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Abstract: Al- and Zn-containing mesoporous molecular sieves (SBA-15) were prepared by an impregnation method and were used as catalysts for the catalytic dehydrogenation and cracking of industrial dipentene, an important natural feedstock. The catalysts were characterized by X-Ray fluorescence spectroscopy (XRF), X-Ray diffraction (XRD), N2 adsorption/desorption, transmission electron microscopy (TEM), magic angle spinning nuclear magnetic resonance (27Al MAS NMR) and Fourier transform infrared spectroscopy (FT-IR) techniques. The characterization results suggest that the active components were introduced without changing the mesostructure of SBA-15. FT-IR revealed that Al/SBA-15 shows weak Brönsted acidity and strong Lewis acidity, while Zn/SBA-15 only possesses moderate Lewis acidity. Dehydrogenation and cracking products, such as toluene, were found in the dipentene conversion over Al/SBA-15, while for Zn/SBA-15, p-cymene was the major dehydrogenation product. Along with the strong Brönsted acidity and high cracking activity of HZSM-5, our results suggest that the reaction pathway is determined by the acidic sites. Stability tests showed the deactivation is also related to the acidity. The highest yield of p-cymene reaches to 86.7% on Zn/SBA-15 at 723K. [Copyright &y& Elsevier]

The acidity and Ga-species status in the zeolite play a crucial role in the CO 2 -assisted propane dehydroaromatization (CO 2 -PDA). In this work, a copper modified Ga-MFI zeolite (Cu/Ga-MFI) with well dispersed framework Ga species was fabricated. A remarkable aromatics selectivity of 73% at propane conversion of 93.6% was achieved on Cu/Ga-MFI catalyst. The Ga atoms in MFI framework can create a moderate acid strength, while the introduced Cu provide an appropriate Brønsted/Lewis acid distribution, enhancing the synergy between metal-related species and the zeolite. Besides, DFT results indicate that the acid sites in Ga-MFI are more preferable for the dehydrogenation of propane instead of the C-C cleavage. Moreover, CO 2 can inhibit coke formation through reverse Boudouard and reverse water gas shift reaction, which endows Cu/Ga-MFI catalyst with superior anti-coking ability and regeneration stability. This work provides a novel approach for designing catalysts with high activity, aromatics selectivity, and stability for CO 2 -PDA reactions. [Display omitted] • H-type Al-free Ga-MFI with Ga located in frameworks is successfully fabricated. • Cu/Ga-MFI shows a superior aromatics selectivity and stability in CO 2 -PDA reaction. • The moderate acid strength from Ga in MFI is favored by propane dehydrogenation. • The synergy between Brønsted/Lewis acid is crucial for catalytic performance. • The introduction of Cu promotes CO 2 activation and inhibits the carbon deposition. [ABSTRACT FROM AUTHOR]

Abstract: Dehydrogenation of ethane to ethylene in the presence of carbon dioxide was investigated over various gallium-based catalysts. Ga2O3/HZSM-5 catalysts show better stability than β-Ga2O3, and the higher Si/Al ratio HZSM-5 supported gallium oxide catalysts are more resistant to deactivation. The Ga2O3/HZSM-5(97) catalyst exhibits both high activity and stability for dehydrogenation of ethane, with an ethane conversion of 15% and ethylene selectivity of 94% without any observable trend of deactivation in 70h. The results of NH3-TPD and FT-IR spectra of adsorbed pyridine revealed that the enhancement of the catalyst stability with increasing Si/Al ratio of the support is caused by the decrease of the acidity of the catalysts, resulting in the suppression of the side reactions, such as cracking and oligomerization. The promoting effect of CO2 on the dehydrogenation reaction is attributed to the reverse water gas shift reaction. The catalyst stability is also enhanced by the introduction of CO2. [Copyright &y& Elsevier]