Influence of clay binders on the performance of Pd/HZSM-5 catalysts for the hydroisomerization of n-butane

The influence of the amount of two clay binders (montmorillonite and bentonite) on the acid properties and performance of Pd/HZSM-5 zeolite with different Si/Al ratios for the hydroisomerization of n-butane has been studied. Temperature-programmed desorption of ammonia, atomic absorption spectroscopy, chemisorption, and surface area measurements were used to characterize the catalysts. After agglomeration, some zeolite protons are neutralized by clay sodium and, consequently, a lower n-butane conversion is obtained. The product selectivity is also strongly influenced by the binder due to the fact that zeolite hydrogen transfer activity, metal/acid site balance, and diffusion of products are modified. If the appropriate binder is selected, the decrease in conversion will be compensated by a much higher isobutane selectivity. Thus, a catalyst based on Pd/HZSM-5, with a zeolite Si/Al ratio of 25, and agglomerated with bentonite in a zeolite/clay ratio of 35/65 wt/wt, showed not only an adequate mechanical resistance but also high isobutane selectivity and isobutane yield (87.1 and 23.9 mol %, respectively). It should be remarked that, under the same reaction conditions, the parent catalyst without binder showed worse isomerization activity (18.5 mol % isobutane yield with 47.3% isobutane selectivity).