Effect of the impregnation order on the nature of metal particles of bi-functional Pt/Pd-supported zeolite Beta materials and on their catalytic activity for the hydroisomerization of alkanes

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作   者：

Rafael Roldan;  Andrew M.Beale;  Manuel Sanchez-Sanchez; 

作者机构：

The Netherlands;  Departamento de Quimica Orgdnica;  Department of Chemical and Environmental Technology;  Campus de Rabanales;  14014 Cordoba;  Faculty of fi Sciences;  Universidad Rey Juan Carlos;  Sorbonnelaan 16;  Universidad de Cordoba;  Spain;  Utrecht University;  Department of Chemistry;  Inorganic Chemistry and Catalysis;  Edificio C-3;  28933 Mostoles;  3584 CA Utrecht;  Madrid;  km 396;  ESCET;  C/Tulipdn s/n;  Ctra.Nnal.IV; 

关键词：

Zeolite Beta;  Platinum;  TPR;  Hydroisomerization;  Palladium;  Bi-metallic catalysts;  EXAFS;  Diffuse-reflectance UV-visible; 

期刊名称：

Journal of Catalysis

i s s n：

0021-9517

年卷期：

2008 年 254 卷 1 期

页   码：

12-26

页   码：

摘   要：

A series of mono- and bi-metallic (Pt and/or Pd) impregnated zeolite Beta samples have been prepared,characterized using a number of experimental techniques and catalytically tested for the hydroisomerization of a mixture of light paraffins.In particular,the effect of the order of Pt and Pd impregnation on the type/structure of the metallic species of the zeolite support and on the catalytic activity has been studied.Studied samples included a zeolite Beta in which both Pt and Pd (0.5 wt% of each) were simultaneously impregnated (and subsequently calcined and reduced) and two equally metal-loaded samples where the metals were sequentially impregnated (samples Pt*-Pd/Beta and Pd*-Pt/Beta,in which Pt and Pd were impregnated first,respectively).Mono-metallic samples were also prepared for comparison.TPR,DR-UV-visible,TEM,and XAS studies confirm that the order of impregnation plays a key role in the formation of metallic particles,influencing aspects as decisive in their catalytic behavior as their size,their dispersion and their composition (e.g.,mono- or bi-metallic).The initial impregnation of Pd and subsequently of Pt produces a higher number of hetero-metallic (Pt-Pd) bonds than the simultaneous co-impregnation and especially for the impregnation in reverse order,which does not produce Pt-Pd bonds in a detectable amount.Based on the results from the different characterization techniques,a model of the metal distribution and composition of the particles was proposed for each bi-metallic sample.In good agreement,the order of the catalytic activity was found to be Pd*-Pt/Beta > Pd-Pt/Beta > Pt/Beta > Pt*-Pd/Beta > Pd/Beta,making clear that not only the presence of both metals,but also an adequate preparation method generating a high number of hetero-metallic bonds must be taken into account to improve the catalytic properties in relation to the mono-metallic samples.