Molecular engineering of zeolite and zeotype solid acid catalysts via post-synthetic modification.

摘要

The main focus of this research has been to design a superior methanol-to-olefin catalyst with high ethylene selectivity that has a reasonable catalytic lifetime. Ethylene is the most valuable product among all the olefins produced from the methanol-to-olefin reaction. Post-synthetic modification of existing zeolites and zeotypes is the modification method of choice since the homogeneity of the catalysts will be maintained and the modification can be controlled using well-known chemical reactions. An equally essential task is to improve our understanding of the effect of these modified catalysts by examining their structures and catalytic mechanisms.; The first post-synthetic modification of zeolites and zeotypes presented was achieved using phenyltrimethylsilane to form stable framework-bound trimethylsilyl species. This research presents a novel monitoring method of post-synthetic modification by means of a gas chromatograph mass spectrometer as well as a technique to count the Bronsted acid sites. In a follow-up experiment, phenylsilane post-synthetic modification was performed on a zeolite to improve the catalyst characterization using various MAS NMR pulse sequences. Furthermore, as the research reveals, the theoretical calculations are in excellent agreement with the experimental results.; The trimethylphosphine post-synthetic modification on a zeolite was the major breakthrough in our research. The phosphate-modified zeolite ZSM-5 suppressed the formation of aromatics in the methanol-to-olefins process while similar phosphate modification on Fe-HZSM-5 improved the phenol selectivity in the benzene to phenol oxidation. Post-synthetic modification of zeotype HSAPO-34 with zinc metal significantly increased the ethylene to propene selectivity.; In another result, polycyclic aromatic hydrocarbons were synthesized selectively in the cages of H-FER. The methanol-to-olefin reaction was completely suppressed, but essentially all of the acid sites in the channels remained active for reactions such as benzene H/D exchange, condensation of methanol, and homologation of light olefins with methanol.; Although we have achieved impressive results with our modified zeolite and zeotype catalysts, there is still a great deal of research that can be done to further improve their catalytic behavior. Nonetheless, this research brings us a step closer toward our ultimate goal.