Synthesis of ZSM 5 in alkaline and fluoride media characterization and catalytic activity

Abstract

Zeolites, an important class of micro porous materials, have been used as catalysts, ion exchangers and adsorbents. They are built with SiO4 and AlO4 tetrahedra. Cerium AlPO-5 molecular sieves were synthesized and reported for oxidation of ethyl benzene and toluene. Since cerium entered the framework of AlPO-5, it was expected same entry in the framework of Silicalite-1. With this logic, in the present study Ce-Silicalite-1 molecular sieves and study of their activity for vapour phase oxidation of ethyl benzene and p- xylene were attempted in air. The major products were p-diethyl benzene (p-DEB) and ethyl benzene (EB), and minor products m- and o-diethyl benzene (m-DEB and o-DEB). The study of time on stream indicated very slow decrease in conversion with the increase in time on stream, but the selectivity of p-DEB increased due to partial blocking of pore with coke. Hence for selective formation of p-dialkyl benzene, high crystallinity and large crystal size were proved crucial. The WHSV was 5.776 h-1 and air flow rate 8ml h-1, acetophenone was 99 % selectivity at 300 °C. Cerium silicalite-1 (50) was more active (48 % conversion) than others. The study of time on stream indicated steady conversion with high selectivity to acetophenone for 6 h. It established absence of coke formations. The major product was p-methyl benzaldehyde. The conversion of p-xylene was 59 % at 300 °C. The other product p-methyl benzyl alcohol was very insignificant. The activity of the catalyst followed the order Ce-Silicalite-1, (50gt75gt100). The study of time on stream indicated study p-xylene conversion and p-methyl benzaldehyde selectivity. Hence the study indicated feasibility of incorporating cerium in the framework of Silicalite-1. Hence ZSM-5 synthesized in fluoride medium was established to have high p-selectivity in alkylation and disproportionation. Ce-Silicalite-1 molecular sieves, synthesized in the fluoride medium, also exhibited high selectivity in the oxidation of alkyl aromatics in air. newline newline newline