# Conversion of Stearic Acid into Bio-Gasoline over Pd/ZSM-5 Catalysts with Enhanced Accessibility
## 3 Results and Discussion  
### Catalysts Properties  
This section discloses the main features of the supports and catalysts employed in this work. Two different types of ZSM-5 zeolites were used as support of the Pd nanoparticles: nanocrystalline and hierarchical ZSM-5 zeolites, named as n-ZSM-5 and h-ZSM-5, respectively. For the hierarchical zeolitic supports, several samples were prepared having different Si/Al atomic ratios (-33-122). Regarding the Pd content, all catalysts presented an amount of this metal slightly lower than the theoretically loaded (1 wt %), with some deviation being observed for the Pd/n-ZSM-5 (32) catalyst, with a Pd amount of 0.84 wt %, which could indicate a lower association of the Pd moieties with the nanocrystalline zeolitic support during the impregnation treatment. Figure 1 displays the high-angle XRD patterns of the reduced Pd catalysts. All the samples exhibited the typical XRD patterns of MFI zeolite, with no trace of amorphous material. Only in the case of the Pd/h-ZSM-5 (33) were less intense reflections appreciated, which suggests the occurrence of smaller crystalline domains in this sample. Despite the low amount of Pd loaded (around 1 wt %), the reflection of Pd metal at 20\(\sim\)40.1\({}^{\circ}\) (marked with an asterisk) may be observed in all the catalysts in a similar way, bearing out the presence of this metal. Figure 2 exhibits the Ar adsorption-desorption isotherms of both carriers and Pd-containing materials. In addition to the adsorption occurring at low relative pressures, arising from the zeolite micropores, the samples also exhibited significant Ar uptake and intermediate relative pressure, which was consistent with the respective nanocrystalline and hierarchical features of the zeolitic supports. In all cases, the incorporation of Pd caused some decreases in the adsorption capacity of the supports. This finding can be assigned to the occurrence of some micro- and mesopore blocking caused by the deposition of the Pd nanoparticles and/or to some contraction of the mesoporous provoked by the thermal treatment of hydrogen reduction at high temperature (450 \({}^{\circ}\)C). On the other hand, almost no hysteresis was appreciated in the desorption branch of the isotherm indicating the absence of bottle-neck pores. Figure 1: X-ray diffraction patterns of the Pd/ZSM-5 catalysts. As inferred from Table 1, the hierarchical Pd/h-ZSM-5 catalysts, irrespective of their Si/Al atomic ratio, showed enhanced textural properties with regard to Pd/n-ZSM-5 (32), with superior BET surface areas (\(\sim\)100 m\({}^{2}\) g\({}^{-1}\) above) and pore volumes (\(>\)0.04-0.120 cm\({}^{3}\)g\({}^{-1}\)). On the contrary, the sample based on the nanocrystalline ZSM-5 support exhibited the highest micropore surface (274 m\({}^{2}\) g\({}^{-1}\)) and the lowest external/mesopore surface area (103 m\({}^{2}\) g\({}^{-1}\)). For the hierarchical Pd/h-ZSM-5 catalysts, an influence of the Si/Al atomic ratio over the micropore and external/mesopore surface area may be observed. In this regard, the micropore surface area decreased at lower Si/Al atomic ratios, while the contrary was appreciated for the external/mesopore surface area. The great proportion of external/mesopore surface areas in all the samples, and in particular for the catalysts prepared from hierarchical ZSM-5 supports, confirms their high accessibility for the reaction of large molecules, such as stearic acid. Figure 2: Ar adsorption–desorption isotherms at 87 K of both the Pd/ZSM-5 catalysts and the corresponding supports. The acid properties of the catalysts were calculated by means of ammonia TPD measurements and their results are summarized in Table 1. Pd/n-ZSM-5 (32) presents a higher content of strong acid sites than Pd/h-ZSM-5 (33). For the hierarchical Pd/h-ZSM-5 catalysts, when the Si/Al atomic ratios increased, there was a parallel abatement in the total acidities, while their strength was fairly similar, according to their respective maximum temperature of ammonia desorption.