Structure, texture, acidity and catalytic performance of AlPO4-caesium oxide catalysts in 2-methyl-3-butyn-2-ol conversion

A series of aluminium orthophosphate-caesium oxide systems with various cae sium oxide loadings (5-30 wt%) were prepared by impregnation of AlPO4 with a methanolic solution of caesium acetate and characterized by TG/DTA, XRD, DRIFT, Raman, SEM-EDX, XPS, Al-27 and P-31 MAS NMR and nitrogen adsorption. Aluminium orthophosphate remained amorphous with caesium oxide incorporati on when calcined at 873 K for 3 h. After thermal treatment at 1423 K it cry stallized in the tridymite form except for materials containing 30 wt% caes ium oxide. DRIFT spectroscopy showed that the P-OH stretching vibration at 3670 cm(-1) decreased in intensity with caesium oxide loading. Materials at 20-30 wt% caesium oxide did not exhibit any hydroxyl bands. Besides, Al an d P atoms remained in tetrahedral coordination as in unmodified aluminium o rthophosphate. Moreover, the incorporation of caesium oxide leads, simultan eously, to a progressive decrease in surface area and pore volume (larger a t 30 wt% caesium oxide) as well as to an increase in the most frequently oc curring pore radius. On the other hand, caesium oxide reduced both the numb er and strength of acid sites as the caesium content increased. Consequentl y, 2-methylbut-3-yn-2-o1 (MBOH) underwent almost exclusively dehydration to 3-methyl-3-buten-1-yne (acid activity) on pure AlPO4, whereas its modifica tion with increasing amounts of caesium oxide developed AlPO4-based materia ls with increased basic properties and hence high selectivities (99 mol%) t o the base-catalysed cleavage of MBOH yielding acetone and acetylene.