催化剂PPT.ppt

Design of Highly Efficient Pt-SnO2 Hydrogenation Nanocatalysts using Pt@Sn Core−Shell Nanoparticles Characterization synthesis 1. 2. Characterization XRD 01 TEM 02 XPS 03 TPO 04 DRIFT-IR 05 XRD patterns showing (a) Pt NPs, (b) Pt@Sn NPs, and (c) Pt-SnO2 NPs obtained by calcination of Pt@Sn NPs at 500 ℃ for 3 h. As shown in Figure 1b, nearly pure Pt diffractions were observed and Sn diffractions were invisible for Pt@Sn NPs. The clear Pt and SnO2 diffractions for Pt-SnO2 NPs in Figure 1c are consistent with the presence of Sn in the Pt@Sn NPs, although the Sn diffractions were not observed in Figure 1b. XRD patterns of individual Pt, assynthesized Pt@Sn, and Pt-SnO2 NPs obtained by calcination of Pt@Sn NPs TEM studies of Pt NPs, Pt@Sn NPs, Pt/Al2O3, and PtSnO2/Al2O3 Small percentages of Snδ+ and Pt2+ are observed for Pt@Sn NPs and Pt2+、Pt4+ are observed for Pt-SnO2 NPs presumably due to the exposure of NPs to air. The binding energies at 486.6/494.9 eV in Figure b can be assigned to 3d5/2/3d3/2 of Sn4+, which is consistent with the XPS database of SnO2 and their XRD patterns. XPS spectra showing (a) as-synthesized Pt@Sn and (b) Pt-SnO2 The higher Sn/Pt ratio for Pt@Sn by XPS is consistent with Pt@Sn core@shell structures The Pt/oxidized Pt ratio of 27.68/72.32 for Pt-SnO2 indicates that more surface Pt atoms are oxidized by calcination Sn/Pt ratio of 2.79/ 1.00 by XPS suggests heteroaggregate nanostructures with a distribution of SnO2 on Pt surfaces. TPO study of Pt@Sn/Al2O3 further confirms the complete oxidation of Sn of Pt@Sn below 300℃ DRIFT-IR spectra with CO probes Only CO bands on Pt are observed, since CO is not adsorbed on tin linear CO on Pt step and kink sites the surfaces mainly consist of Sn and the majority of Pt is in the cores linear CO on Pt step and kink sites linear CO on Pt terrace sites Catalytic Performance Pt-SnO2/Al2O3 with a Pt/Sn ratio of 1/1 has the highest catalytic activity and excellent catalytic selecti