Bulk Compounds

Lactic acid (LA) or 2-hydroxypropanoic acid, is a naturally occurring hydroxycar-boxyhc acid and the sole or main final fermentation product produced by LAB. LA is widely used in the food, pharmaceutical, cosmetic, textile, and chemical industries and it is considered GRAS and recognized as harmless by the US FDA. In the food industry, LA is used as a preservative (acidifier) and flavor-enhancing 

As the raw material for LA fermentative synthesis is almost 34% of the total manufacturing cost, the use of cheap alternative sources has been extensively studied [123, 297]. In this respect, employment of paper sludge, lignocellulose, and starch material from agricultural residues and forestry resources are used. 

The main inconvenience is that the majority of these sources need pretreatment or supplementation with additional nutrients, thus increasing the production cost. LA production using whey as growth substrate by strains of Lb. helveticus, Lb. delbrueckii subsp. bulgaricus. Lb. acidophilus, and Lb. casei has been investigated [55]. The main drawback of using whey as substrate is that owing 

Several strategies, including metabolic engineering, have been applied to improve the optical purity of LA optimizing enantioselective biosynthesis. For instance, a Lc. lactis mutant strain obtained by UV mutagenesis was able to produce d-LA from molasses and hydrolyzed sugarcane with 73% yield [308], while a recombinant strain of Lb. plantarum NCIMB 8826 produced 

Biofuels are defined as fuels of biological origin obtained renewably from organic residues. They can partly replace fossil-derived fuels (i.e., oil) because they can be used in current internal combustion engines and are compatible with the infrastructure that exists now. Biofuels have positive carbon balance compared to fossil fuels the CO2 released to the atmosphere is the same, but in the case of biofuels this is offset by the CO2 captured by the plants from which biodiesel is produced occurring in a closed cycle this reduces the contamination of emissions and improves the ambient air quality [313] (Table 11.2). 

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This reaction is catalyzed by iron, and extensive research, including surface science experiments, has led to an understanding of many of the details (72). The adsorption of H2 on iron is fast, and the adsorption of N2 is slow and characterized by a substantial activation energy. N2 and H2 are both dis so datively adsorbed. Adsorption of N2 leads to reconstmction of the iron surface and formation of stmctures called iron nitrides that have depths of several atomic layers with compositions of approximately Fe N. There is a bulk compound Fe N, but it is thermodynamically unstable when the surface stmcture is stable. Adsorbed species such as the intermediates NH and NH2 have been identified spectroscopically. 

Gaussian-type orbitals, the computational requirements grow, in the limit, with the fourth power in the number of basis functions on the SCF level and with even a higher power for methods including correlation. Both the conceptual and the computational aspects prevent the computational study of important problems such as the chemistry of transition metal surfaces, interfaces, bulk compounds, and large molecular systems. 

All Fe oxide films on Pt have strongly relaxed, unreconstructed bulk-terminated surfaces, but while the Fe304 and Fe203 oxide layers are similar to their respective bulk compounds, the ultrathin FeO layers are true 2D oxide phases that are different from the FeO bulk and stabilized by the metal-oxide interface. 

In fact, phase diagrams as in Figure 2.2 form indispensable background information for the interpretation of reduction experiments. However, one should realize that equilibrium data as in Figure 2.2 and Table 2.1 refer to the reduction of bulk compounds. Figures valid for the reduction of surface phases may be quite different. Also, traces of water present on the surface of catalyst particles or on the support represent a locally high concentration and may cause the surface to be oxidized under conditions which, interpreted macroscopically, would give rise to complete reduction. 

Figure 3. Typical rcvcrsc-phasc-type chromatogram of a diastereomer separation of an aminoelhanol, in this case (ft.S)-propranolol, using an (ft.Si-structure homolog as the internal standard and derivatized with (ft.ft)-DATAAN (Table , Entry 25). This example represents an application for the bioanalysis of a betablocking drug (propranolol), but it can also be used for bulk compound analysis for optical purity determinations.

