Catalyst with distributed activity functions

The activity of CoSx-MoSx/NaY (2. IMo/SC) is shown in Fig.5 for the HYD of butadiene as a function of the Co/Mo atomic ratio. The HYD activity decreased slightly on the addition of Co up to Co/Mo = ca. 1, followed by a steep decrease at a further incorporation of Co. The HYD/HDS activity ratio decreased with increasing Co content and reached the ratio for CoSx/NaY at the Co/Mo atomic ratio of the maximum HDS activity (Fig.3). The product selectivity in the HYD of butadiene shifted from t-2-butene rich distribution to 1-butene rich one on the addition of Co, as presented in Fig.6. It is worthy of noting that at the Co/Mo ratio of the maximum HDS activity, the butene distribution is close to that for CoSx/NaY. It should be noted, however, that these product distributions are not the initial distributions of the HYD over the catalyst but the distributions modified by successive isomerization reactions. It was found that MoSx/NaY showed high isomerization activities of butenes even in the... 

For the TBR, spherical catalyst particles of uniform size with the catalytically active material either uniformly distributed throughout the catalyst or present in a shell were considered. For the MR, channels of square cross section were assumed to have walls covered by the washcoat distributed in such a way that the comers are approximated by the circle-in-square geometry, while the sides are approximated by a planar slab geometry. The volumetric load of catalytic material was a function of the washcoat thickness... 

Zeolite supported Co-Mo composite catalysts were prepared by introducing Co(NO)(CO)3 or Mo(CO)6 into MoSx/NaY or CoSx/NaY, respectively, followed by a subsequent sulfidation at 673 K. Figure 12 shows the HDS activity of the composite catalyst, CoSx-MoSx/NaY (Co was introduced after Mo, 2 Mo/SC), as a function of the CoMo atomic ratio. It is revealed that the maximum activity is obtained around Co/Mo = 1. No activity decrease was observed even after prolonged sulfidation at 673 K. The HYD/HDS activity ratio decreased with increasing Co content and reached the ratio for CoSx/NaY at the composition where the maximum HDS activity is attained. In addition, the butene distribution in the butadiene HYD became identical with that of CoSx/NaY at Co/Mo = ca. 1. The HDS activity of MoSx-CoSx/NaY catalyst in which Mo was added to the pre-existing Co sulfide species was identical with that of CoSx-MoSx/NaY at the same composition. The HDS activity of MoSx/NaY, however, was remarkably decreased by the addition of Fe by using Fe(CO)s (FeSx-MoSx/NaY). 

In the past decade, our group at Penn State has been focusing on a functionalization approach by the combination of metallocene catalysts and reactive comonomers. The chemistry takes the advantage of metallocene catalyst with a tunable single active site to prepare polyolefin copolymers with narrow molecular weight and composition distributions, high catalyst activities, and predictable tacticities and copolymer compositions. 

A wide variety of analytical probes are used to study, characterize and monitor catalysts and catalyst surfaces. Our intent here is to discuss some of the more common and routine techniques. Much more detail and many more techniques can be found in specialized books 33, 32, 27, 12]. A catalyst functions through the highly specific interactions the active sites have with the reactants. The catalyst might be a metal dispersed on an inert carrier, a polycrystalline or amorphous mixture of metal oxides, or a zeolite (a crystalline and highly porous oxide). The experimentalist is typically interested in the catalyst composition, structure of the catalyst, distribution of active sites, presence of poisons/impurities after the catalyst has been used, and number of active sites parameters that influence the catalytic activity. 

If the selectivity of the MIP catalyst is the main objective, the partial poisoning of active centers might be a way to improve the performance of the system. The imprinting procedure generates a statistical distribution of selective and less selective reactions centers. Studies indicate that the least selective sites are the most reactive [27]. The reaction of an MIP catalyst with sub-stoichiometric amounts of a catalyst poison under kinetic control should, therefore, result in a less active but more selective MIP catalyst. As a poisoning reaction, the covalent modification of functional groups or the irreversible complexation of a metal center could be employed (Fig. 20). 

When Co2Rh2(CO)j 2 mixture of Co4(CO)i2 and Rh4(CO)j2 was impregnated onto organic Dowex resins, active hydroformylation catalysts came out [98]. With amine groups in the resin or the addition of NEtj in the hydroformylation of 1-hexene, the corresponding nonanols were formed exclusively with a yield of 95%. The ratio of Rh/Co had a marked effect on the product distribution. Best results were observed with Rh/Co ratios of 2.6-3.6. Other functional groups in the resin did not force the formation of alcohols. 

According to this mechanism, acetone undergoes the sequential activation, first by the protonation and then by the thiol attack. Thus, the highly electrophilic propylidene sulphonium intermediate is created, which successively reacts with phenol molecules. The functional groups are distributed on the catalyst surface near each other, and, they are also located close to the pore walls. Such location of the functional groups significantly increases the catalytic activity of the silica material SBA-15 and provides the steric driving force that favors the formation of the p,p isomer of Bisphenol-A. 

The structure and yield of the propylene dimerization products have been studied as functions of the catalyst composition and solvent [603]. The highest yield is obtained in toluene with a relative molar composition of Nifacac) -AlEt3-PPh3-BF3-OEt2 at 2 1 4 3.5. This corresponds to a B/Ni molar ratio of 15. At a B/Ni molar ratio <5 the system is catalytically inactive. When BF3-OEt2 is preconditioned in anhydrous toluene for a few days, the optimal ratio decreases. At the optimum catalyst composition the yield is the highest in toluene, then in benzene, and much lower in chlorobenzene, yet the relative distribution of products in toluene and chlorobenzene is closer than that in benzene. The Bronsted acids activate the catalyst containing nickel(O). 

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