Dehydration of 1,5-Pentanediol over ZrO2-ZnO Mixed Oxides

Zn addition was found to affect both activity and selectivity of ZrO2 for dehydration of 1,5-pentanediol. ZrO2 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 ZrO2 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 ZrO2, the amorphous phase (ZrO2, ZrZnOx, ZnO), and hexagonal wurtzite structure of ZnO in the catalysts. The interplanar spacing of ZrO2 (111) and ZnO (100) planes for catalysts indicate that Zn incorporates into ZrO2 lattice and vice-versa. Basicity assessed from CO2-TPD and acidity from FTIR-pyridine adsorption techniques indicate that both basicity and Lewis acid sites density increases with increasing Zn proportion on ZrO2 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.