Hydroisomerization of Long-Chain Alkane Over Pt/SAPO-11 Catalysts Synthesized from Nonaqueous Media

SAPO-11 molecular sieves were synthesized from nonaqueous media. The effects of Si and Al sources as well as solvents on the catalytic performance of SAPO-11 were investigated by the hydroisomerization reaction of n-dodecane. The samples were characterized by XRD, XRF, N₂-adsorption, SEM, NH₃-TPD, IR-NH₃ and ²⁹Si CP MAS NMR. The SAPO-11 samples synthesized with tetraethoxysilane as the Si source showed higher Si incorporation contents than the SAPO molecular sieves prepared with polymeric Si sources (fumed silica and Si colloidal gel). The reaction results showed that Pt/SAPO-11 catalysts synthesized from ethylene glycol and glycerol media with the monomeric Si and Al sources (tetraethoxysilane, aluminum isopropoxide) exhibited higher catalytic activities than those catalysts with the polymeric Si or Al (pseudo-boehmite) sources, due to the larger external surface area and higher acidity of the former ones. Especially, the catalyst synthesized in an ethylene glycol medium possessed the highest catalytic activity. Over this catalyst, 88% conversion of n-dodecane was achieved at a low temperature of 250 °C.     

Effect of different TEAOH/DEA combinations on SAPO-34’s synthesis and catalytic performance

SAPO-34 molecular sieves were synthesized hydrothermally using different combinations of amine agents [i.e., tetraethyl ammonium hydroxide (TEAOH) and diethylamine (DEA)]. XRD indicated the good crystallinity directed by single or mixed template for CHA structure. The morphology of crystals from SEM photograph was shown to be cubic shape of typical SAPO-34, but distinct in crystal size, increasing from 0.3–0.8 to 3.1–9.1 μm with the amount of DEA in the gel. NH₃-TPD showed similar acid properties for SAPO-34 with TEAOH content from 1.0 to 0.1, but strong acidity synthesized with DEA only. ²⁹Si MAS NMR demonstrated that Si species in framework with single DEA existed in large size of silicon islands, whereas dispersed finely in siliceous islands of smaller size with remarkable Si (nAl, 4-nSi, 0 < n < 4) environments in the samples using mixed template. In the methanol conversion to olefins over different SAPO-34 catalysts, the sample prepared with the mixtures of 50%TEAOH and 50%DEA showed the longest lifetime and high selectivity to C₂⁼~C₃⁼.     

Characterization and hydroisomerization performance of SAPO-11 molecular sieves synthesized by dry gel conversion

SAPO-11 molecular sieves were synthesized by two types of dry gel conversion (DGC) methods, namely, steam-assisted conversion (SAC) and vapor phase transport (VPT), and by conventional hydrothermal (CHT) method. The properties of these samples were characterized by XRD, XRF, SEM, N₂-adsorption, Pyridine-IR and ²⁹Si MAS NMR methods. The results show that di-n-propylamine (DPA) is a suitable structure-directing agent (SDA) for the preparation of impurity-free SAPO-11. SAPO-11 molecular sieves synthesized by SAC and VPT exhibit higher crystallinity, higher Si content and more strongly acidic sites than that synthesized by CHT. ²⁹Si MAS NMR results demonstrated that the two samples obtained by the DGC methods contain more Si(nAl)(0 < n < 4) species than that obtained by CHT. These facts suggest that the SAC and VPT methods contribute either to better Si incorporation into the AlPO₄ framework or to better Si dispersal, thus decreasing the size of Si islands and increasing the number and strength of acidic sites. The results from the hydroisomerization of n-dodecane indicate that the Pt/SAPO-11 synthesized by SAC possesses the highest hydroconversion activity and isomer yield among those three catalysts, due to the high acidity of the molecular sieve supporter.     

Synthesis of SAPO-34 templated by diethylamine: Crystallization process and Si distribution in the crystals

The crystallization process of SAPO-34 molecular sieve with Si distribution in the crystals using diethylamine (DEA) as the template was investigated by XRD, SEM, IR, NMR, XRF, XPS and EDS techniques. It was found that the solution-mediated transport mechanism occurred during the crystallization, though the gel transformation cannot be completely excluded in the initial crystallization (t  1 h). Si directly participated in the crystallization in the initial stage and incorporated into the framework of SAPO-34 by SM2 (P substitution by Si) and SM3 (pairs of Al and P substitution by 2Si) mechanisms. XPS analysis revealed the enrichment of Si on the surface of crystals. Based on the experimental results, a model of Si distribution in the crystals was proposed, which described a non-uniform distribution of Si in the crystals, with the increasing content from the core to the surface.     

