Many
studies have been conducted on core–shell structured
nanocatalysts thanks to their high thermal and physical stability.
However, for a typical core–shell structure, shell thickness
and pore size that affect mass transfer through the shell are difficult
to control. Herein, we synthesized a different type of core–shell
catalyst, in which a mesoporous silica shell encapsulates the Pd-nanocrystals-grafted-SiO2 nanobeads. With the preparation method introduced, we successfully
controlled the thickness of the shell layer and generated a mesoporous
texture over the shell layer. In activity tests, the production rate
of hydrogen peroxide significantly increased when using the mesoporous
shell catalyst over the microporous shell catalyst of similar shell
thickness. The thickening of the mesoporous shell layer reduced the
production rate of hydrogen peroxide. Thus, the thinner the thickness
of a mesoporous shell, the more favorable in terms of pore-diffusion
rate. However, the shell thickness should be adequately adjusted,
because an extremely thin shell layer cannot protect the core Pd crystals
from thermal agglomeration in a calcination and reduction process.