Elaine C. Decanio

Carbon monoxide adsorption by K/Co/Rh/Mo/Al2O3 higher alcohols catalysts

The room temperature carbon monoxide adsorption characteristics of K/Co/Rh/Mo/AI2O3 catalysts are studied by chemisorption and FT-IR techniques. Most of the IR bands can be traced to those observed for Rh/AI2O3, K/Rh/Al2O3, and K/Rh(111). Several bands in the 1700–2000 cm−1 region become quite intense in these multicomponent catalysts when potassium loadings exceed 3 wt%. Significant intensity is observed only when all four elements are present with appropriate loadings. Studies with one-component precursors show: (1) the presence of Mo(0) in Mo/Al2O3 samples reduced at 673 K, (2) cobalt(+2) in octahedral positions on the alumina distinguishable from cobalt(+2) in particles of cobalt, and (3) the presence of a new band for Rh/Al2O3 at 2007 cm−1. Studies with Rh/Mo/Al2O3 suggest Mo covers mainly the surfaces of the larger particles of Rh and forms a mixed oxide layer that does not chemisorb CO.

Evidence from XPS for the stabilization of high-valent molybdenum by addition of potassium in Mo/Al2O3 catalysts

It has been found that alkali and molybdenum are important components of catalysts which convert synthesis gas into higher alcohols. In general, these catalysts are reduced under relatively mild conditions (e.g., 673 K). The purpose of this study is to determine the oxidation state of molybdenum in reduced, potassium-promoted Mo/Al{sub 2}O{sub 3} samples as a function of the alkali loading. A series of Mo(x)/Al{sub 2}O{sub 3} samples was prepared (x = wt% of molybdenum present) with 3, 6, 12, and 15 wt% molybdenum, using ammonium heptamolybdate ((NH{sub 4}){sub 6} Mo{sub 7}O{sub 24} {center dot} 4H{sub 2}O) and an incipient wetness impregnation technique. XPS analyses were carried out on a Leybold-Heraeus (LH) LS-10 instrument, equipped with a hemispherical analyzer. Reductions were performed in situ using a commercial (LH) temperature probe. The samples were moved from the analysis chamber to a reaction chamber and contacted with flowing hydrogen (100 ml/min, 1 atm) at 673 K for 2 h. After reduction, the materials were moved back into the analysis portion of the spectrometer, without exposure to air, and reanalyzed. Results are discussed.

Determination of zero-valent molybdenum after moderate temperature reduction of alumina-supported catalysts

Molybdenum is an important component of commercial hydrotreating catalysts. Numerous studies dealing with the oxidation state of the molybdenum species in the reduced sulfided catalysts have been carried out in order to elucidate the sites responsible for catalytic activity. ESCA studies of a moderately reduced (800 K), 8 wt% Mo/Al{sub 2}O{sub 3} catalyst revealed the predominant reduction species to be Mo(4+): no lower oxidation state species were detected. Under more extreme reduction conditions (1,173 K), oxygen chemisorption and benzene hydrogenation studies show that metallic molybdenum species formed. More recently, Mo(0) has been observed by IR from samples prepared by the decomposition of Mo(CO){sub 6} on alumina of various degrees of dehydroxylation. The authors have reported that the use of an infrared technique can be used to observe Mo(0) on moderately reduced conventional alumina-supported molybdenum catalysts. This study illustrates the variables that are important in the formation of Mo(0) on these materials.

FT-IR analysis of borate-promoted NiMo/Al2O3 hydrotreating catalysts

A series of boron-modified commercial NiMo/Al2O3 hydrotreating catalysts have been characterized by IR analysis of adsorbed NO and pyridine and by gas-oil sulfur- and nitrogen-removal activities. Sulfur removal activity was found to correlate with the 1690 cm−1 (Mo(NO)22+) band in the NO adsorption spectra. Nitrogen removal activity was found to be dependent on support Bronsted acidity as measured by the density of the pyridinium band at 1540 cm−1 in the pyridine adsorption spectra. At higher boron loadings, over 1.8 wt.% boron, the presence of bulk borate phases results in poor catalytic performance.

Characterization of the acidic properties of niobia-containing aerogels with [18O]ethanol dehydration

DeCanio et al. have recently reported the results of a novel mass spectral temperature-programmed reactions study (TPRS) of the dehydration of isotopically labelled ethanol ([[sup 18]O]ethanol) adsorbed on [gamma]-alumina and flouride-modified alumina. Their key finding is that there are two isotopomeric ether products, (C[sub 2]H[sub 5]O)[sub 2][sup 18]O and (C[sub 2]H[sub 5]O)[sub 2], in addition to ethene. This result suggests that adsorbed ethoxide can form via two routes: (i) by dissociative adsorption on Lewis acid site giving rise to the [sup 18]O-containing ethoxide and (ii) by the nucleophilic attack of the surface oxide on ethanol which is probably activated toward C-O bond cleavage by interacting with a Bronsted acid site. Thus, the product distribution following the adsorption of [[sup 18]O]ethanol provides useful information on the acidic properties of oxides, especially with respect to the nature of Lewis versus Bronsted acid sites. In this note, the authors present results which show that in using this technique to study a series of niobia-containing aerogels, the authors found evidence of stronger Bronsted acid sites on supported niobia than on bulk niobia. 9 refs., 3 figs., 1 tab.

Observation of [Al(OH) n (H2O)6-n] n (MoO4) in hydrotreating catalyst precursors by solid-state27 Al NMR

A previously unobserved octahedral27Al MAS NMR resonance has been detected in rehydrated calcined Mo/Al2O3 hydrotreating catalyst precursors. This resonance is attributed to the presence of hydrated forms of aluminum molybdate such as [Al(OH)n(H2O)6-n]n(MoO4) (n = 1 or 2). The cross-polarization relaxation parameters, obtained from variable contact time experiments, yielded information on the relative sizes of the [Al(OH)n(H2O)6-n]n(MoO4) domains in the catalysts with different molybdenum loadings. Analysis of the27A1 MAS NMR spectra of P-Mo(8)/Al2O3 and P-Mo(12)/Al2O3 (wt%P = 0.0–12.0) shows that a function of the phosphate in the 12 wt% Mo catalyst is to prevent the re-hydration of the molybdate phases on the calcined catalysts.