Petroleum Chemistry最新文献

This paper proposes a novel approach to the extraction of cluster structures from a ZSM-5 zeolite lattice. The approach involves transforming the zeolite crystalline structure into a directed molecular graph followed by identifying cycles from which cluster structures are generated. One advantage of this approach is the complete similarity of the resultant cluster structures at equal input data, making the DBSCAN clustering method applicable to the identification of unique structures. Furthermore, this approach is effective in identifying the active and extended regions within a multilevel ONIOM model for subsequent quantum-chemical calculations. Finally, the proposed approach makes it possible to automate the extraction of cluster structures from ZSM-5 crystals and to select the most important structures for further analysis. To validate its efficiency, the novel approach was applied to identify the most probable location of Zn²⁺ cation-exchange sites in ZSM-5.

Two series of zeolites, vis., the MEL and MFI types, with different Si/Al molar ratios were synthesized by a steam-assisted crystallization method, specifically dry gel conversion (DGC). Their physicochemical properties were characterized by low-temperature nitrogen adsorption, scanning electron microscopy, and X-ray fluorescence analysis. The acidic properties were examined by IR spectroscopy of adsorbed pyridine and 2,6-di-tert-butylpyridine as well as by ammonia temperature-programmed desorption. The DGC-synthesized zeolites were distinguished by high crystallinity, small crystal size, and well-developed surface. All the samples exhibited high activity and deactivation resistance in the oligomerization of a butane–butylene fraction. A comparative assessment of the catalytic performance the MEL and MFI samples demonstrated that the structural difference between the MEL and MFI types barely affects their deactivation resistance. Therefore, MEL zeolite is a valid alternative to the MFI type in the development of oligomerization catalysts.

Based on quantum-chemical computation, a solution with periodic boundary conditions (PBC) was employed within density functional theory (DFT) simulations in order to assign the chemical shifts in the ²⁷Al MAS NMR spectra of Al-BEA (HBEA) zeolite (Si/Al = 31) to the individual crystallographic T-sites calculated for polymorph B of an identical zeolite. The results were compared both to relevant published reports (Si/Al = 71 and 75) and to the experimental data previously obtained by the authors for a mixture of polymorphs (Si/Al = 25). Deconvolution of the ²⁷Al MAS NMR spectrum into Al signals at different T-sites of polymorph B was compared to a similar deconvolution for polymorph A.

The paper describes the physicochemical characterization and catalytic testing of MFI zeolites with different SiO₂/Al₂O₃ ratios synthesized by steam-assisted crystallization (SAC) and modified with phosphorus (4 wt % loading). Their physicochemical properties were characterized by X-ray diffraction analysis, X-ray fluorescence analysis, scanning electron microscopy, low-temperature nitrogen adsorption, ammonia temperature-programmed desorption, and MAS NMR spectroscopy. Both the parent and P-modified MFI zeolites were then subjected to catalytic tests in cracking of n-dodecane. The yield of light olefins was enhanced only in two cases: when MFI zeolites with SiO₂/Al₂O₃ ratios of 30–70 were modified with 4 wt % phosphorus and when parent MFI zeolites with SiO₂/Al₂O₃ ratios of 100–220 were used. It was further found that, in terms of catalytic performance in the cracking of n-dodecane, the MFI zeolites synthesized by SAC were comparable to a commercially available MFI zeolite synthesized under hydrothermal conditions. Moreover, in contrast to the commercially available zeolite, phosphorus modification of the SAC-synthesized zeolite enhanced the yield of C₂–C₄ olefins.

This study investigates the chemical and phase compositions, acidic properties, and porous structure characteristics of an acidic support for a bifunctional catalyst. This catalyst was a high-crystallinity granulated hierarchical H-ZSM-5 molecular sieve promoted with 0.5 wt % Pt. The catalytic transformations of n-hexadecane and a diesel fuel were further investigated using this catalyst. The catalyst exhibited a higher activity in the hydrocracking of higher n-paraffins than a bifunctional catalyst that contained 20 wt % Al₂O₃ as a binder. Furthermore, at 220°C, 3 MPa, 2.0 h^–1, and H₂/feed = 800 m³/m³, a diesel fuel with a pour point of –68 °C was produced over the prepared catalyst with a yield of about 71–72 wt %.

