High Fraction of Penta‐Coordinated Aluminum and Gallium in Lanthanum–Aluminum–Gallium Borates

This study is focused on structural changes induced by increasing treatment temperature of sol‐gel–derived La₂O₃?Al₂O₃?Ga₂O₃?5B₂O₃ system. The structure of samples heated for 30 min up to 900°C was investigated by X‐ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and magic‐angle spinning nuclear magnetic resonance (MAS‐NMR) analysis of ²⁷Al, ¹¹B, and ⁷¹Ga nuclei. The vitreous structure is preserved inclusively after 800°C treatment, and starting with 850°C the only crystalline phase evidenced in XRD patterns is of LaAl_2.03B₄O_10.54 type, of La(Al,Ga)_2.03B₄O_10.54 composition. The FTIR results point out the presence of BO₃, AlO₄, and AlO₆, and starting with 800°C treatment also of BO₄ and AlO₅ structural units, but more detailed information related to boron, aluminum, and gallium environments is obtained from the analysis of MAS‐NMR data. These data evidenced in both amorphous xerogels and in crystallized samples a high fraction of penta‐coordinated aluminum and gallium.     

A high‐resolution solid‐state NMR study on nano‐structured HZSM‐5 zeolite

Variations in the structure and acidity properties of HZSM‐5 zeolites with reduction in crystal sizes down to nanoscale (less than 100 nm) have been investigated by XRD, TEM and solid‐state NMR with a system capable of in situ sample pretreatment. As evidenced by a combination of ²⁷Al MAS NMR, ²⁹Si MAS, CP/MAS NMR and ¹H MAS NMR techniques, the downsize of the zeolite crystal leads to an obvious line broadening of the ²⁷Al, ²⁹Si MAS NMR spectrum, an increasing of the silanol concentration on the external surface, and a pronounced alteration of the acidity distribution between the external and internal surfaces of the zeolite. In a HZSM‐5 zeolite with an average size at about 70 nm, the nonacidic hydroxyl groups (silanols) are about 14% with respect to the total amount of Si, while only 4% of such hydroxyl groups exist in the same kind of zeolite at 1000 nm crystal size. The result of ¹H MAS NMR obtained using Fluorinert^® FC‐43 (perfluorotributyl amine) as a probe molecule demonstrates that most of the silanols are located on the external surface of the zeolite. Moreover, the concentration of Brønsted acid sites on the external surface of the nano‐structured zeolite appears to be distinctly higher than that of the microsized zeolite.     

Synthesis of single phase Ca-α-SiAlON using Y-type zeolite

Single phase Ca-α-SiAlON was synthesized for the first time by the carbothermal reduction-nitridation of a physical mixture of Y-type zeolite and CaO. Under well-optimized conditions, which included both a Si/Al ratio of 2.8 for the starting Y-type zeolite and a Ca/Al ratio of 0.63–0.75, highly crystalline, pure Ca-α-SiAlON was obtained. The formation of pure Ca-α-SiAlON was also confirmed by ²⁷Al and ²⁹Si MAS NMR measurements.     

PERFORMANCE OF ACIDIC MCM-LIKE ALUMINOSILICATE CATALYSTS IN PYROLYSIS OF POLYPROPYLENE

Mesoporous aluminosilicate catalysts having different Al/Si ratios were synthesized following a hydrothermal synthesis route and using different aluminum sources, such as aluminum nitrate and aluminum isopropoxide. These mesoporous materials have high surface areas, in the range of 520–1001 m²/g, and exhibit Type IV nitrogen adsorption isotherms. EDS and ²⁷Al MAS NMR results showed that aluminum was incorporated more effectively into the structure of the catalyst forming a tetrahedral framework when aluminum nitrate was used as the aluminum source. The activities of these catalysts in the polypropylene pyrolysis reaction were tested in a TGA apparatus. Results showed a marked reduction in the degradation temperature in the presence of aluminosilicate catalysts. The activation energy of degradation was 172 kJ/mole without any catalyst. However, using the mesoporous aluminosilicate catalysts synthesized by using aluminum nitrate as the aluminum source, activation energy of the degradation reaction decreased to values of about 24–28 kJ/mole.     

