216
J.A. Anderson et al. / Journal of Catalysis 261 (2009) 208–216
ences found between the impact of Bi (Fig. 4) and Pb (Fig. 6) infers
that Pb is not preferentially located at step and edge sites, in direct
conflict with previous [27] assumptions.
sites and these may be suppressed by modifiers such as Pb in the
Lindlar catalyst. The rates of the initial hexyne hydrogenations are
relatively unperturbed by either modifier. Bi and Pb each modify
selectivity in Pd-catalysed hexyne hydrogenation but their effects
are not the same.
4.3. Role of Pb vs. Bi
Acknowledgments
The use of 1-hexyne as a test reaction did not discriminate be-
tween Pb-containing Lindlar and Pb-free Pd/CaCO3 (Fig. 6) while
there is a stark contrast in behaviour between these two sam-
ples when the internal alkyne, 2-hexyne is selected as test reagent
We acknowledge fruitful discussions with Professors G.A. At-
tard and P.B. Wells, University of Cardiff and thank the College of
Physical Sciences, University of Aberdeen for providing a research
studentship (to J.M.). We thank Johnson Matthey for providing the
Pd salt employed in catalyst preparation and for the gift of the
Varian 3400 GC.
(
Fig. 7). This reaction, when compared in reaction profiles for 1%
Pd/Al2O3 and 5% Pd/Al2O3 (Fig. 8) show that the poorer dispersed
% loaded sample showed less desirable behaviour in that the rate
of conversion of cis-2-hexene to trans-2-hexane was relatively high
when compared to the better dispersed 1% sample). Addition of
5
(
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