ACETYLENE DEUTERATION IN THE PRESENCE OF 14C-ETHYLENE.

The double labeling method, using both a radioactive **1**4C tracer and deuterium gas clearly demonstrated the reaction behavior involved in acetylene hydrogenation over Pd. This demonstration involved use of a static system, an interfaced GS-MS, and splitting the effluent from a GC column into three streams for analysis, radioactivity measurement and deuterium distribution. The method is cumbersome to operate, but to compensate, the results are all obtained at the same state of catalyst surface, precluding the possibility of a system difference resulting in the change in the ratio of different surface reactions. On the Pd black catalyst the authors used for the hydrogenation of ethylene and of acetylene, results could be rationalized by type of site. The ethane formed initially is a result of a parallel reaction of acetylene to ethane and ethylene. With the labeling technique, they established unambiguously that the rate of ethylene desorption is much faster than its further reaction on the surface to form ethane. Thus r//s//3 does exist.