A novel large-pore framework titanium silicate catalyst Paula Branda ˜o, a Anabela Valente, a Andreas Philippou, b Artur Ferreira, c Michael W. Anderson b and Joa ˜o Rocha* a a Department of Chemistry, University of Aveiro, 3810-193 Aveiro, Portugal. E-mail: rocha@dq.ua.pt b Department of Chemistry, UMIST, PO Box 88, Manchester, UK M60 1QD c ESTGA, University of Aveiro, 3810-193 Aveiro, Portugal Received 29th April 2002, Accepted 2nd October 2002 First published as an Advance Article on the web 15th October 2002 The synthesis and characterisation of AM-18 (Aveiro-Manchester structure number 18), a large-pore framework sodium titanium silicate catalyst, is reported. The as-synthesised material was characterised by powder X-ray diffraction (XRD), thermogravimetry (TGA) and differential thermal analysis (DTA), scanning electron microscopy (SEM) and chemical analysis by energy dispersive analysis of X-rays (EDAX), nitrogen and benzene adsorption measurements, 23 Na triple-quantum (MQ) magic angle-spinning (MAS) and 29 Si MAS NMR, Fourier transform infrared (FTIR) and Raman spectroscopies. The latter two techniques indicate that this novel titanium silicate may contain five-coordinated titanium. AM-18 shows high thermostability (in excess of 650 uC). Isopropanol conversion was used as a model reaction to study the acid–base properties of as-synthesised AM-18. This material exhibits high catalytic activity (71% conversion) and selectivity for propene (74%). Introduction Since the discovery of TS-1, an excellent catalyst for a wide range of selective oxidation reactions with aqueous H 2 O 2 as oxidant, 1 titanium has been incorporated into the frame- work of several zeolites 2,3 and mesoporous materials. 4-7 In all these materials titanium is tetrahedrally-coordinated to oxygen. Later, a new family of microporous silicates possess- ing framework Ti(IV) in octahedral coordination and known as ETS (Engelhard titanium silicate) materials, has been reported. 8,9 This early work stimulated research into the synthesis and characterisation of novel mixed octahedral– tetrahedral framework silicates. 10 A much smaller class of titanium silicates are those formed by tetrahedral silicon and five-coordinated titanium. AM-1 11 or JDF-L1 12 and ETS-4 13 are the only synthetic titanium silicates containing titanium in such coordination. AM-1 and JDF-L1, with a composition Na 4 Ti 2 Si 8 O 22 ?4H 2 O, is an unusual non-centrosymmetric tetra- gonal layered solid that contains five-coordinated Ti(IV) ions in the form of TiO 5 square pyramids in which each of the vertices of the base is linked to SiO 4 tetrahedra to form continuous sheets. ETS-4, a microporous material, is essentially the synthe- tic analogue of the mineral zorite. 14 It contains O–Ti(IV)–O chains, where titanium is coordinated to five or six oxygen atoms. In recent years we have been interested in the synthesis of open framework metal silicates with potential applications in adsorption, separation, catalysis and ion exchange, particularly vanadium, 15,16 zirconium, 17 niobium 18–20 and tin silicates. 21 We now wish to report on the synthesis and characterisation of a novel large-pore titanium silicate named AM-18 (Aveiro- Manchester structure number 18). Infrared and Raman spectroscopies suggest that AM-18 possesses five-coordinated framework Ti. Accordingly, AM-18 together with AM-1 and ETS-4 are the only three synthetic titanium silicate materials containing Ti in such a coordination. In addition, the presence of some six-coordinated Ti in AM-18 can not be discarded. Experimental Synthesis of AM-18 The synthesis of AM-18 was carried out in teflon-lined autoclaves under static hydrothermal conditions. An alkaline solution was prepared by mixing 5.00 g sodium silicate solution (Merck), 15.22 g H 2 O, 1.33 g NaOH (Merck). 5.82 g TiCl 3 solution (10% in HCl, Merck) was added to that solution and stirred thoroughly. This gel with a molar composition of 2.9 Na 2 O : 4.0 SiO 2 : TiO 2 : 149.7 H 2 O, was autoclaved for 2 days at 230 uC without agitation. The solid was filtered, washed with distilled water and dried at room temperature, giving an off-white microcrystalline powder. Characterisation Powder XRD data were collected on an X’Pert MPD Philips diffractometer (CuK a X-radiation) with a curved graphite monochromator, an automatic divergence slit (irradiated length 20.00 mm), a progressive receiving slit (slit’s height 0.05 mm) and a flat plate sample holder, in a Bragg–Brentano para-focusing optics configuration. Intensity data were col- lected by the step counting method (step 0.02u, time 38 s) in the range 2h 3–32u. X-ray diffraction pattern auto-indexing was performed with the CRYSFIRE System 22 from the resolved first 20 lines and checked with the Chekcell package. 23 SEM images were recorded on a Hitachi S-4100 Field Emission Gun tungsten filament working with a voltage of 25000 V. The chemical composition was determined by energy dispersive analysis of X-rays (EDAX). TGA and DTA analyses were carried out in a SDT 2960 simultaneous DTA-TGA thermal analyser 2000 TA instrument. The sample was heated in air with a rate of 10 uC min 21 . Nitrogen adsorption mea- surements at 77 K were performed using a Micromeritics ASAP 2010 V1.01 B automatic instrument. Pore size distribu- tions were determined using the density-functional theory (DFT) Plus Software for data files generated from the ASAP instrument. Adsorption of benzene, m-xylene and mesitylene was measured at 298 K, using a gravimetric adsorption appa- ratus equipped with a CI electronic MK2-M5 microbalance and an Edwards Barocel pressure sensor. Before adsorptions measurements, the sample was outgassed overnight at 573 K. 29 Si and 23 Na solid-state NMR spectra were recorded at 79.49 and 105.81 MHz (9.4 T) on a Bruker Avance 400 spectro- meter. 29 Si magic angle spinning (MAS) NMR spectrum was measured with 40u pulses, a spinning rate of 5.0 kHz, and a recycle delay of 35 s. Chemical shifts are quoted in ppm from DOI: 10.1039/b204135a J. Mater. Chem., 2002, 12, 3819–3822 3819 This journal is # The Royal Society of Chemistry 2002