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The structure of five Ni-substituted Ba0.75Ni y Al12-yO19-δ hexaaluminate catalysts at various Ni loadings (y = 0.2, 0.4, 0.6, 0.8 and 1.0) was investigated using EXAFS, XANES, XPS, XRD, and TPR. As Ni-substitution into the hexaaluminate lattice is increased, the unit cell dimension decreases along the c axis. This systematic change is consistent with Ni substitution for Al3+ in the hexaaluminate crystalline structure. XANES analysis suggests that Ni−O bonding is stronger for Ni substituted into the hexaaluminate lattice, relative to that of bulk NiO. The average coordination numbers obtained from EXAFS indicate that Ni is preferentially exchanging with tetrahedrally coordinated Al3+ in the structure which predominates in regions of the hexaaluminate unit cell near the mirror plane. It is at these sites that, preferential substitution of Ni2+ likely occurs to minimize strain in the crystalline lattice.

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The effect of Li and Mn promoters on the structure and selectivity of supported Rh catalysts for CO hydrogenation reaction was examined. Infrared spectroscopy and X-ray absorption were used to investigate the adsorption of reactants and local structure of Rh. These techniques were used in combination with reactivity, H2 chemisorption, and temperature programmed studies to correlate structural characteristics with activity and selectivity during CO hydrogenation of unpromoted Rh/TiO2 and three promoted Rh catalysts: Rh–Li/TiO2, Rh–Mn/TiO2, and Rh–Li–Mn/TiO2. The presence of a promoter slightly decreases the Rh clusters size; however, no evidence for an electronic effect induced by the presence of Li and Mn was found. Higher turnover frequencies were found for the promoted catalysts, which also showed the lower dispersion. The Li promoter introduces a weakened CO adsorption site that appears to enhance the selectivity to C2+ oxygenates. The selectivity to C2+ oxygenates varies inversely with the reducibility of Rh metal, that is, the lower the Rh reducibility, the higher the selectivity.