of large coherence length with a variety of molecules of appropriate shape. No
research directing into this has, however, been communicated so far. Hence, this
field remains largely unexplored. Studies similar to those reported by Arletti et al. on
the high-pressure behavior of dye-ZL hybrid materials for fluorenone as a host, who
observed a remarkable resilience of the supramolecular organization of dye molecules hyper-confined in ZL channels, however, bear the potential for rapidly exploring this kind of new optical materials [49].
8 ZL as a Catalyst
It is remarkable that ZL, which can be used for protecting molecules from photochemically and thermally induced degradation by preventing diffusion controlled
processes and also by inhibiting intramolecular movements such as an intramolecular rotation which may result in an unstable conformation, has also the ability for
acting as an excellent support for catalytically active metal clusters. It has also the
ability for acting itself as a catalyst as, e.g., seen in the selective p-chlorination of
biphenyl in ZL [81] or as proactive agent to extend the lifetime of commercial
lubricants by protecting the performance additives from depletion and adsorbing the
acid formed during oxidation [197]. ZL has been investigated as support for catalytically active Pt [61, 68, 198]. Bimetallic PtSn particles supported by a ZL host
were found to exhibit higher activity and selectivity for isobutane dehydrogenation
and resistance to deactivation than simply Pt-based composites [62]. Cho et al.
observed that incorporation of tin into Pt cluster, consisting of 5–7 atoms inside
potassium ZL, changed the adsorption properties of hydrogen and xenon due to the
formation of bimetallic nanoparticles and caused an important improvement of
n-hexane aromatization. Their data show that cluster formation occurred without
pore blockage [63]. The hydrogenation of citral using Ru clusters prepared from
different precursors and supported by ZL was tested. Different selectivity depending
on the preparation procedures and, hence, also on the size and location of the Ru
clusters was observed [64]. It is well known that the final selectivity of an active
metal can be modified by employing an adequate support which interacts with the
metal or by adding a second component which acts as a promoter. This understanding has been used in a study regarding Pt clusters prepared in ZL hosts of varying
morphology and channel lengths. The authors observed that the morphology and the
channel length of ZL have important influence on the performance of Pt-ZL catalysts
used for the aromatization of n-octane. Catalysts with a larger fraction of small metal
clusters inside the pores were found to be more active for a longer time. The metal
distribution in the ZL is optimum for intermediate crystal size. When the crystal is
too long, Pt particles can be transported outside of the zeolite during the pretreatments. By contrast, when the crystal is too small, the outer surface area dominates,
and a large fraction of metal particles is deposited outside the pores [65]. The reason
for the exceptional catalytic performance of Pt-ZL composites suppressing coke
formation in aromatization of hexane has been elucidated by Davis et al. using
48
G. Calzaferri
research directing into this has, however, been communicated so far. Hence, this
field remains largely unexplored. Studies similar to those reported by Arletti et al. on
the high-pressure behavior of dye-ZL hybrid materials for fluorenone as a host, who
observed a remarkable resilience of the supramolecular organization of dye molecules hyper-confined in ZL channels, however, bear the potential for rapidly exploring this kind of new optical materials [49].
8 ZL as a Catalyst
It is remarkable that ZL, which can be used for protecting molecules from photochemically and thermally induced degradation by preventing diffusion controlled
processes and also by inhibiting intramolecular movements such as an intramolecular rotation which may result in an unstable conformation, has also the ability for
acting as an excellent support for catalytically active metal clusters. It has also the
ability for acting itself as a catalyst as, e.g., seen in the selective p-chlorination of
biphenyl in ZL [81] or as proactive agent to extend the lifetime of commercial
lubricants by protecting the performance additives from depletion and adsorbing the
acid formed during oxidation [197]. ZL has been investigated as support for catalytically active Pt [61, 68, 198]. Bimetallic PtSn particles supported by a ZL host
were found to exhibit higher activity and selectivity for isobutane dehydrogenation
and resistance to deactivation than simply Pt-based composites [62]. Cho et al.
observed that incorporation of tin into Pt cluster, consisting of 5–7 atoms inside
potassium ZL, changed the adsorption properties of hydrogen and xenon due to the
formation of bimetallic nanoparticles and caused an important improvement of
n-hexane aromatization. Their data show that cluster formation occurred without
pore blockage [63]. The hydrogenation of citral using Ru clusters prepared from
different precursors and supported by ZL was tested. Different selectivity depending
on the preparation procedures and, hence, also on the size and location of the Ru
clusters was observed [64]. It is well known that the final selectivity of an active
metal can be modified by employing an adequate support which interacts with the
metal or by adding a second component which acts as a promoter. This understanding has been used in a study regarding Pt clusters prepared in ZL hosts of varying
morphology and channel lengths. The authors observed that the morphology and the
channel length of ZL have important influence on the performance of Pt-ZL catalysts
used for the aromatization of n-octane. Catalysts with a larger fraction of small metal
clusters inside the pores were found to be more active for a longer time. The metal
distribution in the ZL is optimum for intermediate crystal size. When the crystal is
too long, Pt particles can be transported outside of the zeolite during the pretreatments. By contrast, when the crystal is too small, the outer surface area dominates,
and a large fraction of metal particles is deposited outside the pores [65]. The reason
for the exceptional catalytic performance of Pt-ZL composites suppressing coke
formation in aromatization of hexane has been elucidated by Davis et al. using
48
G. Calzaferri