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Dispersed sols of 1-10 nm sized Pt(100--x)Au(x) and Pt(100--y)Sn(y) nanoalloys have been prepared separately at various x and y above and below the miscibility limit in the bulk metals. Pt(100--x)Au(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 H2PtC16 addition and (iii) reducing the bimetallic precursor with glucose on raising the temperature to 373 K. For Pt(100--x)Au(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/SnO2 nanoparticles (<3 nm in size) were adsorbed onto alumina. The Pt interacted with and catalysed the reduction of SnO2, with some Pt(100--y)Sn(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).

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