Catalytic decomposition adsorption

Surface area can accelerate the decomposition of chlorine dioxide up to a point, but sufficient area appears to inhibit catalytic decomposition by adsorption of the intermediates. For example, the presence of fluffed wood pulp or glass wool is reported to stop the explosive decomposition of chlorine dioxide (27). 

In the near future, the possible synthesis of nanotubes with solid-gas potential will be more favorable to adsorption. The effect of hydrogen overpressure on the stability of adsorbed Ha needs to be verified in the near future. The high-purity nanotube produced by laser vaporization, catalytic decomposition, or other techniques should be investigated. It is noteworthy that the synthesis of the SWNT with defined diameters and distances between the walls is difficult to perform at present, but future synthesis routes will allow more... 

Adsorption or catalytic decomposition of labile substances by the syringe needle can be a problem for some compounds using hot vaporizing injectors [25]. For open tubular columns deactivated fused silica syringe needles and cold on-column Injection techniques are used to minimize this problem. Alternatively, syringes fitted with a needle shroud for cold-needle injection can be used [26]. 

The present paper focuses on the interactions between iron and titania for samples prepared via the thermal decomposition of iron pentacarbonyl. (The results of ammonia synthesis studies over these samples have been reported elsewhere (4).) Since it has been reported that standard impregnation techniques cannot be used to prepare highly dispersed iron on titania (4), the use of iron carbonyl decomposition provides a potentially important catalyst preparation route. Studies of the decomposition process as a function of temperature are pertinent to the genesis of such Fe/Ti02 catalysts. For example, these studies are necessary to determine the state and dispersion of iron after the various activation or pretreatment steps. Moreover, such studies are required to understand the catalytic and adsorptive properties of these materials after partial decomposition, complete decarbonylation or hydrogen reduction. In short, Mossbauer spectroscopy was used in this study to monitor the state of iron in catalysts prepared by the decomposition of iron carbonyl. Complementary information about the amount of carbon monoxide associated with iron was provided by volumetric measurements. 

Sabatier and Balandin had predicted a relationship between catal)dic activity and heat of adsorption. If a solid adsorbs the reactants only weakly, it will be a poor catalyst, but if it holds reactants, intermediates or products too strongly, it wiU again perform poorly. The ideal catalyst for a given reaction was predicted to be a compromise between too weak and too strong chemisorption. Balandin transformed this concept to a semiquantitative theory by predicting that a plot of the reaction rate of a catal)Tic reaction as a function of the heat of adsorption of the reactant should have a sharp maximum. He called these plots volcano-shaped curvesl This prediction was confirmed by Fahrenfort et al." An example of their volcano-shaped curve is reproduced in Fig. 9.1. They chose the catalytic decomposition of formic acid... 

Under certain process conditions, high yields of carbon filaments can be obtained on the catalyst during the catalytic decomposition of methane. Currently, there is a great interest in these carbon filaments, as the unique properties exhibited by these materials can be exploited in a number of applications such as catalyst support, energy storage devices, selective adsorption agents and... 

Besides adsorption of analytes, active sites on the supporting surface and in the stationary phase can trigger catalytic decomposition of unstable analytes such as trimethylsilyl derivatives (47). A further source of adsorptive and catalytic activities are the residues of additives often used to deactivate the surface and to catalyze the immobilization of the stationary phase. 

Tamaru, K. Trans. Faraday Soc. 55 (1959) 824. Adsorption during the catalytic decomposition of formic acid on silver and nickel catalysts. 

Hess, G., Froitzheim, H., and Baumgartner, C., The adsorption and catalytic decomposition of C02 on Fe(lll) surfaces studied with high resolution EELSS, /. Surface Sci., 331-333(A), 138-142, 1995. 

To prevent an undesirable degradation of the compounds to be analyzed, glass columns have mostly been used for gas chromatography of alkaloids because they are indifferent to the compounds. Possible catalytic decomposition of sensitive compounds and adsorption phenomena caused by metal columns, e.g. copper, aluminium and stainless steel, may, however, be eliminated in some cases by a simple coating of the tubing material with the stationary phase... 

SCHEME 2.5 Wroblowa s oxygen electroreduction mechanism with electrochemical rate constants k3 forthe direct reduction to water, k2 and k 2 for the parallel electrochemical reduction and oxidation of adsorbed hydrogen peroxide, k3 for the electrochemical decomposition of hydrogen peroxide to water, k4 for the chemical catalytic decomposition of hydrogen peroxide to oxygen, and ks and fc 5 for the parallel adsorption/desorption of the adsorbed hydrogen peroxide. The species with the super index and ° are located at the interface and in the bulk of the solution, respectively. The sub index ads refers to the adsorbed state, and the term dif symbolizes the diffusion to the bulk of the solution and vice versa. 

The presence of amino, carboxyl, hydroxyl, carbonyl, etc., groups in organic molecules increases their boiling points very substantially, and thus, the probability of undesirable interactions (namely, irreversible adsorption and catalytical decomposition) in the GC analytical system. Some very polar biomolecules cannot be volatilized, in a conventional way, without a loss of their chemical individuality. However, as shown repeatedly during the last two decades, suitable derivatives can frequently be prepared that are sufficiently volatile and stable for GC investigations. Even as seemingly non-volatile substances as carbohydrates, amino acids or alkaloids can now be chromatographed successfully as derivatives. 

There is an important number of commercial approaches to NO removal, including adsorptive, thermal and catalytic techniques (Armor 1994, Centi and Forzatti 1995, Fritz and Pitchon 1997). In the case of catalytic processes, the elimination of NO can be carried out by direct catalytic decomposition, or by selective catalytic reduction (SCR) using hydrocarbons or ammonia as reductant. Although several catalytic system have been studied, zeolites have been proposed as interesting catalysts for both reactions. 

It has been shown recently that the adsorption equilibrium function (/) can be used to obtain information on the thermodynamics of chemisorption processes as they occur during a catalytic reaction 2). Thus, the free energy, enthalpy, and entropy of oxygen chemisorption on nickel, platinum, and silver surfaces were determined while these surfaces were being used for the catalytic decomposition of water. 

Continuing the investigations on the adsorption of methanol vapors on aluminum oxide and on silica-alumina in the region of precatalytic temperatures from —20°Cto 110°C, I. V. Smirnova showed that, as the temperature is increased and as it approaches catalytic temperature (a temperature of about 80°C is the limiting temperature for detectable catalytic decomposition of methanol under these conditions on both materials), an increase in the chemisorbed methanol is observed, whereas physical adsorption declines with increasing temperature. 

Balandin (2) shortly afterwards began the publication of a series of papers developed from the theory that the catalytic decomposition of a relatively large molecule could only take place by simultaneous adsorption at several points this was known as the Multiplet Theory. With cyclohexane, for example, attachment at six centers was supposed to be necessary before benzene could be formed by the loss of three hydrogen molecules. Calculations along these lines for metallic catalysts, whose lattice dimen-... 

Fig. 2. Adsorption-isotherm of N2 by carbon nanofibers synthesized via the catalytic decomposition of acetylene over a stainless steel substrate at 873 K.

When the -anisotropy is small the analysis of the orientation-selective ENDOR experiments benefits from the improved resolution of the different -components at high field, e.g. at W-band. This procedure is well illustrated by work to clarify the structures of the adsorption complexes of nitric oxide (NO) interacting with metal ions in zeolites [50]. These structures are of interest from an applied view to elucidate the catalytic decomposition of NO into N2 and O2 over transition metal... 

---