Supported glycerol oxidation

The aqueous phase air oxidation of glycerol with supported noble metal catalysts occurs under mild conditions (60 °C), but is very dependant on the pH of the reaction medium. Relevant data are shown in Fig. 11.3 [48], For Pd, Pt and Bi-promoted Pt the glycerol oxidation rate increases significantly with the pH of the medium, with Pd showing the lower activity. 

The Au-catalyzed glycerol oxidation was influenced by the kind of support, the size of Au particles and the reaction conditions such as concentration of glycerol, p02 and molar ratio of NaOH to glycerol. As metal oxide supports showed inferior selectivity to glyceric acid compared to carbons, due to successive oxidation and C—C bond cleavage to form di-adds such as tartronic acid and glycolic acid, research has focused on Au NPs supported on carbon, as in the case of ethylene glycol oxidation [182]. Indeed, the catalytic activity was influenced by the kind of carbon support in terms of porous texture [183]. 

Demirel S, Lehnert K, Lucas M, Claus P. Use of renewables for the production of chemicals glycerol oxidation over carbon supported gold catalysts. Appl Catal B Environ. 2007 70 637-43. 

A subsequent detailed investigation of glycerol oxidation has been carried out by Prati et al. in Milano. In a first study, the relationship between catalyst morphology and selectivity was explored at full conversion it was found that larger gold particles (20 nm), supported on suitable carbons, show low TOFs but favour glycerate formation under mild conditions (30 °C, 3 bar) allowing yields up to 92% [39]. 

P. Paalanen, B. M. Weckhuysen and M. Sankar, Progress in controlling the size, composition and nanostructure of supported gold-paUadium nanoparticles for catafytic applications, Catal Scl Technol, 2013, 3, 2869-2880. A. Villa et al, Glycerol Oxidation Using Gold-Containing Catalysts, Acc. Chem. Res., 2015, 48(5), 1403-1412. 

Figure 10.8 (Top) Supported Pd-based catalysts for glycerol oxidation (AC, activated carbon). (Bottom) Conversion on req cling of 1% Pd/CTF for glycerol oxidation.

Figure 10. Plot of current density at 1.6 V (j j )/current at 1.15V (jus) together with plot of ratio ofpeak C/peak D versus percentage conversion for various supported Au/C catalysts used for glycerol oxidation.

The liquid-phase oxidation of glycerol was carried out by using carbon-supported gold particles of different sizes (2.7 2 nm) which were prepared by a colloidal route [120]. Indeed, a particle-size effect was observed because the selectivity to glyceric acid was increased to 75% with smaller particle sizes (4)ptmimn = 3.7 nm). 

The selective oxidation of a 50% aqueous solution of glycerol was performed at 50 °C with an oxygen/glycerol ratio of 2, in a continuous fixed bed process using a Pt-Bi catalyst supported on charcoal. Here, a DHA selectivity of 80% at a conversion of 80% was obtained. 

Nitrate respiration can support the synthesis of ATP, while proton pumping has been quantified for several physiological substrates. Stoichiometries of about 4H+/NO, and 2H+/N03" have been found for L-malate and formate, and succinate, D-lactate and glycerol respectively. There is evidence that about one mole of ATP is synthesized by oxidative phosphorylation per mole of nitrate reduced.1440... 

Gas-phase oxidation of glycerol has been less investigated than liquid-phase oxidation it occurs via a two-step catalyzed reaction involving first the dehydration of glycerol into acrolein, catalyzed by an acid, and then its oxidation. The same reactions can be conducted in two distinct reactors, in which the first step can be carried out with an acid catalyst such as phosphoric acid over alumina [107]. Then acrolein is oxidized to acrylic acid with a conventional alumina-supported Mo/V/Cu/O catalyst. 

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