He then joined the research group of H. I. Schlesinger and H. C. Brown to synthesize volatile uranium compounds that might be useful for gaseous diffusion of 235U from 238U.
At the end of World War II, Winston M. Manning, another Metallurgical Laboratory chemist who was a planner of the new institution that was to replace that wartime laboratory, asked Katz to join the staff of the new Argonne National Laboratory.