Reforming of a model biogas on Ni and Rh–Ni catalysts: Effect of adding La Alessandra F. Lucrédio a , José M. Assaf b , Elisabete M. Assaf a, ⁎ a Universidade de São Paulo, Instituto de Química de São Carlos, Av. Trabalhador Sãocarlense, 400, 13560-970 São Carlos, SP, Brazil b Universidade Federal de São Carlos, Rodovia Washington Luis, km 235, 13565-905, São Carlos, SP, Brazil abstract article info Article history: Received 24 March 2011 Received in revised form 17 February 2012 Accepted 18 April 2012 Available online 19 May 2012 Keywords: Catalyst Nickel Biogas Reforming Ni catalysts supported on γ–Al 2 O 3 modified by Rh and La were prepared and evaluated on the reforming of a model biogas. The catalysts were characterized by EDS, XRD, TPR, XANES and surface area estimation (BET). The results showed that in the original Ni catalyst, the Ni interacted strongly with the alumina support, exhibiting high reduction temperatures in TPR tests. In the catalytic tests, the addition of Rh on Ni catalysts improved CH 4 conversion but also increased carbon deposition, possible by causing the segregation of Ni species under the reaction conditions. The presence of La on Ni catalysts reduced the carbon deposition by favoring the gasification of carbon species. Addition of synthetic air to the process improved the CH 4 conver- sion and also decreased the carbon formation. The catalysts Ni, Rh–NiLa, and Rh showed good results in the conversion of model sulfur-free biogas, which suggests that they are promising catalysts to be tested in con- version of real biogas. © 2012 Elsevier B.V. All rights reserved. 1. Introduction Interest in the development of power sources that use renewable fuels and operate with reduced emission of pollutants has been grow- ing for some years [1]. Biogas is generated in the treatment of waste- water and sewage, during the anaerobic digestion of organic matter, and is composed mainly of CH 4 (60–65%) and CO 2 (40–35%). It seems to offer an alternative raw material from which to produce synthesis gas (H 2 + CO). Economical production of synthesis gas is of great impor- tance, considering that this is the most costly step in the GTL process (transformation of gas to liquid) [2,3]. The high levels of CO 2 and CH 4 in biogas allow its conversion to syn- thesis gas by dry reforming (Eq. (1)) or by a combination of this reaction and the partial oxidation of methane (Eq. (2)), enabling H 2 /CO ratios between 1 and 2 in the products. CH 4 þ CO 2 ⇆2CO þ 2H 2 ΔH°247kJ mol -1 ð1Þ CH 4 þ 1=2O 2 →CO þ 2H 2 ΔH° ¼ -38kJ mol -1 ð2Þ For the dry reforming of methane, the advantage of using a cata- lyst based on Ni lies in its lower cost and higher availability [4,5]. However, Ni catalysts suffer deactivation by carbon deposition and sintering of the active metal phase at the temperatures used for dry reforming of methane (above 700 °C). To overcome these problems, various approaches can be used to modify the nickel catalysts, includ- ing altering of the support and adding a second metal to the nickel [6]. It has also been found that the presence of small quantities of noble metals (Rh and Pt) may enhance the reaction rate of Ni cata- lysts markedly. According to Wu and Chou [7], Rh has an important capacity to diminish the carbon deposit and raise the yield of H 2 , when associated with Ni. According to those authors, the synergy of the bimetallic catalysts can increase the conversion of CH 4 and the yield of H 2 . Also, according to the literature, Rh shows the best sulfur tolerance in hydrocarbon steam reforming in the presence of sulfur [8]. It is known that biogas can have constituents in small quantities, such as H 2 S, N 2 ,H 2 and volatile organic compounds. These constituents can be removed by several processes before the biogas is fed into the reforming reactor [9]. However, sulfur is a constituent which can deac- tivate the catalyst even at trace levels [10]. This element is adsorbed at the same sites as those involved in carbon formation. The adsorbed sul- fur forms stable compounds with all transition metals, which may cause sulfur poisoning. Rh raises the surface mobility of oxygen to about sev- eral orders of magnitude higher than on Ni and it is possible that this strong oxygen mobility on Rh favors the oxidation of sulfur [8]. Considering that the strong oxygen surface mobility on Rh can favor sulfur oxidation, it should be interesting to test Rh–Ni catalysts; furthermore, they can lead to a more active system, improving CH 4 conversion and H 2 yield [7,8]. Strohm et al. [9] showed that bimetallic Ni–Rh catalysts supported on CeO 2 –Al 2 O 3 present good sulfur toler- ance in the steam reforming of jet fuel containing sulfur. According to the authors, 2 wt.% Rh catalysts supported on Al 2 O 3 modified by CeO 2 presented activity for steam reforming of sulfur-free jet fuels, but, in presence of sulfur, this catalyst presented fast deactivation. Fuel Processing Technology 102 (2012) 124–131 ⁎ Corresponding author. Tel.: + 55 16 33739951; fax: + 55 16 33739952. E-mail address: eassaf@iqsc.usp.br (E.M. Assaf). 0378-3820/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.fuproc.2012.04.020 Contents lists available at SciVerse ScienceDirect Fuel Processing Technology journal homepage: www.elsevier.com/locate/fuproc