Catalyst for preparing vinyl acetate, process of its preparation and use

摘要

Prodn. of catalysts (I) involves (a) washing the ignited support particles with an acid which does not react with silica or alumina, until no more binder cations are washed out, (b) impregnating with Pd and Au or Cd, (c) contacting with a soln. of a base until there is no further change in the thickness of the noble metal layer produced on the particle surface and (d) impregnating with an alkali cpd. Catalyst contains Pd and/or Pd cpds. and alkali cpds., together with Cd cpds. and/or Au or Au cpds., on particles of a SiO2 or SiO2/Al2O3 substrate which is obtd. by pressing with the binder aid consisting of Li, Mg, Al, Zn, Fe and/or Mn 2-26C carboxylate(s), and igniting for 0.25-5 hrs. at 500-900 deg. C in oxgyen-contg. gas, to give a prod. with surface area 50-250 m2/g, pore vol. 0.4-1.2 ml/g and particle size 1-15mm, in which 5-20 vol. % of the pores have radius = 200-3000 Angstrom and 50-90 vol. % have radius = 70-100 Angstrom. Acid in (a) is pref. HCl, H2SO4, H3PO4 or HNO3, pref. HCl, the base in (c) is an alkali hydroxide, and a potassium cpd. is used in stage (d). Pref. (I) is obtd. by mixing glass microspheres (silica/alumina; at least 95 wt. % silica; obtd. by flame hydrolysis) with 10-20C Mg or Al carboxylate, pressing and igniting as above to give 5-7mm pellets, washing for 10-14 hours, with 10-20% HCl, drying impregnating with a soln. of PdCl2 and AuCl3 or Cd salt (chloride, nitrate etc.), precipitating with NaOH soln., impregnating with KOAc and drying; vinyl acetate prodn. is carried out at 120-200 deg. C and 1-20 bar, using a gas mixt. contg. not above 10 vol. % oxygen.