Synthesis of novel metal/bimetal nanoparticle-modified ZSM-5 zeolite nanocomposite catalysts and application on toluene methylation

Abstract

Synthesis of Ag, Ni, Cu metallic and Ag/Ni, Ag/Cu bimetallic nanoparticles (NPs) was carried out by using metal nitrate salts as precursors via an easy and simple wet chemical method, and the synthesized NPs were loaded into the cavities of ZSM-5 zeolite framework. L-threonine was used as a capping agent and sodium borohydride as a reducing agent. Characterization of NPs and nanoparticle-modified ZSM-5 catalysts were realized with TEM, XRD, BET, FTIR, TGA, etc. The results obtained revealed that the structure of the zeolites was well preserved after the modification with metal NPs. According to the TEM and BET results, Ag-containing nanocomposite catalysts increased average pore diameter due to the small particle size of Ag NPs such as 2-6 nm well dispersed on the surface and partial blockage of the micropores of zeolite. The catalytic activity of the prepared catalysts was tested in toluene methylation at temperatures of 300 degrees C, 400 degrees C, 500 degrees C and different weight hourly space velocities (WHSV). At low temperatures, the modification of NPs in the ZSM-5 matrix increased toluene methylation and p-xylene selectivity. The highest p-xylene selectivity was found to be about 51% at 400 degrees C, while toluene conversion at this temperature was 61% using Ag NP-modified ZSM-5 due to the perfect stability NPs on the zeolite structure. The XRD, TGA and coke formation results of used catalysts show the reusability of these catalysts due to their thermal resistance, minimal coke formation and Ag NPs stability onto the zeolite framework.