Ammonia Raman spectroscopy

In liquid ammonia, Raman spectroscopy indicated that the major species present was the tetraammine.24 This was based on the observation that the band assigned as y(N—Ag—N)Sym at 370 cm-1 in aqueous solutions was absent in liquid ammonia, whilst a new band occurred at 290cm-1. Also, whilst no tetraammine salts have been isolated from aqueous solution, recrystallization of [Ag(NH3)2]C104 from liquid ammonia yielded [Ag(NH3)4]C104. 

It will be shown that, upon interaction with water or ammonia, the T -like symmetry of the Ti(IV) centers in TS-1 is strongly distorted, as testified by UV-Vis, XANES, resonant Raman spectroscopies [45,48,52,58,64,83,84], and by ab initio calculations [52,64,74-76,88]. As in Sect. 3 for the dehydrated catalyst, the discussion follows the different techniques used to investigate the interaction. 

V-Mo-Zeolite catalysts prepared by solid-state ion exchange were studied in the selective catalytic reduction of NOx by ammonia. The catalysts were characterized by chemical analysis, X-ray powder diffraction, N2 adsorption (BET), DRIFT, UV-Vis and Raman, spectroscopy and H2 TPR. Catalytic results show that upon addition of Mo to V-ZSM-5, catalytic performance was enhanced compared to V-ZSM-5. 

The bis-hydroxylamine adduct [Fe (tpp)(NH20H)2] is stable at low temperatures, but decomposes to [Fe(tpp)(NO)] at room temperature. [Fe(porphyrin)(NO)] complexes can undergo one-and two-electron reduction the nature of the one-electron reduction product has been established by visible and resonance Raman spectroscopy. Reduction of [Fe(porphyrin)(NO)] complexes in the presence of phenols provides model systems for nitrite reductase conversion of coordinated nitrosyl to ammonia (assimilatory nitrite reduction), while further relevant information is available from the chemistry of [Fe (porphyrin)(N03)]. Iron porphyrin complexes with up to eight nitro substituents have been prepared and shown to catalyze oxidation of hydrocarbons by hydrogen peroxide and the hydroxylation of alkoxybenzenes. ... 

This enzyme [EC 1.4.99.3], also known as amine dehydrogenase and primary-amine dehydrogenase, catalyzes the reaction of R-CH2-NH2 with water and an acceptor to produce R-CHO, ammonia, and the reduced acceptor. Tryptophan tryptophylquinone (TTQ) is the cofactor for this enzyme. See Resonance Raman Spectroscopy Topaquinone... 

It has been known for many years that elemental sulfur dissolves in liquid ammonia to give colored solutions which are green or blue at room temperature and red at lower temperatures. The blue chromophores have recently been identified by Raman spectroscopy as S N and 610 nm) . The former ion is... 

The dissolution of sulfur in ammonia has been known for more than 100 years [17]. The identification of the chemical species in these solutions was a matter of confusion until the identification of S4N and 83 , by Chivers and Lau [18] and Bernard et al. [19], using Raman spectroscopy. When considering the species formed in the dissolution process, it is quite remarkable that this dissolution is reversible sulfur is recovered after evaporation of ammonia. These solutions are strongly colored (blue), mainly due to the electronic absorption band of S4N at 580 nm. It must be mentioned that this dissolution is moderately fast at room temperature (but much slower than the dissolution of alkali metals) and that the rate is much slower when temperature decreases. It should also be mentioned that concentrated solutions of sulfur in liquid ammonia can be used as the solution at the positive electrode of a secondary battery. The solution at the negative electrode can be a solution of alkali metal in liquid ammonia [20], the electrodes being... 

The H3NAIX3 molecules have been studied in the gas phase by IR/Raman spectroscopy.24 NCA yields Al—N force constants of 1.50N cm-1 (X = C1) and 1.45 N cm-1 (X = Br). The analyses of spectra were supported by ab initio MO calculations which were also extended to H3NAIF3, a molecule which has eluded synthesis. The ammonia adduct of alane (A1H3) is unknown. A hexaammine A1(BH4)3-6NH3 is the product of excess ammonia on KA1(BH4)4.25 It is believed to contain the cation A1(NH3)1+ and it is possible that this species is also present in some of the complexes A1X3(NH3) , noted above, but structural investigation is required. 

