Synthesis of mesoporous sodalite by mixed quaternary ammonium cation templates for knoevenagel condensation reaction

Abstract

Sodalite (SOD) is a microporous zeolite having ultra-fine size of pore about 2.8 Å. This property limits its role as a catalyst for the reaction involving bulky molecules. To overcome this disadvantage, suitable mesotemplate can be added to create mesoporosity in microporous SOD. This study focused on the synthesis of SOD having mesoporosity using dual templates approach. A series of SOD were synthesized by mixing tetrapropylammonium (TPA) with different quaternary ammonium cations. As comparison, microporous SOD (Na-SOD) has also been synthesized without the presence of templates. The resulting SOD samples were characterized using XRD, FTIR and N2 adsorption-desorption measurement. The successful formation of SOD crystal phase for all SOD samples was confirmed from XRD patterns and supported by FTIR results that showed all SOD samples have the characteristic of SOD framework. However, N2 adsorption-desorption results confirmed that only SOD sample prepared by mixing TPA with organosilane (SODTO) showed the characteristic of mesoporosity with a narrow pore distribution peak centered at ca. 66 Å. For basicity study, Hammett indicator test showed that the strength of the basicity of all SOD samples was estimated in the range: 8.2 = pKa = 18.4. The results from back titration method found that the SOD-TO sample possessed the highest average amount of basicity as compared with other SOD samples. The comparison of the strength and the amount of basicity for microporous SOD, Na-SOD and mesoporous SOD, SOD-TO samples were measured using TPDCO2 analysis. The results showed that the SOD-TO sample has higher strength and amount of basic sites than the Na-SOD sample at temperature below 500°C. The catalytic testing of all SOD samples in the Knoevenagel condensation reaction of benzaldehyde and diethyl malonate was carried out giving diethyl-2- benzylidenemalonate as a main product. Results showed that all SOD catalyst were active for the Knoevenagel condensation reaction. From the result of catalyst testing, the basicity and surface area does give an impact during the reaction. The SOD-TO catalyst possessing the highest amount of basicity and the highest surface area with mesoporosity in its structure gave the highest percentage of conversion which was 96.29%.