Acetaldehyde as a probe for the chemical properties of aluminophosphate molecular sieves. An in situ FT-IR study

✍ Scribed by Mi Suk Jeong; Heinz Frei

• Publisher: Elsevier Science
• Year: 2000
• Tongue: English
• Weight: 230 KB
• Volume: 156
• Category: Article
• ISSN: 1381-1169
• DOI: 10.1016/s1381-1169(99)00421-5

✦ Synopsis

Loading of acetaldehyde from the gas phase into transition metal substituted aluminophosphate sieves of AFI structure resulted in mainly physisorbed CH CH-O in the case of FeAlPO -5. By contrast, FT-IR spectroscopy revealed extensive 3 4 chemical reaction upon loading into metal-free AlPO -5 and CoAlPO -5 materials at temperatures as low as y1008C. The 4 4

low temperature product is identified as acetaldol, which dehydrates to crotonaldehyde upon warm-up to room temperature.

The reactive sites are proposed to be Lewis acid sites in the aluminophosphate framework. Using FT-IR monitoring of acetaldehyde in the pores of aluminophosphate sieves as a sensitive method for the detection of Lewis acid sites, we find that their abundance varies substantially with metal substitution. Interestingly, isomorphous Fe substitution of the aluminophosphate framework seems to suppress the formation of such defect sites.