Glucose bimetallic catalyst

In the oxidation of several secondary alcohols an optimum in the catalyst composition Bi/Pts rf 0-50 was found. The formation of a two-dimensional alloy on the surface efficiently sup, sses the by-product formation and increases the conversion by a factor of 3 to 66. Some examples on the beneficial influence of Bi promotion are shown in Table 1. A three-component Degussa catalyst was used as a reference. This catalyst is, to our knowledge, the only commercially available alcohol oxidation catalyst, which has been developed for the selective oxidation of glucose to gluconic acid [20]. We suppose that the superior behavior of our bimetallic catalyst in the reactions studied is due to the more homogeneous distribution of Bi on Pt. 

Table 21.1 Mono- and bimetallic catalysts tested in glucose oxidation under acidic conditions.

Table 13.15 Aerobic oxidation of glucose with monometallic and bimetallic catalysts. Glucose/Au = 3000, T=70°C, p02 = 3 bar, t=6.5h.

Oxidation of Glucose over Bimetallic Solid Catalysts. 83... 

Promoting effects of bismuth in carbon-supported bimetallic Pd-Bi catalysts for the selective oxidation of glucose to gluconic acid... 

In a previous work [13], we reported on the preparation of carbon-supported bimetallic Bi-Pd catalysts by the thermal degradation of Bi and Pd acetate-type precursors under nitrogen at 773 K and described their catalytic properties in glucose oxidation. The formation of various BixPdy alloys (BiPd, BiPds, Bi2Pds) or, at least, associations on the surface of these catalysts during the activation step was heavily suspected. Alloy formation in supported bimetallic Pd-based catalysts has been mentioned several times in the literature in die presence of other promoting elements, like Pb or Te [14-16] and is sometimes assumed as responsible for the deactivation of the catalysts. 

Furthermore, bismuth was found systematically to dissolve in the reaction medium during the catalytic tests, the losses being significantly more extensive from the monometallic Bi/C than from the bimetallic PdBi/C catalysts. Glucose and gluconate in solution were shown... 

The same effect occurs when soluble Bi is in the presence of a monometallic Pd/C catalyst. The weak activity of a monometallic catalyst tested in the presence of a large amount of dissolved Bi may be attributed to a too extensive adsorption of Bi-glucose complexes on the surface Pd atoms, preventing thereby the access of glucose to the surface. As far as pre-formed Pd-Bi bimetallic sites are concerned. 

HNO3 functionalized carbons are used as supports for the preparation of bimetallic Pd-Bi/C catalysts. The aim is to take advantage of the oxygenated surface functions introduced on the carbon, which are expected to act as anchoring sites. Two neutral coordination complexes were selected to incorporate the two metals onto differently functionalized caibon supports. The grafted samples are then submitted to an activation treatment and characterized by SEM, XRD and XPS. It appears that the order of incorporation strongly influences the surface properties of the catalysts and thus modifies their activity in the oxidation of glucose. 

---