Realumination of zeolite Y under acidic conditions

Dealuminated zeolites Y were treated with aqueous solutions of various acids and ammonium salts to investigate the realumination behavior under acidic conditions. From the results of ²⁷Al MAS NMR, ²⁹Si MAS NMR and FT-IR measurements, it was found that a part of non-framework aluminum species in the dealuminated zeolite Y is effectively reinserted into the zeolite framework in CH₃COONH₄ and C₆H₅COONH₄ aqueous solutions. Pyridine adsorption experiments also revealed that most of incorporated aluminum species generate tetrahedrally coordinated framework aluminum species, namely Brönsted acid sites. Although the realumination also proceeded in H₂SO₄ and CH₃COOH aqueous solutions, large amounts of incorporated aluminum species were not necessarily responsible for generation of Brönsted acid sites. Framework connected aluminum species, presumably as 3-fold-coordinated Lewis acidic framework aluminum species, were mainly generated. In the TEM image of the realuminated zeolite Y, needle-like crystals with ca. 25–80 nm in length were observed, which are probably due to AlOOH generated from non-framework aluminum species.     

Synthesis of Higher Aluminum Content Hexagonal and Cubic Mesoporous Aluminosilicates toward Catalysts

High aluminum content (Si/Al < 20) mesoporous aluminosilicate MAS-Y, MAS-X1, MAS-X2 and thick wall high aluminum MAS-X3 had been synthesized using zeolite FAU-Y nanocluster or powder zeolite FAU-X as a precursor with triblock copolymer Pluronic P123 or F127 as a structure directing agent. The samples were characterized by XRD, TEM, nitrogen adsorption, ²⁷A1 MAS NMR, temperature-programmed desorption of ammonia and element analysis. The in situNMR technique was used to investigate the mechanism of the formation of the high aluminum content mesoporous aluminosilicates. The salt effect was also discussed in this work.     

Facile tailoring of hierarchical mesoporous AlSBA-15 by ionic liquid and their applications in heterogeneous catalysis

Significant enhancement in the performance of incorporation of high content of aluminum within hierarchical mesoporous SBA-15 has been achieved by direct route using urea tetrachloroaluminate ionic liquid as novel aluminum source. The fabricated materials were fully characterized by N₂ sorption isotherms, powder X-ray diffraction (XRD), FT-IR, ²⁷Al MAS NMR, XRF, HRTEM and FESEM. The acidic properties of these materials have been examined using NH₃-TPD. The catalytic performance was investigated using cumene cracking and the esterification reaction as a probe molecules to estimate the acidity of the material. It is worth noting that the ionic liquid with accomplished Al–O–Si bonds is an efficient precursor to synthesis AlSBA-15 with high aluminum content (nSi/mAl?=?7) without destroying the structural order of the material in acidic medium. ²⁷Al MAS NMR spectra of AlSBA-15 show that all aluminum species were incorporated into the SBA-15 framework with nSi/mAl ratio up to 7. Overall, this work emphasize that the AlSBA-15 materials contain Bronsted and Lewis acid sites with medium acidity which makes them adequate to be adopted as acid catalysts in heterogeneous catalysis.     

Synthesis of mesoporous molecular sieves: influence of aluminum source on Al incorporation in MCM-41

Three series of mesoporous aluminosilicate molecular sieves, MCM-41, with various Si/Al ratios were synthesized using different aluminum sources (aluminum isopropoxide, pseudo boehmite and aluminum sulfate). XRD analysis, temperature programmed desorption ofn-butylamine,²⁷Al and²⁹Si MAS NMR, and catalytic alkylation test indicated that aluminum isopropoxide is a better source for incorporating aluminum in the framework of MCM-41 type molecular sieves with better crystallinity and acid characteristics.     

Influence of different modified β zeolite on skeletal isomerization of n-hexene in the presence of hydrogen

Zeolite β was modified via treating with oxalic acid and doping with magnesium, and the influence of different modified zeolite β on skeletal isomerization of n-hexene in the presence of hydrogen was investigated. Moreover, parent β and modified β were characterized by XRD, N₂ physisorption, IR, NH₃–TPD, ²⁷Al MAS NMR and ²⁹Si MAS NMR, respectively. The results indicated, compared with parent β, β treated by oxalic acid was found that non-framework aluminum was removed effectively, and surface aluminum and framework aluminum were eliminated partly, which resulted in considerable decrease in the amount of acid sites. In contrast, the introduction of magnesium has little effect on crystalline structure of β, but it can reduce the amount of strong Brönsted acid sites. Noticeably, when β was modified by the combination of oxalic acid treatment and Mg dope, it can not only remove non-framework aluminum and reduce the amount of acid sites, but also facilitate the stability of crystalline structure of β and further eliminate strong Brönsted acid sites due to the introduction of Mg. The evaluation results of skeletal isomerization of n-hexene in the presence of hydrogen showed that, compared with parent β, β modified by the combination of oxalic acid treatment and Mg dope exhibits better activity and stability.     

