SONOCHEMICAL SYNTHESIS OF NANOSTRUCTURED CATALYSTS

Sonochemistry arises from acoustic cavitation; the formation, growth, and collapse of bubbles in a liquid. The implosive collapse of a bubbl e generates a localized hot spot; a temperature of similar to 5000 K a nd pressure of similar to 1800 atm, with cooling rates that exceed 10( 9) K s(-1). Using these extreme conditions, we have developed a new sy nthetic technique for the synthesis of nanostructured inorganic materi als. When irradiated with high intensity ultrasound in low volatility solvents under argon, volatile organometallic precursors produce high surface area solids that consist of agglomerates of nanometer clusters . These sonochemically produced nanostructured solids are active heter ogeneous catalysts for hydrocarbon reforming and CO hydrogenation. For Fe and Co, nanostructured metals are formed: for Mo and W, metal carb ides (e.g., Mo2C) are produced. Using polymeric ligands (e.g., polyvin ylpyrrolidone) or oxide supports (alumina or silica), the initially fo rmed nanoscale dusters can be trapped as colloids or supported catalys ts, respectively.