A study of acidity, adsorption, and reaction in high silica zeolites and aluminophosphate molecular sieves
The relationship between Bronsted acidity and the reactivity of a range of adsorbates was studied using temperature-programmed desorption (TPD), thermogravimetric analysis (TGA), and IR, UV-visible, and EPR spectroscopies in order to form zeolite encapsulated conjugated species. The zeolite acid sites were characterized by adsorption of alcohols and thiols. 2-Propen-1-ol and a series of simple thiols formed adsorption complexes with a stoichiometry of one molecule adsorbed per Al site in high silica zeolites. The chemistry appears to be dominated by proton transfer from the acid sites to the adsorbed species. Acetylene, furan, thiophene, bithiophene, and pyrrole were reacted in acidic zeolites in order to form encapsulated oligomers. Highly colored products are formed in acidic zeolites, but no reaction occurs on zeolites which did not contain acid sites, indicating that the reactions are acid-catalyzed. The UV-visible spectra showed multiple peaks in the visible regime, with the positions dependent on the adsorbate and the zeolite structure. The oligomers appear to remain protonated. Framework substitution of Mg, Mn, and Co into the AlPO-5 structure was studied by adsorption of reactive probe molecules. MeAPO catalysts may serve as redox catalysts and therefore may better catalyze the oligomerization. For low concentrations of metal ($<$2mol%), the number of alkyl amine molecules which decompose in TPD-TGA is equal to the number of substituted metal atoms, indicating that the metals substitute for the Al in the framework to form Bronsted-acid sites. No evidence of changes in the oxidation state of Co or Mn was obtained. Ethylamine, isopropylamine, 2-ethylhexylamine, cylcooctylamine, and 2,2-diphenylethylamine decompose at Bronsted-acid sites to olefin and ammonia products on H-ZSM-5, H-Y, and silica-alumina samples. The concentration of acid sites accessible to each amine was determined by the diameter of the catalyst pores.
Pereira, Candido, "A study of acidity, adsorption, and reaction in high silica zeolites and aluminophosphate molecular sieves" (1992). Dissertations available from ProQuest. AAI9308644.