Acetylene, hydrogenation studies competitive

The hydrogenation of phenyl acetylene, over both catalysts, and 1-phenyl-1-propyne, over the carbon supported catalyst, was performed in the absence of any other species to obtain a reference reaction profile. For both phenyl acetylene and 1-phenyl-1-propyne the order of reaction was zero. In the case of the competitive reactions the reaction of equimolar quantities of trans 1-phenyl-1-propene and 1-phenyl-1-propyne, equimolar quantities of phenyl acetylene and styrene, equimolar quantities of phenyl acetylene and benzonitrile, and equimolar quantities of 1-phenyl-1-propyne and benzonitrile, were studied over the Pd/Carbon catalyst. Only the equimolar reaction of phenyl acetylene and styrene was examined over the Pd/Zr02 catalyst (Figure 1). The same data for the Pd/Carbon catalyst is plotted in Figure 2. In each case 0.4 ml of each reactant was charged to the reactor at 303 K, and the reaction followed over a 1 h period. The effect of the co-adsorbates on activity is shown in Table 1. While the effect on selectivity is shown in Table 2. 

The observed competition among addition and the various abstraction reactions shows that more detailed studies of the variation in H F yield, or in diminution of the CH2=CH F yield can provide relative rate constants for these reactions. The substitution of other RH molecules for methane can then permit the extension of such relative rate constant measurements to many molecules. For example, flie relative rate constants for hydrogen atom abstraction by thermal F atoms from acetylene and methane are 0.06 and 0.11 per hydrogen atom, respectively ( ),a factor of nearly two. 

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