Supported Pd catalysts

With higher alkenes, three kinds of products, namely alkenyl acetates, allylic acetates and dioxygenated products are obtained[142]. The reaction of propylene gives two propenyl acetates (119 and 120) and allyl acetate (121) by the nucleophilic substitution and allylic oxidation. The chemoselective formation of allyl acetate takes place by the gas-phase reaction with the supported Pd(II) and Cu(II) catalyst. Allyl acetate (121) is produced commercially by this method[143]. Methallyl acetate (122) and 2-methylene-1,3-diacetoxypropane (123) are obtained in good yields by the gas-phase oxidation of isobutylene with the supported Pd catalyst[144]. 

Difunctionalization with similar or different nucleophiles has wide synthetic applications. The oxidative diacetoxylation of butadiene with Pd(OAc)i affords 1,4-diacetoxy-2-butene (344) and l,2-diacetoxy-3-butene (345). The latter can be isomerized to the former. An industrial process has been developed based on this reaction. The commercial process for l,4-diacetoxy-2-butene (344) has been developed using the supported Pd catalyst containing Te in AcOH. 1,4-Butanedioi and THF are produced commercially from 1,4-diacetoxy-2-butene (344)[302]. 

AUyl acetate can be obtained by the vapoi-phase reaction of propylene and acetic acid over a supported Pd catalyst (eq. 20) (110). Reaction of acrylic acid and propylene yields isopropyl acrylate (eq. 21), and catalytic reaction with acetic acid produces isopropyl acetate (eq. 22) (110). 

Although supported Pd catalysts have been the most extensively studied for butadiene hydrogenation, a number of other catalysts have also been the object of research studies. Some examples are Pd film catalysts, molybdenum sulfide, metal catalysts containing Fe, Co, Ni, Ru, Rh, Os, Ir, Pt, Cu, MgO, HCo(CN) on supports, and LaCoC Perovskite. There are many others (79—85). Studies on the weU-characteri2ed Mo(II) monomer and Mo(II) dimer on siUca carrier catalysts have shown wide variations not only in catalyst performance, but also of activation energies (86). 

Vinyl acetate is made from ethylene, oxygen, and acetic acid in the vapor phase at 150 to 175°C (302 to 347°F) with supported Pd catalyst in packed tubes, 25 mm (0.082 ft) ID. 

X-Ray diffraction has an important limitation Clear diffraction peaks are only observed when the sample possesses sufficient long-range order. The advantage of this limitation is that the width (or rather the shape) of diffraction peaks carries information on the dimensions of the reflecting planes. Diffraction lines from perfect crystals are very narrow, see for example the (111) and (200) reflections of large palladium particles in Fig. 4.5. For crystallite sizes below 100 nm, however, line broadening occurs due to incomplete destructive interference in scattering directions where the X-rays are out of phase. The two XRD patterns of supported Pd catalysts in Fig. 4.5 show that the reflections of palladium are much broader than those of the reference. The Scherrer formula relates crystal size to line width ... 

Analytical electron microscopy permits structural and chemical analyses of catalyst areas nearly 1000 times smaller than those studied by conventional bulk analysis techniques. Quantitative x-ray analyses of bismuth molybdates are shown from lOnm diameter regions to better than 5% relative accuracy for the elements 61 and Mo. Digital x-ray images show qualitative 2-dimensional distributions of elements with a lateral spatial resolution of lOnm in supported Pd catalysts and ZSM-5 zeolites. Fine structure in CuLj 2 edges from electron energy loss spectroscopy indicate d>ether the copper is in the form of Cu metal or Cu oxide. These techniques should prove to be of great utility for the analysis of active phases, promoters, and poisons. 

The present study was initiated to understand the causes of large differences in perfonnance of various catalyst formulations after accelerated thermal aging on an engine dynamometer. In particular, we wished to determine whether performance charaderistics were related to noble metal dispersion (i.e. noble metal surface area), as previous studies have suggested that the thermal durability of alumina-supported Pd catalysts is due to high-temperature spreading or re-dispersion of Pd particles [20-25]. 

