Influence of pretreatment on the catalytic performance of Ag/CeO2 for formaldehyde removal at low temperature

Abstract

Silver supported on CeO2 nanoparticles (Ag/CeO2) was found to be an efficient catalyst for formaldehyde removal at low temperature. The activity of Ag/CeO2 catalysts in HCHO oxidation was markedly influenced by pretreatment at different calcination temperatures and H2 reduction. A 6 wt%Ag/CeO2 catalyst calcined at 573 K and then reduced at 473 K with 10% H2/N2 showed 100% conversion of 400 ppm formaldehyde at 333 K with high gas hourly space velocity (GHSV = 24,400 h−1). The catalysts were characterized by various techniques, including N2 adsorption–desorption, inductively coupled plasma mass spectrometry, X-ray diffraction, X-ray absorption near-edge structures, X-ray photoelectron spectroscopy, scanning transmission electron microscopy/energy dispersive spectroscopy, high-resolution transmission electron microscopy, Fourier-transform infrared spectroscopy, temperature-programmed reduction with hydrogen, and in situ diffuse reflectance infrared Fourier transform spectrometry. The catalytic activity was correlated with the oxidation state and particle size of silver. Metallic Ag particles well dispersed on CeO2 NPs could adsorb oxygen readily and generate surface-active oxygen species, which contributed to the oxidation of HCHO at low temperatures. The retention of surface hydroxyl groups on the surfaces of CeO2 NPs also promoted catalytic performance for HCHO oxidation, probably by stabilizing the adsorbed HCHO molecules and removing protons from surface intermediates.