Deactivation identifying activators

The typical industrial catalyst has both microscopic and macroscopic regions with different compositions and stmctures the surfaces of industrial catalysts are much more complex than those of the single crystals of metal investigated in ultrahigh vacuum experiments. Because surfaces of industrial catalysts are very difficult to characterize precisely and catalytic properties are sensitive to small stmctural details, it is usually not possible to identify the specific combinations of atoms on a surface, called catalytic sites or active sites, that are responsible for catalysis. Experiments with catalyst poisons, substances that bond strongly with catalyst surfaces and deactivate them, have shown that the catalytic sites are usually a small fraction of the catalyst surface. Most models of catalytic sites rest on rather shaky foundations. 

Figure 1 shows the effects of reaction temperature on the conversions of CO2 and CH4 over Ni-YSZ-Ce02 and Ni-YSZ-MgO catalysts. It was found that the Ni-YSZ-Ce02 catalyst is showed higher catalytic activity than the Ni-YSZ-MgO catalyst at temperature range of 650 850 Ti and the maximum activity was observed at above 800 °C, the optimum temperature for internal reforming in SOFC system [5]. In our previous work, it was identified that Ni-YSZ-MgO catalyst was deactivated with reaction time, however Ni-YSZ-Ce02 showed stable catalytic activity more than Ni-YSZ-MgO catalyst imder tiie tested conditions [6]. 

GL 18] ]R 1] ]P 19a] For a sputtered palladium catalyst, low conversion and substantial deactivation of the catalyst were foimd initially (0.04 mol 1 60 °C 4 bar 0.2 ml min ) [60, 62]. Selectivity was also low, side products being formed after several hours of operation (Figure 5.25). After an oxidation/reduction cycle, a slightly better performance was obtained. After steep initial deactivation, the catalyst activity stabilized at 2-4% conversion and about 60% selectivity. After reactivation, the selectivity approached initially 100%. As side products, all intermediates except phenylhydroxylamine were identified. 

This same [e] experimental protocol leads to a graphical overlay plot that yields valuable kinetic information if the two experiments described in Table 50.1 are plotted together as reaction rate vs. [2], the two curves will fall on top of one another ( overlay ) over the range of [2] common to both only if the rate is not significantly influenced by changes in the overall catalyst concentration within the cycle, including catalyst activation, deactivation or product inhibition. Overlay in same excess plots, therefore, may be used to confirm catalyst robustness or identify problems such as catalyst deactivation or product inhibition. 

Figura 2.9 Dse of th Grob test Mixture to compare tbe activity of various glass surfaces coated with ov-ioi. Surface types A > Untreated pyrex glass, B pyrex glass deactivated by thermal degradation of Ceurbowax 20M, C < SCOT column, prepared with Silanox 101, D pyrex glass column coated with a layer of barium carbonate and deactivated as in (B), and E - untreated fused silica. Components are identified in Table 2.7 with ac - 2-ethylhexanoic acid. (Reproduced with permission from ref. 152. Copyright Elsevier Scientific Publishing Co.)...

Chen et al,33 studied the deactivation of Zr02-promoted cobalt on silica in the FTS using a fixed bed reactor at realistic reaction conditions and high conversions (65-90%). A fraction of the lost activity was regained by a re-reduction, and the selectivity was reported to be unaffected by deactivation and regeneration. The authors identified hydrated cobalt silicates using IR and XRD analyses, and suggested that these species caused the permanent deactivation. 

The authors ascribed the high WGS rates of the Pt/FSM-16 catalysts to confinement effects which increased the activities of Pt surface atoms, as well as to anisotropic morphological effects. Based on infrared studies, the authors identified unidentate formate species as intermediates in Au/NaY, and though the species was also observed on Au/Na Mordenite, the catalyst was found to deactivate by poisoning from a carbonate species. Only stable carbonates were observed on Au/Na-ZSM-5. The authors proposed a mechanism for Au/NaY, depicted in Scheme 94. 

Whilst today we can no longer accept either of these statements as literally and universally valid, they contain two very important and closely related ideas which have been proved useful. The first of these is that a normal, stable ester may become activated by interaction with another species a natural corollary of this is that esters can also be deactivated, or stabilised, by such interaction. The other idea is that in a series of esters gradations of polarity may be found, or that the polarity of any one ester, in particular the reactivity of the bond linking the potentially anionic and cationic moieties, may change according to the environment in which the ester finds itself. The two ideas are thus closely linked. One serious point in which I find myself in disagreement with Schmerling and Ipatieff and some contemporary writers is that, with respect to identifiable reaction intermediates,... 

Phosphinite pincer iridium systems have also been shown to have a lower tendency to oxidatively add TEE to give (vinyl)(hydride) complexes similar to 3 [18]. While this has been identified as one of the major catalyst deactivation processes in phosphine pincer iridium catalysis, apparently with complexes such as 5, only olefin coordination can occur. However, this is a considerably weaker bonding and is less detrimental to catalyst activity. Eased on steric arguments, product olefin coordination (e.g. COE) is favored over TEE coordination, and therefore at a high TON and high product concentrations the phosphinite catalysts 5 are markedly less active than the phosphine analogues 1. 

It has been ten years since Amoco announced the UltraCat process O) for SOx control in FCC units. In those ten years, as well as in the years previous to the announcement, much work was done to develop catalysts that would control SOx emissions. The evidence is the 80 or more U.S. patents that have issued in that time to Amoco and others. One of the first patents issued was to Amoco in 1974 ( ) for the addition of magnesia and other group IIA oxides to cracking catalyst. This paper reviews the SOx catalyst developments and emphasizes the work done at Amoco to identify the active materials, explain the deactivation mechanism and, finally, to make a side-by-side comparison of various catalytic systems that are being pursued commercially today. 

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