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Mesoporous titania prepared by monolayer grafting of Ti on SBA-15: a model support for studying the surface sulfidation of TiO2 in HDS conditions ?

Juliette Blanchard 1,  Fuxiang Zhang 1,  Xavier Carrier 1,  Yuji Yoshimura 2

1. Laboratoire de Réactivité de Surface (UPMC-CNRS), 4 place Jussieu, case 178, Paris 75252, France
2. Hydrotreating Catalysis, Research center for New Fuels and Vehicle Technology (AIST), Ibaraki, Tsukuba 305-8565, Japan

Abstract
Well-ordered mesoporous TiO2 materials were obtained by successive grafting of Ti(OPri)4 at the surface of a SBA-15 material used as a solid template (TiO2-SBA-15). The successive graftings led to a gradual decrease of the surface area (from 800 initially to 420 m2.g-1 after 4 graftings) and pore diameter (from 65 to 42 Å). These differences can be assigned to the partial plugging of the micropores (as shown by the gradual decrease of the microporous volume) together with a coating of the mesopores with titania suggesting that the titania overlayer is ca. 10 Å thick after 4 graftings. The materials obtained after 1 and 4 graftings present the diffraction patterns and TEM images characteristic of SBA-15 materials, confirming that the SBA-15 structure is not modified whatever the number of graftings. Imaging of the material composition by energy-filtered transmission electron microscopy clearly shows that TiO2 is homogeneously dispersed at the surface of the SBA-15 mesopores. UV-visible and XAS spectroscopies indicate the formation of small titania polymers at the surface of the support.

These materials were used for the XAS (Ti K edge) study of the modification of the titania surface (reduction and/or sulfidation) in hydrodesulfurization condition (320 to 600°C, atmospheric pressure in 5% H2S in H2). At temperatures commonly used for the sulfidation of the active phase (320-360°C), no sulfidation and/or reduction of the TiO2 overlayer was observed and only a small fraction of Ti was sulfided after increasing the sulfidation temperature up to 600°C while bulk sulfidation was expected at this temperature (D. Wang et al. J. Catal. 209, 2002, 266). The resistance to sulfidation is assigned to the peculiar nature of the mesoporous TiO2-SBA-15 supports prepared by grafting Ti on SBA-15, leading to surface chemical properties differing from that of bulk TiO2 supports.

 

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Presentation: Oral at E-MRS Fall Meeting 2008, Symposium D, by Juliette Blanchard
See On-line Journal of E-MRS Fall Meeting 2008

Submitted: 2008-04-29 15:36
Revised:   2009-06-07 00:48