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  • IR-spectroscopy  (1)
  • TPRS  (1)
  • active carbon support  (1)
  • adverse effects  (1)
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  • 1
    ISSN: 1572-879X
    Keywords: Iridium catalyst ; supported catalyst ; vapor-phase carbonylation ; methanol carbonylation ; active carbon support
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Iridium on active carbon (Ir/A.C.) is an effective catalyst for the vapor-phase carbonylation of methanol. In contrast to rhodium-catalysts the reaction rate is nearly independent of the partial pressure of the methyl iodide promoter and the methanolysis of an iridium-acetyl species has been found to determine the rate. Undesired methane formation accompanying the carbonylation is suggested to proceed via proteolysis of iridium-methyl species by methanol or water. Methyl chloride has been found to be a less effective promoter than methyl iodide.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1572-879X
    Keywords: Faujasite X hosted rhodium ; rhodium particle size ; IR-spectroscopy ; TEM ; CO hydrogenation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Different metal dispersions of Na-faujasite X hosted rhodium were generated and characterized by transmission electron microscopy (TEM) and IR-spectroscopy. CO hydrogenation has been studied over these Rh/NaX-zeolite catalysts. The finer rhodium dispersion with a mean particle size of 1–2 nm shows a higher selectivity towards oxygenates (methanol, ethanol and dimethyl ether) as compared to the coarser dispersion (4–5 nm), where nearly exclusively methane and higher hydrocarbons are formed.
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  • 3
    ISSN: 1572-9028
    Keywords: ammoxidation ; vanadium phosphate catalysts ; catalyst/feed interaction ; reaction mechanism ; FTIR spectroscopy ; TAP technique ; isotope experiments ; TPD ; TPRS
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The reaction pathway of the ammoxidation of toluene on (VO)2P2O7 used as catalyst and the interaction of potential intermediates with the pyrophosphate were studied by spectroscopic techniques (FTIR, EPR), temperature-programmed chemisorptions/ reactions (TPD, TPRS) and transient studies such as the temporal analysis of products (TAP) technique. NH3 is chemisorbed on the catalyst surface, forming three different species, i.e., NH 4 + ions located on BrØnsted sites, coordinatively bound NH3 on Lewis sites and NH 2 − groups, presumably P-NH2. Toluene that is probably adsorbed on Lewis sites reacts in a first step to a benzyl radical. A subsequent partial oxidation by interaction of VIV=O groups generates a V...O=CH-C6H5 surface structure. This benzaldehyde-like surface species reacts with adsorbed NH3 according to a Langmuir-Hinshelwood mechanism. TAP experiments on ammonium-containing vanadium phosphates revealed that NH 4 + ions could act as potential N-insertion species. No formation of benzylamine as well as the generation of V=NH surface groups as possible intermediates or N-insertion sites were observed.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1432-1041
    Keywords: Emiglitate (BAY o 1248) ; sucrose ; starch ; postprandial hyperglycaemia ; glucosidase inhibitor ; blood glucose ; serum insulin ; serum GIP ; breath hydrogen ; adverse effects
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Medicine
    Notes: Summary The absorbable deoxynojirimycin derivative emiglitate (BAY o 1248) is a potent competitive inhibitor of small intestinal α-glucosidases in man. In two similar randomized, placebo-controlled, double blind investigations, the efficacy, duration of action and tolerability of single doses of 10, 20 and 40 mg emiglitate have been assessed in healthy male volunteers after repeated sucrose or maize-starch loads at 08.00, 12.00 and 17.00 h. Even at the lowest dose used, emiglitate almost abolished the glycaemic (−88%) and hormonal responses after the first sucrose meal, simultaneously evoking significant hydrogen evolution (mean peak H2-concentration 〉100 ppm), which was not related to the dose, and which induced unacceptable symptoms of carbohydrate malabsorption, i.e. at the dosages tested, the inhibition of glycaemic and hormonal responses was at the expense of intolerable gastrointestinal adverse effects. Flattening of postprandial responses of blood glucose, serum insulin and gastric inhibitory polypeptide was still apparent after a second sucrose load 4 h later, demonstrating long-lasting inhibition of α-glucosidase activity. After starch, the dose dependency of inhibition emerged more clearly than after sucrose, i.e. the reduction was less pronounced. However, emiglitate led to significant reduction of the glycaemic and hormonal rises after both the first and second starch meals. Symptoms of carbohydrate malabsorption were absent after 10 mg and were negligible with 20 mg or 40 mg emiglitate. Breath hydrogen concentration increased gradually, indicating slight but significant carbohydrate malabsorption after the highest dose of the α-glucosidase inhibitor. The results show that a single morning dose of 20–40 mg emiglitate might be useful in the control of postprandial hyperglycaemia after breakfast and lunch. This dose of the inhibitor was effective after either both 50 g starch or 50 g sucrose as the substrate, but was only tolerable after the starch meal.
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