(684d) Synthesis and Characterization of Tungsten Containing Ultra Large Pore Mesoporous Silicate KIT-6
Synthesis and characterization of tungsten containing ultra large pore mesoporous silicate KIT-6
Anand Ramanthana, Bala Subramaniama, Rajamanickam Maheswarib and Ulf Hanefeldc
aCenter for Environmentally Beneficial Catalysis, The University of Kansas, Lawrence, KS 66047, USA
bDepartment of Chemistry, Anna University, Chennai – 600025, India
cGebouw voor Scheikunde, Technische Universiteit Delft, Julianalaan 136, 2628 BL Delft, The Netherlands
Tungsten was incorporated into ultra large pore mesoporous silicate, KIT-6, via hydrothermal synthesis method using a Pluronic P123 triblock copolymer as the structure directing agent and n-butanol as additive. Four W-KIT-6 samples with Si/W ratio of 200, 100, 40 and 20 were prepared. Calcined W-KIT-6 samples were characterized by XRD, elemental analysis, N2 sorption, HR-TEM, FTIR, DR-UV-Vis and NH3-TPD. Cubic Ia3d structure was confirmed by presence of 211 reflections around 0.9° (2θ) in Low angle XRD. The incorporation of tungsten is inferred by a slight decrease in unit cell parameter with tungsten content [2,3]. The presence of crystalline WO3 was observed in high angle XRD for samples with Si/W ratio £ 40. Elemental analysis measured by instrumental neutron activation analysis (INAA) revealed that most of the tungsten in the synthesis gel was retained in to the KIT-6 silica matrix. W-KIT-6 samples showed a very high specific surface area of 780 – 930 m2/g with pore volume of 1.19 – 1.45 cm3/g and possessed a narrow pore size distribution of 6.4 – 6.7 nm. The BET surface area and pore volume decreased with increase in tungsten content. The presence of well-ordered cubic 3D mesopores of W-KIT-6 samples was seen by High resolution TEM studies. The average thickness of the wall is found to be 4–5 nm and the pore diameter is around 6-7 nm. This is in agreement with the results of the N2 adsorption study. The incorporation of tungsten was further evident by FTIR spectra which showed a band at 960 cm-1  representative for Si-O-M linkages (M = heteroatom). An intense band at 216 nm observed in Diffuse reflectance UV-Vis spectra confirm this findings, which is due to ligand to-metal charge transfer in isolated [WO4] tetrahedral species  and is a direct proof for the framework incorporation of tungsten species in silica framework. Existence of partially polymerized W species in octahedral coordination with low nuclearity is also observed in these spectra. NH3-TPD study revealed presence of low-medium acid strength sites in these samples.
 T.W. Kim, F. Kleitz, B. Paul and R. Ryoo, J. Am. Chem. Soc. 127 (2005) 7601.
 O. Klepel, W. Bohlman, E.B. Ivanov, V. Riede and H. Papp, Micropor. Mesopor. Mater. 76 (2004) 105.
 P. Trens, V. Stathopoulos, M. J. Hudson and P. Pomonis, Appl. Catal. A 263 (2004) 103.
 D. Zhao, A. Rodriguez, N.M. Dimitrijevic, T. Rajh and R.T. Koodali, J. Phys. Chem. C 114 (2010) 15728.
 M. S. Morey, G. D. Stucky, S. Schwarz and M. Froba, J. Phys. Chem. B 103 (1999) 2037 –2041.