Palladium bismuth promoter

Wenkin, M., Touillaux, R., Ruiz, P., Delmon, B., and Devillers, M. (1996) Influence of metallic precursors on the properties of carbon-supported bismuth-promoted palladium catalysts for the selective oxidation of glucose to gluconic acid. Appl. Catal., A, 148, 181-199. 

M. Besson, F. Lahmer, P. Gallezot, P. Fuertes, and G. Fleche, Catalytic oxidation of glucose on bismuth-promoted palladium catalyst, J. Catal., 152 (1995) 116-121. 

The selective oxidation of lactose to lactobionate with air on palladium-bismuth catalysts was first reported in patents [47]. Hendriks et al. [16] studied the oxidation of a 0.5 mol solution of lactose as a function of pH, temperature and Pd/Bi ratios of promoted Pd/C catalysts. Sodium lactobionate was obtained with 100% selectivity up to 95% conversion on Pd-Bi/C catalysts (Bi/Pd = 0.5) at 333 K and pH 9. Oxygen mass-transfer limited the maximum initial reaction rate (0.47 mol kg s ). The catalyst was recycled 15 times without any significant loss of activity and selectivity. 

The oxidation of glycerol (GLY) to glyceric acid (GLYAC) was carried out with air on palladium and platinum catalysts at basic pH 15). The selectivity to glycerate was 70% at 100% conversion. In contrast, using bismuth-promoted platinum catalyst the selectivity shifted to dihydroxyacetone. 

It has been discovered that the performances of platinum and palladium catalysts may be improved by promotion with heavy metal salts. However, there is little information available about the role and chemical state of the promoter 8,9). We have recently found that a geometric blocking of active sites on a palladium-on-activated carbon catalyst, by lead or bismuth, suppresses the by-product formation in the oxidation of l-methoxy-2-propanol to methoxy-acetone 10). 

The first set of reactions is the mainstay of the petrochemical industry 1 outstanding examples are the oxidation of propene to propenal (acrolein) catalysed by bismuth molybdate, and of ethene to oxirane (ethylene oxide) catalysed by silver. In general these processes work at high but not perfect selectivity, the catalysts having been fine-tuned by inclusion of promoters to secure optimum performance. An especially important reaction is the oxidation of ethene in the presence of acetic (ethanoic) acid to form vinyl acetate (ethenyl ethanoate) catalysed by supported palladium-gold catalysts this is treated in Section 8.4. Oxidation reactions are very exothermic, and special precautions have to be taken to avoid the catalyst over-heating. 

Finally, it has been found that promotion of palladium by bismuth not only increases the selectivity in aldehyde but also limits the deactivation of the catalysts. Similar results have been published in the past decade on the partial oxidation of alcohols with similar catalytic systems (ref. 13) Various interpretations on the role of bismuth have been suggested among them, resistance of Pd/C against overoxidation and surface orientation of the reactant suppressing the formation and strong adsorption of poisoning intermediates are also problably the main reasons of the improved performances in the oxidation of p-cresol. 

Platinum catalysts supported on activated charcoal, with or without promoters such as bismuth or gold, have been examined for selectivity in the air oxidation of aqueous D-glucose and D-gluconate to glucarate. Palladium(II) has been found to inhibit the oxidation of aldoses by alkaline Fe(CN6) , and by Ce(IV). ... 

The most commonly investigated substrates have been Pt and Pd, ranging from well-defined single-crystal surfaces to nanoparticles. Bismuth (Bi) has been the most extensively tested adatom [18-28]. Other adatoms that have also exhibited performance enhancements are lead (Pb) [29-31], antimony (Sb) [2,22,29,32,33], arsenic (As) [34, 35], gold (Au) [36], tellurium (Te) [37, 38], selenium (Se) [39], ruthenium (Ru) [40], and palladium (Pd) [5,40,41]. Researchers have seen that, for the various adatoms, higher coverages promote the direct reaction pathway. 

Interestingly, only BiBrj gave quantitative yields of the products 416, while other bismuth(III) halides and Bi(OTf)3 had absolutely no effect for the reported transformation. The aUcenylbismuth derivatives could also be trapped in sUu with iodine or coupled with acyl chlorides in the presence of a palladium catalyst [119]. Addition of organogold compoimds to activated carbon-carbon triple bonds has also been reported to proceed under palladium catalysis [120]. Thus, (PhjPljPdClj or Pd2(dba)j complexes successfully promoted a regioselective syn carboauration of alkynes at ambient temperature (Scheme 10.143). 

A number of other materials were reported to act as promoters, such as zinc [110, 337], magnesium [111], aluminum [111], bismuth [112], lead [112], gold [112], mercury salts [112], palladium zeolite [113], activated carbon [45] and iron carbonyl [171,979]. Some of these materials were reported to accelerate the hydroformylation but suppress the hydrogenation of the aldehydes formed. 

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