Catalytic Probe of the Surface Statistics of Palladium Crystallites Deposited on Montmorillonite

A viable colloid chemical preparation technique provided a series of low-loaded palladium-montmorillonite catalysts with cubooctahedral Pd particles ranging in size from 1.5 to 6.2 nm in mean diameter. These catalysts were used to test the structure sensitivity of the liquid-phase hydrogenation of styrene to ethylbenzene under mild conditions. An experimental correlation was sought between the specific rate of hydrogenation and the dispersion of the metal. The fractions of high-coordination terrace sites (face atoms) and low-coordination defect sites (edge and corner atoms) were calculated as a function of the crystallite size. The good correlation between the turnover frequencies and the defect site densities suggested that hydrogenation occurs on these defect sites and that terrace sites have only minimal catalytic activity or are inactive.