Suitable acidity of ZSM-5 for the isomerization of styrene oxide to phenylacetaldehyde

• The catalyst lifetimes are affected by both acid strength and concentration.
• Trimerization of phenylacetaldehyde occurs at the external acid sites.
• Aldol condensation of phenylacetaldehyde is not sensitive to the acidity.
• High Si/Al HZSM-5 without external acid sites is more suitable for this reaction.

The effect of acidity of HZSM-5 (SiO2/Al2O3 = 25–360) on isomerization of styrene oxide to phenylacetaldehyde was investigated under gas–phase free of solvents. The reaction was mainly catalyzed by the strong acid sites of HZSM-5 and catalyst lifetimes were affected by both acid strength and concentration. Trimerization of phenylacetaldehyde occurred at external acid sites, leading to a sharp decline in product selectivity. High Si/Al HZSM-5 (e.g., SiO2/Al2O3 = 360), which contains weaker acid sites inside pores and trace amount of external acid sites, was found to be more effective with a higher stability and phenylacetaldehyde yield up to 95%.

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