SHAPE-SELECTIVE OXIDATION CATALYZED BY A PT-PROMOTED ULTRAMICROPOROUSHETEROPOLY COMPOUND

Pt-promoted porous heteropoly compounds, Pt-CsxH3-xPW12O40, have been synthesized and their micro- and meso-pore size distributions determin ed by adsorption of variously sized molecules and the Dollimore-Heal N -2 isotherm method, respectively. 0.5 wt.% Pt-Cs2.1H0.9PW12O40 showed a Type I N-2 adsorption isotherm with a plateau, indicating the presen ce of nearly uniform micropores; 1.0 wt.% Pt-Cs2.1H0.9PW12O40, 1.5 wt. % Pt-Cs2.1H0.9PW12O40 and 0.5 wt.% Pt-Cs2.5H0.5PW12O40 gave Type IV is otherms, as usually observed for mesoporous materials. Adsorption of m olecules such as N-2 [molecular size (MS) = 0.36 nm], n-butane (MS = 0 .43 nm), isobutane (MS = 0.50 nm), benzene (MS = 0.59 nm), 2,2-dimethy lpropane (MS=0.62 nm), and 1,3,5-trimethylbenzene (MS=0.75 nm) demonst rated that the pore width of 0.5 wt.% Pt-Cs2.1H0.9PW12O40 was in the r ange 0.43-0.50 nm and that the external surface area was very small. O wing to the restricted pore size, 0.5 wt.% Pt-Cs2.1H0.9PW12O40 exhibit ed efficient shape selectivity for catalytic oxidation; smaller molecu les such as methane (MS = 0.38 nm) and CO (MS = 0.38 nm) were readily oxidized, whereas benzene (MS = 0.59 nm) was not oxidized. This effici ent shape selectivity indicates that Pt is present exclusively in the pores and not on the external surface of 0.5 wt.% Pt-Cs2.1H0.9PW12O40.