NO reduction with CO over HY zeolite-supported rhodium dicarbonyl complexes: giving insight into the structure sensitivity

Abstract

The activity of Rh(CO)₂ complexes supported on HY zeolites with Si/Al ratios of 30 and 2.6 in NO reduction with CO reaction was investigated. Facile exchange between CO and NO ligands occurred under ambient conditions but no activity towards formation of N₂, N₂O and CO₂ was observed. Significant difference in the catalytic performance of both samples was observed at elevated temperatures. When the temperature was increased to 270 °C, an induction period of about 145 minutes was detected for the HY2.6-supported sample where NO conversion increased from approximately 9% to 100% while HY30-anchored Rh(CO)₂ species remained inactive. In situ Fourier transform infrared (FTIR) spectroscopy and high resolution transmission electron microscopy (HRTEM) measurements revealed that the transient period is associated with decomposition of Rh(CO)₂/Rh(NO)₂ complexes and formation of rhodium particles. These data unambiguously demonstrated that mononuclear Rh(CO)₂/Rh(NO)₂ species which are stabilized by HY30 zeolite under the reaction conditions do not promote NO reduction with CO but conglomeration of Rh atoms is needed to initiate the catalytic cycle.