Base-free glycerol oxidation: studying the effects of structural and acid properties of support in bimetallic catalysts

Glycerol is a highly functionalized bioderived molecule that is recognized as a promising chemical building block for the synthesis of fine chemicals from renewable sources [1]. In particular the selective oxidation of glyce-rol has been shown to produce valuable products such as glyceric acid, hydroxyacetone and tartronic acid. Suppor-ted noble metal nanoparticles have been used as catalysts for this reaction when molecular oxygen is employed as the oxidant [2]. In particular gold nanoparticles reveal peculiar properties in terms of both activity and selectivity. However only recently it was found that the catalytic oxidation of glycerol can be carried out without the use of a basic environment.From an industrial point of view working under non-basic conditions provides a great advantage and a lot of efforts have been devoted to solve this problem. Recent studies showed that alloying gold with a second metal is possible to obtain an effective catalytic systems in terms of activity and selectivity even in the absence of a basic environment. Prati and coworkers [3] demonstrated that by using AuPt bimetallic systems glycerol can be successfully oxidized in pure water. In particu-lar they showed that the support greatly affected the selectivity. Indeed, using an acidic support, H-Mordenite, an enhancement in the selectivity to C3 products (glyceric and tartronic acid) limiting the C-C cleavage can be obtai-ned. Also basic supports such as hydroxy apatite and MgO [4] have been shown to be useful supports. These works opened the way to a new-generation of bifunctional gold-based catalysts where the acid/base properties of the sup-port play a crucial role, affecting activity and selectivity of the reaction. Herein we extended these studies to a series of supports with different acidic character, namely H-Mordenite, SiO2, MCM-41, sulfated ZrO2 in order to clarify the effect of the acid site nature and strength (Lewis and/or Brønsted) on the activity and selectivity of Au-Pt based catalysts in the base-free glycerol oxidation, particularly for the synthesis of glyceraldehyde