Effect of the acid-base properties of metal phosphate molecular sieves on the catalytic performances in synthesis of propylene glycol methyl ether from methanol and propylene oxide

The aim of this study was to investigate correlation between acid-base and catalytic properties of metal phosphate molecular sieves, such as silicoaluminophosphate molecular sieves SAPO-34 and Fe-substituted nickel phosphate Fe-VSB-5, in the reaction of propylene oxide with methanol. This reaction proceeds in two different ways, depending upon the nature of the samples, and gives rise to either primary and/or secondary alkyl ether of propylene glycol. The results indicate that acid-base properties of Fe-VSB-5 and SAPO-34 materials depend on the Fe and Si content, respectively. The increase in Fe content leads to an increase in basicity of VSB-5, while the increase in Si content favors the increase in acidity of SAPO-34. The strength and amount of Brönsted acid sites of Fe-VSB-5 and SAPO-34 are key factors to control their catalytic activity, while the strength and amounts of Lewis-acid sites and base sites are key factors to control the isomer selectivity.