Y-modified MCM-22 supported PdOx nanocrystal catalysts for catalytic oxidation of toluene

Abstract

A series of rare earth elements (REEs)-modified and Mobil Composition of Matter (MCM)-22-supported Pd nanocrystal catalysts were synthesized via a high-temperature solution-phase reduction method and tested for toluene complete oxidation. These catalytic materials were systematically characterized by N2 adsorption/desorption, X-ray powder diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), energy-dispersive spectroscopy (EDS), inductively coupled plasma atomic emission spectroscopy (ICP-AES), temperature-programmed surface reaction of toluene (toluene-TPSR) and X-ray photoelectron spectroscopic (XPS) techniques in order to investigate the structure-catalytic property relationship. Moreover, catalysts with an appropriate yttrium content greatly improved the catalytic activity of 0.2%Pd/MCM-22. PdOx (x=0, 1) nanoparticles, ranging from 3.6 to 6.8 nm, which were well distributed on the surface of MCM-22. Efficient electron transfer from the Pd2+/Pd0 redox cycle facilitated the catalytic oxidation process, and the formation of Pd (or Y)-O-Si bonds improved the high dispersion of the PdOx and Y2O3 particles. Toluene-TPSR experiments suggested that the addition of Y2O3 improved the physical/chemical adsorption of 0.2%Pd/MCM-22, thus increasing the toluene adsorption capacity. Then, 0.2%Pd/7.5%Y/MCM-22 exhibited the highest catalytic performance. In addition, this catalyst maintained 95% conversion with high resistance to water and chlorine poisoning, even after toluene oxidation at 210 °C for 100 h, making it more valuable in practical applications.