Composite SBA-15/MFI Type Materials: Preparation, Characterization and Catalytic Performance

SBA-15 type mesoporous molecular sieve was prepared and used as a parent material for synthesis of a SBA-15/zeolite composite. Thus, after addition of an aluminum source into the pristine sample, it was subjected to recrystallization in the water-vapor phase to give the SBA-15/MFI composites. The samples obtained were characterized by XRD, nitrogen sorption, scanning and transmission electron microscopies, ²⁷Al MAS NMR and FT IR. The materials after recrystallization retained their mesoporous character. Characteristics of the material revealed that all the aluminum added was inserted into the final hybrid. As shown by FT IR and NMR, at least some of aluminum was introduced into the nanoparticles of MFI and adopted four-fold coordination, typical for zeolites. Formation of Brønsted acid centres was directly confirmed by IR studies. The catalytic activity was screened in the liquid-phase isomerization of α-pinene. The main products of α-pinene transformations were camphene, limonene and γ-terpinene. The overall selectivity toward camphene + limonene was ca. 90%. Taking into account the low amount of the MFI phase present in a composite sample, calculated initial reaction rate was comparable with other catalytic systems explored in the isomerization of α-pinene.     

Solid-state NMR characterization of the acid sites in cubic mesoporous Al-MCM-48 materials using trimethylphosphine oxide as a P NMR probe

The acidic properties of Al-MCM-48 with Si/Al ratios ranging from 10 to 67, synthesized with Gemini surfactant as the template, have been characterized by a combination of multinuclear solid-state ¹H, ²³Na, ²⁷Al, ²⁹Si and ³¹P MAS (magic angle spinning) NMR and some double-resonance NMR methods using trimethylphosphine oxide (TMPO) as a probe molecule. XRD and ²⁷Al MAS NMR results indicated that aluminum has been successfully incorporated into the framework of MCM-48 materials up to Si/Al = 17.9 by direct synthesis. ¹H and ³¹P MAS NMR results strongly supported the generation of Brønsted acid sites in the cubic MCM-48 mesoporous material after the incorporation of aluminum, even without ion-exchange treatment. Double-resonance NMR techniques such as ³¹P/²⁷Al TRAPDOR (Transfer Population in Double Resonance) and ²⁹Si/³¹P REDOR (Rotational Echo in Double Resonance) NMR were performed to further correlate the TMPO probe molecule to the Brønsted acid sites in the silica framework. ³¹P/²⁷Al TRAPDOR NMR experiments performed at different temperatures were able to establish the correlation between ³¹P and ²⁷Al spins, further confirms the presence of Brønsted acid sites at 65 ppm in the ³¹P MAS NMR spectrum. Although the assignment of the Lewis acid sites was somehow unambiguous with ³¹P/²⁷Al TRAPDOR NMR, the FT-IR observation of the calcined samples adsorbed with pyridine did reveal the presence of Lewis acid sites. In contrast to the pore size constraints of zeolites, ²⁹Si/³¹P REDOR NMR results indicated that the protonated TMPO was highly mobile inside the mesoporous channels of Al-MCM-48 at the NMR time scale.     

Synthesis and Characterization of Gallosilicate Molecular Sieve with the MCM-22 Framework Topology

Ga-MCM-22 with high gallium content has been synthesized with hydrothermal method and characterized by means of X-ray diffraction, SEM, TGA, ⁷¹Ga and ²⁹Si MAS NMR, BET surface area, and NH₃-TPD. Ga-MCM-22 was obtained as very homogeneous particles of about 5-7 m diameters and showed very similar morphologies to its Al analogue. The Na/Ga ratio of Ga-MCM-22 was much lower than 1.0, indicating that most of the negative framework charges should be compensated by protonated template, HMI. The results from ⁷¹Ga and ²⁹Si MAS NMR demonstrated that gallium was incorporated into the tetrahedral framework of Ga-MCM-22. Also, the ²⁹Si MAS NMR spectra showed that the as-synthesized Ga-MCM-22 has a different distribution of tetrahedral Si sites from its Al analogue. After calcination, however, the distribution of tetrahedral Si sites significantly changed, due to a large degallation from the framework of Ga-MCM-22. The NH₃-TPD showed that Ga-MCM-22 possesses Brönsted and Lewis acid sites.     

