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Evolution of the properties of PtGe/Al2O3 reforming catalysts with Ge content

Paper ID Volume ID Publish Year Pages File Format Full-Text
44139 46005 2007 9 PDF Available
Title
Evolution of the properties of PtGe/Al2O3 reforming catalysts with Ge content
Abstract

The effect of the Pt/Ge atomic ratio on the catalytic activity of PtGe/Al2O3 catalysts used in n-heptane reforming was studied. The samples were prepared by the coimpregnation method on chlorinated alumina. The platinum content was 0.5 wt.%, and Ge-loading was varied to obtain Pt/Ge atomic ratios of 0.3, 0.7, 1.4, 2.1 and 3.5. Pt/Al2O3 and Ge/Al2O3 catalysts were also prepared as references. Characterization was carried out by temperature-programmed reduction (TPR), temperature-programmed desorption of ammonia (NH3-TPD), Fourier transform IR spectroscopy (FTIR) with CO as the probe molecule, X-ray photoelectron spectroscopy (XPS), cyclohexane (CH) dehydrogenation, and n-heptane reforming. The preparation method followed in this work revealed a decrease in the metallic activity of Pt due to the presence of Ge. The Ge2+ and Ge4+ species, after reduction at 500 °C, were detected on the surface of PtGe catalysts. The increase in the Ge content led to a decrease in hydrogenolysis activity and the formation of aromatics; an increase in the formation of isomers and cycloparaffins, and a reduction in the production of gas and in deactivation by coke, thereby improving catalyst stability. The results show that the maximum isoparaffin yield of all catalysts tested was obtained for a Ge-loading of 0.27 wt.% (Pt/Ge atomic ratio = 0.7). These changes in the performance of the PtGe catalysts may be attributed to the modifications occurring in the metallic and in the acid function of Pt/Al2O3 due to the introduction of Ge. The metallic catalytic activity of Pt is modified by the geometrical effect (dilution of Pt ensembles) and changes in the electronic properties of platinum. Ge addition produces a weakening of Pt/Al2O3 acid strength and an increase in the acid sites total density by the presence of Ge oxides.

Graphical abstractThe current interest in reforming products is in the production of isoparaffins that have high octane numbers and low environmental pollution. It is well known that isoparaffin selectivity is controlled by the acid function, which can be altered by the promoter content and at the same time, an improvement of stability can be achieved by decreasing the deactivation by coke formation. Thus, the optimization of the Pt/Ge atomic ratio on the catalytic activity of PtGe/Al2O3 catalysts used in n-heptane reforming has been studied. Figure optionsDownload full-size imageDownload as PowerPoint slide

Keywords
n-Heptane reforming; Isoparaffin selectivity; Pt/Ge atomic ratio optimization; Electronic effect
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Publisher
Database: Elsevier - ScienceDirect
Journal: Applied Catalysis A: General - Volume 327, Issue 2, 15 August 2007, Pages 123–131
Authors
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Subjects
Physical Sciences and Engineering Chemical Engineering Catalysis
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Don't Miss Today's Special Offer
Price was $35.95
You save - $31
Price after discount Only $4.95
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