Pore structure and shape selective catalysis of bifunctional microporous heteropoly compounds

Abstract

The pore structure of Pt-promoted microporous cesium salts of H 3PW 12O 40 and their shape selective catalysis were studied. Pt-Cs 2.1H 0.9PW 12O 40 (0.5 wt% Pt) has only ultramicropores of about 5 Å in width; Pt-Cs 2.5H 0.5PW 12O 40 (0.5 wt% Pt) possesses mesopores as well as micropores. These were revealed by pore size distributions derived from N 2 adsorption-desorption isotherms and adsorption of a variety of molecules having different sizes. While Pt-Cs 2.5H 0.5PW 12O 40 as well as 0.5 wt% Pt/SiO 2 were active for hydrogenation of ethylene, cyclohexene, or cyclooctene, only ethylene was hydrogenated over Pt-Cs 2.1H 0.9PW 12O 40, indicating that Pt-Cs 2.1H 0.9PW 12O 40 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 probably due to product shape selectivity.