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The ethanol steam-reforming reaction was studied by in situ diffuse reflectance infrared Fourier transform spectroscopy and on-line mass spectrometry over ZnO and a Co/ZnO catalyst prepared from impregnation of Co2(CO)8. Acetaldehyde is the primary product. The presence of cobalt favors the reforming of acetaldehyde, via the CC scission of bidentate acetate species. Dimethyl ketone is produced as a by-product on ZnO. The roles of ZnO support and cobalt are discussed on the basis of surface species and their subsequent evolution.

The reaction between CO2 and C2H4 in the presence of H2 over Pt and PtSn-based (SiO2, Al2O3, MgO) supported catalysts has been studied at 34 bar of total pressure and 423 K by in situ diffuse reflectance infrared Fourier transform spectroscopy and on-line mass spectrometry experiments. Over silica-supported PtSn alloy, the reaction yields 2-hydroxypropanoic acid through a C2-carbonylic species and CO2 nondissociatively coordinated. C2H4 chemisorption on PtSn/SiO2 produces a C2-carbonylic species which interacts with the hydroxyl groups of SiO2, and this C2-carbonylic species evolves to acetaldehyde at 423 K. 2-Hydroxypropanoic acid is also produced over PtSn/SiO2 from acetaldehyde, CO2, and H2, but not from ethanol and CO2.

Silica-supported Pt‐Sn catalysts were prepared by two-step impregnation from [PtCl2(PPh3)2] and SnCl2 solutions of appropriate concentrations to yield Pt/Sn atomic ratios ranging from 0.2 to 5.0. In these systems, the presence of true Pt‐Sn alloys was confirmed by X-ray diffraction, transmission electron microscopy, energy dispersive X-ray analysis and electron nanodiffraction. Pt and PtSn alloy phases were found on catalysts with Pt/Sn> 1, PtSn alloy alone on the catalyst with Pt/SnD 1 and PtSn and PtSn2 alloys, together with Sn in the catalysts with Pt/Sn< 1. All these catalysts were tested in the skeletal reactions of n-hexane at 753 K and atmospheric pressure. The selectivity of Pt changed significantly when alloyed with tin. For Sn-rich compositions a segregation of tin toward the catalyst surface was shown by photoelectron spectroscopy, and high hydrogenolysis selectivity and fast deactivation were observed. In contrast, Pt-rich catalysts, in which a well defined PtSn alloy was observed, were much more stable and exhibited high selectivity to dehydrogenation reaction while maintaining low conversions to benzene and hydrogenolysis products. This selectivity pattern can be interpreted in terms of a change in adsorption properties due to differences in the number of adjacent Pt atoms required for the various reaction pathways. c ∞ 1997 Academic Press

Alumina-supported iron catalysts, obtained either by impregnation of iron from a K/sub 4/(Fe(CN)/sub 6/) aqueous solution upon several acid-modified ..gamma..-Al/sub 2/O/sub 3/ samples or by the incipient wetness method, were characterized and their activities for ammonia synthesis at atmospheric pressure and 593 K were studied. Characterization was carried out by temperature-programmed reduction (TPR), kinetics of hydrogen reduction, CO chemisorption, X-ray photoelectron spectroscopy (XPS), IR spectroscopy, and Moessbauer spectroscopy, resulting in the degree of reduction and the dispersion of the metallic phase dependent on the previous acid modification of the ..gamma..-Al/sub 2/O/sub 3/. The XPS surface composition expressed as M 2p/Al 2p (M = Fe, K) gave K 2p/Al 2p > Fe 2p/Al 2p. IR experiments, with NO as probe molecules, exhibited bands for reduced catalysts at 1778 and 1712 cm/sup -1/ whose intensity and position depended on the protonation degree of ..gamma..-Al/sub 2/O/sub 3/ and promoter content, respectively. Moessbauer spectra of the reduced samples showed the presence of surface ..cap alpha..-Fe, superparamagnetic Fe/sup 0/, Fe/sup 2 +/, Fe/sup 3 +/, and ..cap alpha..-Fe/sub 2/O/sub 3/ depending on the catalyst. Finally, the catalytic activity for ammonia synthesis was found to be dependent on the surface structure of the catalyst and hencemore » on the method of preparation.« less

Preparation of the samples of nonprotonated gamma-alumina and protonated -gamma-alumina (for the latter, the addition of standardized solutions of HNO/sub 3/ at different concentrations). The quantitative acid site content was determined by uv spectrophotometry using cyclohexane solutions of pyridine or quinoline as titrants. As soon as the adsorption of titrant upon the solid remained constant formation of a monolayer of base upon the acid sites with equal or lower pK's was assumed. A mathematical expression was used to calculated the results. 10 references, 2 figures.