Catalyst characteristics of the composite catalyst of Ru-Sn and Pd for hydrogenation of terephthalic acid

1,4-Cyclohexanedimethanol (CHDM) is a premium polyester monomer. In this paper, a series of Ru- Sn/γ-Al2O3 and Pd/γ-Al2O3 bimetallic composite catalysts were prepared by the impregnation method. The effects of preparation conditions such as active components, preparation methods, and the ratio of Sn to Ru on the reaction activity of the catalysts were studied. The bimetallic composite catalysts show desirable properties including high surface area and high dispersion of active centers. Pd-based catalysts were found to be effective in the initial stage of benzene ring hydrogenation, while Ru-based catalysts were found effective in the subsequent stage of carboxyl group hydrogenation. The Ru-Sn bimetallic active center was predominantly located in the Ru-based catalysts. In addition, the effects of reaction parameters such as reaction temperature, pressure, and time on hydrogenation reactions were also examined. It was found that increasing reaction temperature had no significant effect on the conversion rate of PTA, but it did affect the yield of CHDM, initially increasing and then decreasing. Increasing the reaction pressure resulted in a gradual increase in the yield of CHDM, while the conversion rate of PTA remained unchanged. The composite catalyst with a Sn/Ru ratio of 0.5 demonstrated the best performance, achieving a CHDM conversion of 96.3% and a yield of 72.2%.

Surface Modification by Amino Group Inducing for Highly Efficient Catalytic Oxidation of Toluene over a Pd/KIT-6 Catalyst

Toluene is one of the typical volatile organic compounds in industry, particularly in energy and fuels production processes, which is required to be eliminated effectively to protect the environment. Catalytic oxidation of toluene is widely studied for its high efficiency, and rational design and synthesis of metal catalysts are keys for toluene oxidation. In this study, an efficient catalyst was designed and synthesized by introducing -NH₂ groups on the ordered mesoporous silica (KIT-6) surface to anchor and disperse Pd species, leading to Pd nanoparticles being highly dispersed with uniform particle size distribution. Meanwhile, it was found that the introduction of -NH₂ made Pd centers present an electron-rich state, and the active Pd centers could activate O₂ molecules to generate more reactive oxygen species and promote the conversion of toluene, which was verified by in situ XPS and O₂-TPD characterization. Compared with the catalysts prepared by an impregnation method, the catalytic performance of the Pd/NH₂-KIT-6 (0.5 wt %) catalyst was significantly improved. A conversion of 90% for toluene (2400 ppm, 24,000 mL·g^-1·h^-1) was achieved at 171 °C, and the toluene conversion was maintained above 90% for 900 min, displaying the excellent activity and stability of the Pd/NH₂-KIT-6 catalyst.

The critical roles of hydrophobicity, surface Ru0 and active O2-/O22- sites on toluene combustion on Ru/ZSM-5 with varied Si/Al ratios

By targeting more feasible catalysts for VOC combustion, 2%Ru/ZSM-5 catalysts were fabricated by supporting RuO₂, a relatively cheaper noble metal, onto HZSM-5 supports with varied Si/Al ratios for toluene combustion. The valence state distribution of Ru and the Ru/RuO₂-support interaction have been explored and elucidated. It has been revealed that the catalytic activity increases with the increase of the Si/Al ratio in the order 2%Ru/ZSM-5-18 < 2%Ru/ZSM-5-40 < 2%Ru/ZSM-5-72 < 2%Ru/ZSM-5-110 < 2%Ru/ZSM-5-255 < 2%Ru/SiO₂-MFI. Interestingly, the hydrophobicity of the samples improves also with the increase in the Si/Al ratio, which impedes H₂O adsorption effectively and its competition for the surface-active sites with the reactants. Both RuO₂ and Ru⁰ are detected on all the catalysts, and the Ru⁰ amount/ratio increases significantly with increasing the Si/Al ratio, which promotes the adsorption/activation of both toluene and O₂ molecules. Furthermore, the amount of surface-active O₂^- and O₂^2- is evidently improved. Therefore, the mixed interaction of higher hydrophobicity, more surface Ru⁰ and active oxygen sites is the major reason for the enhancement in the activity of a Ru/ZSM-5 having a higher Si/Al ratio. It is concluded that the optimal catalyst can be designed by loading Ru/RuO₂ onto an MFI framework structure support with the highest Si content.