Application of Raman spectroscopy to a study of catalyst surfaces is increasing. Until recently, this technique had been limited to observing distortions in adsorbed organic molecules by the appearance of forbidden Raman bands and giant Raman effects of silver surfaces with chemisorbed species. However, the development of laser Raman instrumentation and modern computerization techniques for control and data reduction have expanded these applications to studies of acid sites and oxide structures. For example The oxidation-reduction cycle occurring in bismuth molybdate catalysts for oxidation of ammonia and propylene to acrylonitrile has been studied in situ by this technique. And new and valuable information on the interaction of oxides, such as tungsten oxide and cerium oxide, with the surface of an alumina support, has been obtained. 

In the metal refining of ores, the metal is solubilized in an aqueous solution. The optical control of metal refining requires quick, accurate analysis of the major chemical species present in solution. Raman spectroscopy and resonance Raman are used to identify the amine complexes of Co, Ni, and Cu species, as well as ammonia sulfate and sulfamate, present in these industrial solutions. The Raman spectra of an industrial plant solution from mine tailings are shown in Fig. 7-15. Each solution contains one or more metal species, sulfate, sulfamate, ammonia, ammonium sulfate, and water. From a comparison with model ammine complexes, the vibrations in the spectra are identifiable. Bands were observed at 615, 980 and 1,110 cm-1 and were assigned to the sulfate ion. No bands were observed for free ammonia. A band at 376 cm-1 was assigned to the Ni(NH3)j + specie. A band at 490 cm-1 was assigned to the Co(NH3)g+ specie. 

Similar tests of the fiuidized-bed method have been successful with a variety of molecular adsorbates and catalysts (other zeolites, supported oxides, naphthalene, pyridine, methanol, alkanes, alkenes, acetonitrile, ammonia, etc.) (25). We believe that this fiuidized-bed method is a major step forward for measurements of working catalysts with UV Raman spectroscopy. It should also be a useful method for measurements of catalytic kinetics by reducing heat and mass transfer effects that arise when catalysts are used in the form of pellets. In the limit of low conversions... 

The first evidence of ion pairing in liquid ammonia came from a study of nitrate solutions by means of Raman spectroscopy. A number of bands larger than the ones expected for free nitrate ions were observed. A full understanding of these bands... 

SO2 dissolves in water to give sulfurous acid , which according to Raman spectroscopy contains large amounts of solvated SO2 as well as HSO3, H3O+, and 8205. With ammonia and amines, quite complex reactions, which are not fully understood, occur. In the gas phase, ammonia and SO2 react according to equation (14). 

The catalysts were characterized by N2 adsorption-desorption isotherms, thermogravimetric analysis (TGA), temperature-programmed desorption of ammonia (NH3-TPD), X-ray diffraction (XRD), Raman spectroscopy, in-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), and X-ray photoelectron spectroscopy (XPS). The procedures and experimental conditions have been detailed elsewhere [9]. 

In principle, deprotonation of any of the sulfanes gives polysulfide anions In practice, this route is not employed and rather fewer anions are known compared with the sulfanes. It was established last century that sulfur dissolves in basic media to give intensely colored (often blue) solutions. The well-known polysulfide solution [NH4]2Sjt, which contains mostly X = 4 and 5, is obtained by bubbling H2S through a suspension of sulfur in ammonium hydroxide. It is accepted nowadays that the blue coloration of many of these solutions is a consequence of the 83 radical. This species has characteristic EPR, visible, and Raman spectra that have enabled its detection in a variety of solutions including liquid ammonia,DMF, and HMPA. 82 can be introduced as an impurity into alkali metal halides. In lapis lazuli (lazurite that is made synthetically as ultramarine blue Na8[Al68i6024]8 , n = 2-4), the blue color is due to the presence of 83 radicals, which has also been identified by Resonance Raman Spectroscopy ... 

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