Nature, structure and strength of the acidic sites of amorphous silica alumina: an IR and NMR study.

IR spectroscopy of probe molecules (pyridine, 2,6-dimethylpyridine, and CO) as well as high-resolution solid state NMR and especially double-resonance experiments give a new insight into the acidic sites of amorphous silica alumina (ASA). ASA samples are heterogeneous compounds that contain a silica alumina mixed phase as well as aluminum clusters and pure silica zones. The distribution of various forms depends both on the preparation method and on the Si/Al ratio. Formation of mixed phase leads to the creation of acidic hydroxyl groups of various strength, up to that present in dealuminated HY zeolite. Detailed spectroscopic analyses show that these acidic OH groups correspond to the silanol groups located in close vicinity to an Al atom in tetrahedral environment. The strength of the acidity of the OH species of ASA could be modified both by the location of the vicinal Al atom on the surface or in the bulk and by the number of aluminum atoms in the vicinity of silanol group. Cogelification of high silica-containing ASA appears as the best mean to prepare homogeneous amorphous aluminosilicate, which exhibits the strongest Brønsted acidity.

CO adsorption on CoMo and NiMo sulfide catalysts: a combined IR and DFT study.

Experimental IR spectra of carbon monoxide adsorbed on a series of Mo/Al2O3, CoMo/Al2O3, and NiMo/Al2O3 sulfided catalysts have been compared to ab initio DFT calculations of CO adsorption on CoMo and NiMo model surfaces. This approach allows the main IR features of CO adsorbed on the sulfide phase to be assigned with an uncertainty of 15 cm(-1). On the CoMo system, the band at 2070 cm(-1) is specific of the promotion by Co and is assigned to CO interacting either with a Co atom or with a Mo atom adjacent to a Co atom. On the NiMo system, CO adsorption on Ni centers of the promoted phase leads to a high-wavenumber band at approximately 2120 cm(-1) that strongly overlaps the band at 2110 cm(-1) characteristic of nonpromoted Mo sites. For NiMo and CoMo catalysts, broad shoulders at low wave numbers (below 2060 cm(-1)) are characteristic of Mo centers adjacent to promoter atoms, indicating a partial decoration of the MoS2 edges by the promoter.

Enflurane anesthesia and antipyrine metabolism.

To evaluate the influence of enflurane anesthesia on the hepatic drug-metabolizing capacity, antipyrine half-life was measured in 18 surgical patients before surgery and on days 4 and 8 after anesthesia. The effect of repeated administration of antipyrine on the rate of antipyrine metabolism was also evaluated in nine control subjects. Simultaneous measurement of plasma fluoride concentration allowed enflurane metabolism to be quantitated. Regardless of duration, enflurane anesthesia did not increase the rate of antipyrine metabolism as indicated by the absence of significant change in antipyrine half-life and clearance. Repeated doses of antipyrine to nine normal subjects did not influence the rate of antipyrine metabolism. Preanesthesia elimination rate of antipyrine did not indicate individual capacity to metabolize enflurane. Mean peak fluorides level (10.7 +/- 4.8 mM) was reached 3 hr after anethesia and did not appear to correlate with duration of exposure to enflurane.