THE EFFECT OF SEQUENTIAL ACID AND BASE TREATMENT TOWARD POROSITY AND CATALYTIC PERFORMANCE OF MOR ZEOLITE

• Main Author: Toriq Nur Fajar, Adroit
• Format: Theses
• Language: Indonesia
• Subjects: Kimia
• Online Access: https://digilib.itb.ac.id/gdl/view/38308
• Institution: Institut Teknologi Bandung

MOR zeolite is one of the most important catalyst for many reactions in petrochemical industries e.g. isomerization, alkylation, hydricracking, reforming, and dewaxing. However, MOR zeolite is susceptible to deactivation by cokes formation due to diffusion limitation along its one dimensional (1D) micropores. The molecular diffusion issue can be overcome by introducing additional pores at meso scale (2-50 nm) within zeolite crystal, known as hierarchically porous zeolite. Mesopores act as “molecular highway” for reactants to access the active site within and/or for products to diffuse out of zeolite micropores. Desilication in alkaline media provide good result in introducing mesopores into zeolite crystals. Nevertheless, this method do not have a good agreement with low silica zeolite (Si/Al ratio bellow 25) such as MOR, especially in the complete absence of OSDA (organic structure-directing agent). Furthermore, the highly selective Si dissolution over base treatment consequences to decrease Si/Al ratio which obviously influence the catalytic performance. To overcome these problems, acid treatment can be performed prior to base treatment (sequential acid-base treatment). Performing acid leaching prior to base treatment raise the Si/Al ratio into the optimal range thus Si extraction could be effectively employed to introduce intracrystalline mesopores. These facts strongly suggest that on the sequential acid-base treatment, the acid treatment is the key to design mesoporosity. Moreover, combination between acid and base treatment can possibly maintain the zeolite chemical composition (Si/Al ratio). Rationally, the extraction of Al should depend on the used acid. Thus, in this contribution we perform an investigation into the effect of acid type on the sequential acid- alkaline treatment with regard to mesopores formation in MOR zeolite. The used acids were HCl, HNO3, and H2C2O4 which has different strength i.e. Ka of 1.3×106; 24; and 5.4×10-2, respectively. The results show that the extraction of Al is strongly governed by acid strength. Stronger acid lead to higher Si/Al ratio. The extraction of Al is also proportional with amount of formed silanol groups. The silanol groups are the dominantly dissolved part under base treatment. Thus, the sinergy between increased Si/Al ratio and fabricated silanol groups are the key of successful desilication process to introduce mesoporosity within MOR zeolite. In additon, preserved chemical composition was also demonstrated on the final products of sequential post treatment. From different Si/Al ratio on the acid treated samples, subsequently decrease to about 8 (similar with parent material). Even on the direct base treated sample, the Si/Al ratio is hardly altered. This result indicate that the lowest Si/Al ratio of MOR zeolite is about 8. Catalytic test toward ethanol dehydration demonstrate that sequential acid-base treatment significantly improve MOR zeolite performance. The improvement of catalytic performance is in the order of acid strength used in the acid treatment. On the direct base treated sample, there is also an improvement, however, not as high as sequential post treated samples. These insight are based on the characterzation results of XRD, 27Al and 29Si MAS NMR, Raman dan Infrared spectroscopy, SEM, TEM, and TGA.