Characteristics and catalytic properties of nano-Pd/Tio[subscript 2] catalyst prepared by flame spray pyrolysis

Abstract

The characteristics and catalytic properties of nano-Pd/TiO[subscript 2] catalysts prepared by one-step flame spray pyrolysis with various Pd loadings 0.5-10 wt% and various TiO[subscript 2] crystallite sizes of 9.7 to 24.6 nm were studied. Pd/TiO[subscript 2] catalysts prepared by impregnation method and commercial TiO[subscript 2] were used for comparison. Based on characterization results from various techniques such as XRD, TEM, N[subscript 2] physisorption, CO-pulse chemisorption, and XPS, addition of Pd during one-step flame spray synthesis of Pd/TiO[subscript 2] catalysts resulted in smaller crystallite size of TiO[subscript 2] and higher amount of rutile phase in the TiO[subscript 2]. It is indicated that Pd particles inhibited the crystal growth of TiO[subscript 2] during the flame spray synthesis. Moreover, the single-step flame spray catalysts had much lower amount of Pd on surface than those prepared by conventional impregnation method: this was probably due to that Pd particles were covered by Ti-O groups. However, for a similar Pd loading, the FSP-derived Pd/TiO[subscript 2] catalysts exhibited higher specific activities (TOF) than the impregnated ones in liquid-phase hydrogenation of 1-heptyne with no difference in 1-heptene selectivity. However, the TOFs decreased with increasing amount of Pd loading. The TOFs of FSP-Pd/TiO[subscript 2] catalysts also decreased from 102-23 s[superscript -1] when TiO[subscript 2] crystallite size increased from 9.7 to 24.6 nm whereas the impregnated catalysts and the catalysts prepared on commercial TiO[subscript 2] exhibited similar TOF of around 6-12 s[superscript -1]. It is considered that the single-step flame spray pyrolysis modified and improved the catalytic properties of Pd/TiO[subscript 2] catalysts especially when the catalysts were prepared with low Pd loading and small TiO[subscript 2] crystallite size.