模板剂用量对SAPO-11分子筛的物理化学性质及催化萘与甲醇烷基化性能的影响

考察了二正丙胺(DPA)模板剂用量对合成的SAPO-11分子筛的物化特性及催化萘与甲醇的烷基化的影响,并通过XRD、SEM、N2 adsorption-desorption、NH3-TPD、FTIR和29SiMAS NMR等手段对合成的样品进行了表征。结果表明:改变模板剂用量不仅可以调节SAPO-11的孔结构,还会改变Si在分子筛骨架上的分布,从而调节SAPO-11的酸性。当n(DPA)/n(Al2O3)=1.5时,样品具有较大的比表面积和孔容,分别为215 m2/g和0.173 cm3/g;样品的Si区面积最小,Si(nAl)(0相似文献   

Synthesis and characterization of acidic properties of Al-SBA-15 materials with varying Si/Al ratios

Al-SBA-15 of varying Si/Al ratios in the range 11.4–78.4 was synthesized using tri-block copolymer P123. The calcined materials were examined by XRD, pore size distribution, surface area, ²⁷Al NMR spectroscopy. The acidity and acid strength distribution were studied using microcalorimetric adsorption of NH₃. The acidic properties were also examined by cumene cracking reaction as a function of Si/Al ratios. Systematic variation of acidity and activity was observed as a function of Si/Al ratio. The initial heats of NH₃ adsorption correlated well with activity indicate that acid sites with ΔH > 100 kJ/mole is responsible for cumene cracking activity. Linear correlations were obtained with total acidity and cumene cracking activities. The tetrahedral aluminum was found to be responsible for the observed acidities and catalytic activities.     

Isomerization of α-pinene over dealuminated ferrierite-type zeolites

Isomerization of α-pinene was performed on a series of dealuminated ferrierite (FER)-type zeolites in liquid phase at 363 K using a batch reactor. The course of zeolite dealumination was followed in detail using ²⁹Si, ²⁷Al, ¹H MAS NMR, XRD, FTIR, and sorption of nitrogen. The ammonium form of FER was dealuminated with aqueous solutions of HCl. While retaining the crystallinity of the zeolite particles, the treatments removed up to 53% of the tetrahedrally coordinated aluminum atoms from the FER framework. According to ²⁹Si MAS NMR studies, the framework aluminum atoms located at the 10-membered rings in the main channels of FER (T_B sites) were depleted preferentially from their positions. Even relatively mild dealumination of FER led to an active catalyst containing both Brønsted and Lewis centers, yielding up to 97% conversion of α-pinene at 363 K, in contrast to the 72% observed for the parent hydrogen form. Such catalytic behavior was discussed in terms of the conversion of a reactant inside micropores of the zeolite catalyst, on Brønsted acid centers with enhanced strength located probably in the vicinity of Lewis sites. The selectivity toward camphene and limonene changed smoothly with the dealumination level; thus, a higher selectivity toward limonene was observed at the expense of camphene formation with increasing the n_Si/n_Al ratio of the catalysts. The selectivity toward camphene and limonene was close to 85% for all of the materials studied. The initial rates of α-pinene transformations over FER-type materials exceeded those observed for other catalytic systems, heteropoly acid/SiO₂ and H₂SO₄/ZrO₂. This study demonstrates the successful application of a medium-pore zeolite for the catalytic transformation of α-pinene in liquid phase.     

Effect of Ti5Si3 on wear properties of Ti3Si(Al)C2

Near-fully dense Ti₃Si(Al)C₂/Ti₅Si₃ composites were synthesized by in situ hot pressing/solid–liquid reaction process under a pressure of 30 MPa in a flowing Ar atmosphere at 1580 °C for 60 min. Compared to monolithic Ti₃Si(Al)C₂, Ti₃Si(Al)C₂/Ti₅Si₃ composites exhibit higher hardness and improved wear resistance, but a slight loss in flexural strength (about 26% lower than Ti₃Si(Al)C₂ matrix). In addition, Ti₃Si(Al)C₂/Ti₅Si₃ composites maintain a high fracture toughness (K_IC = 5.69–6.79 MPa m^1/2). The Ti₃Si(Al)C₂/30 vol.%Ti₅Si₃ composite shows the highest Vickers hardness (68% higher than that of Ti₃Si(Al)C₂) and best wear resistance (the wear resistance increases by 2 orders of magnitude). The improved properties are mainly ascribed to the contribution of hard Ti₅Si₃ particles, and the strength degradation is mainly due to the lower Young's modulus and strength of Ti₅Si₃.     

