Synthesis of Pd nanoparticles with controlled size (d(Pd) = 1-3.6 nm) was carried out within the pores of the mesoporous HMS and SBA-15 silicas. Pd was ion-exchanged on non-calcined silicas, prepared by solvent extraction of the templates. A high concentration of silanol groups on the mesopore surface allowed attaining Pd loading up to 4.4. wt.%. The Pd/HMS and Pd/SBA-15 were characterised by chemical analysis, XRD, N2 adsorption-desorption and transmission electron microscopy (TEM) methods. The materials possess a high SSA and narrow pore size distribution. Introduction of Pd nanoparticles in HMS resulted in a progressive loss of the regularity in the mesoporous structure. On the contrary, all Pd/SBA-15 composites retained the original well-ordered 2D hexagonal structure of SBA-15. The thick walls of the SBA-15 framework are accounted for the higher stability observed. The TEM investigations confirmed that the Pd nanocrystals were located within the SBA-15 mesoporous framework channels. The particle size did not exceed the mesopore diameter (2-6 nm) at Pd loading of 0.1-4.4wt.%. Pd clusters were found to be resistant against sintering during air-calcination (550 degreesC, 4h). The catalyst 2.1%Pd/SBA-15 used in methane combustion at 520 degreesC demonstrated stable activity during 6h on stream.
Thi Ha My Pham, Youngdon Ko, Liping Zhong
Vasiliki Tileli, Robin Pierre Alain Girod, Michele Bozzetti, Yen-Chun Chen, Secil Unsal