Pt-based catalysts for NOx reduction from H2 combustion engines

Abstract

Platinum supported on SSZ-13 zeolite has been found to be a potential catalyst for the selective catalytic reduction of NO by H₂. This work has studied the effects of the H₂/NO molar feed ratios (0/4.4/8.8/13.2) and the impact of water on the performance of the H₂-SCR of NO on the Pt/SSZ-13 catalyst. A higher H₂/NO ratio promoted the start of the reaction at lower temperatures and favoured the production of N₂. The effect of Pt loadings was also studied with three loadings of 0.5/1.0/2.0 wt%. It was found that the 0.5 wt% Pt sample displayed the highest N₂ selectivity of 75%. In addition, an inhibiting effect of water for H₂-SCR at low temperatures was proved. Pt/SSZ-13 has shown good hydrothermal durability after 6 h in total ageing pretreatment at 800 °C and interestingly the nitrogen formation even increased. The support effect of SSZ-13, BETA and Al₂O₃ on H₂-SCR was evaluated in terms of catalytic performance and their catalytic durabilities by hydrothermal ageing experiments, showing that zeolites are significantly better for H₂ SCR. In situ DRIFT measurements helped to explore the mechanism of H₂-SCR on the Pt catalyst. A careful design of the measurements was used to distinguish the overlapping peaks of the water on the DRIFT spectrum. NH₄⁺ ions are formed and it was shown that they play a role as intermediates during the reaction to assist the NO reduction.