Gold vaporisation

Olafsson [472] described a similar procedure, in which the sample (450 ml) is acidified with nitric acid, aqueous stannous chloride is added, and the mercury is entrained by a stream of argon into a silica tube wound externally with resistance wire and containing pieces of gold foil, on which the mercury is retained. The tube and its contents are then heated electrically to about 320 °C and the vaporised mercury is swept by argon into a 10 cm silica absorption cell in an atomic absorption spectrophotometer equipped with a recorder. The absorption (measured at 253.7 nm) is directly proportional to the amount of mercury in the range 0 - 24 ng per sample. 

Table 6.7 Activities of gold catalysts prepared by laser vaporisation.70...

Au/ZrC>2 catalysts are less active than Au/TiC>2 catalysts, whatever method of preparation is used deposition of colloidal gold,83,91 DP12 or laser vaporisation.70 Activity depends on the method used (Table 6.12), and appears to be due only to the presence of Au°. The reason for the difference between zirconia and titania is not understood Zr4+ is more difficult to reduce than Ti4+, so anion defects may be harder to form. The lattice structures also differ in monoclinic zirconia (baddleyite) the Zr4+ ion is unusually seven coordinate, and phase transitions into tetragonal and cubic structures occur at >1370 and >2570 K, respectively. However, the... 

Au/Ti02 formed by laser vaporisation of gold onto anatase suffered from low activity because the gold content was only 0.02%.13,28 The World Gold Council Au/TiC>2 catalyst performed better, showing 70% selectivity at 80% conversion (353 K). 

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