A method for calculating catalytic-site amount and judging antagonistic/synergetic effect in multi-metallic catalyst

Abstract

Bimetallic doping is widely utilized to increase the catalytic activity of TiO2-supported catalyst in selective catalytic reduction of nitrogen oxide (SCR). However, a “bimetallic enhancement” is hard to judge since the ratio of active sites, which actually devotes to the catalytic Turnover frequency (TOF, s−1), is difficult to obtain. In this work, Mn, Fe, V, and their pairs were loaded on TiO2, and applied in SCR. Diffuse Reflection Fourier Transform Infrared Spectrometer established a method to evaluate the ratio of working catalytic sites. TOF of these sites were calculated. As a result, single-metallic Mn and V resulted in an average TOF of 0.17 s−1 and 0.11 s−1, respectively, bigger than that (0.10 s−1) of bimetallic MnV. With the increase of loading amount, single-atom cation was agglomerated to form cation pair, and then cluster. Among these three species, cation pair had the biggest TOF, indicating a synergetic effect. Mn obtained the best TOF of 0.18 s−1 at a loading of 1 mmol. One cation species accelerated agglomeration and crystal transformation of the other cation, thus decreasing the TOF and exhibiting an antagonistic effect. These results are in favor of mechanism understanding and catalyst optimization.