In conclusion, an ultra-thin Pd nanocoating has been synthesized in the pore channels of selectively modified mesoporous material SBA-15 by an in-situ reduction process. The outer surface of SBA-15 was first modified with Si-CH 3 groups, thus avoiding the formation of large particles outside the channels. The inner surface was uniformly functionalized with a layer of Si±H groups by reaction with trimethoxysilane; hence, the Pd 2+ could only be reduced by the Si±H groups on the inner surface to form a nanocoating of Pd. It is believed that this new approach will prove to be a general technique for the introduction of other metal nanocoatings in porous silica, and this kind of new material could be widely applied in catalysis.
Experimental
Preparation of SBA-15: In a typical synthesis, a sample of Pluronic P123 (4.0 g) was dissolved in a mixture of water (30 g) and 2 M HCl (120 mL). Tetraethoxysilane (TEOS, 8.5 g) was added to this homogeneous solution with vigorous stirring for 20 h at 40 C and then heated at 100 C for 2 days. The resultant solid was filtered off and then extensively washed with deionized water. Drying at 120 C for 24 h yielded SBA-15.
Preparation of SBA-CH 3 : SBA-15 (1.5 g) was dispersed in dry toluene (50 mL) at 70 C under an N 2 atmosphere and then (CH 3 ) 3 SiCl (10 mL) was added whilst stirring. The mixture was stirred for 24 h, filtered, and the residue dried in vacuo at 90 C for more than 8 h. After modification of the external surface, the surfactant template was removed by solvent extraction in refluxing ethanol whilst stirring for 2 days.
Preparation of SBA-H: SBA-CH 3 (1.5 g) was dispersed in dry CH 3 Cl (50 mL) and (CH 3 O) 3 SiH (10 mL) was added dropwise whilst stirring. The mixture was refluxed under an N 2 atmosphere for 24 h and then filtered. The solid obtained was washed repeatedly with CH 3 Cl.
Preparation of Pd-SBA: SBA-H (1.5 g) was dispersed in dry tetrahydrofuran (THF; 20 mL) and then a 0.05 M Pd(OAc) 2 /THF solution (30 mL) was added slowly. After stirring for 4 h, the solid was filtered and washed with THF and dried in vacuo at room temperature.
Characterization: The XRD patterns of prepared samples were recorded on a Rigaku D/MAX-2200PC X-ray diffractometer using Cu Ka radiation (40 kV, 40 mA). High resolution TEM (HRTEM) images and energy dispersive spectra (EDS) were obtained with a JEOL 200CX electron microscope operating at 200 kV. N 2 adsorption and desorption isotherms were measured at 77 K on a Micromeritics Tristar 3000 system. The specific surface area and the pore-size distribution were calculated using the Brunauer±Emmett±Teller (BET) and Barrett±Joyner±Halenda (BJH) methods, respectively. FTIR spectra were obtained on Nicolet 7000-C with 4 cm ±1 resolution. Powder samples were dispersed in KBr pellets for IR analysis.