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Gold has been supported upon Si02 and y-A1203 using an impregnation technique and HAuC14 solutions. The severity of the conditions required to effect the reduction/decomposition of the acid to metallic Au upon the support decreased and the activity per unit weight of metal in the hydrogenation of pent-l-ene at 373 K increased, as the concentration of Au decreased from 5.0 to 0.01 %.Au supported upon SiOz at these concentrations could be atomically dispersed, but in lower dispersions when upon y-A1203. An increase in Au dispersion as its concentration decreased, which would provide an explanation for the unusual activity of these catalysts, may have been detected only by electron spin resonance and not by more traditional methods of characterisation. Preliminary results for Si02-supported Ag and Pt are compared with Au.The ability of metals within group IB of the periodic classification to catalyse hydrogenation reactions is relatively low in comparison with that exhibited by group VIII transition metals; a fact which may be explained by their lack of vacant d-orbitals at ambient temperatureel Thus for example, Au neither dissociatively adsorbs H2 nor catalyses hydrogenation reactions below 473 K to a significant extent, unless supplied with H atoms or protons from an external source.2 Above 473 K vacant d-orbitals are generated by the thermal promotion of 5d e1ectrons.l However even at high temperature (i.e. 1200-1800 K) the rate of H2 dissociation upon Au is only one-fifteenth of that upon PL3 At 200-400 K Au is only more effective than Ni in catalysing the decomposition of HCOOH.4Recent results now suggest that supported particles and films of Au exhibit significant activity in hydrogenation, hydrogen exchange and hydrocracking 'reactions. In this study the activity of Au supported in varying concentrations in hydrogenation reactions has been considered in greater detail. EXPERIMENTAL MATERIALSSolutions of HAuC14 (Specpure grade ; Johnson Matthey) of suitable strength were used to fill completely the pores of the following supports: Si02 powder (Davison 70, surface area 270 mz g-l and pore volume 1.3 cm3 g-l) and y-A1203 powder 0.C.I. 13/1, surface area 150 m2 g-l and pore volume 0.5 cm3 g-l).

The rates and extents of hydrogen sorption by platinised tungsten trioxide and molybdenum trioxide have been measured between 273 and 363 K and between 3 and 101 kNm-'. Maximum diffusion coefficients for hydrogen spilling-over from platinum to the trioxide supports have been estimated. X-Ray diffraction, differential thermal analysis and thermogravimetric analysis, e.s.r. and i.r. spectroscopy indicate that the products of this spillover are hydrogen bronzes of tungsten and molybdenum. These may be represented as H,WO3, where x has a maximum value of 0.46, and HxMo03, where x has a maximum value of 1.63. The latter violates the ranges of composition previously accepted for bronzes. The chemical and thermal stability of these bronzes is discussed in terms of their structures.