The physicochemical properties of ZSM-5 zeolite samples modified with alkali metal cations (e.g., Li⁺, Na⁺, K⁺, and Cs⁺) were characterized. It was demonstrated that increasing the metal load led to a decrease in the textural properties of the zeolite such as specific surface area, total pore volume, and micropore volume; furthermore, it reduced the total concentration of acid sites by 23–25% (at 0.72 × 10^–2 mol % potassium or 0.38 × 10^–2 mol % cesium). In the cracking of n-dodecane, the modification of ZSM-5 with 2.34 × 10^–2 mol% cesium enhanced the yield of light olefins up to 40.1 wt %, which is comparable with the value achieved by a phosphorus-based ZSM-5 sample (40.3 wt %).

The physicochemical properties of a series of pelletized SAPO-11 molecular sieves differing in the binder (Al₂O₃) content were characterized; their activity and selectivity were investigated in the hydroisomerization of n-hexadecane. An increase in the binder content from 20 to 60 wt % was found to decrease the specific micropore volume and increase the external specific surface area as well as the mechanical strength, activity, and selectivity of Pt-containing samples in the hydroisomerization of n-hexadecane. The study proposes the formulations of pelletized SAPO-11 that ensure mechanical (axial crushing) strength of 9.9 to 15.1 N/mm² and the yield of C₁₆ isomers up to 78% in the hydroisomerization of n-hexadecane.

A series of BEA-type zeolites with SiO₂/Al₂O₃ ratios of about 50 were synthesized by steam-assisted (SAC) and hydrothermal crystallization (HTC) in fluoride and alkaline media. Their physicochemical properties were characterized by low-temperature nitrogen adsorption, XRD, SEM, XRF, and NH₃-TPD. The catalytic performance was investigated in liquid-phase toluene disproportionation. The SAC-synthesized samples were distinguished by a higher concentration of acid sites. The BEAs prepared by SAC in alkaline media exhibited a higher activity in toluene disproportionation. The samples synthesized in fluoride media, both by steam-assisted and hydrothermal crystallization, proved to be comparable in activity.

A series of ZSM-5 samples were synthesized by template-free hydrothermal synthesis without adding seed crystals. When synthesis parameters such as temperature, duration, and molar ratio of components being equal, various silicas (specifically, Silica-Fumed from Sigma-Aldrich; Rosil-175 from the Bashkir Soda Company (BSC), Russia; Silica from the Salavat Catalyst Plant (SCP), Russia; and Aerosil-300 from Evonik, Germany) and of aluminum (Al(NO₃)₃∙9H₂O and NaAlO₂) were varied. In the presence of sodium aluminate, highly crystalline ZSM-5 samples were synthesized, whereas the use of aluminum nitrate led to an amorphous product due to accelerating aluminosilicate condensation. The ZSM-5 crystals prepared from various SiO₂ sources have different morphology, including the crystal size (ranging from 5.9 to 12.2 µm) and the aspect ratio (from 1.9 to 2.6). The ZSM-5 samples synthesized from available Russian-manufactured SiO₂ sources (Rosil-175 (BSC) and Silica (SCP)) in the presence of sodium aluminate consisted of crystals with average sizes of 5.9 and 6.9 μm, respectively, and a narrow particle size distribution (c_v < 20%).

A series of tandem catalysts based on a ZnGa₂O₄ spinel and on MFI-type acidic components with varying SiO₂/Al₂O₃ ratios were prepared by mechanical mixing at a spinel to MFI weight ratio of 2 : 1. These catalysts were tested in the conversion of carbon dioxide to olefins at 380°C and 27 bar. The hydrogenating component (ZnGa₂O₄) was prepared by co-precipitation of the corresponding hydroxides followed by heat treatment. The zeolites were synthesized by steam-assisted crystallization. A reference catalyst was prepared from ZnGa₂O₄ and a hydrothermally synthesized commercial zeolite CBV28014. The physicochemical properties of the catalysts and their components were characterized by low-temperature nitrogen adsorption–desorption, chemical analysis, NH₃-TPD, H₂-TPR, XRD, and SEM. The sample with the highest SiO₂/Al₂O₃ ratio (250) achieved the highest CO₂ conversion; this parameter dropped as the aluminum content in the samples increased. The highest selectivity towards light olefins was observed for the catalyst with SiO₂/Al₂O₃ = 172 in the acidic component, likely because this zeolite had an optimum acidity for the production of light olefins.