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Pd-In/Al O single-site catalyst was able to show high selectivity (up to 98 %) in the gas phase semihydrogenation of propyne. Formation of intermetallic Pd-In compound was studied by XPS during reduction of the catalyst. FTIR-CO spectroscopy confirmed single-site nature of the intermetallic Pd-In phase reduced at high temperature. Utilization of Pd-In/Al O in semihydrogenation of propyne with parahydrogen allowed to produce ≈3400-fold NMR signal enhancement for reaction product propene (polarization=9.3 %), demonstrating the large contribution of pairwise hydrogen addition route. Significant signal enhancement as well as the high catalytic activity of the Pd-In catalyst allowed to acquire H MR images of flowing hyperpolarized propene gas selectively for protons in CH, CH and CH groups. This observation is unique and can be easily transferred to the development of a useful MRI technique for an in situ investigation of selective semihydrogenation in catalytic reactors.

The geometric and electronic properties of supported Pt particles have been altered by modifying the ionicity (acid base properties) of the Al 2 O 3 support via the sol-gel method. The Si modifier resulted in the most acidic and Cs in the most basic Al 2 O 3 support. Application of the new Delta XANES technique shows that, above 373K in vacuum, the Pt surface is covered with hydrogen chemisorbed in an atop site for Pt particles dispersed on an acidic Cl-Al 2 O 3 and mostly in the n-fold sites on Pt particles dispersed on a basic Rb-Al 2 O 3 . Further, FTIR data shows a significant bridged CO coverage in the Rb-Al 2 O 3 case but not in the Cl-Al 2 O 3 . At low temperatures, when the coverage of both CO and H should be nearly complete, the Delta XANES results show that the coverage of H on Pt/Cl-Al 2 O 3 is about twice that of Pt/Rb-Al 2 O 3 , consistent with the FTIR data which shows a similar reduction of linear CO adsorption on Pt/Rb-Al 2 O 3 . This is attributed to the different dispersions of the particles. EXAFS analysis makes clear that this difference in dispersion is mostly due to different particle morphologies, almost flat (for Pt/Cl-Al 2 O 3 ) versus (hemi)spherical (for Pt/ Rb-Al 2 O 3 ), although the sizes are also different. The observed changes in CO and H 2 chemisorption properties at high temperature and in Pt particle morphology are due to a shift of the Pt valence band to higher binding energy with decreasing ionicity (increasing acidity) of the support, as indicated by the atomic XAFS results. These atomic XAFS results can be directly correlated, assuming the oxygen Madelung potential model, with the XPS shift of the O 1s BE of about 2 eV, showing a decrease of the net electron charge on the support oxygen atoms with decreasing ionicity of the support. The hydrogen Delta XANES results are combined with a three-site (atop, 2-or 3-fold, and ontop H, in order of decreasing bond strength) Langmuir adsorption model for hydrogen chemisorption. This combination accounts for the variation in hydrogen coverage with change in T, P, and support ionicity as described above. The consequences of these results for Pt-catalyzed CO oxidation and hydrogenolysis/hydrogenation reactions are discussed.

aThe aqueous phase reforming (APR) of xylitol was studied over five Pt/C catalysts. The correlation between physico-chemical properties of the catalysts and catalytic performance was established. The Pt/C catalysts have different textural properties as well as different mean Pt cluster sizes and surface acidity. The average Pt cluster size was investigated by means of CO chemisorption as well as by TEM.The reaction was found to be structure sensitive and TOF linearly increases with increasing average Pt cluster size in the studied domain. The catalysts which possess higher surface acidity favoured higher rates of hydrocarbon production. On the contrary the Pt/C materials with lower acidities generated hydrogen with high selectivity and TOF.

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