Maximum hydrogen chemisorption on KL zeolite supported Pt clusters

Abstract

Platinum clusters supported on KL zeolites were characterized by EPR, HRTEM, and EXAFS. Two kinds of hydrogen chemisorption experiments both result in a saturation value of 2.9 hydrogen atoms per platinum atom, significantly more than that reported so far. A hydrogen coverage-dependent cluster restructuring is suggested.

Platinum–hydrogen vibrations and low energy electronic excitations of 13-atom Pt nanoclusters

“…3,6 Then the first spectrum is recorded and used as a background for the following difference spectra when the hydrogen pressure is stepped up in increments before measurement of the difference spectra. Hydrogen adsorption and measurement of spectra was conducted at room temperature.…”

“…4 In contrast to bulk Pt which chemisorbs one hydrogen atom per surface Pt atom the nanoclusters adsorbs up to 3 H per Pt. 3 The adsorption isotherm was shown to saturate at this value already at a hydrogen pressure of ca. 70 mbar at room temperature.…”

“…70 mbar at room temperature. 3 Up to 3 H atoms per Pt were also reported for small size (1 nm) -Al 2 O 3 -supported Pt nanoparticles, albeit at temperatures of 166-188 K. 5 It is known that the HPt binding energy depends considerably on the type of support. 6 Thus, the H 2 desorption energy from the Pt 13 clusters amounts to 2.10 eV in LTL zeolite, 6 1.36 eV in Y zeolite, 4 but only 0.8 eV from Pt(111) single crystal surfaces, 7 and while the preferred binding site on the (111) surface is the three-fold hole the large number of adsorbed H per cluster suggests that H forms preferentially a bridging bond between two neighbouring atoms (edge site).…”

“…1 It has been demonstrated that it is possible to generate nearly monodisperse platinum nanoclusters with 132 atoms. 2,3 They are of close to icosahedral or cuboctahedral symmetry, but the exact structure varies to some extent as a function of the amount of chemisorbed hydrogen due in part to the open shell electronic structure. 4 In contrast to bulk Pt which chemisorbs one hydrogen atom per surface Pt atom the nanoclusters adsorbs up to 3 H per Pt.…”

Charge Polarization at Catalytic Metal–Support Junctions, Part A: Kelvin Probe Force Microscopy Results of Noble Metal Nanoparticles

“…The finding is not understood at this point, but it should be reminded that under the given conditions the surface even of a noble metal is not always a blank metal. After reduction in hydrogen it may be covered by chemisorbed hydrogen 38 or if exposed to air it may be contaminated with oxygen species. In particular, it has also been reported that after hydrogen reduction the metal of Ru/TiO 2 and other titania-supported noble metal catalysts are covered to a substantial degree with a titania overlayer and that this affects the turnover number considerably.…”