PORE STRUCTURE AND SHAPE-SELECTIVE CATALYSIS OF BIFUNCTIONAL MICROPOROUS HETEROPOLY COMPOUNDS

The pore structure of Pt-promoted microporous cesium salts of H3PW12O4 0 and their shape selective catalysis were studied. Pt-Cs2.1H0.9PW12O4 0 (0.5 wt% Pt) has only ultramicropores of about 5 Angstrom in width; Pt-CS2.5H0.5PW12O40 (0.5 wt% Pt) possesses mesopores as well as microp ores. These were revealed by pore size distributions derived from N-2 adsorption-desorption isotherms and adsorption of a variety of molecul es having different sizes. While Pt-Cs2.5H0.5PW12O40 as well as 0.5 wt % Pt/SiO2 were active for hydrogenation of ethylene, cyclohexene, or c yclooctene, only ethylene was hydrogenated over Pt-Cs2.1H0.9PW12O40, i ndicating that Pt-Cs2.1H0.9PW12O40 exhibits reactant shape selectivity by its constrained pores. In skeletal isomerization of n-butane, the selectivity to isobutane was found to depend significantly on the pore width of Pt-promoted heteropoly compounds and Pt-exchanged zeolites; the selectivity decreased as the pore width became smaller, this is pr obably due to product shape selectivity. (C) 1998 Elsevier Science B.V . All rights reserved.