HYDRODECHLORINATION OF CFC 114a OVER Pd
357
chloride, suggested that hydrodechlorination reactions may
be structure insensitive on group VIII metals.
It is surprising that sulfur modifies the reaction selectivity
when changes in the catalyst morphology will not affect the
A comparison of our rates with reaction rates reported rates. The fact that it affects the selectivities of a structure
in the literature was difficult because there are not many insensitive reaction is an indication that sulfur is changing
studies reported for CFC 114a on Pd. Gervasutti et al. (15) the binding energies of the reaction intermediates.
also studied hydrodechlorination of CFC 114a, but these
5. CONCLUSION
authors did not report a turnover rate, making a compari-
son with our rates very difficult. Karpinski et al. (16) studied
The reaction of hydrodechlorination of 1,1-dichloro-
this reaction on Pd supported on alumina, but their reac-
tetrafluoroethane is insensitive to the structure of the Pd
catalyst. This result implies that the rates of hydrodechlo-
rination will be proportional to the total Pd surface area.
Sulfur decreases the rates of all products, but it decreases
tion order in HCl appears to be zero, as it is apparent from
the contact time versus conversion plot, and not ꢄ1 order
in HCl as in this case. Thus a comparison cannot be made
in this case since the reaction chemistry seems to be very
the rate of HFC 134a more strongly than the other two
different on alumina-supported samples. Another possibil-
products, thus decreasing the reaction selectivity for this
ity for comparison is to use the rate data for similar CFCs.
most desirable product.
However, this is difficult because the rate is highly depen-
dent on the distribution of halogens in the molecule, and
there is no correlation available to account for these differ-
ACKNOWLEDGMENTS
ences.
This research was supported by the Laboratory Technology Research
Comparison of activation energies is also difficult for the
same reasons discussed above for the turnover rates. The
only additional comment is that if the inhibition by HCl is
not accounted for in the calculation of the rate constant,
the resulting Arrhenius plot (usually obtained by varying
the temperature and keeping the other variables constant)
will produce an “apparent activation energy” that will be
two times lower than the one with the HCl effect accounted
for. In other words, the rates will appear not to increase as
much as expected with the temperature due to the effect of
HCl. The activation energies here are higher than the ones
observed by Karpinski et al. (16) by a factor of almost two
but the difference may be again related to the alumina sup-
port. It appears that the activation energy increases with the
number of halogen atoms that are removed from the reac-
tant (Table 3). The mechanism advanced from the foil data
for the two most abundant products (134a and 124) (2) has
a common rate-determining step for these two compounds
and thus the activation energies should be the same. More
experiments are necessary to decide if there is a trend of
Program (ER-LTR), Office of Computational and Technology Research,
U.S. Department of Energy under a CRADA (Cooperative Research and
Development Agreement) between Ernest Orlando Lawrence Berkeley
National Laboratory (LBNL) and E.I. DuPont de Nemours and Company,
Wilmington, Delaware, under U.S. D.O.E. Contract DE-AC03-76SF00098.
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