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.