Catalytic performance, importance

Beyond the catalytic ignition point there is a rapid increase in catalytic performance with small increases in temperature. A measure of catalyst performance has been the temperature at which 50% conversion of reactant is achieved. For carbon monoxide this is often referred to as CO. The catalyst light-off property is important for exhaust emission control because the catalyst light-off must occur rehably every time the engine is started, even after extreme in-use engine operating conditions. 

The performance of a supported metal or metal sulfide catalyst depends on the details of its preparation and pretreatraent. For petroleum refining applications, these catalysts are activated by reduction and/or sulfidation of an oxide precursor. The amount of the catalytic component converted to the active ase cind the dispersion of the active component are important factors in determining the catalytic performance of these materials. This investigation examines the process of reduction and sulfidation on unsupported 00 04 and silica-supported CO3O4 catalysts with different C03O4 dispersions. The C03O4 particle sizes were determined with electron microscopy. X-ray diffraction (XRD), emd... 

Olefin metathesis is one of the most important reaction in organic synthesis [44], Complexes of Ru are extremely useful for this transformation, especially so-called Grubbs catalysts. The introduction of NHCs in Ru metathesis catalysts a decade ago ( second generation Grubbs catalysts) resulted in enhanced activity and lifetime, hence overall improved catalytic performance [45, 46]. However, compared to the archetypal phosphine-based Ru metathesis catalyst 24 (Fig. 13.3), Ru-NHC complexes such as 25 display specific reactivity patterns and as a consequence, are prone to additional decomposition pathways as well as non NHC-specific pathways [47]. 

Recently, however, the development of nanotechnology may provide the changes on the research and development of practical catalysts. As mentioned in the previous section we can now design and synthesize a metal nanoparticle with not only various sizes and shapes, but also with various combinations of elements and their locations. Thus, we can now design the synergetic effect of two elements. In the case of core/shell structured bimetallic nanoparticles, the shell element can provide a catalytic site and the core element can give an electronic effect (a ligand effect) on the shell element. Since only the atoms on the surface can be attached by substrates, the thickness of the shell should be an important factor to control the catalytic performance. 

In the present work, the transient reaetivity and the ehanges of the snrface charaeteristies of an eqnihbrated VPP in response to modifications of the gas-phase composition have been investigated. As the VN atomic ratio is one of the most important factors affecting the catalytic performance of the VPP (6), two catalysts differing in VN ratio were stndied. Data obtained were used to draw a model about the nature of the surface active layer, and on how die latter is modified in function of the reaction conditions. 

A complete list of the reaction conditions tested for this response surface design can be found in [76], The center point reaction condition was repeated six times. This was done to measure the variability of the reaction system. Also, the space velocity is kept constant, as it was the least important factor predicted by screening design, for all the reaction conditions. The purpose of this nested response surface design was to develop an empirical model in the form of Eqn (5) to relate the five reaction condition variables and the three catalyst composition variables to the observed catalytic performance. 

Comparing the TPSR results obtained with Co-HFER and Co/Pd-HFER catalysts, it is possible to verify that the introduction of palladium has a major importance for the improvement of the catalytic performance. The presence of Pd species and the redistribution of cobalt oxide species with the formation of Co-oxo cations can have a major role as catalytic sites for the lower temperature activation of CH4 with N02 and N2 formation. A conversion of 80 % of NOx into N2 is obtained with the bimetallic catalyst. 

It is evident that the silica support influences the catalytic performance and it is important to understand the details of the processes involved. For the sol-gel material it was shown by 31P NMR spectroscopy that the immobilised cationic complex completely transforms to the neutral rhodium-hydride species under a CO/H2 atmosphere (Scheme 3.3). On dried silica, however, this conversion might not be complete since the dried support is more acidic [32], It is therefore very likely that the neutral and cationic rhodium complexes co-exist on the silica support. 31P NMR measurements on homogeneous rhodium complexes have shown that a simple protonation indeed converts the neutral rhodium hydride species into the cationic complex. 

From the above results, one can conclude that different NiO/MgO solid-solution catalysts can have very different catalytic performances. For example, Fujimoto et aV s Nio.03Mgo.97O solid-solution catalyst exhibited relatively low activities. To reach about 82% conversion of CH4 in the presence of this Nio.03Mgo.97O catalyst, the space velocity had to be reduced to 18,670 mL (g catalyst)-1 h-1 at 1123 K (Fig. 15) (238). In contrast, Ruckenstein and Hu s NiO/MgO catalysts have very high activities (>91% conversion of CH4 and >95% selectivities of CO and H2 at the space velocity of 60,000 mL (g catalyst)-1 h-1 at 1063 K) (Fig. 14) (239). Hu and Ruckenstein (239,257,259) noted that the properties of the MgO, such as its surface area, pore size distribution, and crystal structure, have important effects on the NiO/MgO solid-solution catalysts. They found that the MgO supplied by Aldrich, which has... 

In summary, the basicity and the strong NiO-MgO interactions in binary NiO/MgO solid solution catalysts, which inhibit carbon deposition and catalyst sintering, result in an excellent catalytic performance for C02 reforming. The characteristics of MgO play an important role in the performance of a highly efficient NiO/MgO solid-solution catalyst. Moreover, the NiO/MgO catalyst performance is sensitive to the NiO content a too-small amount of NiO in the solid solution leads to a low activity, and a too-high amount of NiO to a low stability. CoO/MgO solid solutions have catalytic performances similar to those of NiO/MgO solid solutions, but require higher reaction temperatures. So far, no experimental information is available regarding the use of a FeO/MgO solid solution for CH4 conversion to synthesis gas. 

The comparison of catalytic properties was made under identical reaction conditions, among three important candidate catalysts, namely, the Pt/y-Al203, Au/a-Fe203, and Cu Ce, x02 y systems [50], The catalytic tests were performed in the reactant feed containing CO, H2, C02, and HzO — the so-called reformate fuel. The effects of the presence of both C02 and H20 in the reactant feed on the catalytic performance (activity and selectivity) of these catalysts as well as their stability with time under reaction conditions have been studied. The composition of the prepared samples and their BET specific surface areas are presented in Table 7.6. The results obtained with the three catalysts in the presence of 15 vol% COz and of both 15 vol% COz and 10 vol% H20 in the reactant feed (with contact time wcat/v = 0.144 g sec/cm3 and X = 2.5) are shown in Figure 7.12. For comparison, the corresponding curves obtained under the same conditions but without water vapor in the feed are also shown in Figure 7.12. 

PICA) show excellent activity and enantioselectivity for reaction of such bulky ketones.Selection of alcoholic solvent is important to achieve high catalytic performance. Thus, hydrogenation of pinacolone with the (5)-TolBINAP/PICA-Ru catalyst (S/C = 100,000) in C2H5OH quantitatively gives (5)-3,3-dimethyl-2-buta-nol in 98% ee (Figure 1.21). The reaction in conventional 2-propanol with the same catalyst results in the S alcohol in only 36% ee. 

The dendrimer framework also plays an important role. The catalytic performance measured by activity, selectivity, stability, and recyclability depends on the dendritic architecture, and it is important to distinguish periphery-functionalized, core-functionalized, and focal point-functionalized dendrimers (Fig. 1). Periphery-functionalized dendrimers have catalytic groups located at the surface where they are directly available to the substrate. In contrast, when a dendrimer is functionalized at its core, the substrate has to penetrate the dendrimer support before it reaches the active center, and this transport process can limit the rate of a catalytic reaction if large and congested dendrimers are involved. 

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