Catalysis Today 61 (2000) 49–54
Surface modified amorphous titanosilicate catalysts for
liquid phase epoxidation
R. Van Grieken
a,∗
, J.L. Sotelo
b
, C. Martos
a
, J.L.G. Fierro
c
,
M. López-Granados
c
, R. Mariscal
c
a
Department of Experimental Sciences and Engineering, Rey Juan Carlos University, 28933 Móstoles (Madrid), Spain
b
Department of Chemical Engineering, Complutense University of Madrid, 28040 Madrid, Spain
c
Institute of Catalysis and Petrochemistry, CSIC, Cantoblanco, 28049 Madrid, Spain
Abstract
Titanium-containing mesoporous silica has been prepared by silylation of mixed oxides obtained via sol–gel method.
These samples displayed enhanced activity in the epoxidation of styrene with Bu
t
OOH in comparison to normal xerogels
or other titanium-containing catalytic systems. The influence of the extension of the silylation reaction, as well as the use
of different silylating agents, have been investigated. Samples were characterised by FTIR, XRF,
29
Si-MAS NMR, diffuse
reflectance UV–Vis and N
2
adsorption–desorption isotherms, X-ray photoelectron spectroscopy (XPS) and FTIR of adsorbed
deuteroacetonitrile. The improvement in the catalytic activity achieved has been related to the removal of OH groups by means
of calcination or silylation treatments. © 2000 Elsevier Science B.V. All rights reserved.
Keywords: Amorphous titanosilicate; Epoxidation; Sol–gel method; Silylation reaction
1. Introduction
Epoxidation of olefins is a widely used process in
the chemical industry, since the epoxide functional
group is one of the most useful intermediates in
organic synthesis. Traditionally percarboxylic acids
have been employed in these processes. However,
this alternative presents several drawbacks such as
the use of corrosive conditions and the production of
pollutants with a considerable environmental impact.
To overcome these problems heterogeneous cataly-
sis is proposed as alternative. Among these systems,
zeolitic materials have been extensively studied, the
oxidation activity being provided by the incorporation
∗
Corresponding author. Tel.: +34-91-4887007;
fax: +34-91-6647490.
E-mail address: r.vangrieken@escet.vrjc.es (R. Van Grieken).
of transition metals with redox properties into the
solid framework (such as Ti-silicalite-1 [1] and Ti-
zetolite [2]) or grafting metal containing compounds
on the silica surface [3]. However, they present some
problems for the oxidation of bulk molecules with
organic peroxides due to the relatively small average
diameter of the channel system in the case of zeolites
and the possible leaching of the metal during the
reaction for grafted compounds.
Very promising catalytic systems are based on
amorphous materials obtained through the sol–gel
route [4] in which many variables could be manip-
ulated to obtain the desired properties in the solid.
Recently we have reported a simple method to obtain
selective catalysts for epoxidation with tert-butyl hy-
droperoxide (TBHP) by chemical modification of the
surface of a titania–silica gel by trimethylsilylation
[5]. This treatment not only allows the synthesis of
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