Ship-in-a-Bottle Synthesis of Vanadyl Phthalocyanines in Faujasite

The absence of efficient processes for converting light alkanes to a liquid that can be readily transported results in millions of cubic feet of natural gas being flared annually. Converting natural gas to alcohols would solve this problem, but unfortunately the exothermic nature of such reactions makes them to difficult to control. Nature uses porphyrins for such reactions, however difficulties in syntheses mean that these are not economically viable catalysts. Phthalocyanines have many of the same catalytic properties as porphyrins, but they are much more efficient to synthesize. However, they suffer from a tendency to agglomerate in solution, leading to decreased catalytic activity. One approach that circumvents this problem is to incorporate the phthalocyanine into a zeolite. This can be accomplished either by synthesizing the zeolite around the phthalocyanine, or by a “ship-in-a-bottle” synthesis. The metal ion and the phthalonitrile precursors are both small enough to pass through the pores of many zeolites, and can be made to react within the zeolite. The phthalocyanine formed is too large to escape from within the cages of the zeolite, leaving it trapped like a ship in a bottle. Since the cages are only large enough to accommodate a single molecule this leads to completely dispersed phthalocyanines.

As part of a larger project to study oxidation reactions of phthalocyanines in zeolites we are using Electron Paramagnetic Resonance (EPR) to study various, paramagnetic phthalocyanines trapped faujasite. To obtain the best resolved EPR spectra requires that the phthalocyanine be very dilute within the zeolite. This has been difficult to do, and so we have been using dealuminated faujasite where the number of exchangeable ions is low. Vanadyl and copper ions were exchanged into Zeolyst CBV780 and CBV901 and into Tosoh HSZ-390HUA. EPR showed that the ions were dispersed best in the CBV780. The ion exchanged zeolite was then added to an excess of phthalonitrile and heated to induce reaction. After washing and repeated extraction using a Soxhlet extractor the zeolites were observed to be a deep blue (copper) and green (vanadyl) color, consistent with formation of copper and vanadyl phthalocyanine. EPR spectroscopy was carried out on the zeolite sample showing changes in the spectrum consistent with the formation of copper phthalocyanine in CBV780, and the vanadyl phthalocyanine in CBV780 and CBV901.