Crystallographic study of direct methanol oxidation to formaldehyde by the fully Mn2+-exchanged zeolite Y (FAU, Si/Al=1.56) by

The direct oxidation of methanol to formaldehyde was crystallographically observed within fully dehydrated, fully Mn2+-exchanged zeolite Y by treating with methanol at 297(1) K, followed by evacuation. The structure of the formaldehyde complex of Mn2+-exchanged zeolite Y was determined by single-crystal synchrotron X-ray diffraction techniques in the space group Fd (3) over barm at 100(1) K and was refined using all intensities to the final indices R-1 = 0.066 and wR(2) = 0.192. In this structure, the 37.5 Mn2+ ions are found at four crystallographic sites: I, I', II', and II with the occupancies of 12, 5, 2.5, and 18, respectively. 18 formaldehyde molecules per unit cell were all found opposite 6-rings in supercages, each coordinating to a site II Mn2+ ions. The formaldehyde molecules appear to be formed by oxidation of sorbed methanol molecules within zeolite Y cavities. The bond length of C = O in formaldehyde molecule is 1.399(20) angstrom. And the distances of Mn(2) to oxygen and carbon atoms of formaldehyde, 2.83(7) and 2.95(8) angstrom, respectively. These bond lengths are relatively long, indicating that each formaldehyde molecule binds weakly to Mn2+ ion. The distances of carbon and oxygen of formaldehyde to the closest framework oxygens O(2) and O(4) are 3.23 and 3.49 angstrom, respectively which indicate hydrogen atoms interact with framework oxygens by van der Waals force.

Automated summary

The direct oxidation process of methanol to formaldehyde was observed and the structure of formaldehyde complex in zeolite Y was determined using crystallographic techniques. The formaldehyde molecules were coordinated to specific Mn2+ ions in the zeolite structure.