The synthesis, characterization and catalytic activity of sulfated zirconia

Sulfuric acid and hydrofluoric acid, two types of liquid superacids used in many hydrocarbon catalytic reactions, are very toxic and volatile chemicals. Their perceived danger is one of the reasons for the 1990 Clean Air Act. Another of the catalytic materials covered by the Clean Air Act is chlorinated alumina, because of the loss of chlorine during the catalytic process. Solid superacids have been thought to be potential replacements for the above catalysts, and have been intensively studied in recent years. Sulfated zirconia has surfaced as one of the most promising solid acids. There are many different preparation methods for these solid acids which result in a variety of catalytic materials. One of the main objectives for this research was the synthesis of various sulfated zirconia samples in order to evaluate the effect of preparation methods on the resulting catalytic activity. The work in this dissertation is based on the synthesis of zirconia using 3 methods: (a) zirconyl chloride octahydrate and ammonium hydroxide; (b) zirconyl nitrate and urea; and (c) aerogels synthesized from zirconium n-propoxide and acetic acid.; Materials prepared by these methods were sulfated and then evaluated using the n-butane isomerization reaction. The acidity of the samples was investigated after the adsorption of pyridine by FTIR and TGA. Also, {dollar}sp{lcub}31{rcub}{dollar}P NMR data was obtained after the adsorption of trimethylphosphine. The aerogel samples showed the highest activity, but the zirconyl nitrate samples show the highest consistent selectivity. FTIR studies of the aerogels indicate that after sulfation and calcination, organic groups still remain on the sample surface and this may be the reason for the high activity. Different synthetic preparations indicate that the physicochemical characteristics can be controlled by varying numerous factors including the addition rate of the sulfating reagent (the zirconyl nitrate samples), the concentration of zirconium n-propoxide and acetic acid (the aerogel samples), the pretreatment of the hydrous zirconia (the zirconyl chloride octahydrate samples).; All of the sample classes produced high surface area samples, but this was not found to directly correlate with catalytic activity. Indeed, the sample with the highest surface area after calcination proved to be the least active. More important was the surface area/%sulfur ratio and this was found to be correlated with the observed catalytic activity.