Robert L. Garten

The influence of the support on the catalytic behavior of ruthenium in COH2 synthesis reactions

The support material, including carbon, silica, alumina, and particularly titania, on the activity and the selectivity of ruthenium catalysts in the CO hydrogenation reaction was reported. The nature of the interaction between the support and the Ru crystallites is unclear. Alumina and silica supports do not alter turnover frequencies and molecular weight distributions markedly although alumina does not increase the olefin/paraffin ratio to some extent. Carbon strongly shifts selectivity toward methane formation and also reduces specific activity. Ozaki and coworkers found that carbon-supported ruthenium was much less active than alumina- or silica-supported ruthenium in the ammonia synthesis reaction. Apparently the same trend may exist for the hydrogenation of these two isoelectronic molecules - CO and N/sub 2/, with carbon supports reducing the catalytic activity of ruthenium in these reactions. 4 tables.

Chemisorption properties of iridium on alumina catalysts

Abstract Highly dispersed 0.3 to 1.0% iridium on alumina catalysts exhibit H Ir and CO Ir ratios near two for the strongly bound fraction of these adsorbates. Iridium particles in such catalysts are not detectable by high-resolution TEM which places an upper limit of 0.6 nm on their size. Increasing the metal concentration or oxidative calcination resulted in an increase in the average iridium particle size and a corresponding decrease in adsorbate/metal ratios. Average crystallite sizes calculated from chemisorption data and observed directly by TEM for partially agglomerated catalysts were found to be in good agreement. Infrared spectra of adsorbed carbon monoxide were observed to be dependent upon both iridium crystallite size and surface coverage. Under saturation coverage conditions ( CO Ir > 1 ), highly dispersed catalysts displayed a major carbonyl band at 2060 cm −1 . Agglomerated catalysts ( CO Ir ), in contrast, exhibit a band maxima centered in the 2020–2025 cm −1 region. Taken together the chemisorption, TEM, and infrared data indicate that isolated iridium atoms can adsorb up to two adatoms while iridium clusters (>0.6 nm) adsorb a single adatom per exposed metal site.

Mössbauer spectroscopy as a probe of FeO on TiO2 and Ir-Fe on TiO2 - unique preparation of a highly dispersed bimetallic system

Abstract Previous studies have shown that noble metals when reduced on TiO 2 show unconventional suppression of H 2 on CO chemisorption. This paper describes the application of Mossbauer spectroscopy to study the interaction of the coordinatively unsaturated sites (CUS) of TiO 2 with iron and iron-iridium. In this study, the CUS of TiO 2 are coupled with a Mossbauer probe ion, Fe 2+ , and the interaction of the probe with highly-dispersed Ir metal is monitored by Mossbauer spectroscopy and by CUS or acid center titration using the Benesi method. The combination of these two techniques suggests that the CUS sites of TiO 2 act as a template for Fe 2+ as well as for the Fe-Ir cluster. This paper shows that metal catalyst design may be facilitated by use of CUS of oxide surfaces.