Synthesis of Sulfated Pt/ZrO 2 Catalysts Using Different Precipitants for n-Hexane Hydroisomerization
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Synthesis of Sulfated Pt/ZrO2 Catalysts Using Different Precipitants for n-Hexane Hydroisomerization Guo-Xian Yu1,*, Wei Pan1, Xiao-Long Zhou2, Li-Fang Chen3*, Jin-An Wang3 1
School of Chemistry and Environmental Engineering, Jianghan University, Wuhan 430056, China School of Chemical Engineering, East China University of Science & Technology, Shanghai 200237, China 3 ESIQIE, Instituto Politécnico Nacional, Av. Politécnico S/N, Col. Zacatenco, 07738 México D.F., México 2
ABSTRACT Ammonia (AOH), dimethylamine (DME) and triethanolamine (TEA) as precipitants were used to prepare Pt-SO42-/ZrO2 catalysts, and the crystalline structures, textural structures and surface acid properties of the catalyst samples were characterized and n-hexane hydroisomerization activity over the samples were investigated. DME and TEA as the precipitants would delay the crystallization process. The organic amines were difficult to remove during the washing process, leading to the rinsing times increase, which probably decreased the catalyst BET area. Super Lewis acid sites in SZ catalysts would play very important roles in catalytic hydroisomerization activity. Keywords: Precipitant; n-Hexane; Hydroisomerization; Sulfated Zirconia INTRODUCTION Sulfated zirconia (SZ) promoted with metals demonstrated high catalytic activities in alkane hydroisomerization at low temperatures [1-3]. The strong acidity of SZ has attracted much attention because of its ability to catalyze many reactions, such as cracking, alkylation, and isomerization. For this reason a large number of researches were focused on this kind catalyst and many reviews are available [4-7]. Nevertheless, SZ showed rapid deactivation during catalytic reactions. Therefore, in recent years, oxides or metals promoted zirconia catalysts to gain its catalytic stability have attracted much attention for isomerization reactions due to their superacidity, non-toxicity and a high activity at low temperatures [8-11]. A number of transition metals promoters (e.g. Fe, Mn, and Ni) have been added to SZ, resulting in catalysts with higher activity than unmodified SZ [12]. However, rapid deactivation was still observed [12, 13] and the marked promoting effect disappeared if the reaction was performed at temperatures higher than 250 ºC [14, 15]. Recently, it has been found that addition Al to zirconia can also promote the catalytic activity and stability of sulfated zirconia for n-butane and n-hexane isomerization [15-17]. In the Zr4+ containing solution for zirconia preparation, Zr4+ and OH- form complicated big molecules, and the increase of OH- concentration will cause the complicated molecules to grow and finally hydrous zirconium oxide gel forms [18]. Traditionally, ammonia water as a precipitant provides OH- to produce Zr(OH)4. In the paper, ammonia (AOH), dimethylamine (DME) and triethanolamine (TEA) as precipitants were used to prepare PSZ catalysts, and the crystalline structures, textural structures and surface acid properties for the catalyst samples, and n-hexane hydro-isomerization activi
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