In this work, we studied how TiO₂ and ZrO₂ coatings enhance the CO oxidation performance of SiO₂-supported Pt catalysts under conditions relevant to automotive emissions control. SiO₂ was coated with metal oxides TiO₂ or ZrO₂ by sol-gel method and the subsequent Pt loading was done by incipient wetness method. The prepared catalysts Pt/TiO₂-SiO₂ and Pt/ZrO₂-SiO₂ were compared with Pt/SiO₂ and Pt/Al₂O₃ in fresh, sulfated, and hydrothermally aged states. The structure of the catalysts was characterized with BET, XRD, TEM, EDS, EXAFS, XANES, TPD and TPR to help interpret the CO oxidation performance. Higher dispersion, stability, and oxidation state of Pt were achieved on TiO₂-SiO₂ and ZrO₂-SiO₂ supports due to stronger metal-support interaction leading to superior CO oxidation performance compared to Pt/SiO₂ and Pt/Al₂O₃. TiO₂ and ZrO₂ coatings introduced surface acidity but negligible basicity, which is a likely reason for the weak and low adsorption of SO₂. The results suggest that the sol-gel coating of SiO₂ with metal oxides could be an attractive strategy for designing automotive oxidation catalysts with enhanced performance such as low-temperature activity, sulfur tolerance, and hydrothermal stability.

Lean NOx Trap (LNT) catalysts are capable of reducing NOx in lean exhaust from diesel engines. NOx is stored on the catalyst during lean operation; then, under rich exhaust conditions, the NOx is released from and reduced by the catalyst. The process of NOx release and reduction is called regeneration. One method of obtaining the rich conditions for regeneration is to inject additional fuel into the engine cylinders while throttling the engine intake air flow to effectively run the engine at rich air:fuel ratios; this method is called “in-cylinder” regeneration. In-cylinder regeneration of LNT catalysts has been demonstrated and is a candidate emission control technique for commercialization of light-duty diesel vehicles to meet future emission regulations. In the study presented here, a 1.7-liter diesel engine with a LNT catalyst system was used to evaluate in-cylinder regeneration techniques. Characterization of the exhaust reductant chemistry during in-cylinder regeneration was performed. The effects of various injection strategies and fuels and the resulting exhaust chemistry on the performance of the LNT catalyst were analyzed. In addition, exhaust species measurement of NOx and select reductants were performed inside of the catalyst cells with a capillary-based mass spectrometry technique. The effect of various injection parameters on exhaust chemistry species and LNT performance are discussed. Results indicate that fuel chemistry does affect engine-out hydrocarbon (HC) species, but not engine-out carbon monoxide (CO) or hydrogen (H2) generation. Higher engine-out CO and H2 correlate to improved NOx reduction, irrespective of HCs.