Palladium on porous glass

Scheme 7.122 Heck couplings utilizing palladium on porous glass.

In the same report, the Strauss group furthermore presented the effective use of palladium on porous glass to achieve quantitative conversions in couplings of phe-nylacetylene with iodobenzene and 4-bromobenzaldehyde. Additionally, satisfactory results were obtained for couplings of phenylacetylene with 4-bromoacetophenone and 2-bromopyridine [146]. 

Obtainable with freshly reduced 1% palladium on Gas-Chrom P at 260° C or 5% platinum on porous glass at 210°C. The parent hydrocarbon of the acid moiety is obtained with platinum catalysts. 

Heck C-C coupling reactions were also facilitated by the presence of a palladium catalyst when Pd was deposited on a tubular membrane of porous glass. Thus, the coupling of iodobenzene with allyl alcohol affording 3-phenylpropionaldehyde in the presence of this Pd catalyst had several advantages - the ease of catalyst manufacture, mechanical strength, thermal stability, and resistance to organic solvents [46],... 

Uemiya, S. et al., Separation of hydrogen through palladium thin film supported on a porous glass tube, /. Membr. Sci., 56, 303,1991a. 

Electroplating. Basically in electroplating, a substrate is coated with a metal or its alloy in a plating bath where the substrate is the cathode and the temperature is maintained constant Membranes from a few microns to a few millimeters thick can be deposited by carefully controlling the plating time, temperature, current density and the bath composition. Dense membranes made of palladium and its various alloys such as Pd-Cu have been prepared. Porous palladium-based membranes have also been made by deposition on porous support materials such as glass, ceramics, etc. 

The applications and the research studies performed on this kind of reaction were realized by many scientists. In particular, a great literature is present on this issue concerning the use of palladium-based membrane reactors, as resumed briefly in Table 2.7, where CO conversion values obtained in MR and compared with the thermodynamic equilibrium ones of some scientific works are reported. In particular, among these works, Kikuchi et al. [115] demonstrated that, using a 20 pm layer of palladium-coated onto a porous glass tube produced by the electroless plating method, allows to obtain almost complete CO conversion. 

Palladium-based composite membranes consist of a thin dense layer of palladium or a palladium alloy on a porous support. Tubes or disks of porous glass, porous ceramics, or PSS can all be employed as supports. 

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