Fig. 6.8. At left comparison of adsorption bond lengths at surfaces (arrows showing uncertainty) with equivalent bond lengths in molecules and bulk compounds (blocks extending over range of values found in standard tables). At right induced charge transfers (obtained as discussed in text) for adsorption...

Fundamental studies by reflection angle infrared spectroscopy of the bonding of EME coupling agents to metal oxides reveal a significant shift in the carbonyl absorbance band when the coupling agent is applied as a very thin layer on a metal oxide. The shift is reproducible and the extent varies with the type of oxide. These results were obtained both by use of copper mirrors and from CuzO powder coated with very thin layers of model compounds. The compounds were not removable by isopropanol, a solvent for the bulk compound. The thiol absorbances of thin layers of model compounds were also found to decrease in relative intensity with time. This illustrates that a specific chemical interaction has occurred. 

The most obvious choice to determine phases that may be present in the molybdena catalyst is XRD. Matching of diffraction lines obtained for the catalyst with those of pure bulk compounds gives unequivocal identification of phases present. This is one of the few techniques that yields positive results. The absence of matching diffraction lines, however, is not proof that the phase in question is not present in the catalyst. The XRD technique is limited to particle sizes of above approximately 40 A for oxides or sulfides, lower sized particles giving no discernible pattern over that of the broad alumina pattern. Thus, the presence of a highly dispersed phase, either as small crystallites or as a surface compound of several layers thickness will not be detected. Also, if the phase is highly disordered (amorphous), a sharp pattern will not be obtained, although some broad structure above that of the alumina may be detected. It is a moot point as to whether such a case is considered as a separate phase or a perturbation of the alumina structure. Ratnasamy et al. (11) have examined their CoMo/Al catalyst from the latter point of view, with particular emphasis on the effect of calcination temperature. 

One of the earliest studies on the CoMo/Al catalyst was done by Richardson (59) employing magnetic measurements. He characterized the oxidized catalyst in terms of bulk compounds, which is clearly incorrect in view of later work. On this basis, and the known sulfidibility of the compounds, he deduced the active catalyst consisted of an MoS2 phase containing Co of an unknown stoichiometry. 

S solid-state MAS spectra at 19.6 T have been acquired for some bulk compounds representative of sulphate speciation in cement paste ettringite, [Ca6Al2(S04)3(0H)6 26H20],107,108 and three different samples of gypsum, [CaS04 -2H20].108 At 33S natural abundance, the acquisition of spectra with a... 

Figure 13 represents measurements at 363 K with silica as a support. The curve measured with suspended silica in a nickel(II) solution at 363 K remains appreciably below the curve measured with nickel nitrate alone and does not approach the curve measured without suspended silica. The course of the pH with suspended silica indicates formation of a bulk compound with the support, as schematically indicated in Fig. 8. Formation of nickel antigorite (a 1 1 clay mineral) or nickel hectorite (a 1 2 clay mineral) is evident from X-...

LEED 6 Sulfur atoms reside in high-coordination sites all nearest-neighbor Ni—S bond lengths are less than those of stable bulk compounds... 

A further problem arises from the fact that catalysts Vork by forming chemical bonds with the substrate molecules. Thus metals form hydrides with H2 and H donors such as CH4 or NH3, or oxides with O2 and 0 donors such as CO2 or NO2. It is presumably these surface compounds that play the role of active intermediates in the catalytic reaction. Under slightly different conditions, however, it is possible to extend the catalyst-adsorbate reaction to produce bulk compounds, e.g., hydrides and oxides. In view of this ability of the surface phase to propagate into the bulk in many instances, it is not at all clear that only the surface of the solid catalyst is active in the reaction. Such complexities add enormously to the difficulty of interpreting the kinetic data from heterogeneously catalyzed reactions. 

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