Oxides reaction stoichiometry

Table VI Ammonia—Nitric Oxide Reaction Stoichiometry ...

Cr(VI) reduction in the presence of hematite and biotite has been proposed to occur exclusively by homogeneous Fe(II) oxidation in solution (4). However for Fe(II) oxides, reaction stoichiometry requires that 3 Fe(III) ions be produced for every Cr(VI) ion reduced (equation 14) (70). The slopes for aqueous increases in Fe(III) and Cr(III) are nearly identical (Figure 4B) indicating that only one aqueous Fe(III) ion is being produced for every Cr(III) ion produced. 

Butane-Based Fixed-Bed Process Technology. Maleic anhydride is produced by reaction of butane with oxygen using the vanadium phosphoms oxide heterogeneous catalyst discussed earlier. The butane oxidation reaction to produce maleic anhydride is very exothermic. The main reaction by-products are carbon monoxide and carbon dioxide. Stoichiometries and heats of reaction for the three principal reactions are as follows ... 

The a—time curves for the oxidation reactions [60] of both nickel maleate (534—568 K) and nickel fumarate (548—583 K) were similar to those characteristic of each reactant in vacuum, though E values were reduced to 150 10 kJ mole-1. It was concluded that the distributions of nucleation sites and subsequent patterns of product development were little altered by the change in composition of product from Ni/C (and Ni3C) to NiO. This difference, however, significantly changed the temperature coefficient and stoichiometry of the interface processes, since all carbonaceous material in the reactants was converted to CO2. A constant value of E (150 kJ mole-1) was thus found for the oxidations of the four nickel salts studied [60], the maleate, fumarate, formate and malonate. 

Basically, the oxidation of iron pyrite, FeS2, results in the production of iron(III) sulfate and sulfuric acid, H2SO4. However, two overall reaction stoichiometries are possible and each will yield a different acid generation capacity (e.g., Langmuir, 1997 Baird, 1995) ... 

Ceria-based OSC compounds may have an impact on oxidation reactions especially when the catalysts are working around the stoichiometry (as this is the case under TW conditions). One of the first systematic studies was reported by Yu Yao [53,54], Most results were obtained in 02 excess (0.5% CO + O.5% 02 or 0.1% HC+ 1% 02). Several series of Pt, Pd and Rh/Al203 of various dispersion, as well as metal foils, were investigated in CO, alkane and alkene oxidation. The effect of metal dispersion in CO and the propane oxidation are shown in Figure 8.5. 

The catalyst consists of silver supported on alumina and, while it is reasonably specific, appreciable amounts of C02 and H20 are also formed. Over the range of interest, the yield of ethylene oxide is relatively constant so that for present purposes, we may regard the reaction stoichiometry as... 

Depending on the fabrication techniques and deposition parameters, the pH sensitive slope of IrOx electrodes varies from near-Nemstian (about 59 mV/pH) to super-Nemstian (about 70mV/pH or higher). Since the compounds in the oxide layers are possibly mixed in stoichiometry and oxidation states, most reported iridium oxide reactions use x, y in the chemical formulas, such as lr203 xH20 and IrOx(OH)y. Such mixed oxidation states in IrOx compounds may induce more H+ ion transfer per electron, which has been attributed to causing super-Nerstian pH responses [41],... 

It was found that the hydrogen-producing activity of catalysts declined during consecutive reduction and oxidation cycles. The authors concluded that the catalyst deactivation could be prevented by careful balancing of the stoichiometry of the reduction oxidation reactions. The amount of H2 produced was estimated at 210 Nm1 2 3/kL of vacuum HRO [57],... 

The oxidative reaction catalyzed by XOR is unusual relative to most oxidative enzymes, certainly P450, in that a molecule of water is the source of the oxygen atom that is transferred to hypoxanthine rather than a molecule of oxygen (90). This means that the overall reaction provides electrons rather than consuming them. The stoichiometry... 

A standard cell potential depends only on the identities of the reactants and products in their standard states. As you will see in the next Sample Problem, you do not need to consider the amounts of reactants or products present, or the reaction stoichiometry, when calculating a standard cell potential. Since you have just completed a similar Sample Problem, only a brief solution using the subtraction method is given here. Check that you can solve this problem by adding a reduction potential and an oxidation potential. 

In additional experiments, a second catalytic monolith was added immediately after the first monolith. Although tiie residence time was doubled in these experiments, neither the water-gas shift reaction (2) or the steam reforming reaction (1) was found to significantly improve the reaction conversion and selectivity. From these data, it is apparent that the primal hurdle to achieving the perfect reactor operation involves the selective oxidation of CH4 to H2 and CO only. If CO2 and H2O are formed, the amount of available O2 is obviously reduced accordingly. From stoichiometry, this results in unreacted CH4 in the product gases since the reforming reaction is too slow to consume this metiiane at these short residence times. Thus, the only way to improve Sh2 and Sep at these short residence times is to maximize the partial oxidation reaction selectivity. 

Oxides are widely exploited as catalysts for the selective oxidation of hydrocarbons. They provide lattice oxygen in selective oxidation reactions and exchange it with oxygen gas (e.g. from air in the reactant stream). The periodic lattice oxygen loss for the hydrocarbon oxidation occurs because of reducing gases, despite the presence of gas phase oxygen in the reactant stream. This results in the formation of anion vacancies, local non-stoichiometry and defect structures as discussed in chapter 1. 

The EM studies show that the novel glide shear mechanism in the solid state heterogeneous catalytic process preserves active acid sites, accommodates non-stoichiometry without collapsing the catalyst bulk structure and allows oxide catalysts to continue to operate in selective oxidation reactions (Gai 1997, Gai et al 1995). This understanding of which defects make catalysts function may lead to the development of novel catalysts. Thus electron microscopy of VPO catalysts has provided new insights into the reaction mechanism of the butane oxidation catalysis, catalyst aging and regeneration. 

This example illustrates the qualitative nature of information that can be gleaned from macroscopic uptake studies. Consideration of adsorption isotherms alone cannot provide mechanistic information about sorption reactions because such isotherms can be fit equally well with a variety of surface complexation models assuming different reaction stoichiometries. More quantitative, molecular-scale information about such reactions is needed if we are to develop a fundamental understanding of molecular processes at environmental interfaces. Over the past 20 years in situ XAFS spectroscopy studies have provided quantitative information on the products of sorption reactions at metal oxide-aqueous solution interfaces (e.g., [39,40,129-138]. One... 

III. Stoichiometry and Identification of Oxidized Reaction Products in Concentrated Solutions... 

Detailed information on mechanistic aspects of the ligand oxidation reactions is limited by the fact that well-defined tractable kinetics is only found for systems so very dilute in the metal ion reactants that stoichiometric studies including isolation of reaction products have not yet been practicable. Some selected systems have, however, been studied in some detail, but at significantly higher metal ion concentrations than used for the kinetic studies. It is relevant to recall, however, that under such conditions the rate usually does not follow Eq. (1) and the stoichiometry does not conform to Eq. (2) with a value of n about 6. 

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