Supported
Au25 clusters were prepared through the calcination
of Au25(SC12H25)18 on
hierarchically porous carbon nanosheets under vacuum at temperatures
in the range of 400–500 °C for 2–4 h. TEM and EXAFS
analyses revealed that the thiolate coverage on Au25 gradually
decreased with increasing calcination temperature and period and became
negligibly small when the calcination temperature exceeded 500 °C.
The catalysis of these Au25 clusters was studied for the
aerobic oxidation of benzyl alcohol. Interestingly, the selectivity
for benzaldehyde formation was remarkably improved with the increase
in the amount of residual thiolates on Au25, while the
activity was reduced. This observation is attributed to the dual roles
of the thiolates: the reduction of the oxidation ability of Au25 by electron withdrawal and the inhibition of the esterification
reaction on the cluster surface by site isolation.
The superior catalytic performance of amine-grafted hierarchical basic FAU-type zeolite nanosheets for the aldol condensation of 5-hydroxymethylfurfural (5-HMF) and acetone (Ac) has been achieved due to the synergistic effect of hierarchical structures, featuring basic active sites together with surface modification. This results in an unprecedented yield of 4-[5-(hydroxymethyl)furan-2-yl]but-3-en-2-one (HMB) close to 100%. The catalytic activity can be easily tuned by changing the degree of basicity corresponding to the nature of basic sites and surface modification.
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