Selective Self‐Condensation of Butanal over Zr‐BEA Zeolites.

Butanal conversion has been studied over Zr‐BEA zeolites with different amount of partially hydrolyzed open Zr‐sites and fully condensed closed sites. The kinetic study pointed that the main reaction pathway of butanal conversion involves its self‐condensation into 2‐ethyl‐2‐hexenal (2‐EN), the selectivity to 2‐EN being within 80–85 %. Besides, small amounts of 1‐butanol and butanoic acid are formed via Cannizzaro disproportionation of butanal. Secondary reactions include butanoic acid ketonization to 4‐heptanone and esterification to butyl butanoate and tandem hydrogenation/dehydration of 2‐EN into octadienes. A number of techniques, including FTIR spectroscopy of adsorbed CO, pyridine, 2,6‐di‐tert‐butylpyridine (DTBPy), TPD of isopropylamine and selective poisoning with DTBPy were applied for characterization of Zr‐sites and elucidation of their activity. Open Zr‐sites were found to be more active with respect to closed Zr‐sites in butanal condensation: the TOF values estimated at 433 K being 1.4 s−1 for open Zr‐sites and 0.6 s−1 for closed sites. On the contrary, selectivity into 2‐EN was similar for open and closed sites. The results point that Zr‐BEA catalysts with enhanced content of open sites are perspective catalysts for the selective synthesis of 2‐EN. [ABSTRACT FROM AUTHOR]