小晶粒SAPO-11分子筛合成及其正己烷异构化催化性能

以二正丙胺和二异丙胺为双模板剂,通过低温预晶化及向SAPO-11分子筛合成体系中加入添加物(异丙醇、聚乙二醇或氢氟酸)等方法阻止其晶粒的生长与聚集,达到控制分子筛颗粒尺寸的目的,在水热条件下一步法合成小晶粒SAPO-11分子筛。结果表明,合成条件对SAPO-11分子筛的晶粒大小和催化性能影响很大,晶粒尺寸由常规方法合成的(5～10)μm减小至约400 nm,小晶粒Pt/SAPO-11催化剂对正己烷加氢异构化反应表现出优异的催化活性和选择性。     

Synthesis, characterization and catalytic properties of SAPO-34 synthesized using diethylamine as a template

SAPO-34 molecular sieve was successfully synthesized using diethylamine (DEA) as a template. The influence of template concentration and silica concentration on the synthesis were investigated. Pure SAPO-34 could be obtained when n(DEA)/n(Al₂O₃)  1.5 and n(SiO₂)/n(Al₂O₃) > 0.1 in the synthesis gel. Further increase of DEA concentration in the starting gel [n(DEA)/n(Al₂O₃) > 3] has a negative effect on both crystallinity and crystal yield. The products were characterized by XRD, XRF, SEM, NMR, FT-IR, TG-DTA and nitrogen adsorption techniques. It was found that SAPO-34 synthesized with DEA as a template has the characteristic of high silicon incorporation and exhibits good thermal and hydrothermal stability. The catalytic performance of SAPO-34 was tested by methanol-to-olefin (MTO) reaction and high olefins (C₂H₄ + C₃H₆) selectivity was obtained.     

Silicoaluminophosphate number eighteen (SAPO-18): a new microporous solid acid catalyst

SAPO-18, which has a microporous framework structure related to, but crystallographically distinct from, that of the solid acid catalyst SAPO-34, was synthesized hydrothermally from a silicoaluminophosphate gel containing N,N-diisopropylethylamine as a structuredirecting template. Although both materials have similar Si/(Si + Al + P) ratios, the content of Brønsted acid sites in SAPO-18 is considerably less than that in SAPO-34. As catalysts for methanol conversion to light olefins, SAPO-18 and SAPO-34 have closely similar initial activity and selectivity, but the lifetime of SAPO-18 is distinctly superior to that of SAPO-34.     

Study of the Keggin structure and catalytic properties of Pt-promoted heteropoly compound/Al-MCM-41 hybrid catalysts

Aluminum-containing mesoporous molecular sieves (referred as WSAn, where n = Si/Al molar ratio = 50, 30 and 10) were synthesized via a surfactant templated approach by using fumed silica and aluminum sulfate as Si and Al precursors, respectively. When the 12-tungstophosphoric acid was grafted onto the surface of WSAn, a high dispersion of the heteropolyacid was achieved on the heteropoly compound/WSAn hybrid catalysts. The Keggin structure of the dispersed 12-tungstophosphoric acid was primarily preserved without destruction, but it was distorted in some degree, as confirmed by FTIR, ³¹P NMR-MAS and UV–vis spectroscopic characterizations. The surface Brönsted acidity of the catalysts was greatly enhanced by several times in comparison to that of the bare WSAn support. In the hydroisomerization reaction of n-heptane, the Pt/H₃PW₁₂O₄₀/WSA30 catalyst exhibited the highest catalytic activity and the best isomerization selectivity among the catalysts tested, which can be generally correlated with its large number of Brönsted acid sites and high structural regularity. After the n-heptane hydroisomerization reaction, a high molar ratio of multibranched to monobranched isohexanes was obtained, indicating that Pt-promoted heteropoly compound/WSAn hybrid catalysts have a great potential for the hydroisomerization of long carbon chain hydrocarbons.     

