Catalyst Design by NH₄OH Treatment of USY Zeolite

Abstract

Hierarchical zeolites are a class of superior catalysts which couples the intrinsic zeolitic properties to enhanced accessibility and intracrystalline mass transport to and from the active sites. The design of hierarchical USY (Ultra‐Stable Y) catalysts is achieved using a sustainable postsynthetic room temperature treatment with mildly alkaline NH4OH (0.02 m) solutions. Starting from a commercial dealuminated USY zeolite (Si/Al = 47), a hierarchical material is obtained by selective and tuneable creation of interconnected and accessible small mesopores (2–6 nm). In addition, the treatment immediately yields the NH4+ form without the need for additional ion exchange. After NH4OH modification, the crystal morphology is retained, whereas the microporosity and relative crystallinity are decreased. The gradual formation of dense amorphous phases throughout the crystal without significant framework atom leaching rationalizes the very high material yields (>90%). The superior catalytic performance of the developed hierarchical zeolites is demonstrated in the acid‐catalyzed isomerization of α‐pinene and the metal‐catalyzed conjugation of safflower oil. Significant improvements in activity and selectivity are attained, as well as a lowered susceptibility to deactivation. The catalytic performance is intimately related to the introduced mesopores, hence enhanced mass transport capacity, and the retained intrinsic zeolitic properties.

Hydrodeoxygenation of Methyl Laurate over Ni Catalysts Supported on Hierarchical HZSM-5 Zeolite

“…Catalysts 2017, 7, 383 5 of 13 Figure 5 shows the NH3-TPD patterns of HZSM-5 treated with NaOH. Two ammonia desorption peaks can be observed, in which the low temperature peak is due to the weakly adsorbed ammonia molecules via hydrogen bonding, instead of the acid sites [21]. The high temperature peaks can be attributed to strong Bronsted acid sites.…”

“…Under NaOH treatment conditions, the lager mesopores were created by the amorphization and framework atom leaching to the filtrate [21]. Due to the strong alkaline nature of the NaOH solution, the treatment condition was very harsh with high pH values of 12.7-13.3 (0.05-0.2 M).…”

“…Especially for HZSM-5-1, the derived pore size distributions reveal that the newly formed pores were very uniform small mesopores, centered around 5 nm. Furthermore, the pore diameters shifted to large mesopores, around 15-30 nm when the NaOH concentration was1.5 M. Under NaOH treatment conditions, the lager mesopores were created by the amorphization and framework atom leaching to the filtrate [21]. Due to the strong alkaline nature of the NaOH solution, the treatment condition was very harsh with high pH values of 12.7-13.3 (0.05-0.2 M).…”

“…With the increase of NaOH concentration, the crystal structure of the hierarchical HZSM-5 was basically maintained. At the same time, the intensity of the diffraction peak decreased gradually, indicating the decrease of the relative crystallinity of HZSM-5 [21]. The relative crystallinity was calculated according to the intensity of the typical diffraction peak located at 22.4 degrees, assuming that the crystallinity of the parent HZSM-5 material was 100%.…”

“…Desilication of a microporous zeolite using an alkaline solution, such as NaOH [20] or ammonia [21], creating intracrystalline mesopores through hydrolysis of the skeleton atom, is the most feasible preparation method for the hierarchical zeolite at large-scale industrial grade, which has been successfully applied to the Hβ [20], HUSY [21], and HZSM-5 [22] zeolites. Here, HZSM-5 was treated by a simple NaOH solution method.…”