Yidan Cao

NO reduction by CO over Rh/Al2O3 and Rh/AlPO4 catalysts: Metal–support interaction and thermal aging

Rhodium was impregnated on γ-Al2O3 and AlPO4 followed by treating in a wet air at 1050°C for 5h. The catalytic activities of the catalysts were evaluated by temperature-programmed reactions in a stoichiometric mixture of NO and CO. The fresh Rh/Al2O3 and Rh/AlPO4 catalysts exhibit similar catalytic activities. After the hydrothermal aging, Rh/Al2O3 experiences a significant deactivation, whereas Rh/AlPO4 shows even higher activity than the fresh sample. A series of structural and surface characterizations were performed to explore different aging mechanisms of these two catalysts. The fresh Rh/AlPO4 catalyst shows superior low-temperature redox property, but its NOx adsorption is weakened due to the acidic nature of the support. Thus, two fresh catalysts present similar catalytic activities. The hydrothermal aging at high temperature leads to the formation of inert Al5Rh2 alloy. Contrarily, no such strong interaction occurs between rhodium and AlPO4. Furthermore, large Rh particles, which facilitate the dissociation of NO, are formed on the aged Rh/AlPO4 catalyst. Thus, a superior high activity for NO-CO is achieved over the aged Rh/AlPO4.

Nanostructured platinum in ordered mesoporous silica as novel efficient catalyst for propane total oxidation

Mesoporous SBA-15 and KIT-6 supporting platinum catalysts were prepared and subsequently used in propane total oxidation. The properties of the prepared catalysts were investigated by low-angle X-ray diffraction, nitrogen physisorption, transmission electron microscopy, CO chemisorption, X-ray photoelectron spectroscopy and H2-titration methods. Significant reaction rate enhancements have been achieved via mesopore introduction, with turnover frequencies (TOF) in the sequence: Pt/KIT-6 (60.30 × 10−3 s−1) ≫ Pt/SBA-15 (19.27 × 10−3 s−1) > Pt/Al2O3 (5.11 × 10−3 s−1). The results indicate that the synthesized catalysts have ordered mesoporous structures and well-dispersed Pt species. They exhibit superior catalytic activities for propane total oxidation in comparison to the conventional Pt/Al2O3 catalyst. The 2-D hexagonal channels in SBA-15 and the 3-D cubic structure in KIT-6 can successfully control the particle sizes of platinum in the mesopores. By contrast, the platinum nanoparticles in KIT-6 are smaller than those in SBA-15, with homogeneous size distribution and exist in lower oxidation state, which are beneficial to the catalytic activity.

Improved activity and durability of Rh-based three-way catalyst under diverse aging atmospheres by ZrO 2 support

The catalytic activity and durability of Rh/ZrO2 catalyst were investigated compared with Rh/Al2O3 catalyst under diverse aging atmospheres, including lean, rich and lean-rich cyclic aging atmospheres, to simulate the real working conditions of three-way catalyst. Oxidation states and microstructures of rhodium species were investigated to correlate with the catalytic performance of the catalysts. The catalytic performance and durability of the Rh catalyst under diverse aging atmospheres were drastically enhanced by ZrO2 support. ZrO2 support was confirmed to be able to effectively inhibit rhodium sintering even under diverse aging conditions. It can also successfully keep Rh species in an active low-valence state on the surface of the catalyst. The superiority of ZrO2 support compared to Al2O3 was verified by the Rh-based monolith catalyst.