Complete oxidation of formaldehyde over a Pd/CeO2 catalyst at room temperature: tunable active oxygen species content by non-thermal plasma activation

Abstract

Formaldehyde is a main indoor pollutant and its removal is essential to protect human health and meet strict environmental regulations. It is highly desirable to develop efficient catalysts to achieve complete oxidation of formaldehyde at room temperature. However the preparation of catalysts generally requires harsh conditions and long times. In this work, a quick, mild and efficient alternative method was employed to prepare a Pd/CeO₂ catalyst and adjust its characteristics via non-thermal plasma activation. The plasma activation could obtain tunable active oxygen species content since it can change the metallic Pd percentage, oxygen vacancy concentration and Pd particle size simultaneously. A close relationship between the active oxygen species content and HCHO catalytic oxidation activity was established. The Pd/CeO₂ catalyst activated by plasma for only 2 minutes showed the best conversion of over 76% due to its highest active oxygen species amount. The results of in situ DRIFTS of HCHO oxidation over the Pd/CeO₂ catalyst suggested that the intermediates mainly included formate, dioxymethylene and polyoxymethylene species. The high content of active oxygen species could promote the rate determining step of formate species oxidation. This study provides a quick and efficient catalyst activation method for HCHO catalytic oxidation at room temperature.