(532dv) Application of Strong Electrostatic Adsorption Using Formed Alumina Commercial Supports for Pt Catalyst

Strong electrostatic adsorption (SEA) is an established and useful method for synthesis of ultra-small monometallic and bimetallic nanoparticles on oxide and carbon supports. To this point, however, studies of SEA have been conducted with powdered and not formed supports, so the influence of imbibition and diffusion of protons and metal precursors on the metal distribution in the support structure is unknown.

To study the effect of mass transfer of protons and metal precursors as a function of the alumina support pore distribution, six types of formed alumina were selected with different surface areas and microporous or mesoporous pore size distributions. These were impregnated with acidic solutions with and without Pt hexachloride metal precursors to measure the transients in proton and metal uptake equilibria. XRF was used to characterize the degree of penetration of Pt into the spheres as a function of time.

The time required to achieve uniform metal profiles was remarkably long – requiring days of contact for 3 mm alumina spheres. As expected, the mesoporous alumina supports equilibrated much quicker than microporous aluminas, but still required many hours for uniform metal distributions to be achieved. Modelling of proton and metal precursor diffusion and equilibration can simulate the effect of pore size distribution on all samples and and can be used as to predict the behavior in other formed supports with known pore size distributions.