Palladium support type

Once the reaction kinetics were determined and the appropriate reaction conditions were set, the analyses of different catalysts was launched. A variety of different heterogeneous catalysts were evaluated for the deprotection of 20 mmol Cbz-glycine (1, R=-H). Catalysts composed of different platinum group metals supported on activated carbon were evaluated as well as palladium supported on alumina. Figure 5 confirms that Pd supported on activated carbon is indeed the catalyst of choice for this type of hydrogenolysis reaction. 

Colloidal palladium or platinum supported on chelate resin beads were employed for the stereoselective hydrogenation of olefins 86). Colloidal palladium supported on iminodiacetic acid type chelate resin beads was prepared by refluxing the palladium chloride and the chelate resin beads in methanol-water. Using the resin-supported colloidal palladium as a catalyst, cyclopentadiene is hydrogenated to cyclopentene with 97.1% selectivity at 100 % conversion of cyclopentadiene under 1 atm of hydrogen in methanol at 30 °C. Finely dispersed metal particles ranging from 1 to 6 nm in diameter are the active species in the catalyst. 

Having in consideration the problem of chemical probing of Pd/support systems, it is relevant to know the catalytic properties of unsupported palladium. Three types of reactions will be considered in this article ... 

The hydrogenation of 2-ethyl-5,6,7,8-tetrahydroanthraqumone (THEAQ) at the oxygen in the presence of a palladium supported catalyst is a key step in the industrial production of hydrogen peroxide. In industrial plants, the performance of the catalyst slowly decreases because of deactivation. Two types of catalyst poisoning are operative, a reversible one, related to the presence of water, and a permanent one, probably due to the condensation of two or more anthraquinone molecules on the palladium surface. The kinetic data obtained from laboratory runs are used to simulate the performance in industrial plants. 

Figure 1 shows the TPR profiles of Pd and some of the Pt supported catalysts. Palladium supported catalysts reduce at low temperature. The hydrogen consumption is much higher than in the case of the Pt catalysts. The latter display, in all cases the peak between 100 and 150 °C approximately, and a second reduction zone between 350°C and 550°C, as usually found for this type of materials. This second reduction zone represents a higher proportion of the metal than the first peak. 

In addition, Jacobs group developed the DKR of benzylic amines in the presence of a combination of palladium supported on an alkaline earth type... 

One example is the pellistor-type sensor first described by Baker (2) which is shown in Figure 12.2. This sensor uses palladium supported on thoria as the catalyst. This is deposited on the surface of a refractory bead of c. 1 mm diameter encapsulating the platinum coil. Palladium is more active than platinum for hydrocarbon oxidation and readily oxidizes methane at temperatures of about 500 °C. Encapsulation of the coil within a spherical bead in this way produces a device which is insensitive to orientation and also resistant to shock. This type of sensor is widely used in all types of flammable gas detection instruments. 

The same parallels can be drawn when looking at different types of CNF structures. It was found that palladium supported on platelet type CNFs exhibited higher performances for the ORR than fish-bone-type CNFs which was a result of the greater edge to basal plane atoms of the platelet type CNFs. Tsuji et al. found similar results where they tested and compared the activity of platinum-ruthenium on different types of CNF structures platelet, tubular, and herringbone, and found that catalysts prepared on platelet-type CNFs exemplified higher onset reduction potentials and current peak potentials for the ORR than the other structures (Tsuji et al., 2007). 

In addition, Jacobs et al. have developed the DKR of benzylic amines in the presence of a combination of palladium supported on an alkaline earth-type support such as BaS04 with a lipase. Hence, this heterogeneous catalytic system has allowed various benzylic amines to be transformed into their corresponding enantiomerically pure amides with excellent yields and enantioselectivities of >99% ee, as shown in Scheme 8.70. 

Another appHcation for this type catalyst is ia the purification of styrene. Trace amounts (200—300 ppmw) of phenylacetylene can inhibit styrene polymerization and caimot easily be removed from styrene produced by dehydrogenation of ethylbenzene using the high activity catalysts introduced in the 1980s. Treatment of styrene with hydrogen over an inhibited supported palladium catalyst in a small post reactor lowers phenylacetylene concentrations to a tolerable level of <50 ppmw without significant loss of styrene. 

The sitosterol hydrogenation and deactivation kinetics was determined in a shaking constant-pressure batch reactor by using the new type of synthetic support material (mesoporous carbon Sibunit) for palladium (4wt% Pd) [55]. 

Supported platinum-palladium. This aspect of the study focused on the characterization of platinum and palladium on alumina. The analytical capability of STEM Is fully demonstrated In a problem of this type, because of the rapid manner In which crystallite composition can be analyzed. This study Is especially Interesting because of Che use of platinum and palladium combinations In automotive catalysis. 

Synthesis (TCS). The very same term was independently proporsed by Corain and associates for the size controlled synthesis of palladium nanoparticles in 2004 [68]. In a number of cases they observed that palladium nanoclusters, supported on gel-type resins of different nature and obtained with the RIMP method, exhibited a remarkable agreement between the size of the cavities of swollen supports (as assessed by means of ISEC, see Section 4) and the diameter of the metal nanoclusters (Table 4, Entries 1-3) [10,11,66,71,72,87]. 

The reduction of palladium(II) with an alcoholic solution of NaBH4 [101] or by treatment in situ of the methanol-swollen material under hydrogen [129] yielded a supported palladium catalyst, referred to as self supported by the authors [101,129]. The same co-polymerization reaction was carried out inside the nanopores of a DMF-swollen gel-type resin made by DMA and MBAA (crosslinker, 4% mol) [101,129], thus obtaining a sequential IPN [131]. Also this material was transformed into a... 

The catalysts most frequently used are based on noble metals (mainly palladium and platinum) on various supports, or on nickel catalysts (mainly Raney type). Hydrogenations are generally performed in the liquid phase, under relatively mild conditions of temperature and pressure (1—40 bar). Most processes are performed batch-wise using powder catalysts in stirred tank or loop-type reactors with sizes up to 10 m . 

Table 1 Catalytic performance of the debenzylation reaction on different types of supported palladium catalyst. ...

The micrographs of the samples Pd/C type 1 and Pd/C type 2 are shown in Figure 2 and Figure 3, respectively. The structure of the catalysts is rather uniform. The surface of the support is covered evenly by the palladium. The... 

The type of intermediate shown in structure (B) has also been supported by Muller and Gault (119) who showed that in the reaction of 1,1-dimethylcyclopropane with deuterium over a series of thick evaporated metal film catalysts, it was only on platinum that 1,1,3-da-neopen-tane (and 1,1,3,3-d4-neopentane) were dominant products. On palladium, iron, rhodium, nickel, and cobalt the major product was 1,3-d2-neopentane. 

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