Chemistry Reference
In-Depth Information
(a)
(b)
0.31 nm
0.38 nm
2 nm
50 nm
(c)
(d)
0.39 nm
2 nm
50 nm
Figure 3.17 TEM images of fresh (a, b) and used (c, d) Pd
0
/CaF
2
catalysts for hydrodehalogenation
of CHClF
2
. (Reprinted with permission from [32] (2008) Elsevier Ltd.)
The two marked lattice distances correspond to two different phases. Within CaF
2
the
{111} lattice plane distance of d
111
¼
0.31(4) was determined and for the metallic Pd the
distance of the {100} lattice plane of d
100
¼
0.38(2). Only these two phases could be
detected in these and in other fresh samples investigated, giving evidence for the absence
of PdF
2
or PdCl
2
, all Pd is in the metallic state as had already derived from the XRD
patterns (see above). In case of the used catalyst (Figures 3.17 c and d) the lattice plane
distance of 0.39 nm does not rule out the possible formation of PdF
2
or PdO as result of the
highly corrosive reaction conditions [33].
Hydrodehalogenation, the selective replacement of halogen by hydrogen on saturated
halocarbons, depends on the strength of the C-X bond, the catalyst and the reaction
conditions. Thus, upon hydrodehalogenation of CHClF
2
C-C coupling products have
been observed using Ni catalysts [41], whereas only CH
3
F and CH
4
were obtained with
silica-supported Pd [42].
