Catalytic and magnetic properties of nanostructured materials generated by ultrasound

High intensive ultrasound is a new and effective technique to generate nanostructured materials. The synthesis, characterization, and properties of three kinds of nanostructured materials produced sonochemically will be discussed in this thesis. Silica supported iron catalysts have been generated by ultrasonic irradiation of {dollar}rm Fe(CO)sb5{dollar} in decane solution in the presence of silica. The iron loading on silica can be easily controlled by changing the concentration of {dollar}rm Fe(CO)sb5{dollar} solution. These sonochemically prepared supported iron clusters are amorphous and have particle sizes of 3-10 nm. The sonochemically prepared {dollar}rm Fe/SiOsb2{dollar} samples have different surface morphologies compared to the conventional {dollar}rm Fe/SiOsb2{dollar} samples. For the sonochemically prepared {dollar}rm Fe/SiOsb2{dollar} catalysts, most iron metal clusters remain on the outer silica surface, while in the conventional {dollar}rm Fe/SiOsb2{dollar} catalysts, most iron metal clusters remain within the pores of the silica particles. As compared to the conventional {dollar}rm Fe/SiOsb2{dollar} catalysts, the sonochemically prepared {dollar}rm Fe/SiOsb2{dollar} catalysts have more than ten times higher catalytic activity in Fischer-Tropsch Synthesis and different catalytic selectivity in dehydrogenation and hydrogenolysis of cyclohexane. Nanophase Fe-Co alloys have been generated by ultrasonic irradiation of volatile organometallic precursors ({dollar}rm Fe(CO)sb5{dollar} and {dollar}rm Co(CO)sb3(NO){dollar}). The sonochemically prepared Fe, Co, and Fe-Co alloys have large surface areas and are active catalysts for the dehydrogenation and hydrogenolysis of cyclohexane. Compared to the conventionally prepared Fe-Co alloys, the sonochemically prepared Fe-Co alloys have much higher catalytic selectivities for the dehydrogenation of cyclohexane to benzene, with 1:1 ratio Fe-Co alloys having selectivities as high as 100%. The carbonaceous deposit on the surfaces of sonochemically prepared catalysts is at least one of the factors responsible for the higher dehydrogenation selectivity. Nanosized iron colloids have been produced by ultrasonic decomposition of {dollar}rm Fe(CO)sb5{dollar} in a polyvinylpyrrolidone (PVP) colloid. Transmission electron micrographs show that these colloidal iron particles range in size from 3 to 8 nm. Magnetic studies indicate that both polymer-dispersed and silica supported iron clusters are superparamagnetic materials and have interesting magnetic properties.