Decomposition and selective catalytic reduction of NO by propane on CuZSM-5 zeolites: a mechanistic study

Abstract

NO decomposition and selective catalytic reduction (SCR) of NO by propane in oxygen were compared over Cu-ZSM-5 with various Si/Al ratios and extent of exchange. It was established that the turnover frequency (TOF) values referred to copper ions species characterized by NO desorption, are independent of the Si/Al ratio and the extent of exchange. The presence of propane and oxygen accelerates N 2 formation and higher conversion can be reached at lower temperature. TPD experiments indicate that the Cu 2+(O)(NO)(NO 2) surface complex, which is formed as an intermediate in the decomposition of NO, is not the active pathway in SCR. In SCR of NO by propane in the presence of oxygen, the first step is Cu(I) to Cu(II) conversion by oxygen. NO 2 formation is facilitated by Cu(II) species, which react with propane forming a nitrito–propane compound. Its result in N 2 formation at a lower temperature than what is required for decomposition of NO.