Pd-doping

Maitlis filtration test. To investigate whether the Pd-doped perovskite is the actual catalyst, or a reservoir of soluble Pd, a Maitlis filtration test (10) was performed. The reaction of 4-bromoanisole with 4-phenylboronic acid, catalyzed by BaCeo 95Pdo os02 95, was intemipted at 20 s and 1 min, corresponding to conversions of 16 and 45%, respectively, by filtering the hot reaction mixture to remove the solid perovskite. The filtrates were allowed to cool to room temperature without stirring. After 3 h, the biatyl yields in both samples were estimated to be 100% by H NMR. 

Catalyst recycling. The solid Pd-doped perovskite catalysts are easily filtered from the reaction mixtnre for reuse. The activity of the recycled BaCco 95Pdo.o502 95 catalyst was investigated in the coupling of 4-bromoanisole with 4-phenylboronic acid. The results in Table 27.3 show that high activity was retained even after seven cycles of catalyst use. 

The greater rearrangement of the perovskite stmeture in the catalyst associated with the higher level of Pd-doping may be responsible for the longer indnetion period. After the onset of catalytie activity, the slopes of the two conversion vs. time eurves for X = 0.05 and x = 0.10 in Figure 27. la are very similar, demonstrating that the two catalysts produce the same soluble aetive site in similar amounts. 

Scheme 27.1. Proposed mechanism for Suzuki coupling by Pd-doped perovskite catalysts.

Fig. 9.3. Thermoelectric power of Pd doped with Fe (in ppm) as a function of temperature. The value for the pure sample has been multiplied by 10 for sake of clarity [64].

First chemical test measurements have been conducted with the array chip. Figure 6.19 shows the results that have been obtained simultaneously from three microhotplates coated with different tin-dioxide-based materials at operation temperatures of 280 °C and 330 °C in humidified air (40% relative humidity at 22 °C). The first microhotplate (pHPl) is covered with a Pd-doped Sn02 layer (0.2wt% Pd), which is optimized for CO-detection, whereas the sensitive layer on microhotplate 3 contains 3 wt% Pd, which renders this material more responsive to CH4. The material on microhotplate 2 is pure tin oxide, which is known to be sensitive to NO2. Therefore, the electrodes on microhotplate 2 do not measure any significant response upon exposure to CO or methane. The digital register values can be converted to resistance values by taking into account the resistor bias currents [147,148]. The calculated baseline resistance of microhotplate 1 is approximately 47 kQ, that of hotplate 2 is 370 kQ and the material on hotplate 3 features a rather large resistance of nearly 1MQ. 

As it is evident from Fig. 6.19, the responses of the three sensitive materials to the test gases CO and CH4 are very different. The lightly Pd-doped (0.2%) tin dioxide shows large responses to CO, and very small responses to CH4, whereas the heavily Pd-doped (3%) tin oxide exhibits comparably smaller responses to CO, but also... 

J. Kappler, N. Birsan, U. Weimar, A. Dieguez, J.L. Alay, A. Romano-Rodriguez, J.R. Morante, and W. Gopel. Correlation between XPS, Raman and TEM measurements and the gas sensitivity of Pt and Pd doped Sn02 based gas sensors Fresenius Journal of Analytical Chemistry 361 (1998), 110-114. 

S. Harbeck, A. Szatvanyi, N. Barsan, U. Weimar, and V. Hoffmann. DRIFT studies of thick film un-doped and Pd-doped Sn02 sensors temperature changes effect and CO detection mechanism in the presence of water vapour . Thin Solid Films 436 (2003), 76-83. 

N. Barsan, A. HeUig, J. Kappler, U. Weimar, and W. Gopel. CO-water interaction with Pd-doped Sn02 gas sensors simultaneous monitoring of resistances and work functions , Proc. Eurosensors XIII, The Hague, Netherlands (1999), 183-184. 

Figure 6.13 Schematic illustration of a lattice model for diffusion of Ag atoms on Pd doped Cu(100). The diagrams on the right show the fourfold surface sites in terms of the four surface atoms defining the site. The section of the surface shown on the left includes two well separated Pd atoms in the surface. The Pd atoms are located at the centers of the two grey squares in the diagram on the left.

In a one-step process a Pd-doped sulfonated resin (e.g. a standard macro-porous type with U.l-5 % Pd) catalyzes both the condensation of 4 yielding 6 and the hydrogenation of b to ] in a single reactor. RWE-DEA has been producing ] for many years by this process developed in their labs and pilot plants. 

Since a Pd-doped resin would be too expensive even if tne palladium was recovered for reloading, a two-step process using an inexpensive resin and subsequent hydrogenation with a coninon catalyst is suitable for the manufacture of MIK and MIPK (Fig. 4). A molar excess of MEK (approx. 4 1) is fed together with an aqueous solution of formaldehyde (approx. 40 %) to the first reactor R-l containing a nondoped resin. Here the same fouling problem occurs... 

Acylamidoxime-butadiene-acrylonitrile terpolymers, SAW detection of simulant vapors, 309-319 Additivity, spectroscopic response, general discussion, 274 Adsorption of water, effect on TPD spectra of oxygen on Pd-doped tin(IV) oxide, 75,78f... 

Catalytic Oxidation of Ethene to Acetaldehyde and Acetic Acid. -Evnin et al120 studied Pd-doped V2 Os catalysts for the vapor-phase oxidation of ethene to acetaldehyde in a heterogeneous type of Wacker process. From a mechanistic study they establish a redox mechanism with Pd both as the site of the ethene oxidation and of the reoxidation of the catalyst. On the basis of the role of the V4+ ions proposed by these authors, Forni and Gilardi121 substantiated this mechanism by adding tetra- and hexa-valent dopants to the V2 05 and studying the effects on the catalytic reaction. 

The objective of the present study was to analyze the reasons for the deactivation effects observed in solid Wacker-type catalysts for 1-butene oxidation. For this purpose the catalytic behavior and characteristics of Pd-V205 on alumina catalysts, prepared using either a N PdC or a PdS04 salt, were compared with those of alternative catalysts prepared by substituting the V-oxide with Ce02 in order to obtain a better understanding of the role of V-oxide. In addition, the behavior of a Pd-doped V-heteropolyacid also is discussed to further extend the analysis. 

Reported in Fig. 2b is an example of the catalytic behavior of a Pd-doped V-phospho-molybdic add catalyst Differently from the above samples, this catalyst shows a high in-... 

Bimetallic Cases. In addition, we have discovered that a result, perhaps related to this differential charging effect, may, in some cases, be chemically induced. In this regard, we have examined a series of Pd doped-alumina systems that are also infused with different alkali cations. Even without physical abuses, these systems produce the aforementioned negative shift (with respect to "normal" Pd°), and one also finds that the size of the shift seems to depend, in a regular fashion, on which alkali cation is employed (i.e., the relative ionicity of the latter ), see Figure 4. This result seems to suggest two possible explanations. Either the... 

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