Abstract:
Flame spray pyrolysis (FSP) method was used for the synthesis of nano-Pd/SiO[subscript 2] catalysts containing 0.5 - 10 wt% Pd. Well-dispersed Pd nanoparticles with average Pd particle size not larger than 3 nm were obtained even for the Pd loading as high as 10 wt%. For comparison purposes, the catalysts prepared by conventional impregnation on the flame-made silica with Pd loading 0.5-10 wt% and reference catalysts (0.5-2 wt% Pd loading on commercial SiO[subscript 2] prepared by ion-exchange method and Lindlar catalyst) were studied. The catalyst activities were tested in liquid-phase semihydrogenation of 1-heptyne under mild conditions. The remarkable high TOF values were noticed for the flame-made catalysts compared to those of the impregnation-made and the reference catalysts especially for those with low Pd loadings ([is less than or equal to ]2 wt%). It is suggested that for the flame-made catalysts with low Pd contents, there was a growth of Si-O groups covering small Pd metals and/or strong Pd-SiO[subscript 2] interactions resulting in an inhibition of CO chemisorptions. The TOFs of flame-made catalysts decreased from 66.2 to 4.3 s[superscript -1] with increasing Pd loading from 0.5 to 10 wt% whereas those of the other catalysts were varied between 3-9 s[superscript -1]. However, in all cases, there was no effect on 1-heptene selectivity.
