Supported palladium route

The partial oxidation of alcohols, to afford carbonyl or carboxylic compounds, is another synthetic route of high industrial interest For this, scC02 was investigated as a reaction medium for the aerobic oxidation of aliphatic, unsaturated, aromatic and benzylic acids with different catalytic systems, mainly based on the use of noble metals, both in batch [58-64] and in continuous fixed-bed reactors [65-70]. In this context, very promising results have been obtained when studying the catalytic activity of supported palladium and gold nanoparticles in the oxidation of benzyl alcohol to benzaldehyde these allowed conversions and selectivities in excess of 90% to be achieved [71-73]. 

The partial oxidation of natural gas, consisting chiefly of methane, currently holds tremendous industrial potential. Possible routes for the direct synthesis of formaldehyde from methane, either via chlorine-based catalysts or with the use of chlorine-containing compounds in the gas feed (both using chlorine-modified supported palladium catalysts and at temperatures of 450-650°C) gave formaldehyde yields less than 7.7% under optimum conditions... 

There are two possibilities for formation of the products from the acylpalladium species. One is the direct attack of the nucleophile on the acyl ligand and the other involves coordination of the NuH to the palladium center. The palladium-bound NuH ligand, such as alcohol, is deprotonated by a base to give an acylpalladium alkoxide, which releases the ester as the reductive elimination product. Recent studies on model complexes provided some evidence supporting a route via reductive elimination [59]. 

The chemo- and regiospecific palladium-catalyzed four-component reaction of aryl iodides followed by incorporation of carbon monoxide, a polymer-supported allene, and a range of secondary cyclic amines has been reported as a short and high-yielding route to complex heterocycles with three points of diversity, such as 7 <2000CC2241>. 

The oxidative hydrolysis and acetylation of olefins in the presence of palladium(II) salts are well-established as commercial routes to acetaldehyde and vinylacetate (46). Both processes have been investigated using supported catalysts. The oxidative hydrolysis has been briefly studied using palladium(ll) chloride supported on a cross-linked polystyrene resin containing cyano groups (64). Oxidative acetylation was effected using palladium(II) chloride supported on phosphinated silica (5). 

Supported metal clusters play an important role in nanoscience and nanotechnology for a variety of reasons [1-6]. Yet, the most immediate applications are related to catalysis. The heterogeneous catalyst, installed in automobiles to reduce the amount of harmful car exhaust, is quite typical it consists of a monolithic backbone covered internally with a porous ceramic material like alumina. Small particles of noble metals such as palladium, platinum, and rhodium are deposited on the surface of the ceramic. Other pertinent examples are transition metal clusters and atomic species in zeolites which may react even with such inert compounds as saturated hydrocarbons activating their catalytic transformations [7-9]. Dehydrogenation of alkanes to the alkenes is an important initial step in the transformation of ethane or propane to aromatics [8-11]. This conversion via nonoxidative routes augments the type of feedstocks available for the synthesis of these valuable products. 

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