In situ investigation of Pt100−xAux and Pt100−ySny nanoalloys

Abstract

Dispersed sols of 1–10 nm sized Pt_100−xAu_x and Pt_100−ySn_y nanoalloys have been prepared separately at various x and y above and below the miscibility limit in the bulk metals. Pt_100−xAu_x was derived from trisodium citrate reduction of aqueous solutions of H₂PtCl₆ and HAuCl₄. Pt_100−y–Sn_y was produced by (i) complexing Sn²⁺ with glucose at 323 K at pH > 7, (ii) neutralising this with H₂PtCl₆ addition and (iii) reducing the bimetallic precursor with glucose on raising the temperature to 373 K. For Pt_100−xAu_x (where both metals were zero-valent) as x increased the average size of nanoalloy particles increased. These particles adsorbed onto graphite, where the extent of hydrogen chemisorption at 298 K decreased by 67% at 9 at% Au. Pt/SnO₂nanoparticles (<3 nm in size) were adsorbed onto alumina. The Pt interacted with and catalysed the reduction of SnO₂, with some Pt_100−ySn_y nanoalloy formation at about 673 K which even in the bulk occurs over a wider range of compositions than Pt–Au) and enhanced H₂ chemisorption at 17–33 at% Sn. Nevertheless some Sn must remain in a positive oxidation state on the alumina surface. The ratio of rates of 2MP/3MP formation from MCP and n-hexane may be informative in chemically fingerprinting (and revealing fundamental differences in) these nanoalloy surfaces. The reasons for this are seen in terms of the surface structures on these two types of nanoalloy particles (i.e. the availability of contiguous asymmetric pairs of active surface atoms *, which, as expected, is found to pass through a maximum or decrease beyond specific values of x and y).