Communication TPD-TG-MS Investigations of the Catalytic Conversion of Glycerol over MO x -Al 2 O 3 -PO 4 Catalysts The catalytic performance of bifunctional catalysts, MO x -Al 2 O 3 -PO 4 , that contain acidic centers and different transition metal oxide components were evaluated in the gas-phase dehydration of glycerol using the TPD-TG-MS technique and a continuous flow reactor experiment. The initial catalytic activity and selectivity to acrolein and acetol significantly depends on the acidity and the type of transi- tion metal oxide. The higher the total acidity, the higher the acrolein selectivity in the order W > Mo > Cu > V~ Fe ~Cr > Ce. On the other hand, Mn-, Cr-, and Fe-containing catalysts favor the formation of products of oxidative C-C cleavage. TPD-TG-MS investigations of catalysts loaded with glycerol are useful tools for fast-screening of initial activities of catalysts in the gas-phase dehydration of glycerol. Keywords: Acetol, Acrolein, Catalysis, Dehydration, Glycerol, TPD-TG-MS Received: July 26, 2010; revised: August 27, 2010; accepted: August 27, 2010 DOI: 10.1002/ceat.201000316 1 Introduction Bio-glycerol is an important platform raw material for the pro- duction of numerous fine chemicals, pharmaceuticals, cos- metics, plastics, etc. It is obtained as a by-product in the pro- duction of biodiesel. One of the potential products obtained from glycerol are acrolein and hydroxyacetone (acetol) [1, 2]. The present method of producing acrolein is based on the oxi- dation of propylene over Bi/Mo/W-oxide catalysts. The syn- thesis of acrolein from glycerol proceeds via a double dehydra- tion reaction and is considered as a promising alternative. The other main product of the dehydration of glycerol is acetol, which is also an intermediate for fine chemicals and pharma- ceutics. However, the selective catalytic conversion to acrolein and/or hydroxyacetone remains very challenging. Different solid acidic catalysts, including zeolites and metal oxides impregnated with phosphates have been proposed for glycerol dehydration in the gaseous phase [2–6]. The applica- tion of acidic catalysts is, however, associated with various problems such as harsh hydrothermal reaction conditions, rap- id catalyst deactivation due to coke deposition and the forma- tion of large amounts of by-products [6, 7]. It was reported that the addition of transition metal oxide components to sol- id acids can enhance the performance of such catalytic sys- tems. Recently, Ulgen et al. [4] and Wang et al. [8] proposed WO 3 -ZrO 2 and VPO (vanadium phosphate oxides), respec- tively, as active catalytic systems for the selective gas-phase de- hydration of glycerol to acrolein. Other metal oxides, such as Nb 2 O 5 , CuO, CrO x , and CeO 2 showed promising results with respect to long-term stability [9–12]. Apart from transition metal-loaded catalysts, supported het- eropoly acids on the basis of W, Si, and Mo were found to se- lectively catalyze the dehydration of glycerol. For example, Chai et al. [13] reported that 12-tungstophosphoric acid sup- ported on zirconia can almost fully convert glycerol with selec- tivities of 70–75% to acrolein at 330 °C. Tsukuda et al. [14], Atia et al. [4], and Alhanash et al. [15] used different support- ed heteropoly acids as catalysts for the gas-phase dehydration of glycerol. Selectivities of 75–96 % to acrolein and conversions of 80–95 % were observed at 275–285 °C. So far, most of the catalyst screenings were mainly carried out using a continuous fixed bed flow reactor setup coupled with GC analysis [3–15]. The present paper reports on the application of a thermo- gravimetric (TG) setup coupled with temperature-pro- grammed desorption (TPD) and online MS analysis for the determination of the catalytic performance of alumo- phosphates loaded with different transition metal oxides (MO x -Al 2 O 3 -PO 4 ). The method can also deliver detailed infor- mation about the formation of different products formed by various parallel and consecutive reaction pathways. www.cet-journal.com © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Chem. Eng. Technol. 2011, 34, No. 1, 134–139 Wladimir Suprun 1 Michal Lutecki 2 Helmut Papp 1 1 Institut für Technische Chemie, Universität Leipzig, Germany. 2 Department of Chemical Engineering and Biotechnology, University of Cambridge, Cambridge, UK. – Correspondence: Dr. W. Suprun (suprun@chemie.uni-leipzig.de), Institut für Technische Chemie, Universität Leipzig, Linnestraße 3–4, 04103 Leipzig, Germany. 134