Carbon - Supported Platinum Catlyst for N-Hexane dehydrogenation

Activated carbon (AC) from coconut shells is used as support for platinum catalysts. A series of catalysts based on platinum and Pt doped Sn were prepared by impregnation on different supports like AC and SiO2. It was shown that the nature of the support has a significant influence on the activity and selectivity to alkenes of the catalysts in the dehydrogenation of nhexane to alkenes. The higher activity and selectivity of the carbon supported platinum catalyst can be explained by higher dispersion of platinum particles of the catalysts. The addition of Sn led higher stability and activity and that may be related to the formation of a PtSn alloy on the surface and the modification of interaction between the alkenes and the metal sites, making it weaker and keeping the metallic surface more free of cokes by migration of that to the carbon surface.
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Carbon - Supported Platinum Catlyst for N-Hexane dehydrogenationJournal of Chemistry, Vol. 41, No. 1, P. 110 - 114, 2003 CARBON - SUPPORTED PLATINUM CATALYST FOR N-HEXANE DEHYDROGENATION Received 01-7-2002 Nguyen Thi Dung, Tran Manh Tri Institute of Chemical Technology, Hochiminh City Summary Activated carbon (AC) from coconut shells is used as support for platinum catalysts. A series of catalysts based on platinum and Pt doped Sn were prepared by impregnation on different supports like AC and SiO2. It was shown that the nature of the support has a significant influence on the activity and selectivity to alkenes of the catalysts in the dehydrogenation of n- hexane to alkenes. The higher activity and selectivity of the carbon supported platinum catalyst can be explained by higher dispersion of platinum particles of the catalysts. The addition of Sn led higher stability and activity and that may be related to the formation of a PtSn alloy on the surface and the modification of interaction between the alkenes and the metal sites, making it weaker and keeping the metallic surface more free of cokes by migration of that to the carbon surface. I - Introduction presence of Li but is not dependent on the concentration. Castrol [7] found that bimetallic Platinum supported catalysts are widely Pt-Sn catalyst doped by alkali metals has aused in many industrial processes including better yield in alkenes and lower selectivityhydrogenation, dehydrogenation, and reforming towards gases and aromatics compared toof n-alkanes. Its chemical stability in both monometallic platinum. Bimetallic Pt-Ge andoxidizing and reducing conditions makes this Pt-Pb catalysts show a similar performancemetal an ideal catalyst in many applications. compared to Pt-Sn. However, their selectivity toCatalytic dehydrogenation of alkanes is of alkenes is lower. Yang et al. [8] indicated thatincreasing importance due to the growing the oxidation states of tin and the possibility ofdemand for linear alkenes as raw materials for alloy formation between platinum and tinthe production of biodegradable detergents. seems to be depended on the method of preparation, the nature of supports and the Bimetallic Pt-Sn/Al2O3 catalysts have been loading of the catalytic component.extensively studied by many research groups [1- 4] due to their importance in industrial Recent studies have showed that, the naturepetrochemical processes. Many of these studies of the support is one of the importanthave focused on hydrocarbon conversion such characteristics of great influence on activity andas isomerization, aromatization, dehyrocyc- selectivity of the catalyst .lization and dehydrogenation of light alkanes. Activated carbon as a catalyst support is ofTimofeeva et al. [6] studied Pt/Al2O3 and Li- increasing interest today due to its uniquedoped Pt/Al2O3 catalysts and showed that the properties like stability in both acidic and basicselectivity to monoalkenes is dependent on the media and thermal resistance but only a few110publications are devoted to the investigation of impregnating solution under stirring at roomthe selective dehydrogenation of n-alkanes to temperature for 2 h. Following impregnation,alkenes over carbon supported platinum the catalysts were filtered, dried overnight atcatalysts. 110oC and then calcined at 450oC in flowing The aim of the following study is the nitrogen for 2 h. Subsequently Sn was added bypreparation and characterization of platinum impregnation from a solution of SnCl2 (0,04catalysts supported on activated carbon mol/l) following the same procedure.obtained from coconut shells of Vietnam in The composition of the catalysts used in thecomparison with supported Pt/SiO2 catalysts in catalytic tests are given in table 2 (For selectedthe selective dehydrogenation of n-hexane to catalysts the metal dispersions were determinedalkenes as a model reaction by transmission electron microscopy) carried out with a Philips EM-420 Instrument operated II - Experiment at 120 kV.1. Preparation and characterization of the Table 2: Composition of the catalysts used AC support ...