Degree Type

Dissertation

Date of Award

1990

Degree Name

Doctor of Philosophy

Department

Chemical and Biological Engineering

First Advisor

Terry S. King

Abstract

Proton magnetic resonance spectroscopy, or nuclear magnetic resonance of hydrogen, has been applied to investigate silica-supported Group VIII monometallic and Group VIII-Group IB bimetallic catalysts and alumina- and silica-supported platinum-rhenium bimetallic catalysts. A number of other techniques such as volumetric chemisorption by hydrogen, thermogravimetric analysis, X-ray fluorescence, and model reaction studies were also used to assist the investigations on these catalysts;Two adsorbed states of hydrogen, i.e., irreversible and reversible hydrogen, on the surfaces of monometallic Ru, Pt, and Cu particles and bimetallic Ru-Group Ib, Pt-Group Ib, and Pt-Re particles were observed directly via proton NMR. The same amounts of the irreversible hydrogen adsorbed on pure Ru catalysts were measured by both proton and the volumetric technique. This strongly chemisorbed hydrogen was used to determine the dispersion of Group VIII monometallic catalysts and the overall dispersion of the Ru-Cu and Pt-Cu bimetallic catalysts. A metal-to-metal hydrogen spillover phenomenon was observed on Group VIII-Cu bimetallic catalysts. Also, the weakly adsorbed hydrogen could spill over from the metal surfaces onto the support and exchange with the OH group;The electronic environments on surfaces of monometallic catalysts are sensitive to changes in metal dispersion, state of adsorbed hydrogen, and residual chlorine. Hydrogen tends to bond more strongly with smaller metal particles containing more defect-like sites but adsorbs more weakly on chlorine-contaminated ruthenium surfaces. Minor perturbations of the valence electrons were inferred on Ru-Cu and Pt-Cu bimetallic systems. Strong electronic interactions between Pt and Re were found in the Pt-Re bimetallic catalysts;Surface compositions for the Ru-Cu and Pt-Cu bimetallic catalysts were determined by NMR of adsorbed hydrogen. The Group Ib elements segregate strongly to the surfaces of Group VIII metal particles. Copper has the strongest tendency to form bimetallic particles with a Group VIII element among the Group lb metals. Platinum is miscible with Re in the bulk but selectively segregates to the bimetallic surfaces. The catalytic activity of cyclohexane dehydrogenation was much higher on Pt-Re bimetallic catalysts than on Pt catalysts.

DOI

https://doi.org/10.31274/rtd-180813-9157

Publisher

Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/

Copyright Owner

Xi Wu

Language

en

Proquest ID

AAI9100507

File Format

application/pdf

File Size

419 pages

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