Selective liquid phase oxidation of glycerol to glyceric acid over novel supported Pt catalysts

Elina Sproge, Svetlana Chornaja, Konstantins Dubencovs, Svetlana Zhizhkun, Valdis Kampars, Vera Serga, Lidija Kulikova, Eriks Palcevskis
2013 Journal of the Serbian Chemical Society  
Several supported platinum catalysts were prepared by the extractive-pyrolytic method for the selective production of glyceric acid from glycerol, γ-AlO(OH) and C were used as the catalyst supports. Glycerol oxidation was performed in alkaline solutions and oxygen was used as the oxidant. The optimal catalyst preparation parameters and glycerol oxidation conditions to obtain glyceric acid were determined. The best result (57 % selectivity to glyceric acid with 92 % glycerol conversion) was
more » ... onversion) was achieved on a 4.8 % Pt/Al 2 O 3 catalyst. Copyright (C)2013 SCS 1360 SPROGE et al. dehyde (GLYAD), etc. 1,6-12,14-26 Glyceric acid and its derivatives are important compounds as raw materials for chemical products, such as bioplastics, pharmaceuticals for acceleration of alcohol metabolism or liver disease treatment and cosmetics. 3, 9, 11 Most of the studies concerning the heterogeneous oxidation of glycerol were dedicated to the selective oxidation of glycerol over supported gold catalysts using oxygen as the oxidant. 12-14 Gold catalysts are very selective to glyceric acid. Using an Au/C catalyst, Carretin et al. reported a selectivity to glyceric acid of 100 % at a glycerol conversion of 56 %. 14 For gold catalysts, many supports have been investigated, i.e., carbon materials, several metal oxides and polymers. 8, 15, 16 The main drawback of gold catalysts is that they are active only in the presence of base, whereas platinum catalysts work in basic, acidic and neutral conditions. [17] [18] [19] Liang et al. 6 reported that multi-wall carbon nanotubes (MWNT)-supported Pt catalysts were more active and selective than Pt/activated carbon (AC) catalysts, but this type of support is expensive and the preparation of catalyst is complicated, so in further studies, the authors returned to activated carbon. Liang et al. compared glycerol oxidation over 5 % Pt/MWNT catalyst under alkaline and base-free conditions. 8 The 5 % Pt/MWNT catalyst in a base-free aqueous solution was more selective to glyceric acid (68 %) at the same glycerol conversion (90 %). The authors also concluded that the activity and selectivity to glyceric acid increased with decreasing particle size of the carbon support (from 253 to 9 μm). The most active were catalysts with a Pt particle size of less than 6 nm. 1, 6, 8 A general drawback of platinum-containing catalysts is poisoning with molecular oxygen and deactivation. Therefore, Pt catalysts are used in oxidation processes at low partial pressures of oxygen or the platinum is alloyed with gold, thereby allowing higher oxygen partial pressures. Prati et al. [20] [21] [22] [23] reported that in the alkaline solutions at 3 atm bimetallic Pt-Au/C catalysts were more active and selective to glyceric acid compared with Pt/C catalysts. For example, in the presence of 1 %Pt-Au/C, the glycerol conversion was 46 % higher than in the presence of 1 %Pt/C and the selectivity to glyceric acid was increased by 13 %. 22 It is obvious that during the past years, many authors dedicated their time to the investigation of glycerol oxidation only in base-free solutions because these, together with recyclable catalysts, are the environmentally friendly route. 1, 8, [23] [24] [25] Since 1993, when Kimura et al. 17 reported glycerol oxidation over Pt/C, mainly carbon material supports have been studied for monometallic Pt catalysts, i.e., activated carbon, graphite and MWNT. Recently, several authors reported about selective glycerol oxidation over bimetallic Au-Pt catalysts supported on MgO, Mg(OH) 2 , 35,36 H-mordenite 37 and Al 2 O 3 . 38 The preparations of Pt catalysts are based on 3 methods -impregnation, immobilization and ion
doi:10.2298/jsc121203037s fatcat:k2tmhqcdozayxbvxkmq6qwugza