Hydrogen dissociation atoms

At elevated temperatures, molecular hydrogen dissociates into the atomic form, which can readily enter and diffuse through the steel. Under these conditions, the diffusion of hydrogen in steel is more rapid. As discussed in Section 4, Forms of High Temperature Hydrogen Attack, hydrogen may react with the carbon in the steel to cause either surface decarburization or... 

The primary radical yields are often 3. A much higher value (>10) indicates chain reaction. In fact, the chain reaction mechanism for the formation of HC1 from a gaseous mixture of hydrogen and chlorine exposed to radium irradiation is one of the earliest example of this kind, although the detailed chemistry was later shown to involve dissociated atoms rather than electrons and ions, as was originally proposed (see Bansal and Freeman, 1971). 

TPR of supported bimetallic catalysts often reveals whether the two metals are in contact or not. The TPR pattern of the 1 1 FeRh/SiOi catalyst in Fig. 2.4 shows that the bimetallic combination reduces largely in the same temperature range as the rhodium catalyst does, indicating that rhodium catalyzes the reduction of the less noble iron. This forms evidence that rhodium and iron are well mixed in the fresh catalyst. The reduction mechanism is as follows. As soon as rhodium becomes metallic it causes hydrogen to dissociate atomic hydrogen migrates to iron oxide in contact with metallic rhodium and reduces the oxide instantaneously. 

The acidity of a C-H bond is influenced by the hybridization state of the carbon atom attached to the acidic hydrogen. Dissociation of the acid generates an anion whose lone pair of electrons is held in a hybridized orbital. We can consider sp orbitals to have more s character than sp orbitals, and similarly sp orbitals to have more character than sp orbitals (see Section 2.6.2). Since orbitals are closer to the nucleus than p orbitals, it follows that electrons in an p-hybridized orbital are held closer to the nucleus than those in an sp orbital those in an sp orbital are similarly closer to the nucleus than those in an sp orbital. It is more favourable for the electrons to be held close to the positively charged nucleus, and thus an p-hybridized anion is more stable than an p -hydridized anion, which is more stable than an p -hybridized anion. Thus, the acidity of a C-H bond decreases as the character of the bond decreases. 

From the H/M values for the catalysts NiSn-BM (Sn/Ni = 0.29) and PtSn-BM (Sn/Pt = 0.71), and the H/M values for the corresponding monometallic ones, it can be inferred that Sn blocks about 70% of the originally accessible M atoms. For these systems, based on the dispersion measured for Pt and Ni, the atomic ratios Sn/M correspond to values higher than 1. Notably, even in these cases, an important portion of the metallic surface has sites accessible to hydrogen dissociative adsorption, which is essential for the phase to be active in hydrogenation reactions. 

Al high temperatures, the loss of heat from a glowing wire in hydrugen is l.irger than expected on regular assumptions. This is believed lu be due lo dissociation of ordinary hydrogen into atomic hydrogen (H). See Table I. 

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