The inhibiting effect of CO

Carbon monoxide has been widely used to characterise the hydroxyl groups of solid acids, since its interaction with acidic protons modifies the strength of the C-O bond.I Analysis by IR spectroscopy is a tool of choice to obtain information on the surface of the catalyst. CO acts as a basic probe and according to previous studies, its complexation with Lewis acid sites (LAS) decreases the acidity and consequently, the activity of the catalyst in n-butane isomerization. However, it is uncertain if the interaction of CO with LAS is the main origin of catalyst deactivation, since n-butane isomerisation is also inhibited by CO in the absence of LAS. 

In the last decade, deuterium labelling of alkanes or solid acid catalysts has proved to be a preferred tool for mechanistic studies. The availability of high resolution multinuclear NMR spectroscopy and mass spectrometry has facilitated the interpretation of the experimental results. It appears that despite the differences in media between liquid and solid acids, all results in acid-catalysed hydrocarbon chemistry can be rationalised by mechanisms involving solvated carbenium ion intermediates, as known from classical organic chemistry. Nevertheless, the determination of the real nature of the 

Application of C Radiotracer for the Study of Heterogeneous Catalytic Reactions 

Investigation of Reaction Pathways by Using Mixtures Containing Labelled Reactant 

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According to the reports of Tascon et al., the inhibiting effect of NO on subsequent CO adsorption is larger than the inhibiting effect of CO on NO adsorption over both LaCoOs and LaMn03[65]. It is thus speculated that CO appears to be more weakly adsorbed than NO at... 

The inhibition effect of CO is widely accepted and reasonably well documented for coal char gasification but not for biomass. The lack of extensive literature for wood char CO2 gasification kinetics including CO has strongly motivated this investigation. 

Consequently, in contrast to Ga/MFl cataly sts no complementary synergy between extraframework A1 species and zeolite acid sites is observed in the early stages of propane activation. Aprotonic sites do not play a direct role in propane activation. The correlation observed between the initial rate of propane scrambling and the amount of framework A1 atoms, the dependence of propane activation rate on acid site strength, and the inhibiting effect of co-adsorbed bases ohserved on niire H-MFI siippe< t monofnnctional nronane activation on stronp acid sites... 

Both forward and backward permeation are considered in order to analyze both cases where the membrane behaves as hydrogen purifier (forward permeation) or hydrogen supplier (backward permeation). The permeation process is considered to be divided into several elementary steps, each of which is characterized by its own model equations. The details of such a model can be found elsewhere where the model introduced in was modified in some steps to take into account the presence of an inhibitor species (CO). The same approach was followed by Catalano et al., who analyzed the inhibiting effect of CO without considering the concentration polarization. ... 

Kurokawa, H., Yakabe, H., Yasuda, I. et al. (2014) The inhibition effect of CO on hydrogen permeability of Pd-Ag membrane applied in a microchannel module configuration. International Journal of Hydrogen Energy, 39,17201-17209. 

Platinum seems to be the best catalyst for benzene and toluene oxidation provided that there is no CO or alkenes in the gas mixture. " Rhodium, very active in CO and alkene oxidation, may help platinum to work in oxidation of aromatics free of inhibition. " An example of the inhibiting effect of CO on HC oxidation is presented in Table 1.13. 

Another group of information is the extraction of kinetic data for a defined reaction (activation energy, fi-equency factors, etc.). This analysis work is much more elaborate and usually requires measiu-ements at different temperature levels and partial pressures of reactants. Also the inhibiting effect of CO might be included in such investigations. Derived data are typically used in kinetic models for process design or evaluation. 

When low flow rates of CO2 were used the increase of pore volume is especially noticeable for the pore volume contribution of pores with a radius smaller than 3.7 nm. These results are in agreement with our previous results (ref. 19) and with the studies of Rand and Marsh (ref. 18), who observed that a greater micropore volume is developed by gasification when a lower flow rate is used, presumabiy because of the inhibiting effect of CO in the outermost section of the particle. 

Summarizing, two different mechanisms are proposed to explain the inhibition effect of CO molecules the direct blocking of the adsorption sites (reduction of the membrane surface for the H2 permeation) and the increase of the transition state energy controlling the hydrogen dissociation, a preliminary step for the subsequent atom diffusion in the Pd-alloy (Eriksson and Ekedahl, 1998). Really, these two mechanisms should be considered... 

The first term in R (0) accounts for inhibition effects due to chemisorption of CO and C3H6. The second term is required to fit the experimental data at higher concentrations of CO and C3H6. The third term accounts for the inhibition effects of NO. Each rate parameter is of the form... 

The influence of electronegative additives on the CO hydrogenation reaction corresponds mainly to a reduction in the overall catalyst activity.131 This is shown for example in Fig. 2.42 which compares the steady-state methanation activities of Ni, Co, Fe and Ru catalysts relative to their fresh, unpoisoned activities as a function of gas phase H2S concentration. The distribution of the reaction products is also affected, leading to an increase in the relative amount of higher unsaturated hydrocarbons at the expense of methane formation.6 Model kinetic studies of the effect of sulfur on the methanation reaction on Ni(lOO)132,135 and Ru(OOl)133,134 at near atmospheric pressure attribute this behavior to the inhibition effect of sulfur to the dissociative adsorption rate of hydrogen but also to the drastic decrease in the... 

The degradation of trichloroethene by methylotrophic bacteria involves the epoxide as intermediate (Little et al. 1988). Further transformation of this may produce CO that can toxify the bacterium, both by competition for reductant and by enzyme inhibition (Henry and Grbic-Galic 1991). The inhibitory effect of CO may, however, be effectively overcome by adding a reductant such as formate. 

The anion electronic effect in a recent analysis of the inhibition effect of bisulfate and comparison with the effect of OH adsorption (Pt-OH formation), Wang and co-workers found that the electronic effect must also be operative [Wang et al., 2004]. 

Co-trimoxazole is a combination of trimethoprim and the sulfonamide sulfamethoxazole. Since THF synthesis is inhibited at two successive steps, the antibacterial effect of co-trimoxazole is better than that of the individual components. Resistant pathogens are infrequent a bactericidal effect may occur. Adverse effects correspond to those of the components. 

Most transition metals (for Fe, Co and Ni see the following paragraphs) are located on the descending branch of the volcano curve. For these metals, the adsorption of H is strong and 5h close to saturation, making H2 desorption from the surface difficult. For these metals, the inhibiting effect of 5h prevails over the... 

This follows the inhibiting effect of tetrahydrothiophene, excess CO, and PR3. The catalytic cycle may then proceed analogously to that supposed in similar reactions ... 

The CO oxidation appears to be kinetically limited in these ternary fuel mixtures due to the inhibiting effect of methane and the competition of methane for the OH radicals. 

CO reactants and the H2O product of the synthesis step inhibit many of these secondary reactions. As a result, their rates are often higher near the reactor inlet, near the exit of high conversion reactors, and within transport-limited pellets. On the other hand, larger olefins that are selectively retained within transport-limited pellets preferentially react in secondary steps, whether these merely reverse chain termination or lead to products not usually formed in the FT synthesis. In later sections, we discuss the effects of olefin hydrogenation, oligomerization, and acid-type cracking on the carbon number distribution and on the functionality of Fischer-Tropsch synthesis products. We also show the dramatic effects of CO depletion and of low water concentrations on the rate and selectivity of secondary reactions during FT synthesis. 

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