Dissociative chemisorption defined

Evidence of dissociative chemisorption resulting in the final formation of atomic carbon and its incorporation in the metal lattice at 1000°K to form the carbide was reported. These methods when used in combination are informative, and the surfaces studied are clean and well defined. It is to be hoped that other metals will be so studied in the future. 

Equation (8) gives the limiting, potential-independent current density predicted for complete control of sequence (5b) -h (5c) by the dissociative chemisorption of H2 (process (5b)) at a catalyst surface with a small number of CO-free sites (see 18a). Such a limiting rate of hydrogen electro-oxidation at low anodic overpotentials has been observed recently in RDE experiments with H2/CO mixtures, performed with platinum and PtRu RDEs [18d,e]. This limiting current density (Eq. (8)) explains the PEFC characteristic observed with low CO levels in the fuel feed stream, depicted in Fig. 13. Under such conditions, the fuel cell will exhibit ordinary anode losses up to the current density defined by Eq. (8), but higher current demands would require a... 

Sulfur poisoning occurs through two competing reaction systems. The first is dissociative chemisorption of hydrogen sulfide according to Reaction 2.10 [1,9,10]. The second system begins in Reaction 2.11 defined as the adsorption of steam, which further reacts with hydrogen sulfide, as in Reaction 2.12, to form inactive sulfur poisoned nickel catalyst and water. 

Chemical Characterization. Titration methods in aqueous medium are not very informative, because H2O tends to strongly modify surface properties by molecular or dissociative chemisorption (70). Therefore, nonaqueous methods have been proposed, where the solvent (eg, benzene or isooctane) does not (or not strongly) interact with the catalyst surface. Hammett indicators were used to determine the acid strength in terms of the Hammett-Deyrup function Hq which is defined as... 

Hydrogen spillover is a well-documented phenomenon in the catalysis literature. Hydrogen spillover is defined as the dissociative chemisorption of hydrogen on metal nanoparticles, and subsequent migration of hydrogen atoms onto adjacent surfaces of a receptor via spillover and surface diffusion [8,57,58] (Figure 6.6). The comprehensive review by Coimer and... 

Fic. 2. Chemisorption and dissociation of a diatomic AB. (a) The traditional Len-nard-Jones one-dimensional potential diagram E versus R, where R is an ill-defined reaction coordinate, say the AB-surface distance, (b) The conventional two-dimensional potential diagram E versus R(x, y). The reaction coordinates are the A — B distance ( ) and the AB-surface distance (y). The energy minima correspond to the (nondissociated) molecular chemisorbed state DAB + QAB and atomic (dissociated) chemisorbed state gA + gB, the maximum to the transition state (TS) with some finite A — B bond length, (c) The multidimensional BOC potential diagram, similar to (b), but the reaction coordinate is the A — B bond order xAB. The M — AB bond order is conserved to unity (xA + xAB + xB = 1) up to the transition state where 1 > = c > 0 and 8 = 1/2(A ,abj6 + gAB). See text for notations... 

The measurement of the metallic surface area in a multi-component system as a bimetallic supported catalyst or an alloy is feasible by selective chemisorption on the metallic phase. The chemisorption stoichiometry is defined with reference to the adsorbate related to the metallic element [8]. Therefore, the chemisorption process is very different if the adsorbed gas molecule is dissociated or not. The two kinds of chemisorption involve different energetic behaviours and different theoretical models define them associative and dissociative adsorption. In the first case, the gas is adsorbed without fragmentation in the second case, the gas molecule is adsorbed after its decomposition in one or more fragments. Hydrogen, for example, is always adsorbed in its dissociated form. 

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