PREPARATION, CHARACTERIZATION, AND CATALYTIC ACTIVITIES OF SILICA-SUPPORTED TANTALUM OXIDE FOR THE VAPOR-PHASE DECOMPOSITION OF METHYL TERT-BUTYL ETHER

Silica-supported tantalum oxide catalysts [Ta oxide/SiO2 (ALK)] were p repared by chemical reaction between tantalum alkoxide and surface hyd roxyl groups of SiO2. The structure and physicochemical properties of Ta oxide/SiO2 (ALK) were compared with those of Ta oxide/SiO2 (IMP) pr epared by impregnation on SiO2 with acidic TaCl5 solution, and of bulk hydrated tantalum oxide. Highly dispersed tantalum oxide species were formed on the surface by controlling the preparation conditions, such as type of alkoxy group of tantalum alkoxide, concentration of alkoxi de in the solution, and impregnation temperature, as confirmed by Four ier transformation of the Ta L(m)-EXAFS data. Tantalum oxide of Ta oxi de/SiO2 (ALK) did not crystallize up to temperatures as high as 1500 K , while bulk hydrated tantalum oxide and tantalum oxide of Ta oxide/Si O2 (IMP) crystallized at 970 K, The acid strength of Ta oxide/SiO2 (AL K) was moderate, while hydrated tantalum oxide and Ta oxide/SiO2 (IMP) were strongly acidic. Ta oxide/SiO2 (ALK) displayed mainly a Lewis ac id character, Ta oxide/SiO2 (ALK) was initially less active in the dec omposition of methyl tert-butyl ether, but the selectivities for 2-met hylpropene-1 and methanol were higher, as compared with hydrated tanta lum oxide and Ta oxide/SiO2 (IMP). Furthermore, the activity and selec tivity of Ta oxide/SiO2 (ALK) were preserved for ten hours and not inh ibited upon addition of water.