Activity in hydrogenation

Fig. 7.10 Ni Mossbauer spectra of LaNi5 samples after various treatments (a) no hydrogen exposure, (b) activated in hydrogen, (c) after 1,584 thermally induced absorption-desorption cycles, as described in the text. The solid lines are least-squares fits to a single Lorentzian in (a) and (b). (c) was fitted with a single Lorentzian (representing nonmagnetic nickel atoms) and a 12-line hyperfine spectrum (from [20])...

Fe/Ir catalysts In situ Fe and Ir Mossbauer spectroscopy of silica-supported Fe/Ir catalysts with different iron to iridium ratios following pretreatment in hydrogen show that the reduction of the Fe component is enhanced by the presence of Ir metal. The presence of Ir was found to increase the catalytic activity in hydrogenation of carbon monoxide and also to influence selectivity... 

That chemisorbed oxygen was active in hydrogen abstraction, resulting in water desorption and the formation of chemisorbed sulfur, was first established by XPS at copper and lead surfaces.42 An STM study of the structural changes when a Cu(110)-O adlayer is exposed (30 L) to hydrogen sulfide at 290 K indicates the formation of c(2 x 2)S strings. 

The results report in Figure 4a show that there is no linear correlation between the basic activity and the carbon dioxide retained at RT. In the case of eta and gamma, some basic sites were detected by C02 adsorption but could not be active in hydrogen transfer at 250°C. 

Except for Prussian blue activity in hydrogen peroxide, reduction has been shown for a number of transition metal hexacyanoferrates. The latter were cobalt [151], nickel [152], chromium [150], titanium [153], copper [154], manganese [33], and vanadium [28] hexacyanoferrates. However, as was shown in review [117], catalytic activity of the mentioned inorganic materials in H202 reduction is either very low, or is provided by impurities of Prussian blue in the material. Nevertheless, a number of biosensors based on different transition metal hexacyanoferrates have been developed. 

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. 

Activities in hydrogen and fuel cells are increasing within the framework of national and European... 

Figure 1. Initial rate of isotopic exchange of the oxygen of oxides with molecular oxygen at 370°C, Curve 1 and their relative activity in hydrogen oxidation at 340°C, Curve 2. The activity of lanthanum oxide is taken to be unity (1).

Figure 5.13. In situ atomic-resolution ETEM image of Pt/titania catalyst (a) finely dispersed Pt particles (b) in situ real-time dynamic activation in hydrogen imaged at 300 C. The 0.23 nm (111) atomic lattice spacings are clearly resolved in the Pt metal particle, P and (c) the same particle imaged at 450 C, also in H2. SMSI deactivation with a growth of a Ti-oxide overlayer (C), and the development of nanoscale single-crystal clusters of Pt, with atomic resolution (arrowed). (After Gai 1998.)...

Samples which have been sintered in air show the break in the Arrhenius plot even after a similar activation in hydrogen. Activation in vacuo, for both sintered and unsintered samples, leads to some irrepro-ducibility of the rates, which tends to disappear after the samples are heated in the reacting mixture. The difference between activations in... 

A wide range of soluble metal complexes has proved to exert catalytic activity in hydrogenation of unsaturated molecules. Most attention, however, has focused on Group Vm elements since they give rise to the most active catalytic systems. 

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