Synthesis of Hierarchical Metal Incorporated Zeotypes Isomorphous substitution of copper and iron into CHA and AFI topologies
Doctoral thesis
Permanent lenke
https://hdl.handle.net/11250/3044146Utgivelsesdato
2023Metadata
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- Institutt for kjemi [1404]
Sammendrag
The goal of the work in this dissertation is to synthesize catalysts needed for a greener future in which we utilize our limited resources more sustainably. In particular, the work focuses on the creation of isomorphous substituted metal-contaning zeotypes (MeCHA or MeAFI, Me = Cu or Fe) while simultaneously develop a hierarchical porous structure. Here, the traditional micropores are co-exisiting with larger sized mesopores functioning as superhighways for reactants and products. Secondly, the isomorphous substitution of the transition metal (copper or iron) generates single site zeotypic catalysts.
The main focus has been the development of the hierarchical CuSAPO-34. By the employment of X-ray Absorption Spectroscopy (XAS), copper was confirmed isomorphically substituted within the zeotypic framework, bonded to 4 nearest oxygen neighbours at 1.96 Å having a tetragonally distorted geometry. Presence of mesopores was elegantly confirmed by the employment of the catalytic model reaction selective catalytic reduction of nitrogen oxides having hydrocarbons as the reductant (HC-SCR). By changing the size of the hydrocarbon reductant, the shape selective properties of the hierarchical and conventional CuSAPO-34 were exploited, and mesopores were confirmed. The catalytic model reaction propene oxidation showed that the hierarchical CuSAPO-34 experiences increased lifetime when compared to that of the conventional, microporous CuSAPO-34. In Situ XAS confirmed that introduction of mesopores in hierarchical CuSAPO-34 promotes copper specie reduction when compared to that of the conventional. The increased degree of copper species reduction in presence of propene, was further correlated to enhanced catalytic activity in the selective reduction of nitrogen oxides using propene as a reductant (propene-SCR) in comparison to the conventional, microporous CuSAPO-34.
Three other relevant side projects have been included in the dissertation being the development of the syntheses of hierarchical FeSAPO-34, hierarchical CuAFI, and hierarchical FeAFI. Iron has been successfully confirmed incorporated through isomorphic substitution in hierarchical FeSAPO-34 as well as the conventional analogue. XAS showed that iron is bonded to 4 nearest oxygens having a Fe-O bond distance of 1.97-2.0 Å. Phase pure, hierarchical CuAlPO-5 has been synthesized as well as the hierarchical FeAlPO-5, where XAS confirmed ismorphous substitution of the metal cation. However, the synthesis of the acidic SAPO-5 analogues requires further work-up as copper or iron could not be fully confirmed isomorphically substituted single site. Neither of the successful metal-incorporated samples in the three side projects have been subjected to catalytic model reactions or further characterization.