Evaluating characterization methods for new porous functional materials

Abstract

This thesis is concerned with the development and evaluation of characterization methods for new porous functional materials. Functionalized one-dimensional silicoaluminophosphates (SAPOs) were chosen as model systems for this purpose, where functionalization of the SAPOs was in the form of bimodal porosity to make so-called hierarchical SAPOs and via isomorphous substitution of a transition metal-ion into the SAPO framework. Following a thorough general characterization, model reactions were investigated as new characterization methods for characterizing the topological location of catalytically active sites, such as Brønsted acid sites, and to probe the porosity and pore connectivity of the functionalized SAPOs. The integrity of model reactions as characterization methods was verified by comparing the results with isostructural, non-functionalized (conventional) reference SAPOs.

Two model reactions were investigated as new characterization methods for functionalized SAPOs, namely the methanol-to-hydrocarbons (MTH) reaction and the vapor phase isomerization of cyclohexanone oxime (Beckmann rearrangement, BMR). The product shape selectivity of the MTH model reaction was found to be a highly effective method to probe the topological location of Brønsted acid sites. This property of the MTH model reaction was additionally utilized to verify the bimodal porosity of hierarchical SAPO-11 when conventional methods could not. Furthermore, the MTH model reaction could effectively infer the pore connectivity of the high acid density hierarchical SAPO-5, whereas the BMR model reaction was better suited for discerning the pore connectivity of the low acid density hierarchical SAPO-11. Finally, the incorporation of iron(III) in hierarchical SAPO-11 generated basic sites in the proximity of the iron sites. The BMR model reaction’s sensitivity to base catalyzed processes could thus be utilized to elucidate the topological location of incorporated iron(III) in hierarchical SAPO-11.

In this dissertation, a critical evaluation on the techniques that have been employed to characterize the porosity, pore connectivity and acid/base properties of the functionalized SAPOs is provided. Additionally, this work gives contributions to the characterization procedures for new porous functional materials, such as functionalized SAPOs, where the use of ad hoc model reactions as characterization tools has not previously been reported.