Synthesis and catalytic activity of Ti-ITQ-7: a new oxidation catalyst with a
three-dimensional system of large pore channels
María-José Díaz-Cabañas, Luis A. Villaescusa† and Miguel A. Camblor*
Instituto de Tecnología Química (CSIC-UPV), Avda. Los Naranjos s/n, 46022 Valencia, Spain.
E-mail: macamblo@itq.upv.es
Received (in Oxford, UK) 18th January 2000, Accepted 28th March 2000
Isomorphous substitution of Si by Ti in the framework of
ITQ-7, the crystalline silica polymorph of lowest density, has
been achieved by direct synthesis, affording its three
dimensional system of large pore channels to be used in
selective oxidation reactions.
composition of the gel was SiO2+0.05 TiO2+0.10 H2O2+0.5
SDAOH+0.50 HF+3 H2O. The mixture was poured into Teflon-
lined stainless steel autoclaves and crystallised under rotation at
150 °C for 12 days (yield: 27.48 g Ti-ITQ-7 per 100 g synthesis
mixture; Si/Ti ratio of Ti-ITQ-7+120). The solid presents an
XRD pattern characteristic of zeolite ITQ-7 and, in order to
remove its guest species, it can be calcined to 580 °C without
structural damage (Fig. 1).
After the discovery of the medium pore zeolite TS-11 and of its
outstanding properties as a catalyst for the selective oxidation of
organic compounds with aqueous hydrogen peroxide,2 the
isomorphous substitution of Si by Ti in zeolites has received
much attention.3 Aside from a fundamental interest in under-
standing the remarkable catalytic properties of TS-1, there has
been a considerable effort in making new Ti-zeolites that could
enlarge the field of application of these materials in industrially
important oxidation reactions. Within this aim, the search for
catalysts with larger pores allowing processing of larger
molecules and/or the use of oxidising agents larger than H2O2
has been particularly relevant. New materials with larger pores
such as zeolite Ti-beta4 and the non-zeolite mesoporous Ti-
MCM-415 have been developed and their catalytic properties
tested. Although those materials, particularly Ti-beta, have clear
advantages from the point of view of pore size, they are also
intrinsically less active than TS-1. Very interestingly, Ti-beta
presents peculiar differences in catalytic properties when
compared to TS-1 (with regard to catalytic behaviour in
different solvents and selectivity in the epoxidation of olefins
and in the hydroxylation of phenol) which appear to be due to
the different crystalline structure of both materials6 rather than
to differences in their hydrophobicity, Al content or degree of
isolation of Ti in tetrahedral positions as initially assumed.
Unfortunately, a detailed structural investigation of those
differences is hindered by the very complex, severely inter-
grown nature of the structure of zeolite beta.7 Here, we present
Ti-ITQ-7 (structure code ISV), a new three dimensional large
pore zeolite which presents a more ordered structure than
zeolite beta.8 In addition to the opportunities that Ti-ITQ-7 may
offer in the investigation of the structure/activity/selectivity
relationships in Ti-zeolites, its distinct pore architecture could
give rise to differences in its catalytic performance when
compared to Ti-beta.
In the absence of seeds, the crystallisation of Ti-ITQ-7 in the
presence of relatively high Ti contents (Si/Ti ≤ 30) does not
proceed to completion: while the zeolite nucleates and starts
growing, the crystallisation stops at certain point and the
partially crystallised solid remains essentially unchanged by
powder XRD even if heating is extended for an additional
month. At present we do not have a clear explanation for this
observation, which appears difficult to rationalise given that Ti-
ITQ-7 may be crystallised from gels with even higher Ti
contents if seeds are used (see example above). For Si/Ti ratios
of 50 or above in the starting gel, no seeds are required.
The isomorphous substitution of Si by Ti in the framework of
ITQ-7 (the crystalline silica polymorph of lowest density known
to date)8 has been confirmed by the usual techniques. The
diffuse reflectance UV spectra of calcined Ti-ITQ-7 sample
(Fig. 2) show a band at 205–220 nm, typically assigned to a
electronic transition with ligand to metal charge transfer
character involving isolated Ti in the framework of zeolites.9
Only for TiO2 contents of 1.1% or above, does the band have a
tail at high wavelength which suggests the presence of a small
amount of TiO2 anatase. The IR spectra of the calcined
materials in the region of framework vibrations show a band at
960 cm21, characteristic of Ti-zeolites and assigned to the Si–O
stretching in Si–O–Ti groups.10
The activity and selectivity of Ti-ITQ-7 in the selective
epoxidation of hex-1-ene with H2O2 was tested and compared to
the performance of aluminium-free Ti-beta synthesised in
fluoride media6 (Table 1). Three main conclusions may be
derived from the results in Table 1. First, the activity and
selectivity of Ti-ITQ-7 for the oxidation of this alkene is
equivalent to that of Ti-beta with similar Ti content. Second, the
Ti-ITQ-7 can be prepared in conditions similar to those
described for the pure silica polymorph,8 by first cohydrolyzing
tetraethylorthotitanate (TEOTi) and tetraethylorthosilicate
(TEOS) in an aqueous solution of the hydroxide form of the
structure directing agent (SDA) 1,3,3-trimethyl-6-azonium-
tricyclo[3.2.1.46,6]dodecane. Crystallites of ITQ-7 may be
added as seeds to promote the crystallisation. In a typical
synthesis, 0.76 g TEOTi and 13.87 g TEOS were hydrolysed in
27.77 g of a solution of the hydroxide form of the SDA (1.0
mol kg21). Then, 0.65 g H2O2 (aq. 35 wt.%) were added and the
mixture was stirred at room temperature allowing evaporation
of all the ethanol and of the water needed to obtain the final
composition given below. Then, 1.38 g HF (aq. 48 wt.%) were
added before the final addition of a suspension of SiO2 ITQ-7
crystallites in water (0.20 g zeolite, 2.50 g water). The final
† Current address: School of Chemistry, University of St. Andrews, St.
Andrews, UK KY16 9ST.
Fig. 1 X-Ray diffractograms of (from bottom to top) as-made and calcined
Ti-ITQ-7 and as-made Ti-beta (TiO2 contents: 1.24, 1.24 and 1.40%).
DOI: 10.1039/b000539h
Chem. Commun., 2000, 761–762
This journal is © The Royal Society of Chemistry 2000
761
Diaz-Cabanas, Maria-Jose
