| Popis: |
For accurate FT i.r. analysis, especially in the hydroxyl region, zeolites must be desorbed of water, hydrocarbons, or other sorbates. We have designed and demonstrated a novel, integrated apparatus that can rapidl desorb zeolite samples in vacuo using a laser, then can acquire FT i.r. spectra. Infrared radiation from a CO 2 laser is directed at a sample that is held in a vacuum cell. Selective absorbance in the TO 4 stretching region heats the zeolite while the stainless-steel cell remamins cool. Since only the thin sample must cool after being blocked from the laser beam, and not the large thermal mass of the cell, spectra are acquired shortly after desorption is completed. Sample heat-up/cool-down cycles are reduced to 1–3 min from 4–5 h for conventional resistively hested cells. Thermal stress on windows and seals is avoided without external cooling. Illustrative results for ZSM-5 are discussed. |
