Effect of Pt Particle Size on Propane Combustion Over Pt/ZSM-5

Reversible Intrapore Redox Cycling of Platinum in Platinum-Ion-Exchanged HZSM-5 Catalysts

Isolated platinum(II) ions anchored at acid sites in the pores of zeolite HZSM-5, initially introduced by aqueous ion exchange, were reduced to form platinum nanoparticles that are stably dispersed with a narrow size distribution (1.3 ± 0.4 nm in average diameter). The nanoparticles were confined in reservoirs within the porous zeolite particles, as shown by electron beam tomography and the shape-selective catalysis of alkene hydrogenation. When the nanoparticles were oxidatively fragmented in dry air at elevated temperature, platinum returned to its initial in-pore atomically dispersed state with a charge of +2, as shown previously by X-ray absorption spectroscopy. The results determine the conditions under which platinum is retained within the pores of HZSM-5 particles during redox cycles that are characteristic of the reductive conditions of catalyst operation and the oxidative conditions of catalyst regeneration.

Low-Temperature Propane Activation and Mineralization over a Co3O4 Sub-nanometer Porous Sheet: Atomic-Level Insights

Light alkanes make up a class of widespread volatile organic compounds (VOCs), bringing great environmental hazards and health concerns. However, the low-temperature catalytic destruction of light alkanes is still a great challenge to settle due to their high reaction inertness and weak polarity. Herein, a Co3O4 sub-nanometer porous sheet (Co3O4-SPS) was fabricated and comprehensively compared with its bulk counterparts in the catalytic oxidation of C3H8. Results demonstrated that abundant low-coordinated Co atoms on the Co3O4-SPS surface boost the activation of adsorbed oxygen and enhance the catalytic activity. Moreover, Co3O4-SPS has better surface metal properties, which is beneficial to electron transfer between the catalyst surface and the reactant molecules, promoting the interaction between C3H8 molecules and dissociated O atoms and facilitating the activation of C-H bonds. Due to these, Co3O4-SPS harvests a prominent performance for C3H8 destruction, 100% of which decomposed at 165 °C (apparent activation energy of 49.4 kJ mol-1), much better than the bulk Co3O4 (450 °C and 126.9 kJ mol-1) and typical noble metal catalysts. Moreover, Co3O4-SPS also has excellent thermal stability and water resistance. This study deepens the atomic-level insights into the catalytic capacity of Co3O4-SPS in light alkane purification and provides references for designing efficacious catalysts for thermocatalytic oxidation reactions.

Excellent activity and selectivity of Pd/ZSM-5 catalyst in the selective catalytic reduction of NOx by H2

Superior de-NO_x activity and N₂ selectivity of the Pd/ZSM-5 catalyst was observed at low temperature (<200 °C) for the selective catalytic reduction of NO_x by H₂ (H₂-SCR). Various Pd/ZSM-5 catalysts were prepared by calcinating at different temperatures (e.g., 500 °C, 650 °C, 750 °C, and 850 °C) and treated at reductive conditions before the H₂-SCR reaction was performed. Among the prepared catalysts, the one prepared at the calcination temperature at 750 °C resulted in 96.7% NO_x conversion and 96.8% N₂ selectivity at 150 °C. Based on the H₂-O₂ reaction, the higher activity of the Pd/ZSM-5 catalyst calcined at 750 °C was attributed to its superior H₂ activation ability for the H₂-SCR reaction. The combined X-ray diffraction (XRD), temperature-programmed hydride decomposition (TPHD), and transmission electron microscopy (TEM) results revealed that highly dispersed Pd particles were generated on the catalyst calcined at 750 °C, while large Pd agglomerates were formed on the one calcined at 500 °C. It can be concluded that the catalytic activity of Pd/ZSM-5 improves by optimizing the calcination temperature, resulting in high Pd dispersion. Moreover, the Pd catalyst calcined at 750 °C showed high resistance to CO, maintaining >94% NO_x conversion at 175 °C under 1000 ppm CO in the feed gas. Therefore, the catalyst calcined at 750 °C can be potentially used for industrial applications because of its simple preparation method and high resistance to CO.

Total Oxidation of Light Alkane over Phosphate-Modified Pt/CeO2 Catalysts

Developing efficient catalysts for the total oxidation of light alkane at low temperatures is challenging. In this study, superior catalytic performance in the total oxidation of light alkane was achieved by modulating the acidity and redox property of a Pt/CeO₂ catalyst through phosphorus modification. Surface modification with phosphorus resulted in electron withdrawal from Pt, leading to platinum species with high valency and the generation of Brönsted acid sites, leading to increased acidity of the Pt/CeO₂ catalyst. Consequently, the ability of the Pt/CeO₂ catalyst to activate the C-H bond increased with increasing P content in the catalyst owing to the synergistic effect of Pt^δ+-(CeO₂-PO_x)^δ- dipolar catalytic sites. In contrast, the redox property of the Pt/CeO₂ catalyst weakened at first; subsequently, it was partially restored owing to the recovery of a part of the bare ceria surface with increasing P content. The turnover frequency in propane oxidation over the phosphate-modified Pt/CeO₂ catalyst with a P/Ce atomic ratio of 0.06 was 10-fold higher than that over the unmodified Pt/CeO₂ catalyst at 220 °C. This comprehensive study not only sheds light on the mechanism underlying the surface modification process but also offers a strategy for realizing higher catalytic activity in the total oxidation of light alkanes.

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

Nanostructured platinum in ordered mesoporous silica SBA-15 and KIT-6 were synthesized. Pt particles with lower oxidation state were more homogeneously dispersed within the pores of KIT-6, making it an efficient catalyst for propane total oxidation.

Importance of platinum particle size for complete oxidation of toluene over Pt/ZSM-5 catalysts

Pt-1.9/ZSM-5 exhibits the highest activity in the removal of toluene due to a balance of Pt dispersion and Pt⁰ proportion.