ALPO4-AL2O3 CATALYSTS WITH LOW ALUMINA-CONTENT .3. SURFACE BASICITY OF CATALYSTS OBTAINED IN AQUEOUS AMMONIA

The amount of basic sites of AlPO4-Al2O3 (APA1-A, 5-15 wt% Al2O3) cata lysts at two basic strengths was measured by studying the liquid-phase adsorption of two acidic molecules (benzoic acid (BA, pK(a) = 4.2) an d phenol (PH, pK(a) = 9.9) from cyclohexane solutions, through the app lication of a spectrophotometric method. The data obtained follow the Langmuir adsorption isotherm and the monolayer coverage at equilibrium (at 298 K), X(m), is assumed as the amount of basic sites correspondi ng to the specific pK(a) of the acid used as titrant. The amount of ba sic sites of any AlPO4-Al2O3 catalyst is higher than that of AlPO4, bu t lower than that Of Al2O3. Besides, an increase in the Al2O3 content from 10 wt% gradually increases the basicity of the APA1-A catalyst. M oreover, calcination at increasing temperatures does not practically a ffect the surface basicity of APA1-A-5 and APA1-A-10 catalysts. Howeve r, for AlPO4 content higher than 10 wt% we observe a decrease in surfa ce basicity, this decrease depends on alumina content, i.e. it is high er as the amount of alumina increases. The basic sites of APA1-A syste ms catalyze the Knoevenagel condensation of p-methoxybenzaldehyde and malononitrile at room temperature and in the absence of solvent.