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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