Trivalent metal cation

The acidic character of 5A zeolite as a function of the calcium content has been explored by different techniques propylene adsorption experiments, ammonia thermodesorption followed by microgravimetry and FTIR spectroscopy. Propylene is chemisorbed and slowly transformed in carbonaceous compounds (coke) which remain trapped inside the zeolite pores. The coke quantities increase with the Ca2+ content. Olefin transformation results from an oligomerization catalytic process involving acidic adsorption sites. Ammonia thermodesorption studies as well as FTIR experiments have revealed the presence of acidic sites able to protonate NH3 molecules. This site number is also correlated to the Ca2+ ion content. As it has been observed for FAU zeolite exchanged with di- or trivalent metal cations, these sites are probably CaOH+ species whose vas(OH) mode have a spectral signature around 3567 cm"1. 

Di or trivalent cations are able to induce the dissociation of coordinated water molecules to produce acidic species such as MOH+ (or MOH2+ for trivalent metal cations) and H+. Several infrared studies concerning rare-earth or alkali-earth metal cation exchanged Y zeolites have demonstrated the existence of such species (MOH+ or MOH2+) [3, 4, 5, 6]. However, the literature is relatively poor concerning the IR characterization of these acidic sites for LTA zeolites. The aim of the present work is to characterize 5A zeolite acidity by different techniques and adsorption tests carried on 5A zeolite samples with different ion exchange. 

Hydrotalcitelike compounds (HTs) are layered double hydroxides with the general formula Mm2 Mm3 (OH)2(j Ax m/r V H20, where M2 and M3 are divalent and trivalent metal cations, re-... 

The replacement of a part of the third component M(II) in the tricomponent system by a trivalent metal cation, M(III), with ionic radius smaller... 

In conclusion, to make an excellent catalyst system, it is important to activate bismuth molybdate by both the divalent and trivalent metal cations with ionic radii smaller than 0.8 A at the same time. A part of the increasing activity of the Mo-Bi-M(II)-M(III)-0 system compared to the pure bismuth molybdate comes from the increase in surface area and the remains arise from the increase in specific activity. Semiquantitative evaluations of tri- and tetracomponent bismuth molybdates are listed in Table V in comparison with simple bismuth molybdate catalyst. 

Surface analyses were investigated mainly by using XPS (Fig. 7). It was clearly indicated that many composite oxides found by XRD are located un-homogeneously in the catalyst particle. Molybdenum and bismuth are undoubtedly concentrated in the surface layer of the catalyst particle and divalent and trivalent metal cations are found in the bulk of the catalyst. As a result, it is clear that bismuth molybdates, especially its a-phase, is located on the surface of each particle, and metal molybdates of divalent and trivalent cations are situated in the bulk of the catalyst. 

Strictly speaking, it is difficult to conclude which model is most reasonable. However, summing up the results obtained by the surface analyses, it is sure at least that bismuth molybdates are concentrated on the surface of the catalyst particle. Our investigations for Mo-Bi-Co2+-Fe3+-0 also support the conclusion mentioned above, and the core-shell structure proposed by Wolfs et al. may be essentially reasonable. However, since small amounts of divalent and trivalent metal cations are observed in the surface layers, the shell structure may be incompletely constructed. The epitaxial effect has been assumed on the condensation of bismuth molybdates on the divalent and trivalent metal molybdates on the basis of the fact that the y-phase of bismuth molybdate is mainly formed on NiMo04 but the a-phase is predominant on other divalent and trivalent metal molybdates (46). The... 

As a rough approximation (neglecting the activity coefficients), the distribution ratio of a given trivalent metallic cation (DM) can be derived from the logarithm expression of the concentration equilibrium constant Kex ... 

V,. V -l )imethyl-/V,/V -dioctyl hcxylcthoxymalonamidc, used in the DIAMEX process, which extracts trivalent metallic cations from highly acidic feeds by solvation, thus avoiding any adjustment of the acidity of PUREX raffinates. 

Most trivalent metal cations would be anticipated to cause DNA collapse (aggregation) into condensed toroidal structures that are considered to be a model for DNA packaging in viruses and chromosomes. [Co(NH3)6] + induces this effect at five times lower concentration than spermidine, [+H3N-(CH2)4-NH3+-(CH2)3-NH3+], whcrcas divalent metal ions and putrescine, [+H3N-(CH2)4-NH3+], are incapable of causing DNA condensation in aqueous solution. 7302 polyvalent metal compounds, including Ap+ ions, also can relax supercoiled DNA, probably through single-strand DNA cleavage (see Section 7). 