SAPO-11/HBeta composites for catalytic cracking of 2-butylene: effects of defect structure

SAPO-11/HBeta composite was synthesized by using hydrothermal method (SB-H) and applied as catalyst for cracking of 2-butylene to C₂–C₃ olefins. SB-H sample exhibited comparatively high selectivity and high yield of C₂–C₃ olefins. XRD, IR, ²⁷Al and ³¹P MAS NMR, Py-IR characterizations indicate that defect structure P(AlO₄) _n (n < 4) really existed in SB-H sample. SAPO-11 and HBeta chemically bonded and the defect P(AlO₄) _n (n < 4) formed during the hydrothermal synthesis of SB-H sample. P(AlO₄) _n (n < 4) unit caused new B acidic sites, which increased B acidic amount and B acidic distribution on SB-H sample. The improvement of B acidity decreased apparent active energy of cracking of 2-butylene to C₂–C₃ olefins on SB-H sample. Therefore, the high selectivity and high yield of C₂–C₃ olefins were obtained on SB-H sample in catalytic cracking of 2-butylene.     

双模板剂法SAPO-34分子筛的合成及其MTO催化性能调变

以四乙基氢氧化铵（TEAOH）和二乙铵（DEA）为混合模板剂，在低投料硅铝比[n (SiO₂) ∶n (Al₂O₃)=0.2]及低模板剂用量[n (模板剂) ∶n (Al₂O₃)=1.9]下，考察了两种模板剂比例的调变对合成的SAPO-34分子筛物化性能及其催化甲醇制烯烃反应（MTO）催化性能的影响。研究发现，通过改变两种模板剂比例，可以明显调变SAPO-34分子筛晶粒尺寸、硅分布（晶粒表面和体相的硅分布）、硅原子的配位环境，从而影响其MTO催化反应的效果。在低模板剂用量制备的SAPO-34产品中，晶粒尺寸是影响其催化寿命的最主要因素，小晶粒分子筛因其扩散路径短有利于延长催化寿命。此外，硅分布也是影响催化寿命的因素之一，表面富硅的分子筛导致外表面积炭程度大于晶内积炭，积炭趋势由外向内发展，加速分子筛“假性”失活。硅分布还影响MTO反应产物分布，表面富硅分子筛外表面更易发生非择形催化，显著提高C₄～C₆等产物的选择性，不利于目标产物双烯（乙烯+丙烯）选择性的提高。     

Synthesis, characterization and hydroisomerization catalytic performance of nanosize SAPO-11 molecular sieves

A new static hydrothermal method was developed for synthesizing nanosize SAPO-11 molecular sieve.The new method involves aging pretreatment step followed by crystallization process of a precursor gel. The effect of the aging pretreatment on morphology and size of SAPO-11 molecular sieves was investigated. The results of XRD and SEM showed that the aging pretreatment changed the size and morphology of the SAPO-11 dramatically, and the size could be controlled by varying the time for aging. Nanocrystals of SAPO-11 molecular sieves were synthesized by aging the precursor gel at 150 °C for 135 min and then crystallizing the gel at 190 °C for 24 h. Compared with the SAPO-11 samples that exhibit the pseudo-spherical aggregates ranging from 3 to 15 μm synthesized by conventional method, the SAPO-11 samples synthesized by the new method not only possessed much smaller cubic single crystals of about 400–500 nm, but were more uniform in size. Moreover, the SAPO-11 samples synthesized by the new method had larger specific surface area and larger external specific surface area. The results of n−hexadecane hydroisomerization showed that the Pt/SAPO-11 prepared with the new method exhibited higher catalytic activity and better hydroisomerization selectivity than the Pt/SAPO-11 synthesized by conventional hydrothermal method.     

