In Situ DRIFTS Study of Na-Promoted Pt/ZSM5 Catalysts for H2-SCR

Platinum was supported on ZSM5 at loadings from 0.1 to 1 wt% and tested for the Selective Catalytic Reduction of NO with H2 under excess O2 in a fixed bed reactor to address the issue of NOx emission abatement from H2-fueled internal combustion engines avoiding the additional devices for urea storage and injection. To reduce the undesired NO oxidation to NO2, which is activated by platinum at T > 200 °C, the 0.1%Pt/ZSM5 catalyst was further promoted with sodium. 5 wt% loading of Na strongly inhibited the NO oxidation while giving only a limited impact on the H2-SCR activity. Unpromoted and Na-promoted catalysts were characterized by XRD, SEM/EDX, N2 physisorption, and NH3-TPD to investigate the morphological, structural, and acid properties; H2 pulse chemisorption and DRIFTS of CO chemisorption were used to investigate the nature of Pt active species. Steady-state and transient operando DRIFTS experiments under NO+H2+O2 flow were employed to identify the adsorbed NOx species interacting with H2, and reaction intermediates as a function of the reaction conditions. The formation of ammonium intermediates via the reduction of surface nitrate species, playing a key role in H2-SCR catalyzed by 0.1Pt/ZSM5, was preserved at low Na load whilst NO2 formation was largely inhibited.