Dehydration of 1,5-Pentanediol over ZrO ₂ -ZnO Mixed Oxides

Zn addition was found to affect both activity and selectivity of ZrO ₂ for dehydration of 1,5-pentanediol. ZrO ₂ tends to produce more or less equimolar mixture of tetrahydropyran (THP) derivatives and 4-penten-1-ol from 1,5-pentanediol. The conversion of 1,5-pentanediol on ZrO ₂ increases with increasing Zn content up to 30–50 mole percent; however, catalyst containing Zn beyond 50 mole percent had an adverse effect on both conversion of diol and the selectivity for unsaturated alcohol (i. e., 4-penten-1-ol). XRD and Raman analysis infer that the presence of tetragonal ZrO _2, the amorphous phase (ZrO ₂ , ZrZnO _x , ZnO), and hexagonal wurtzite structure of ZnO in the catalysts. The interplanar spacing of ZrO ₂ (111) and ZnO (100) planes for catalysts indicate that Zn incorporates into ZrO ₂ lattice and vice-versa. Basicity assessed from CO ₂ -TPD and acidity from FTIR-pyridine adsorption techniques indicate that both basicity and Lewis acid sites density increases with increasing Zn proportion on ZrO ₂ up to 50:50 molar ratios of Zn to Zr. An optimum Zn:Zr mole ratio is required to achieve higher density of oxygen vacant metal sites (i. e., Lewis acidity) and balanced acid-base strength which improves the diol conversion.