4
4
G.-P. Yong et al. / Journal of Molecular Catalysis A: Chemical 323 (2010) 40–44
catalytic action is dependent on the Ag-nanoparticles size (Table 3).
The maximum reaction yield has been observed for an average
Ag-nanoparticle size of about 8 nm, because Ag-nanoparticles with
average size of 7 nm show more excellent catalytic activity [58].
With a decrease in particle size, a trend of decreasing reaction yield
has been found for Ag-nanoparticle size of less than 8 nm, even if
the catalytic amount of AgSBA-15-2 catalyst (particle size ∼4–5 nm)
was increased in order to make Ag content up to 6.78%, which was
similar to the Ag content (6.86%) of AgSBA-15-6 catalyst (particle
size ∼8 nm). Furthermore, those above 8 nm also show a steady
decline of reaction yield with increasing Ag-nanoparticles size. It
has been postulated that in the case of particles of average size
less than 8 nm, a downward shift of the Fermi level takes place,
with a consequent increase of band gap energy. As a result, the
particles require more energy to pump electrons to the adsorbed
ions for electron transfer reaction [44]. This leads to a reduction
in reaction yield when catalyzed by smaller particles. As for Ag-
nanoparticles larger than 8 nm, the decrease in catalytic efficiency
could be ascribed to less adsorption surface area with increasing
particle size. From Table 3, it is also found that with similar Ag-
nanoparticles size (AgSBA-15-3–AgSBA-15-6), the reaction yield
increases with increasing Ag content.
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Appendix A. Supplementary data
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1