ACID PROPERTIES OF ZINC-OXIDE CATALYSTS P REPARED BY SEVERAL METHODS

Zinc oxide catalysts were prepared from zinc chloride, sulfate, and ni trate and diethyl zinc by several methods and subjected to acid proper ty measurement, X-ray diffraction, DTA, TG, and chemical analysis. The catalysts were prepared by thermal decomposition of hydrolysis produc ts which had been precipitated by ( 1 ) dropwise addition of ammonia w ater to zinc salt solution (method I), ( 2 ) dropwise addition of salt solution to ammonia water (method II), ( 3 ) the homogeneous precipit ation method (method HP), or ( 4 ) the continuous flow method (method CF) ; diethyl zinc was hydorolysed by ( 5 ) dropwise addition of its h exane solution to water. The chemical analysis and x-ray diffraction s howed that the hydrolysis products were mainly Zn5(OH)8Cl2 (from the c hloride by methods I, II, and CF), Zn4(OH)6(SO4).H2O (from the sulfate by method I), Zn4(OH)8(NO3)2.2H2O (from the nitrate by method I), and Zn4(OH)6(CO3).H2O (from the chloride by method HP). Every catalyst pr epared from the zinc salts was shown to contain a substantial amount o f the corresponding anion and to exhibit a strong acidity of -3.3<H-0 less-than-or-equal-to 1.5. Especially, the catalysts prepared from the chloride according to method I contained 1.6 mmol g-1 of the salt eno ugh to explain its anomolously large acidity as much as 2. 1 mmol g-1. The catalyst prepared from diethyl zinc, however, was free from the a nions and showed a weak acidity of 0. 01 mmol g-1 (3.3<H-0 less-than-o r-equal-to 4. 0).