CHEMCATCHEM
HIGHLIGHTS
DOI: 10.1002/cctc.201402585
Multifunctional Solid Surfaces for Enhanced Catalysis
Ken Motokura*[a]
Multifunctional solid surfaces
can significantly enhance the
heterogeneous catalysis of or-
ganic reactions.[1] In particular,
the multifunctionalization of sur-
faces allows the accumulation of
several types of catalytically
active sites as well as fine-tuning
of hydrophilic and hydrophobic
regions around the active sites.
The accumulated multi-active
sites can promote both reaction
Scheme 1. a) Pd/TS-1 and b) Pd/SiO2@Ti-MS for the one-pot oxidation of sulfide using in situ-produced H2O2.[3b]
sequences (one-pot reaction)
and dual interactions of sub-
strate molecules, which lead to
an enhancement in the catalytic
activity and/or selectivity (synergistic catalysis). This Highlight
summarizes recent advances in multifunctionalized surfaces for
enhanced catalysis.
Oxidation of organic substrates with in situ-generated H2O2
from H2 and O2 has recently received much attention.[2] This
methodology helps circumvent several issues associated with
H2O2 synthesis, such as H2O2 decomposition by the catalyst
and separation from the reaction mixture. Several bifunctional
heterogeneous catalysts containing Pd or Au metals for H2O2
production and Ti or Fe sites for oxidation of organic com-
pounds have been studied previously.[2] For example, sulfide
oxidation is facilitated by in situ-produced H2O2 on Pd nano-
particles supported on titanium silicate-1 (TS-1), as shown in
Scheme 1a).
Scheme 2. One-pot oxidation of sulfide using in situ-produced H2O2.[3b]
Yamashita and co-workers reported Pd/SiO2@Ti-containing
mesoporous silica (MS) core–shell catalysts for the one-pot oxi-
dation of sulfide to sulfoxide using in situ-produced H2O2
(Scheme 1b).[3] High-resolution TEM analysis of the Pd/SiO2@Ti-
MS clearly indicates its core–shell structure, the presence of
mesopores at the shell, and Pd nanoparticles on the SiO2
core.[3b] H2O2 generated from H2 and O2 on Pd nanoparticles on
a SiO2 core reacts with sulfide substrates at the Ti site in MS
shells, producing sulfoxide. This core–shell catalyst showed
high oxidation activity compared with Pd/TS-1 (Scheme 2). In
addition, reference samples that consisted of Pd nanoparticles
in Ti-containing MS shells (SiO2@Pd/Ti-MS) showed a lower cat-
alytic performance than Pd/SiO2@Ti-MS. The main reason for
the high catalytic performance of Pd/SiO2@Ti-MS is the imme-
diate interaction between the generated H2O2 with the Ti site;
this prevents dispersion into the solvent and/or decomposi-
tion. The position of Pd nanoparticles, mesopore diameter, and
shell thickness of Pd/SiO2@Ti-MS can be precisely controlled to
achieve a high catalytic activity and selectivity. Additionally, hy-
drophobic modification of the Pd/SiO2@Ti-MS catalyst by trie-
thoxyfluorosilane can enhance the catalytic performances.[4] In-
troduction of fluorine into the Ti-MS shell accelerates both ad-
sorption of organic substrates into the mesopores and diffu-
sion of hydrophilic oxygenated products to the outside, result-
ing in improved catalytic activity. The efficient diffusion of
methyl phenyl sulfoxide increases the selectivity of the sulfox-
ide toward methyl phenyl sulfone.
Accumulation of several kinds of catalytically active sites on
the same solid surface enables the dual interactions between
substrate molecules and active sites. Several examples of the
synergistic catalysis between metal complexes or metal nano-
particles and organic functional groups on the same solid sur-
[a] Dr. K. Motokura
Department of Environmental Chemistry and Engineering
Tokyo Institute of Technology
4259 Nagatsuta-cho, Midori-ku, Yokohama, 226-8502 (Japan)
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemCatChem 2014, 6, 3067 – 3068 3067
Motokura, Ken
