Enhanced activity and stability of the monolithic Pt/SiO2–Al2O3 diesel oxidation catalyst promoted by suitable tungsten additive amount

Constructing a Pt/YMn2O5 Interface to Form Multiple Active Centers to Improve the Hydrothermal Stability of NO Oxidation

The hydrothermal stability of NO oxidation is the key to the practical application of diesel oxidation catalysts in diesel engines, which in the laboratory requires that NO activity does not decrease after aging for 10 h with 10% H₂O/air at 800 °C. On the one hand, the construction of a metal/oxide interface can lead to abundant oxygen vacancies (O_v), which compensate for the loss of activity caused by the aggregation of Pt particles after aging. On the other hand, YMn₂O₅ (YMO) has excellent thermal stability and NO oxidation capacity. Therefore, a Pt/YMn₂O₅-La-Al₂O₃ (Pt/YMO-LA) catalyst was prepared by the impregnation method. The support of the catalyst, YMn₂O₅-La-Al₂O₃ (YMO-LA), was obtained by mixing high specific surface LA and YMO ball-milling. Under laboratory-simulated diesel exhaust flow, the NO oxidation performance of Pt/YMO-LA did not decrease after hydrothermal aging. Combining high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and oxygen temperature-programmed desorption (O₂-TPD), the Pt/YMn₂O₅ interface was formed after hydrothermal aging, and the increased O_v can provide reactive oxygen to Pt and YMO. The cooperative catalysis of multiple active centers composed of Pt, YMO, and O_v is the crucial factor to maintain the NO oxidation performance. In addition, in situ diffuse reflectance infrared Fourier transform spectra (DRIFTs) show that an increase in O_v is beneficial to the adsorption and desorption of more nitrate and nitrite intermediates, thus achieving the hydrothermal stability of NO oxidation.

Promotional effect of ZrO2 and WO3 on bimetallic Pt-Pd diesel oxidation catalyst

Diesel oxidation catalysts Pt-Pd-(y)ZrO₂-(z)WO₃/CeZrO_x-Al₂O₃ with total Pt & Pd loading of only 0.68 wt.% were prepared and investigated for oxidation activity and stability of CO, C₃H₆, and NO. Introduction of ZrO₂ greatly improved low-temperature activities and retained stability especially for CO and C₃H₆ oxidation after treated at 800 °C. With the optimal loading amount of 6 wt% ZrO₂, 2 wt% WO₃ was introduced to the system and showed higher activity. Reaction temperature for 50% CO and C₃H₆ conversion declined to 160 and 181 °C, and the maximal NO conversion increased to 50%. By using XRD, TEM, CO chemisorption, XPS, and H₂-TPR analysis, it was found that ZrO₂ could inhibit aggregation of Pt and Pd, improve metal dispersion, and increase surface-chemisorbed oxygen after high-temperature treatment, accounting for promoted performance. Also, there were more reducible oxide species in ZrO₂-doped catalysts. ZrO₂ could induce reduction of noble metal oxides and surface ceria by weakening Pt-O-Ce interaction, which increased the ability to dissociate H₂ and spillover effect of dissociated hydrogen to ceria. Doping WO₃ increased metal dispersion of fresh samples and brought more Pt⁰ species that were active sites for oxidation reactions. Thus, ZrO₂ and WO₃ could be effective additives for oxidation catalysts to synergistically improve their activities and thermal stability.

Improved low-temperature catalytic oxidation performance of Pt-based catalysts by modulating the electronic and size effects

The electronic effect between PVA and platinum could be modulated though reaction time, restraining the chain movement and affecting the platinum dispersion, both of which closely affects the low-temperature performance of the Pt-based catalyst.

The promotion effect of tungsten on monolith Pt/Ce0.65Zr0.35O2 catalysts for the catalytic oxidation of toluene

The temperature for the complete conversion of toluene on the monolith Pt-WO₃/Ce_0.65Zr_0.35O₂ catalyst decreases by about 30 °C compared to that on Pt/Ce_0.65Zr_0.35O₂.