Preparation and catalytic properties of supported nanoscale metal particles.

摘要

{dollar}rm Irsb4(CO)sb{lcub}12{rcub}{dollar} was selectively formed inside zeolite NaY by carbonylation of absorbed Ir(CO){dollar}sb2{dollar}acac. {dollar}rm Irsb4(CO)sb{lcub}12{rcub}{dollar} was also deposited on the external surface of zeolite NaY from a cyclohexane solution. Activation of these two materials produced zeolite NaY-supported Ir catalysts termed "Ir in NaY" and "Ir on NaY".; The two Ir/NaY catalysts displayed different activities and selectivities in the hydrogenolysis of butane. "Ir on NaY" was 85% selective towards ethane, whereas "Ir in NaY" was 50% selective towards ethane. The former catalyst was ca. 30 times more active than the latter catalyst. The catalytic differences exhibited by these two systems are ascribed to particle size limitations.; Zeolite NaY-supported Ir/Sn particles have been prepared by the activation of absorbed organometallic precursors. Utilizing Ir(CO){dollar}sb2{dollar}acac and SnMe{dollar}sb3{dollar}OH as precursors produced supported metal particles that were ca. 1 nm in diameter. Utilizing (COD){dollar}sb2{dollar}Ir-SnMe{dollar}sb3{dollar} as a precursor produced a material that contained metal particles ca. 0.5 mm in diameter. The temperature programmed reaction of adsorbed CO indicates that the Ir centers in the Ir/Sn/NaY system are more electron rich than the Ir present in Ir/NaY.; The Ir/Sn catalysts are highly efficient for the dehydrogenation of propane, producing propene at thermodynamic limits and with a selectivity of 95%. The catalytic behavior of the Ir/Sn system results from the geometric and electronic modifications of Ir by Sn.; A series of carbon-supported Pt, Pt/Ru, and Ru nanoparticles were prepared by activation of the precursors {dollar}rm Pt(Csb8Hsb{lcub}12{rcub})sb2, Ptsb2Rusb4(CO)sb{lcub}18{rcub}, PtRusb5C(CO)sb{lcub}16{rcub},{dollar} and {dollar}rm Rusb5C(CO)sb{lcub}15{rcub}{dollar} dispersed on amorphous carbon. The average metal particle size of these materials was between 1 and 2 nm. The particles had elemental compositions similar to the molecular precursors.; The materials were active catalysts for the decomposition of methanol to CO and H{dollar}sb2,{dollar} but the catalyst derived from {dollar}rm Ptsb2Rusb4(CO)sb{lcub}18{rcub}{dollar} displayed enhanced activity and stability. The behavior of these materials as thermal catalysts is expected to relate to their behavior as electrooxidation catalysts in Direct Methanol Oxidation Fuel Cells.