Products adsorption

At low temperatures unstable adsorption products or reaction intermediates could be trapped. Thus, carbonite CO, ions arise on CO interaction with basic oxygen ions which account for catalytic reaction of isotopic scrambling of CO or thiophene on activated CaO. 

Comparable patterns are followed by other organic substances such as formaldehyde and formic acid. All these substances are dissociatively adsorbed on platinum [4] and it was suggested that they build the same adsorption product [35]. 

The inhibition of the oxidation process between -0.3 V and 0.4 V must be due to the poisoning of active sites, since there are no obvious adsorption products, and so the poison must be present in very low amounts. Similar inhibition was observed by the authors in acid solution. In order to increase the sensitivity of their system, the authors carried out a PDIR experiment and observed adsorbed CO which, they concluded, was the main poison in acid and base. At potentials > 0.4 V, the oxidation recommences as a result of the freeing up of active sites as the poison is oxidised. 

Fig. 4.56 In pulsed-laser stimulated field desorption with coadsorption of N2 and H2, if the temperature of the Pt tip is between 120 and 150 K, then reaction intermediates of NH3 can be detected as shown in (a). If the surface temperature of the tip is only —50 K lower, no reaction intermediates of NH3 can be detected. Instead, only field adsorption products, N2 and N2H+ are detected.

Si(100)-2 x 1 surface. Indeed, similarities in adsorption products between the two surfaces have been reported, as will be seen later in this chapter. 

Furthermore, the organic functionalization studies have indicated that multiple reaction products can form even for simple systems. Kinetic and thermodynamic influences must be considered in any analysis of the product distribution. Moreover, the studies have revealed differences in the dominance of kinetic vs. thermodynamic control between the silicon and germanium surfaces. The dissimilarity primarily stems from the fact that adsorbate bonds are usually weaker on Ge than on Si. This difference in energetics leads to observable differences in the degree of selectivity that can be achieved on the two surfaces. Another important motif is the significance of interdimer bonding in the products. Many molecules, even as small as ethylene, have been observed to form products that bridge across two dimers. Consequently, each analysis of adsorption products should include consideration of interdimer as well as intradimer species. 

J. Walker and S. A. Kay showed that the brown product of the action of iodine in aq. or chloroform soln. on magnesia is a case of adsorption analogous to the adsorption of acids by silk, and of iodine by starch. P. Guichard studied the adsorption products with iodine vapour and alumina, silica, magnesia, and beryllia. 

Another interesting observation is almost identical behavior of samples exposed for SOj adsorption. Regardless the carbonization temperature the same amounts of SO, are adsorbed on the samples exhausted in the HjS breakthrough test. This suggests that after exhaustion of all active centers responsible for HjS adsorption the differences in surface chemistry, which play a role in sulfur dioxide adsorption/oxidation on fresh surfaces, seem to be somehow screened by HjS adsorption products. Nevertheless, it is interesting that still some capacity exists. 

Hsu, F. L., Wang, P. M., Lu, S. Y., and Wu, W. T. 2002. A combined solid-state and submerged cultivation integrated with adsorptive product extraction for production of Monascus red pigments. Bioprocess Biosyst. Eng. 25(3), 165-168. 

This explains why the C02 adsorption capacity of PEI-MPS increases as temperature increases from 25 to 75 oC. However, the reaction between amine groups and C02 is exothermal, therefore, the further temperature increases, the slower C02 adsorption becomes. At a certain temperature, the reaction (1) starts shifting to left side, which accelerates the decomposition of adsorption product and is apply to desorb C02 and regenerate adsorbent. This is the reason why the C02 adsorption capacity of PEI-MPS deceases as temperature increases to 100 and 110 oC. In fact, PEI impregnated adsorbents are usually regenerated at a temperature above 100 oC. 

First principles calculations based on DFT were used to investigate the adsorption of urea onto a nonpolar ZnO(lO-lO) [83] surface. The results indicated that molecular urea adsorption was favored, and that stable adsorption products were formed through the reaction between nitrogen atom or oxygen atom from urea and zinc atom on the surface. The adsorption energy was -1.48 and -1.41 eV, respectively. 

The CD step was first used by Union Carbide in the IsoSiv process in a Texas PSA plant in 1961 (Avery and Lee, 1962 Keller, 1983 Cassidy and Holmes, 1984). The process separated 1,000 barrels per day of natural gasoline feed into n-paraffins and branched/cyclic hydrocarbons. The feed contained 54.4% n-paraffins and 45.6% branched/cyclic hydrocarbons (Symoniak, 1980). The n-paraffin (strong adsorptive) product purity was 95-98%, whereas the purity of the isomer was 98-99% (Symoniak, 1980). Additional and larger IsoSiv plants have been built since 1961. The CD step was mentioned, as part of more complex PSA processes, in several patents that were all filed later than its first commercial practice in 1961 (Kiyonaga, 1965 Wagner, 1969). 

Besides energy conservation and increased product recovery, the flow of the strong adsorptive product is smoothed by the pressure equalization steps. The four-bed process has been subsequently developed into the Polybed process, consisting of 9 to 10 beds, which is successfully used for large-scale production of high-purity hydrogen. 

Lukaszewski M, Siwek H, Czerwinski A (2010) Analysis of the electrochemical quartz crystal microbai-ance response during oxidation of carbon oxides adsorption products on platinum group metals and alloys. J Solid State Electrochem 14(7) 1279-1292... 

Magnesium hydroxide exhibits a remarkable adsorptive property for certain dyestuffs. This adsorption is to a certain degree the organic counterpart of the adsorption of iodine on magnesium hydroxide (see test (1)). For certain dyestuffs of the azo series, there is a difference in color between the adsorption product (color lake) and the non-adsorbed dyestuff. Since the adsorption is instantaneous, it affords an excellent test for magnesium. 

Siwek, H., Tokarz, W., Piela, P. Czerwinski, A. Electrochemical behavior of CO, CO2 and methanol adsorption products formed on Pt-Rh alloys of various surface compositions. J. Power Sources 181... 

Siwek, H., Lukaszewski, M., Czerwinski, A. Electrochemical study on the adsorption of carbon oxides and oxidation of their adsorption products on platinum group metals and alloys. Phys. Chem. Chem. Phys. 2008, 10, 3752-3765. 

The chemisorbed substance which forms on platinum in formaldehyde solutions behaves like the chemisorption product from methanol [20, 21, 52, 53]. Dehydrogenation and destructive hydrogenation take place during chemisorption of acetaldehyde, and the rates of these processes are higher than the rates of the analogous processes in saturated alcohols [20, 38, 55, 57, 59]. The adsorption product from acetaldehyde probably contains both HCO particles (Fig. 1) and particles with two carbon atoms. During cathodic polarization the latter are removed as ethane [59]. 

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