Compared with microporous phosphates, there are few microporous arsenates. The syntheses and structures of arsenates are similar to those of phosphates when divalent metal cations such as Zn + and Be + are employed as framework tetrahedral atoms. However, there is very tittle similarity between alumino- (or gallo-) arsenates and the corresponding phosphates. In the intermediate range where both divalent and trivalent metal cations are present, some similarities between arsenates and phosphates have been observed. ... 

Beryllium forms an enolate complex with lapachol (11a), a versatile ligand that also forms complexes with a variety of other divalent cations, e.g. Pd(ll) and ZrO(II), and trivalent metallic cations , e.g. In(lll) and Rh(lll), for which there is quantitative stability data. There are no data on related saturated derivatives, e.g. the analogous species 11b, to assess additional stabilization due to jt-metal interactions. 

In addition to forming complexes with divalent cations, the porphycenes act as ligands for certain trivalent metal cations. In many cases this chemistry parallels that seen in the porphyrin series. For instance, the (x-oxo-diiron(lll)porphycenates 3.72 and 3.73 were prepared from the corresponding free-base porphycene 3.20 or 3.23 using a procedure analogous to that used to prepare the corresponding p-oxo-diiron(III)porphyrinates. Thus, the reaction of 3.20 or 3.23 with Fe(acac)3 in... 

All early actinides from thorium to plutonium possess a stable +4 ion in aqueous solution this is the most stable oxidation state for thorium and generally for plutonium. The high charge on tetravalent actinide ions renders them susceptible to solvation, hydrolysis, and polymerization reactions. The ions are readily hydrolyzed, and therefore act as Bronsted acids in aqueous media, and as potent Lewis acids in much of their coordination chemistry (both aqueous and nonaqu-eous). Ionic radii are in general smaller than that for comparable trivalent metal cations (effective ionic radii = 0.96-1.06 A in eight-coordinate metal complexes), but are still sufficiently large to routinely support high coordination numbers. 

The anti-HSV-1 activity of Ca-SP was assessed by plaque yield reduction and compared with those of dextran sulphate as a representative sulphated PS. These data indicate that Ca-SP is a potent antiviral agent against HSV-1, as even at low concentrations of Ca-SP, no enhancement of virus-induced syncytium formation was observed, as occurred in dextran sulphate-treated cultures. Reeently, Lee et al. [73] investigated the effects of structural modifications of Ca-SP on antiviral activity. Calcium ion binding with the anionic part of the molecule was replaeed with various metal cations, and their inhibitory effects on the replication of HSV-1 were evaluated. Replacement of calcium ion with sodium and potassium ions maintained the antiviral activity, while divalent and trivalent metal cations reduced the activity. Depolymerization of sodium spirulan with hydrogen peroxide decreased the antiviral activity as its molecular weight decreased. 

Alumina carries high positive and silica carries negative surface charge at pH 5 (the pHjo assumed in the model calculations). Therefore the presented calculations represent specific adsorption at unfavorable electrostatic conditions on the one hand and favorable electrostatic conditions on the other. Detailed analysis is limited to specific adsoiption of one divalent metal cation. One example for specific adsorption of trivalent metal cation, and one example for specific adsorption of an anion will be shown in the end of this seetion. 

CPO may act via chelation of trivalent metal cations (e.g., Fe, for which it has a high affinity, or may act to inhibit metal-dependent enzymes (e.g., catalase/peroxidase), which participate in the intracellular degradation of peroxides resulting in an increase in ROS generation. 

MFI zeolite upon alkaline treatment (see also Fig. 1) [6]. Following those results, an optimal framework Si/Al ratio of 25-50 for mesopore formation has been established. The fitting of the data in the range Si/Al ratio 50-200 was somehow arbitrary, due to lack of zeolites with a suitable Si/Al ratio. The increased mesopore surface area of 120 m g obtained upon desilication of FeS, coupled to a framework Si/Fe molar ratio of 77, however perfectly correlates with the previously proposed fitting, despite the different nature of the trivalent framework cation (solid circle in Fig. la). Additionally, the newly created mesoporosity centered around 20 nm also agrees well with the mesopore size vs. Si/Al ratio dependency, as shown in Fig. lb. These results provide supplementary convincing evidence of the crucial role of the trivalent metal cation in framework positions on the mesopore formation process, which appears to be independent on the nature of the trivalent metal cation. In addition, this confirms the universality of the pore formation mechanism as previously proposed for the alkaline treatment of MFI zeolites [18]. 

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