柠檬酸复合改性对多环芳烃选择性开环铂/Beta催化剂性能的影响

通过水热处理、柠檬酸处理及其复合处理对Beta分子筛进行后改性,并以改性后的载体制得铂/Beta催化剂。采用X射线衍射（XRD）、X射线荧光光谱仪（XRF）、程序升温脱附（NH₃-TPD）、红外吡啶吸附（Py-IR）、骨架铝核磁共振技术（²⁷Al MAS NMR）及骨架硅核磁共振技术（²⁹Si MAS NMR）等表征了改性前后Beta分子筛的物化性质,并考察了改性前后铂/Beta的多环芳烃选择性开环性能。结果表明,Beta分子筛在柠檬酸处理过程中可同时发生络合脱铝与骨架补铝,实现骨架铝的再分布;Beta分子筛在水热处理过程中优先脱除稳定性相对较低的Si（2 Al）处骨架铝,产生骨架缺陷的同时生成一定比例的二次介孔结构;水热-柠檬酸复合处理影响Beta分子筛骨架补铝及骨架铝再分布的效果,水热处理后Beta分子筛中存在更多的骨架缺陷,促进活性Al（OH）₂⁺物种的骨架补铝作用。当Beta分子筛采用水热-柠檬酸复合处理顺序时,骨架补铝及骨架铝再分布效果显著,样品以中强酸为主,且具有较高的B酸量与L酸量的比值,所制备催化剂的多环芳烃选择性开环活性及稳定性最优。     

Hydrothermal stabilization of ZSM-5 catalytic-cracking additives by phosphorus addition

ZSM-5 zeolites with different Si/Al ratios (15, 25, 40) were impregnated with phosphorus (0.5–3 wt%) in form of H₃PO₄ or NH₄H₂PO₄. The samples were characterized before and after severe hydrothermal treatment by XRD, IR, ²⁷Al, ²⁹Si, ³¹P MAS NMR, and their activity for the cracking of n-decane was measured. It was found that phosphorus impregnation increases the hydrothermal stability of framework aluminum whatever the source of phosphorus used. The acidity and cracking activity of steamed samples reached an optimum for a P/Al molar ratio of ca. 0.5–0.7. A chemical model for the phosphorus–zeolite interaction is proposed in which the framework aluminum pairs are stabilized by extra-framework cationic species formed by protonation of orthophosphoric acid. The influence of isolated versus pairs of aluminum on activity and selectivity after steaming is discussed. When P-impregnated ZSM-5 sample is used as an additive for cracking industrial feeds, selectivity to propylene and butenes increases.     

Catalytic and multinuclear MAS NMR studies of a thermally treated zeolite ZSM-5

Catalysts of ZSM-5 type were obtained by synthesis with tetrapropyl-ammonium-bromide (TPABr) as a template and subsequent hydrothermal treatment up to 1173 K. ¹H-, ²⁷Al-, and ²⁹Si-NMR spectroscopy and the direct oxidation of benzene with N₂O as a catalytic test were applied to characterize the products. ²⁷Al MAS NMR and ²⁷Al 3QMAS NMR studies of the samples give evidence that fivefold-coordinated extra-framework aluminum species exist if the product is treated at 1173 K and then rehydrated. The values of all characteristic catalytic key data are highest when the catalysts are precalcined at 1173 K. This is a clue that species giving rise to fivefold-coordinated aluminum species in the hydrated products are responsible for the high catalytic key data. The nature of these species is not yet clear. Two models for the species are in agreement with our experimental findings.     

The role of alkali cations in zeolite synthesis from silicate solutions containing N,N,N-trimethyl-1-adamantammonium cations

Zeolite synthesis from aqueous N,N,N-trimethyl-1-adamantammonium (TMAA⁺)-alkali (Na⁺, K⁺, Rb⁺, and Cs⁺) silicate mixtures is studied using X-ray diffraction, elemental analysis, scanning electron microscopy, and²⁹Si magic angle spinning (MAS),¹H-¹³C cross-polarization (CP) MAS and¹H-²⁹Si CP MAS NMR spectroscopies. SSZ-24 forms in the presence of potassium cations, and SSZ-31 crystallizes in the presence of sodium cations. This is the first report of SSZ-31 synthesis from Na-TMAA silicate mixtures. Unknown silicates form in the presence of rubidium and cesium cations, whereas no crystalline material is observed in synthesis mixtures devoid of alkali cations. The alkali cations do not appear to serve as templates or void fillers during zeolite crystallization, nor do they stabilize soluble silicate anions which serve as building blocks during zeolite crystallization. Rather, the alkali cations appear to regulate the transformation of the amorphous synthesis gel into either crystalline zeolite or other silicate phases.     

