The use of XAS studies on Co@Pt and Ni@Pt pseudomorphic overlayer catalysts along with a ethylene hydrogenation descriptor reaction have shown that the d-band of Pt can be effected by the parent metal that it is overlayed on. Pt bond distances were found to be shorter than pure Pt when atop the base Ni and Co indicating that the base metal was exerting compressive strain on the Pt and, for two reasons, causing the Pt d-band to broaden and therefore shift downwards in energy. First, the compressive strain alone has been shown to broaden the d-band of larger atoms atop of smaller ones (i.e. Pt atop Ni) and in the case of the Co@Pt sample Co has one less valence electron then Ni and Pt. This allows for more, than Ni and Pt, of a synergistic interaction between Co and Pt in the overlayer samples resulting in even larger Pt d-bandwidth broadening and shifting. This XAS data was confirmed via reactivity studies as the overlayer samples of both Ni and Co based catalysts had lower reactivity than the pure Pt samples.

Re@Pd (core@overlayer) catalysts are analyzed via X-ray absorption spectroscopy to correlate structural and electronic properties with previous reactivity results. The ethylene hydrogenation turnover frequency of the Re-Pd bimetallic and the Re@Pd catalysts is much lower than that of the pure Pd. A reduction of activity agrees with the computationally predicted properties of the overlayer catalysts and indicates that the overlayer catalysts have been synthesized. The FEFF fitted EXAFS yields a Pd-Pd inter-atomic distance in the Re@Pd SD small particle (2.7 nm) catalyst of 2.79 Å and in the Re@Pd SD large particle (6.3 nm) catalyst of 2.76 Å . The fitted Pd-Pd inter-atomic distance of Pd foil is 2.74 Å . The small particle overlayer Re@Pd SD catalyst is also longer than the Pd-Pd inter-atomic distance seen in the, as synthesized, structureless bimetallic Re-Pd (2.73 Å ). The disparity in calculated inter-atomic distances indicates an electronic effect is being exerted upon the disperse Pd atoms by the larger Re crystals and vice versa. The Pd K-edge and Re L III -edge white line data also show the electronic interaction between the Pd overlayer and the core Re atoms. The Pd white line of the overlayer catalysts shifted up relative to Pd foil indicating Pd d-band broadening as a result of the interaction of Pd with Re. The Re d-band of the overlayer catalysts narrowed, which is evidenced by the decreased white line absorption relative to Re foil. These observed changes in the Pd and Re d-band are consistent with computational predictions for catalysts with overlayer structures. Graphical Abstract

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Overlayer Pt on Ni (Ni@Pt) or Co (Co@Pt) were synthesized and tested for H2 generation from APR of lactose. H2 chemisorption descriptor showed that Ni@Pt and Co@Pt overlayer catalysts had reduced H2 adsorption strength compared to a Pt only catalyst, which agree with computational predictions. The overlayer catalysts also demonstrated lower activity for ethylene hydrogenation than the Pt only catalyst, which likely resulted from decreased H2 binding strength decreasing the surface coverage of H2. XAS results showed that overlayer catalysts exhibited higher white line intensity than the Pt catalyst, which indicates a negative d-band shift for the Pt overlayer, further providing evidence for overlayer formation. Lactose APR studies showed that lactose can be used as feedstock to produce H2 and CO under desirable reaction conditions. The Pt active sites of Ni@Pt and Co@Pt overlayer catalysts showed significantly enhanced H2 production selectivity and activity when compared with that of a Pt only catalyst. The single deposition overlayer with the largest d-band shift showed the highest H2 activity. The results suggest that overlayer formation using directed deposition technique could modify the behavior of the surface metal and ultimately modify the APR activity.