Two distinct but related topics constitute the subject of this communication: preparation and characterization of bimetallic colloidal sols which have not hitherto been reported; and the catalytic performance of these bimetallic particles of colloidal dimension after supporting them on graphite.Monometallic colloidal sols are of ancient lineage1" with those of Ptl'l and Ad3' receiving particular attention; and it has long been recognized[41 that they are potentially powerful catalysts. Effort is currently being expended in devising new ways of preparing and characterizingi5] such sols. However, as a result of their greater catalytic selectivity and resistance to poisoning, metal alloys are of increasing importance.[61 We have therefore explored sol routes to the preparation of bimetallic particles as they could have advantages over the traditional methods of co-impregnation, co-adsorption or co-precipitation. This approach to the production of uniform bimetallic particles of colloidal size has not, to our knowledge, been reported.We chose PtToo-,Au, (O
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).
Beren Antimonatome aus der Aquatorebene in Richtung der jeweiligen Sulfonatgruppe gekippt sind (Mittelwert der 01 I-Sb-C-Winkel (C=CI I, C21, C31): 82.3"), und der 01-Sbl-011-Winkel rnit 174.4(2)O ebenfalls starker von der Linearitat abweicht als der 01-Sb2-01'-Winkel. Der grol3e Sbl-011-Abstand von 250.9(5) pm (vgl. Tabelle l), die auch in anderen, vergleichbaren Verbindungen beobachtete Verzerrungl6I und die IR-Daten (Tabelle 2) weisen auf einen relativ hohen ionischen Anteil an den Sb-OS02-Bindungen hin.
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