Promotion mechanism of CeO sub(2) addition on the low temperature SCR reaction over MnO sub(x)/TiO sub(2): a new insight from the kinetic study

CeO sub(2) addition showed a notable improvement on the low temperature selective catalytic reduction (SCR) performance of MnO sub(x)/TiO sub(2). In this work, a new insight into the promotion mechanism was established from the steady state kinetic study. The kinetic rate constants of the SCR reaction through the Eley-Rideal mechanism, those of the SCR reaction through the Langmuir-Hinshelwood mechanism, and those of the non-selective catalytic reduction (NSCR) reaction over MnO sub(x)/TiO sub(2) and MnO sub(x)-CeO sub(2 )/TiO sub(2) were obtained according to the steady state kinetic analysis. After comparing the reaction kinetic constants of NO reduction over MnO sub(x)/TiO sub(2) and MnO sub(x)-CeO sub(2 )/TiO sub(2), the mechanism of the addition of CeO sub(2) for NO reduction over MnO sub(x)/TiO sub(2) was discovered according to the relationship between the reaction rate constants and the catalyst properties. Because the oxidation ability of MnO sub(x)/TiO sub(2) increased, the rate constant of the SCR reaction over MnO sub(x)/TiO sub(2) increased remarkably after CeO sub(2) addition, resulting in a notable promotion of N sub(2) formation. The oxidation of NH sub(3) to NH over MnO sub(x)/TiO sub(2) required two Mn super(4+) cations on the adjacent sites. However, the probability of two Mn super(4+) cations occurring on the adjacent sites on MnO sub(x)/TiO sub(2) obviously decreased after CeO sub(2) addition, although the oxidation ability of MnO sub(x)/TiO sub(2) increased. Therefore, the rate of N sub(2)O formation during NO reduction over MnO sub(x)/TiO sub(2) did not vary notably after CeO sub(2) addition. As a result, both the SCR activity and N sub(2) selectivity of NO reduction over MnO sub(x)/TiO sub(2) improved after CeO sub(2) addition.