SELECTIVE OXIDATION OF ISOBUTENE TO METHACROLEIN ON MULTIPHASIC MOLYBDATE-BASED CATALYSTS

Synergetic effects in the selective oxidation of isobutene to methacro lein have been studied over catalysts containing several molybdate pha ses. Two types of catalysts have been analysed: (1) pure bismuth molyb dates with Bi/Mo ratios of 2/2 and 2/3 [BiMo(2/2) and BiMo(2/3)] and c obalt molybdate [CoMo(1/1)]; and (2) multiphasic molybdates consisting of three or four molybdates prepared by: (a) coprecipitation of cobal t and bismuth salts and calcination at high temperatures, (b) mechanic ally mixing in dry conditions the separate molybdates and calcining at high temperatures and (c) dispersing the separate molybdates in n-pen tane and calcining at high temperatures. Synergetic effects are observ ed in multiphasic BiMo(2/2)CoMo and BiMo(2/3)CoMo catalysts. For BiMo( 2/2)CoMo catalysts the highest synergetic effects in the conversion, y ield and selectivity are observed. For the catalysts before test no ne w phase is formed after calcination while after test X-ray measurement s indicate a practically complete transformation of alpha-Bi2Mo3O12 in to gamma-Bi2MoO6 and MoO2 and traces of MoO3 and Bi2xMo1-xO3. Neither contamination between phases is observed. The synergetic effects are e xplained by the cooperation between separate gamma-Bi2MoO6, MoO3 and ( alpha+beta)-CoMoO4 phases in contact. The cooperation between phases i s more effective when MoO3 is present in a large proportion.