Stability of the tetrahedral aluminium sites in zeolite beta

Calcination of as-synthesized or ammonium-exchanged forms of zeolite BETA induces an extensive loss of framework aluminium evidenced by²⁷Al MAS NMR, XRD and FTIR spectroscopies. Treatment of the calcined solids in ammonium nitrate restores the tetrahedral Al sites. Material balances show that the latter process is quantitative.     

Effect of different synthesis methods on the structural and catalytic performance of SBA-15 modified by aluminum

Two different aluminum-containing mesoporous Al/SBA-15 were prepared by post-synthesis method and direct synthesis method using P123 as structure directing agent and aluminum isopropoxide as the aluminum source. Samples were characterized in detail by XRD, N₂ adsorption, TEM,²⁷Al MAS NMR, and the acidic properties were performed by FT-IR of pyridine adsorption (Py-IR). The results show that Al/SBA-15 prepared by the direct synthesis method possessed higher BET surface area and larger pore volume. The acidic properties were investigated in Friedel–Crafts alkylation of phenol tert-butylation. The different synthesis method leads to distinct coordination of Al and intensity of acidity. Kinetics of the alkylation over Al/SBA-15 was also investigated. These results indicated that Al/SBA-15, prepared by post-synthetic grafting method, has more activity ability than the corresponding one synthesized by direct method since they contain more Lewis acid sites and Brönsted acid sites. The catalysts preserved almost their initial catalytic activity after four reuses.     

Supported BETA zeolite on preshaped β-SiC as clean Friedel-Crafts liquid-phase catalyst

Beta zeolite coated on a preshaped medium surface area silicon carbide carrier was prepared via an hydrothermal synthesis. ²⁷Al MAS NMR analysis revealed that all the aluminium was in a tetrahedral coordination and no trace of extraframework aluminium was observed. The Full Width at Half Maximum of the NMR peak was about 10 ppm, which indicates the presence of small zeolite crystals inside the sample. SEM observation has shown that zeolite homogeneousely coated the outer surface of the silicon carbide extrudate support with different size and shape and random orientation. The existence of a layer of silica and silicon oxycarbide on the surface of the support allows a strong anchoring of the coated zeolite. Thus, no zeolite loss was observed after sonication treatment for various durations. The as-prepared catalyst exhibits a high catalytic activity in the acylation of anisole by the anhydride acetic in batch mode configuration.     

TEABr directed synthesis of ZSM-12 and its NMR characterization

Synthesis of ZSM-12 using tetraethylammonium bromide (TEABr) as the template was investigated. Among the various parameters that affect the crystallization of ZSM-12, aluminum content of the gel, OH⁻/SiO₂ and TEA/SiO₂ ratios were the important determinants. Systematic variations of these parameters revealed that the TEABr-assisted synthesis had many similarities to the synthesis using TEAOH template reported earlier, with the exception that the OH⁻/SiO₂ ratios had to be maintained at lower values. Furthermore, the OH⁻/SiO₂ ratios favorable for ZSM-12 formation lie in a very narrow range. The source of alkalinity also affected the rate of crystallization and the composition of the product. The crystallization was found to be faster and better incorporation of aluminum in the zeolite framework was obtained when NaOH was used to provide alkalinity rather than KOH. Successful synthesis of highly crystalline ZSM-12 samples with Si/Al ratio around 30 was achieved using a minimal amount of relatively inexpensive TEABr (TEA/SiO₂=0.125).

Aluminum-27 NMR spectroscopy unambiguously revealed that all aluminum atoms are incorporated in the zeolite framework in tetrahedral coordination. The NMR line-widths of aluminum signals of the calcined samples were significantly larger than those with template incorporated samples. Spin-lattice relaxation times, conventional and rotating frame, as well as magic angle spinning (MAS) cross-polarization data with variable contact time support that there is a significant proton reservoir in the aluminum framework. The NMR data indicate that many distorted tetrahedral sites are formed upon removal of the template and some of these sites contain Al–OH moieties.