Title

The effect of catalyst preparation on catalytic activity

Date of Award

1987

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biomedical and Chemical Engineering

Advisor(s)

James A. Schwarz

Keywords

CO-TPR spectra, metal-support interaction

Subject Categories

Chemical Engineering

Abstract

The objective of my research has been to examine the effect of preparation procedures including metal concentration and pH of the impregnation solution on the catalytic properties and structures of supported-metal catalyst systems.

Design parameters have been identified for Ni/Al$\sb2$O$\sb3$ catalysts prepared by wet impregnation and incipient wetness from nickel nitrate solution in contact with a $\gamma$-Al$\sb2$O$\sb3$ support. The metal dispersion, activity for C$\sb1$, C$\sb2$, and C$\sb3$ formation under synthesis conditions, and the carbon deposited during reaction have been shown to be predictable based solely on the properties of the electrolytes from which these catalysts were formed.

Regardless of the method of preparation, NiAl$\sb2$O$\sb4$ was found to be the only active Ni species on low weight loading Ni/Al$\sb2$O$\sb3$ catalysts; both Ni and NiAl$\sb2$O$\sb4$ are present on high weight loading catalysts. The high-temperature methane peak observed only from CO-TPR spectra of low weight loading catalysts is due to NiAl$\sb2$O$\sb4$; the low-temperature peak that appears as the weight loading is increased is due to Ni.

Steady-state reaction kinetics for Ch$\sb4$ production yield activation energies which increase with increasing weight loading. The apparent activation energies for catalysts with a single methane peak in their CO-TPR spectra were found to be normally distributed. The apparent activation energies for catalysts with two methane peaks in their CO-TPR spectra were found to also be normally distributed when the method of preparation was considered in testing the statistical nature of the distribution.

Titration experiments of the carbon pool subsequent to steady-state reaction of H$\sb2$ and CO in conjunction with temperature-programmed surface reaction were used to assess the impact of Ni speciation on the rate-determining step in the methanation reaction.

In situ ESCA experiments and microreactor studies were used to examine the existence of metal-support interaction (MSI) between dispersed Ni and the Al$\sb2$O$\sb3$ carrier. Thermal treatment of a high weight loading Ni/Al$\sb2$O$\sb3$ catalyst in He resulted in the disproportionation of surface NiAl$\sb2$O$\sb4$ concomitant with (Al$\sb{\rm x}$O$\sb{\rm y}$) $\sb{\rm n}$ aggregates partially covering surface Ni. A subsurface layer of NiAl$\sb2$O$\sb4$ was found upon the removal of the alumina overlayer.

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