Role of the preparation method on properties of Pd/Cu-MCM-41 hydrodechlorinating catalysts

• The synthesis method determines the chemical–physical properties of Pd/Cu MCM-41.
• The template removal by calcination provoked the segregation of Pd and Cu oxides.
• Ionic exchange rather than calcination avoids metal segregation.
• Pre-formed Pd/Cu nanoparticles were used to control the active phase composition.

The effect of the preparation method on properties of Pd/Cu MCM-41 catalysts tested in the hydrodechlorination of CF3OCFClCF2Cl to CF3OCFCF2 was studied. MCM-41 samples were synthesized using sodium silicate as silica source and cetyltrimethylammonium bromide as template. The incorporation of Pd and Cu active species has been performed by impregnation, inclusion in the MCM-41 synthesis procedure and using pre-formed Pd/Cu nanoparticles. The effect of the removal of the template was also studied using calcination and ionic exchange procedures. The hexagonal structure of MCM-41, large specific surface area and pore volume were preserved after inclusion of active species both as cations during the synthesis of MCM-41 or as Pd/Cu preformed nanoparticles. PXRD and HRTEM evidenced the formation of bimetallic particles in all the prepared catalysts; however their particle size and composition varied with the synthesis procedure. The template removal by ionic exchange avoided the sintering of copper species observed in calcined sample. The use of preformed nanoparticles led to small and well dispersed bimetallic species in the MCM-41 structure; however, also in this case, the template removal by calcination provoked both the increase of the particle size and the oxidation of metals. Catalytic performances in the hydrodechlorination of CF3OCFClCF2Cl, namely the dehalogenating activity and product selectivities, were dependent on catalysts properties.

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