a faculty study.