Pd/Al203-FeCl3, and Ce-Pd/Al203-FeCl3 catalysts exhibit activity for the synthesis of ethylphenylcarbamate from the reductive carbonylation of nitrobenzene with ethanol at 453 K and 2.07 - 2.93 MPa. The advantage of the use of Al203-supported Pd catalyst is the easy of catalyst recovery form the reactants/product mixture. 

We have demonstrated that supported Pd and Cu catalysts are effective in catalyzing the oxidative carbonylation at low pressure reaction condition and the supported metal catalysts can be easily separated from the product mixture in both fixed bed and slurry phase reactors (12,17). The objective of this study is to investigate the feasibility of using Al203-supported Pd catalysts for catalyzing the reductive carbonylation of nitrobenzene with ethanol. 

Palladium gave the highest activity of all the platinum group metals evaluated platinum, rhodium and ruthenium exhibited very poor activity. The choice of support was also demonstrated to be very important the activated carbon supported Pd catalyst showed a nearly fourfold increase in activity than did Pd supported on alumina. 

Highly mesoporous carbon supported Pd catalysts were prepared using sodium formate and hydrogen for the reduction of the catalyst precursors. These catalysts were tested in the enantioselective hydrogenation of isophorone and of 2-benzylidene-l-benzosuberone. The support and the catalysts were characterized by different methods such as nitrogen adsorption, hydrogen chemisorption, SEM, XPS and TPD. 

Table 4 Enantiomeric excesses in the enantioselective hydrogenation of isophorone and 2-benzyl- 1-benzosuberone on highly mesoporous carbon supported Pd catalysts.

The reduction of the catalyst precursor with sodium formate resulted in a lower Pd dispersion than the catalyst prepared by hydrogen reduction, the particle size is much larger in the former catalyst. The mesoporous carbon supported Pd catalysts are near to those of Pd on titania with respect to their enantiodifferentiating ability. Besides the metal dispersion, the availability of the Pd surface in the pores for the large modifier molecules seems to be the determining factor of the enantioselectivity. 

Laska, U., Frost, C.G., Price, G.J. and Pludnski, P.K. (2009) Easy-separable magnetic nanopartide-supported Pd catalysts kinetics, stability and catalyst reuse.Journal of Catalysis, 268 (2), 318—328. 

The E/Z ratio of the isomers formed over a supported Pd catalyst differed from that obtained with the homogeneous counterpart. The activity of the catalyst under the action of microwave and conventional conditions was comparable, but micro-wave irradiation improved yields and reduced reaction times. 

Arylation of alkenes with iodobenzene in the presence of supported Pd catalyst [45]. Reaction conditions acetonitrile as solvent, pressure CEM reactor. 

Palladium-catalyzed cyclic carboxylation of dienes can be utilized for the synthesis of lactones.2 Polymer-supported Pd catalyst could also be used for this reaction (Scheme 42).61 The reaction is initiated by dimerization of two molecules of diene to give a bis-7r-allylpalladium intermediate such as 123. The incorporation of C02 takes place at the internal position of an allyl unit to afford the 7r-allylpalladium carboxylate 124 which, after reductive elimination/ cyclization, yields the (5-lactone 121 (Scheme 43). 

There are other possibilities for selective reduction in the hydrogenation of symmetrically substituted dienes. Raney-nickel afforded 1-alkenes, whereas supported Pd catalysts gave a mixture of 1- and 2-alkenes148. A selective reduction of a terminal double bond was carried out in the presence of an endocyclic double bond, which was trisubstituted149-152. 

Ru, RuCo, and Co carbonyl cluster-derived catalysts, 38 362-363 structural model, 38 366-367 synthesis gas conversion, 38 364-365 ZSM-5-supported Pd catalysts, 39 207-208... 

Saponite, idealized formula, 33 337 SAPO-n-zeolite-supported Pd catalysts, 39 208 Sarin, reaction with cyclohexaamylose, 23 237 Saturation in ESR, 22 280 SbF 37 168-172... 

The colloidal suspensions obtained by the neutralization or thermohydrolysis procedures described previously have been used to prepare supported Pd catalysts. The support is impregnated with a volume of colloidal oxide suspension corresponding exactly to the porous volume of the solid, according the well-known incipient wetness impregnation. 

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