Available online at www.sciencedirect.com ScienceDirect Journal of Natural Gas Chemstry www.elsevier.m%catdjomnoeate/jngc Journal of Natural Gas Chemistry 15(2006)247-252 SCIENCE PRESS Article The Effect of Sulfate Ion on the Isomerization of n-Butane to iso-Butane Sugeng Triwahyonol*, Zalizawati Abdullah2, Aishah Abdul Jali12 1. Ibnu Sina Instatute for Fundamental Science Studies, 2. Faculty of Chemical and Natural Resources Engineering, Universiti Teknologi Malaysia, 8131 0 Skudai, Johor, Malaysia [Manuscript received October 18, 20061 Abstract: The effect of sulfate ion (SO%-) loading on the properties of Pt/SO:--ZrOz and on the catalytic isomerization of n-butane to iso-butane was studied. The catalyst was prepared by impregnation of Zr(0H)A with H2S04 and platinum solution followed by calcination at 600 "C. Ammonia TPD and FT-IR were used to confirm the distribution of acid sites and the structure of the sulfate species. Nitrogen physisorption and X-ray diffraction were used to confirm the physical structures of Pt/SO:--ZrO2. XRD pattern showed that the presence of sulfate ion stabilized the metastable tetragonal phase of zirconia and hindered the transition of amorphous phase to monoclinic phase of zirconia. Ammonia TPD profiles indicated the distributions of weak and medium acid sites observed on 0.1 N and 1.0 N sulfate in the loaded catalysts. The addition of 2.0 N and 4.0 N sulfate ion generated strong acid site and decreased the weak and medium acid sites. However, the XRD results and the specific surface area of the catalysts indicated that the excessive amount of sulfate ion collapsed the structure of the catalyst. The catalysts showed high activity and stability for isomerization of n-butane to iso-butane at 200 "C under hydrogen atmosphere. The conversion of n-butane to iso-butane per specific surface area of the catalyst increased with the increasing amount of sulfate ion owing to the existence of the bidentate sulfate and/or polynucleic sulfate species ((ZrO)zSOz), which acts as an active site for the isomerization. Key words: sulfate ion; strong acid site; isomerization; n-butane; Zr; Pt 1. Introduction Catalyzed isomerization of alkane is one of the important processes in petroleum refining to pro- duce high quality gasoline because of the capability to modify the octane number of gasoline. In indus- trial processes, acid catalyst is known as a media for the conversion of alkane into iso-alkane. However, the catalysts such as HF, and catalysts containing halides have many disadvantages and are not suitable for the isomerization of alkanes. HF is particularly danger- ous while catalysts containing halides such as AlC13 or sulphuric acid are corrosive and pose significant envi- ronmental challenges including the disposal of waste [l-3). * Corresponding author. E-mail: sugeng8ibnusina.utm.my Considerable interest has been focused on the use of strong solid acids based on anion-modified zirco- nium oxide catalyst. Recently, many investigations have been focused on Pt/SO;--ZrOz because it was reported to exhibit higher activity and selectivity in the isomerization of c 4 - C ~ [4,5]. In addition, the sulfated zirconia showed catalytic activities for di- versified acid-catalyzed reactions at low temperature. This catalytic performance is unique when compared to typical solid acid catalysts, such as zeolites, which are mesoporous materials showing no activity for the reaction at such low temperature. Zirconia possesses weak acid and basic properties and has no capacity for alkane isomerization. It has been realized that the catalytic activity depends on