Role of Baria Dispersion in BaO/Al 2 O 3 Catalysts for Transesterification J. A. Anderson Æ A. Beaton Æ A. Galadima Æ R. P. K. Wells Received: 30 April 2009 / Accepted: 2 June 2009 / Published online: 13 June 2009 Ó Springer Science+Business Media, LLC 2009 Abstract The transesterification of two vegetable oils containing different quantities of free fatty acid have been compared over a series of BaO/Al 2 O 3 catalysts with a range of baria loadings/dispersions. Dispersion of baria on the alumina was determined by pulse chemisorption of carbon dioxide. Limited agreement was found between the num- bers of exposed sites for CO 2 adsorption and the reaction rate and the rates measured were different for the two oils. The latter was unexpected as the rate determining step appears to involve only the activated adsorption of metha- nol, consistent with the change in rate measured when methanol was replaced by ethanol. Differences between the behaviour of the two oils and the lack of correlation between rates and available basic sites can both be accounted for by the strong dissociative adsorption of the free fatty acid which results in a less active catalyst for the transesterification of the triglyceride. Higher dispersed samples show less sensitivity to free fatty acid and give the highest rate per exposed surface site. Keywords Biodiesel Á Transesterification Á Supported BaO Á Baria dispersion 1 Introduction Transesterification, the reaction of an ester in which with an alcohol replaces the alkoxy, may be used in the pro- duction of biodiesel. It can be used in commercial diesel engines both on its own or blended with commercial diesel fuels. The advantages of the use of biodiesel fuel include: high cetane number, biodegradability and less production of unburned hydrocarbons, carbon monoxide and polyar- omatic hydrocarbons. While used cooking oils provide a source of some of the raw material [1], the use of fresh materials feedstocks grown specifically for this purpose raise issues related to land use in food vs fuel and also whether they can be classified as a true renewable and carbon neutral given the use of inorganic fertilizers in their cultivation. However, in the shorter term, adoption of such processes is inevitable in order to comply with EU direc- tives (2003/30/EC) which include a target figure of 5.75% renewables in transport fuels on an energy basis by 2010 [http://ec.europa.eu/energy/res/legislation/doc/biofuels/en_ final.pdf]. Although traditionally NaOH or KOH have been used as homogeneous base catalysts for the process [2, 3], there are obvious benefits to be made by moves to heter- ogeneous catalysts. Although bases suffer from the for- mation of soaps in the presence of free fatty acids [3], in general the rate of reaction is superior to that of the acid catalysed process [4]. The use of base catalysts such as K on alumina [5], alumina supported KI [6], Li–Al layered double hydroxides [7] along with MgO [8], CaO [9] and BaO [10] have all been reported. The use of supported alkaline earth oxides have received less attention which is surprising given the potential advantages in terms of greater surface areas and maximising exposure to available, basic sites and also access to commercially available materials as a result of their use in NSR catalyst formula- tions [11, 12]. In this article, we describe the use of BaO on alumina at loadings between 1 and 10% and study the role of dispersion in the transesterification of groundnut and cotton seed oils with methanol. Key differences between these oils are in the compositions with respect to oleate, J. A. Anderson (&) Á A. Beaton Á A. Galadima Á R. P. K. Wells Surface Chemistry and Catalysis Group, Department of Chemistry, University of Aberdeen, Meston Walk, Old Aberdeen AB24 3UE, UK e-mail: j.anderson@abdn.ac.uk 123 Catal Lett (2009) 131:213–218 DOI 10.1007/s10562-009-0051-7