Dehydrogenation of n-butane over Pd–Ga/Al 2O 3 catalysts

Abstract

Dehydrogenation of n-butane over alumina-supported Pd and Pd–Ga catalysts was studied. Catalysts were prepared by incipient wetness impregnation with a Pd content of 0.66 wt% and atomic Ga/Pd ratios from 0 to ∞, using aqueous solutions of PdCl 2 and Ga(NO 3) 3. Fresh (uncalcined) and calcined catalysts were characterized by X-ray fluorescence spectroscopy (XRF), N 2 adsorption, temperature programmed reduction (TPR), CO and H 2 chemisorptions and O 2/H 2 titrations. n-Butane dehydrogenation reaction was carried out at 500 °C, atmospheric pressure and a H 2/C 4H 10 ratio of 10. An increase in the Pd dispersion with increasing Ga content was observed for the fresh catalysts, according to CO chemisorption results. H 2 chemisorption and H 2/O 2 titrations were not reliable methods to determine the Pd dispersion in the fresh catalysts. For the calcined catalysts with low Ga contents, the CO/Pd, H/Pd and O/Pd values were very similar, but different for those with the higher Ga contents. These differences were explained based on the presence of chlorine. Coke deposition produced the deactivation of the catalysts and inhibited hydrogenolysis reactions on Pd, favoring the dehydrogenation selectivity. In the fresh catalysts, the Ga addition caused an effect similar to that produced by coke, reducing the activity and increasing the dehydrogenation selectivity. In the calcined catalysts, the effect of Ga addition on activity was diminished by the calcination treatment. The combination of calcination and high Ga content led to a catalyst with enhanced activity and very high dehydrogenation selectivity.