Hydrogen absorption in oxide-supported palladium nanocrystals

Abstract

Substantial hydrogen absorption in nanometer-sized palladium crystallites on a thin film alumina support is observed at $90--350\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ under low ${\mathrm{H}}_{2}$ pressure conditions $(<2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}\phantom{\rule{0.3em}{0ex}}\mathrm{Pa})$ by $^{1}\mathrm{H}(^{15}\mathrm{N},\ensuremath{\alpha}\ensuremath{\gamma})^{12}\mathrm{C}$ nuclear reaction analysis. The enthalpy of H solution varies with the absorbed H content and with $\ensuremath{-}(0.28\ifmmode\pm\else\textpm\fi{}0.02)\phantom{\rule{0.3em}{0ex}}\mathrm{eV}∕\mathrm{H}$ exceeds that of bulk Pd at $\mathrm{H}∕\mathrm{Pd}$ ratios below 0.20. By resolving absorbed H from surface-adsorbed H, this enhanced H stability is identified as an intrinsic volume property of the small crystallites rather than being associated with particular binding sites on or near their surfaces.