Production of metal hydrosols and supported metal catalysts using a metal cluster colloid reactor (MCCR)
Abstract
A metal cluster colloid reactor (MCCR) was designed to produce metal hydrosols from an aerosol stream of bare metal clusters. The cluster source for the MCCR is a multiple expansion cluster source (MECS), which is capable of producing nanometer sized metal clusters of controlled size and narrow size distribution. The MCCR is designed to stabilize these clusters as colloids by scrubbing them from the gas phase with a solvent spray generated with an ultrasound horn. Silver clusters are stabilized in aqueous solutions of sodium or ammonium citrate and tetraethyl orthosilicate(TEOS)/NH$\sb4$OH. TEM analysis of the silver sols shows that particles in the 2 to 5 nm size range are stabilized. This size range compares favorably with the 4 nm average diameter of the MECS aerosol as measured using TEM. The particle size obtained from the molar extinction coefficient and the halfwidth of the silver plasmon absorption band is also in agreement with TEM. The characteristics of the plasmon absorption are found to correlate well with the expected effect of carrier gas (He or Ar) on the growth of clusters in the MECS. Silver sols produced using TEOS/NH$\sb4$OH exhibit partial agglomeration. This agglomeration, which is found to be a function of the age of the sol, is believed to occur during the drying process. Supported silver catalysts were produced by drying or flocculating the TEOS/NH$\sb4$OH stabilized sols. The silver dispersion of these catalysts was determined using H$\sb2$ titration of adsorbed oxygen with a dynamic pulse apparatus. H$\sb2$ uptakes were strongly related to the oxidation temperature and reduction time used in pretreatments. It is believed that changes in silver particle shape and surface structure with extent of oxidation can explain this range of dispersions. Particle size measurements using TEM were difficult due to poor particle resolution and electron beam damage to the support. The range of particle diameters obtained from H$\sb2$ titration, in general, agreed with the size range observed in TEM micrographs.
Degree
Ph.D.
Advisors
Andres, Purdue University.
Subject Area
Chemical engineering|Chemistry
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