Synthesis, Characterization and Hydroisomerization Performance of SAPO-11 Molecular Sieves with Caverns by Polymer Spheres

Silicoaluminophosphates SAPO-11 molecular sieves with caverns were synthesized using polystyrene (PS) micro-spheres as template. The morphologies of the cavitary SAPO-11 molecular sieves exhibit spherical particles ranging 7–10 μm aggregated from cubic plate microcrystallites which just like the SAPO-11 molecular sieves synthesized with the conventional method, but some caverns of 500–1,200 nm pore size in diameter can be observed on the former material. The strength and distribution of the acid sites of the cavitary SAPO-11 are similar to that of the conventional SAPO-11, but the acid density is slightly low owing to the decreased crystallinity of the cavitary SAPO-11. The micropores size and mesopores size of the conventional SAPO-11 are centered at about 0.45 and 3.8 nm, respectively, while the cavitary SAPO-11 has, in addition to the micropores and mesopores, large mesopores ranging 5–30 nm and macropores ranging from about 100 to 1,200 nm, which were derived from the PS sphere template. Hydroisomerization of n-hexadecane was performed to investigate the catalytic performance of the cavitary SAPO-11. The result showed that, in comparison with the conventional SAPO-11, the cavitary SAPO-11 has high activity based on per active site and high selectivity, owing to the fast diffusion of the reactant and isomer products inside the catalyst.     

Synthesis of SAPO-34 with only Si(4Al) species: Effect of Si contents on Si incorporation mechanism and Si coordination environment of SAPO-34

SAPO-34 molecular sieves with different Si coordination environment were synthesized by adjusting SiO₂/Al₂O₃ molar ratio in starting gel. The crystal structure, element composition and Si coordination environment of the as-synthesized samples were characterized by XRD, SEM, XRF and NMR. SAPO-34 molecular sieve could be obtained when the SiO₂/Al₂O₃ molar ratio of the starting gel was higher than 0.075. The content and modeling of Si incorporated into SAPO-34 framework varied with the SiO₂/Al₂O₃ molar ratios in the starting gel and different Si chemical environments were formed correspondingly. SAPO-34 with only Si(4Al) coordination structure could be prepared when the SiO₂/Al₂O₃ molar ratio of the starting gel was in range of 0.075–0.15.     

Isopropylation of ethylbenzene over MCM-22 molecular sieve

MCM-22 materials (Si/Al ratios 24, 50 and 75) were synthesized and characterized. The catalytic activity was examined in the vapour phase isopropylation of ethylbenzene with isopropyl alcohol. Based on ethylbenzene conversion, the order of activity of the catalysts is found to be MCM-22(50) > MCM-22(24) = MCM-22(75). The selective formation of p-isopropyl ethylbenzene (p-IPEB) suggests that the reaction occurs mainly inside the 10-membered ring channel. The time on stream study over MCM-22(50) showed steady conversion for 6 h with nearly the same selectivity to p-isopropyl ethylbenzene (p-IPEB) and o-isopropyl ethylbenzene (p-IPEB).     

Changes upon heating of the distribution of Al,P and Si atoms in the SAPO-37 molecular sieve

A drastic change in the environment of Si atoms in SAPO-37 after heating at 1173 K is seen in the²⁹Si MAS NMR spectrum. This suggests a modification of the location of Si, Al and P atoms. Three main phases would coexist in large amounts in the faujasite structure, the SAPO-37 originating phase, pure SiO₄ islands and an aluminosilicate phase comparable to Si-Al faujasite.     

The Sites of Molecular and Dissociative Hydrogen Adsorption in High-Silica Zeolites Modified with Zinc Ions. III DRIFT Study of H2 Adsorption by the Zeolites with Different Zinc Content and Si/Al Ratios in the Framework

study of dihydrogen adsorbed at 77K by the zinc-modified hydrogen forms of mordenite and ZSM-5 zeolites with the different Si/Al ratios in the framework indicated the existence of several adsorption sites connected with the modifying zinc ions. The fraction of the sites of the strongest perturbation of adsorbed molecular hydrogen with the H–H stretching frequency of ca. 3930–3950 cm^-1 is the highest at the highest Si/Al ratios of 41 or 80. These sites dissociatively adsorb hydrogen at moderately elevated temperatures. Adsorption of hydrogen with the higher H–H stretching frequency of about 3970–4000 cm^-1 predominates at the lower Si/Al ratios. It does not result in the dissociation of adsorbed molecules. It was concluded that the most active sites are most probably connected with the zinc ions, which compensate two distantly separated negatively charged [AlO₄]^- tetrahedra localized in the adjacent five- or six-membered rings on the walls of the large channels of the pentasil's framework. The sites of the weaker perturbation of adsorbed hydrogen are most probably connected with Zn⁺² ions at the conventional exchangeable cationic positions with two aluminum atoms in the same five- or six-membered ring.