Carbon monoxide calorimetric studies

One of the conclusions deduced from the thermochemical cycle 2 in Table V, for instance, is that in the course of the catalytic combustion of carbon monoxide at 30°C, the most reactive surface sites of gallium-doped nickel oxide are inhibited by the reaction product, carbon dioxide. This conclusion ought to be verified directly by the calorimetric study of the reaction. Small doses of the stoichiometric reaction mixture (CO + IO2) were therefore introduced successively in the calorimetric cell of a Calvet microcalorimeter containing a freshly prepared sample of gallium-doped... 

From the calorimetric study of the first sequence of adsorptions, it is possible to propose a mechanism (I) for the catalytic oxidation of carbon monoxide on NiO(250). 

Reaction Mechanism. The rate of production of heat as a function of time gives indications of the velocity of the process taking place on the catalyst surface (Figure 4B). For instance, it has been shown (20) that, on NiO(200), the adsorption of oxygen and the formation of CO.r(adfo ions are fast processes compared with the adsorption of carbon monoxide or the reaction between CO and CCV ds)- From calorimetric results and a kinetic study of the reaction, it has been concluded (8) that the decomposition of COa uds) ions by adsorbed carbon monoxide to yield carbon dioxide is the slowest step of the reaction mechanism on NiO(200) (Mechanism I). 

The compatibility of blends of poly (vinyl chloride) (PVC) and a terpolymer (TP) of ethylene, vinyl acetate, and carbon monoxide was investigated by dynamic mechanical, dielectric, and calorimetric studies. Each technique showed a single glass transition and that transition temperature, as defined by the initial rise in E" at 110 Hz, c" at 100 Hz, and Cp at 20°C/min, agreed to within 5°C. PVC acted as a polymeric diluent which lowered the crystallization temperature, Tc, of the terpolymer such that Tc decreased with increasing PVC content while Tg increased. In this manner, terpolymer crystallization is inhibited in blends whose value of (Tc — Tg) was negative. Thus, all blends which contained 60% or more PVC showed little or no crystallinity unless solvent was added. 

Another relevant phenomenon is the reaction of carbon monoxide with the lithium trimethylsilyldiazomethanide (MesSiCNaLi) to form either an ynolate (MesSiC COLi) or a ketenide (Me3SiC(Li)=C=0) derivative. The corresponding neutral species Mes SiCHN2 reacts with CO, in the presence of Co2(CO)s, to form Me3SiCH=C=0 . Neither reaction was studied calorimetrically. Accordingly, they cannot be compared with the energetics of the reaction of HCNi with CO to form HCCO and N2, a quantity indirectly obtainable from the deprotonation enthalpies of diazomethane and ketene. ... 

Later studies by Garner and his co-workers showed that the fraction of carbon monoxide or hydrogen reversibly chemisorbed at room temperature varied from oxide to oxide. Zinc oxide was shown to be a case where the adsorption of carbon monoxide at room temperature was completely reversible. The heat of adsorption, determined both calorimetrically (5) and isosterically 6), was in the range 12-20 kcal./mole. For several other oxides, however, notably chromia, Mn20s and Mn20s Cr20s, the heat of adsorption of carbon monoxide was higher and the chemisorption was... 

The same sequence of adsorptions (O2-CO) was also studied on the surface of NiO(250°) [41). As in the case of NiO(200°), adsorption of carbon monoxide on the sample containing preadsorbed oxygen (1.90 cm /gm) (Table II) changes the color of the sample from black to green and decreases its electrical conductivity (1.8 x 10- ohm-i cm- ) to the low initial value. However, this time, carbon dioxide is found in the cold trap placed near the sample. Calorimetric results reported in Table II indicate also that carbon monoxide interacts with preadsorbed oxygen since the heats of adsorption of carbon monoxide are higher on the black sample (Table II) than on the pure surface of NiO(250°) (Fig. 12). 

The reverse interaction, between preadsorbed carbon dioxide and oxygen from the gas phase, was also studied (66). A small quantity of oxygen can be adsorbed (1.08 cra /gm) and the electrical conductivity of the sample increases. The initial heat of adsorption (83 kcal/mole) shows that oxygen reacts with adsorbed carbon dioxide. A subsequent adsorption of carbon monoxide is again possible (1.05 cm /gm) which produces a decrease of the electrical conductivity of the sample. These results were explained, from the calorimetric data, by the formation of a small number of C03"(ads) ions by the interaction of oxygen with preadsorbed carbon dioxide. These complex ions are then converted by carbon monoxide into carbon dioxide which remains adsorbed on the oxide surface. From these experiments it was concluded (66) that, although a small quantity of preadsorbed carbon dioxide may react with oxygen, this interaction is not a possible step of the reaction mechanism and that, consequently, adsorbed carbon dioxide is an inhibitor of the catalytic process. 

The calorimetric study of interactions on the surface of gallium-doped nickel oxide therefore yields results which are similar to those obtained on pure Ni0(250°), although the incorporation of trivalent ions changes somewhat the surface affinity toward oxygen. In both cases, two reaction mechanisms for the production of gaseous carbon dioxide are probable. In mechanism II, a reaction intermediate, C03-(ads) is formed whereas, in mechanism I, gaseous carbon dioxide is produced directly by the interaction of carbon monoxide with adsorbed... 

In this section are reported the results of a calorimetric study of the catal3d)ic oxidation of carbon monoxide on a divided nickel oxide [NiO(200°)] at 200° (84). At this temperature, carbon monoxide reduces the oxide with the formation of gaseous carbon dioxide. As the reduction extent increases, the color of the sample changes from yellowish green to black and the solid becomes ferromagnetic. Differential heats of reduction decrease rapidly from an initial value of 45 to 15 kcal/mole (Fig. 33). Calorimetric curves recorded during the reaction of doses A to G (Pig. 33) are reported in Fig. 34. Differential heats for doses... 

J.J. Prinsloo and P.C. Gravelle, Volumetric and calorimetric study of the adsorption of hydrogen, at 296 K, on supported nickel and nickel-copper catalysts containing preadsorbed carbon monoxide, J. Chem. Soc., Faraday Trans. I, 1980, 76, 512. 

Metals other than A1 have been successfully introduced in numerous zeolite frameworks. Aluminum substitution by other metals, such as Fe, Ga, Zn, Co or Cu in the zeolite framework results in modified acidity, and subsequently modified catalytic activity, for certain reactions such as selective catalytic reduction of NOx by hydrocarbons. For example, a calorimetric and IR spectroscopic study of the adsorption of N2O and CO at 303 K on Cu(II)-exchanged ZSM-5 zeolites with different copper loadings has been performed by Rakic et al. [92]. The active sites for both N2O and CO are Cu (I) ions, which are present on the surface as a result of the pre-treatment in vacuum at 673 K. The amounts of chemisorbed species adsorbed by the investigated systems and the values of the differential heats of adsorption of both nitrous oxide (between 80 and 30 kJ mof ) and carbon monoxide (between 140 and 40 kJ mol ) demonstrate the dependence of the adsorption properties on the copper content. 

Cone calorimetric measurements of these systems showed an improvement in fire retardancy as indicated by a reduced peak release rate. Cone calorimetry determines fire relevant properties such as heat release rate (HRR) and carbon monoxide yield during combustion of the material using oxygen depletion-based calorimetry. Gilman et have conducted a thorough study of the flamm-... 

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