ACID PROPERTIES OF ZINC-OXIDE CATALYSTS PREPARED BY SEVERAL METHODS

Zinc oxide catalysts were prepared from zinc chloride, sulfate, and nitrate and diethyl zinc by several methods and subjected to acid property measurement, X-ray diffraction, DTA, TG, and chemical analysis. The catalysts were prepared by thermal decomposition of hydrolysis products which had been precipitated by ( 1 ) dropwise addition of ammonia water to zinc salt solution (method I), ( 2 ) dropwise addition of salt solution to ammonia water (method II), ( 3 ) the homogeneous precipitation method (method HP), or ( 4 ) the continuous flow method (method CF) ; diethyl zinc was hydorolysed by ( 5 ) dropwise addition of its hexane solution to water. The chemical analysis and x-ray diffraction showed that the hydrolysis products were mainly Zn5(OH)8Cl2 (from the chloride 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 prepared from the zinc salts was shown to contain a substantial amount of 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 enough 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 anions and showed a weak acidity of 0. 01 mmol g-1 (3.3<H-0 less-than-or-equal-to 4. 0).