In situ phase transformation

Reactions involving hydrolysis, leaching, dissolution, precipitation and in situ phase transformation have been discussed in reviews by Smart et al. 4), Myhra et al. [84], Blesa et al. [82], Casey [17], Brown et al. I6] and Schoonheydt [83]. The strategies, methodologies and techniques are essentially the. same as those described in Section 4.7 and, for this reason, no additional examples will be given in this section. 

Most studies of surface reactions on glasses have been concerned with the three processes of leaching or ion exchange, base-catalyzed hydrolysis of the glass network, and in situ phase transformation or reprecipitation. Reviews of the techniques applicable to physical characterization of gla.ss surfaces can be found in the work of Hench and Clark (123,124], Myhra et al. ]4], Kruger ]22], and references therein. 

Liquid multiphasic systems, where one of the phases is catalyst-philic, are attractive for organic transformation, as they provide built-in methods of catalyst separation and product recovery, as well as advantages of catalytic efficiency. The present chapter focuses on recent developments of catalyst-philic phases used in conjunction with heterogeneous catalysts. Interest in this field is fueled by the desire to combine the high catalytic efficiency typical of homogeneous catalysis with the easy product-catalyst separation features provided by heterogeneous catalysis and in situ phase separations. 

Dimethyl sulfoxide (DMSO) has recently been detected in marine air masses. To date nothing is known about the atmospheric fate of DMSO in the gas phase. Reported here are product and kinetic studies on the reactions of OH, NO3 and Cl radicals with DMSO. The investigations were performed in a 420 1 reaction chamber at atmospheric pressure using long path in situ Fourier transform (FTIR) absorption spectroscopy for detection of reactants and products. 

Hug, S. J., and Sulzberger, B. (1994) In Situ Fourier Transform Infrared Spectroscopic Evidence for the Formation of Several Different Surface Complexes of Oxalate on Ti02 in the Aqueous Phase, Langmuir 10, 3587-3597. 

Hug, S.J. and Sulzberger, B., In situ Fourier transform infrared spectroscopic evidence for the foimation of several different surface complexes of oxalate on TiOj in the aqueous phase, Langmuir, 10, 3587, 1994. 

Figure 2. Schematics of the SRXRD setup for in-situ phase mapping and real time observation of phase transformation in fusion weld [ 13].

Joe Wong, M. Froba, J.W. Elmer, P.A. Waide, E. Larson, In-situ phase mapping and transformation study in fusion welds, J. Mater. Sc., 32, 1493-1500 (1997)... 

The hydride phase may be present in a catalyst as a result of the method of its preparation (e.g. hydrogen pretreatment), or it may be formed during the course of a given reaction, when a metal catalyst is absorbing hydrogen (substrate—e.g. in H atom recombination product—e.g. in HCOOH decomposition). The spontaneous in situ transformation of a metal catalyst (at least in its superficial layer) into a hydride phase is to be expected particularly when the thermodynamic conditions are favorable. 

The effects of tin/palladium ratio, temperatnre, pressnre, and recycling were studied and correlated with catalyst characterization. The catalysts were characterized by chemisorption titrations, in situ X-Ray Diffraction (XRD), and Electron Spectroscopy for Chemical Analysis (ESCA). Chemisorption studies with hydrogen sulfide show lack of adsorption at higher Sn/Pd ratios. Carbon monoxide chemisorption indicates an increase in adsorption with increasing palladium concentration. One form of palladium is transformed to a new phase at 140°C by measurement of in situ variable temperature XRD. ESCA studies of the catalysts show that the presence of tin concentration increases the surface palladium concentration. ESCA data also indicates that recycled catalysts show no palladium sulfide formation at the surface but palladium cyanide is present. 

Biological activity can be used in two ways for the bioremediation of metal-contaminated soils to immobilize the contaminants in situ or to remove them permanently from the soil matrix, depending on the properties of the reduced elements. Chromium and uranium are typical candidates for in situ immobilization processes. The bioreduction of Cr(VI) and Ur(VI) transforms highly soluble ions such as CrO and UO + to insoluble solid compounds, such as Cr(OH)3 and U02. The selenate anions SeO are also reduced to insoluble elemental selenium Se°. Bioprecipitation of heavy metals, such as Pb, Cd, and Zn, in the form of sulfides, is another in situ immobilization option that exploits the metabolic activity of sulfate-reducing bacteria without altering the valence state of metals. The removal of contaminants from the soil matrix is the most appropriate remediation strategy when bioreduction results in species that are more soluble compared to the initial oxidized element. This is the case for As(V) and Pu(IV), which are transformed to the more soluble As(III) and Pu(III) forms. This treatment option presupposes an installation for the efficient recovery and treatment of the aqueous phase containing the solubilized contaminants. 

Except for those catalysts subjected to the previously mentioned conditions, which lead to irreversible transformation of the active phase and/or the support material, the HDT catalysts are regenerable [37], Through a systematic and careful procedure, the spent catalyst is unloaded from the reactor and regenerated by specialized companies. The possibility of in situ regeneration is also commercially offered and the decision, on which method would be used, is typically based on economical considerations [38],... 

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