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The effect of H2, H2O, and CO2 on the NOx removal characteristics of a non‐PGM material (Ag/MgO/γ‐Al2O3) is investigated, which is shown to be active for both NOx adsorption and reduction. H2O facilitates NOx adsorption at early times but inhibits it at longer times. The inhibiting effect of CO2 is observed at low temperatures and is proposed to be due to bicarbonates. However, the inhibiting effect of both H2O and CO2 decreases at higher temperatures. The formation of NO2 at low temperatures is attributed to NO oxidation, and the contribution of stored NOx to NO2 formation increases with temperature. H2O inhibits NH3 oxidation at high temperatures as well as NOx reduction by NH3‐SCR at low temperatures. However, the NOx reduction activity is not affected by CO2. H2 significantly promotes the NH3‐SCR reactions, which is attributed to the facilitation of NOx spillover from the reduced Ag sites to the support. [ABSTRACT FROM AUTHOR]

The potential of Ag/MgO/ γ -Al2O3 (Ag/Mg–Al) as a passive NOx adsorber is evaluated, and is found to be superior as compared to Ag/ γ -Al2O3. Two different adsorption sites exist on both Ag/Mg–Al and Ag/ γ -Al2O3, and it is inferred that the primary role of MgO is not to provide additional adsorption sites but to decrease the Ag particle size, which results in a higher activity towards NOx adsorption. The product distribution profile with either NO or NO2 in the feed is found to be nearly the same at early times, which indicates the formation of the same surface species with either of the reactants. It is deduced that the facile conversion of nitrites to nitrates occurs in the presence of H2, but the extent of conversion decreases at longer times. A sequential configuration of the in-house Ag/Mg–Al and a commercial Cu/SSZ-13 catalyst yielded a NOx reduction efficiency of 85% at low temperatures as against 7% with the standalone Cu/SSZ-13 catalyst. [ABSTRACT FROM AUTHOR]

• Incorporated crystallite-scale features into reactor-scale model to predict NO reduction. • Model predicts higher NO reduction with Pd/SBA-15 than Pd/MCM-41 in absence of H 2. • Difference in catalytic activity ascribed to different extent of spillover. • Higher spillover on SBA-15 due to higher fraction of Pd crystallites in support channels. • Extent of spillover quantified and correlated to Pd-support interfacial contact. The extent of hydrogen spillover on two different Pd-based catalysts supported on mesoporous SBA-15 and MCM-41 is quantitatively predicted using a crystallite-scale model, which considers the effect of size and location of crystallites, metal-support interfacial contact, and diffusivity of the adsorbed species on the support surface. The developed model, in combination with a fixed-bed reactor model predicts that in the absence of any reductant in the feed, the NO conversion is higher (= 37 %) on the SBA-15 supported catalyst as compared to 25 % on MCM-41, which is consistent with the reported data in the literature. The difference in the catalytic activity is ascribed to the different spillover rates of hydrogen on SBA-15 and MCM-41, which is further correlated to the fraction of Pd crystallites present in the support channels. The model is also used to study the effect of cycle time, H 2 concentration, Pd dispersion, and Pd loading on NO reduction under cyclic conditions. Consistent with the literature findings, the model predicts that the Pd surface area and the metal-support interfacial contact increase with an increase in the Pd loading and dispersion, which result in higher spillover and hence increase the NO conversion. Even though the present model has been developed for the H 2 -SCR system, it can also be extended to other catalytic systems where spillover effects are significant. [ABSTRACT FROM AUTHOR]

The conventional operation of a hydrogen internal combustion engine (ICE) under lean conditions results in low NOx emissions, however, at the cost of power generated. In this study, the power output of a hydrogen-fueled ICE was increased while maintaining the NOx emissions at low levels. The power output was increased by turbocharging, relatively richer operation, and spark timing optimization, whereas a combination of exhaust gas recirculation (EGR) and H2-selective catalytic reduction (H2-SCR) aftertreatment was used to reduce NOx emissions. Turbocharging resulted in a maximum torque output of 168 N·m at 3200 rpm as compared to 70 N·m at 1600 rpm for the naturally aspirated operation. However, the turbocharger could not generate enough boost at low speeds and the equivalence ratio was increased to obtain a high power output which resulted in a substantial increase in the NOx emissions. The use of EGR resulted in an average reduction of 72% in the NOx emissions. Retarding of spark timing significantly reduced the NOx emissions too, but was limited by the adverse impact on the torque. Since hydrogen would be available onboard a hydrogen-fueled vehicle, we for the first time report external injection of H2 for use as a reductant in the selective catalytic reduction unit. Even under extremely oxidizing conditions, the efficiency of aftertreatment was found to be 35.4% averaged over various speeds. A maximum of 83.7% overall reduction in NOx emissions was achieved by using the combined EGR and H2-SCR strategies. [ABSTRACT FROM AUTHOR]