Enhanced low-temperature H2-selective catalytic reduction performance and selectivity of Pt/ZSM-5-TiO2 washcoated monolithic catalysts for NOx reduction

Hydrogen-selective catalytic reduction (H-2-SCR) is a promising technology for reducing nitrogen oxide (NOx) emissions at low temperatures, but the selectivity of this process is limited by the generation of N2O. To achieve enhanced denitrification (deNOx) performance, H-2-SCR catalysts with mixed zeolite and TiO2 supports washcoated on monolithic cordierite were developed. The catalyst support, active metal type and content, and monolithic cordierite cell density significantly influenced the H-2-SCR performance. The xPt/TiO2 catalysts (where x is the metal content, wt.%) achieved >90% NOx conversion 135-180 degrees C, whereas the xPd/TiO2 catalysts exhibited poor H-2-SCR activity, with <30% NOx conversion. In contrast to 0.5Pt/TiO2, the 0.5Pt/zeolite catalysts achieved high NOx conversion at 140-150 degrees C (91% at 140 degrees C for 0.5Pt/ZSM-5 > 89% at 140 degrees C for 0.5Pt/BETA >85% at 150 degrees C for 0.5Pt/SSZ-13), suggesting that zeolite supports significantly promote H-2-SCR activity at low reaction temperatures. For the 0.5Pt/ZSM-5 washcoated monolithic catalyst, increasing the cell density from 400 to 900 cpsi significantly improved the NOx conversion from 52% to 90% at 100 degrees C owing to the increased geometric surface area and open frontal area of monolithic cordierite. For catalyst with mixed supports (0.5Pt/yZSM-5zTiO(2)) changing the ZSM-5/TiO2 ratio (y:z) from 25:75 to 90:10 increased the low-temperature NOx conversion from 39% to 89% at 100 degrees C, indicating that the deNOx characteristics can be tuned. With NO as the reactant, the 0.5Pt/90Z10T catalyst produced the lowest N2O share (8-17%) within the temperature window of maximum NOx conversion, resulting in an increased N-2 share (83-88%). Thus, the synergetic effect of mixed ZSM-5/TiO2 catalyst supports can enhance low-temperature NOx conversion and mitigate N2O formation.