%0 Journal Article
%T -Butane Isomerization over Silica-Supported Heteropolyacids: Study of Some Parameters
%A Eva Grinenval
%A Anthony Garron
%A Fr¨¦d¨¦ric Lefebvre
%J Journal of Catalysts
%D 2013
%I Hindawi Publishing Corporation
%R 10.1155/2013/828962
%X Isomerization of -butane was studied on silica-supported heteropolyacids. The activity depends strongly on the solvent used for the preparation and on the polyoxometalate loading. This behavior was explained by different proportions of isolated and bulk heteropolyacids. Silicotungstic acid is inherently more selective than phosphotungstic acid. In presence of platinum and hydrogen the catalysts are stable and highly selective (more than 97%) to isobutane. A study as a function of temperature shows that there is an optimal temperature for performing the reaction. 1. Introduction Skeletal isomerization of low carbon -paraffins to isoparaffins is of great importance for the petroleum industry as it allows preparation of fuel mixtures of improved performance, low-octane-number compounds being replaced by high-octane-number ones [1]. As a consequence, the use of lead-containing fuel additives could be suppressed completely, resulting in economic and environmental benefits. In particular, -butane can be transformed to isobutane, which is used in the synthesis of MTBE (methyl-tert-butyl ether, another fuel additive) or in the alkylation of butenes [2]. Various alternatives have been tested so far in order to replace the currently employed commercial system (which among other inconveniences is water sensitive and requires constant addition of a small quantity of organic chloride precursor to the feed gas) or Pt/mordenite (less active than the former but resistant to poisoning). Sulfated zirconia was, for instance, reported to catalyze butane-isobutane isomerization already at room temperature [3]. Although it deactivated rapidly, its activity was higher than those of zeolites and is rather similar to mordenite [4, 5]. The presence of in the feed gas was shown to increase and stabilize the activity even in the absence of a noble metal cocatalyst and was ascribed to the suppression of the agglomeration of polymeric cracking products at the surface of the catalyst. However, when the concentration of hydrogen was too high a inhibiting effect was noted [4]. Some other proposed systems for this reaction were based on sulfated titania [6] or tungstated zirconia [7]. Polyoxometalates can be perceived as discreet analogues of metal oxide surfaces [8]. Particularly, the Keggin family members are widely used in homogenous catalysis, because of their pronounced and tuneable acidic and redox properties [9]. There are however only few examples of applications of pure solid heteropoly oxometalates in heterogeneous catalysis, due to their very low specific surface area (only
%U http://www.hindawi.com/journals/jcat/2013/828962/