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.     

Novel promotional effect of yttrium on Cu–SAPO-34 monolith catalyst for selective catalytic reduction of NOx by NH3 (NH3-SCR)

Cu–SAPO-34 and CuY–SAPO-34 catalysts for NH₃-SCR were prepared by the wet-impregnation method. XRD, UV–vis DRS, ESR and NH₃-TPD results showed that the introduction of Y effectively improved the dispersion of copper species, increased the amount of isolated copper ions and enhanced the acid density. In addition, the activity test, NH₃-TPD and TGA results reflected that the CuY–SAPO-34 catalyst showed better C₃H₆ oxidation activity, lower dropping degree of acid sites after C₃H₆/O₂ treatment and less adsorption of C₃H₆/O₂ than Cu–SAPO-34 catalyst. Therefore, the addition of Y promoted the NH₃-SCR performance and the hydrocarbon (HC) resistance of Cu–SAPO-34 catalyst.     

SAPO-34 supported Pt–Sn-based novel catalyst for propane dehydrogenation to propylene

The Pt–Sn-based catalyst was intensified using SAPO-34 as support for direct propane dehydrogenation to propylene. The catalyst was prepared by sequential impregnation method and characterized by XRF, BET, XRD, NH₃-IR, NH₃-TPD, H₂-TPR, HR-TEM and O₂-pulse coke analysis. NH₃-TPD, IR spectra and XRD results suggested that the doping of metals on SAPO-34 did not affect its acidic strength and structural topology of support, respectively. Propylene selectivity of 94% and total olefins selectivity greater than 97% was achieved using Pt–Sn/SAPO-34. The results were compared with Pt–Sn/ZSM-5 under identical conditions. The possible reasons for improvement were the larger surface area, shape selectivity and particular by suitable acidity of SAPO-34.     

Nature and catalytic performance of PtSAPO-5 molecular sieve catalyst synthesized by one step

Pt catalysts supported on silicoaluminophosphate molecular sieves were synthesized by adding platinum salts directly to the gel mixture of SAPO. The synthesized products were marked as PtSAPO-5, in order to distinguish with the SAPO-5 supported platinum catalyst prepared by impregnation, which was marked as Pt/SAPO-5. The as-synthesized and calcined PtSAPO-5 samples were characterized by XRD,²⁹Si MAS NMR,¹²⁹XeNMR and NH₃-TPD, and their catalytic activities were evaluated by the hydroisomerization of n-hexane. The results revealed that in PtSAPO-5, the platinum could catalyze the removal of the templates entrapped in the as-synthesized samples. The presence of Pt in the gel mixture can increase silicon content in the framework of SAPO-5, and the acid sites. In the activated PtSAPO-5 catalyst, Pt was highly dispersed in the channel of SAPO-5 molecular sieve. Pt exists in the form of big particles outside of the channel of Pt/SAPO-5 prepared by impregnating method, and impregnation with H₂PtCl₆ improved the strength of acid sites. PtSAPO-5 has a higher activity and selectivity than Pt/SAPO-5 in the hydroisomerization of n-hexane. This is because the former has medium acid sites and high dispersion of Pt, while the channel of Pt/SAPO-5 is somewhat retarded by the big platinum particles, and the acid sites are stronger than the former.     

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⁼.     

Enhancement of Pd-Pt/Al2O3 catalyst performance in naphthalene hydrogenation by mixing different molecular sieves in the support

The hydrogenation of naphthalene in hexane was carried out over the catalyst Pd-Pt supported on alumina mixed with different molecular sieves including ZSM-5, Beta, USY and SAPO-11. The catalyst was characterized by N₂ sorption, NH₃-TPD, TPR, and H₂-O₂ titration. The results indicated that the catalyst performance for naphthalene hydrogenation is related to its acid property, pore structure, Pd-Pt dispersion, and metal-support interaction, which may be well regulated by mixing proper molecular sieves in the alumina support. The catalyst Pd-Pt supported on a two-component support of Al₂O₃-SAPO-11 is provided with proper acidity, large pores and moderate metal dispersion; it exhibits excellent performance in the saturated hydrogenation of naphthalene to decalin (over it a complete conversion of naphthalene is observed and the selectivity to decalin exceeds 90% at 260-300 °C).     

Performance of Pt/MgAPO-11 Catalysts in the Hydroisomerization of n-dodecane

MgAPO-11 molecular sieves with varying Mg contents synthesized by the hydrothermal method were used as supports for bifunctional Pt/MgAPO-11 catalysts. MgAPO-11 molecular sieves and the corresponding catalysts were characterized by X-ray diffraction (XRD), X-ray fluorescence spectroscopy (XRF), temperature-programmed desorption of NH₃ (NH₃-TPD), differential thermogravimetric (DTG) analysis, temperature-programmed reduction of H₂ (H₂-TPR), H₂ chemisorption and catalytic reaction evaluation. The results indicated that the acidity generated via the substitution of Mg²⁺ for Al³⁺ in the framework increased with the Mg content. Acting as acidic components, the MgAPO-11 molecular sieves loaded with Pt were tested in the hydroisomerization of n-dodecane. Optimum isomer yield was obtained over the Pt/MgAPO-11 catalyst that had neither the highest acidity nor the highest Pt loading among the tested catalysts. In fact, the activity and the isomer yield both could attain a maximum on 0.5 wt.% Pt/MgAPO-11 catalysts with differing Mg contents. A lower Mg content resulted in an insufficient acidity, whilst a higher Mg content weakened the dehydrogenation/hydrogenation function of the Pt. These inappropriate balances between the acidic and the metallic functions of the catalysts would lead to low activities and isomer yields. On the other hand, the 0.5 wt.% Pt/MgAPO-11(3) catalyst was found to have a good balance between the acidic and the metallic functions, and thus exhibited both high activity and isomer yield in comparison with the conventional 0.5 wt.% Pt/SAPO-11 catalyst.     

Synthesis, characterization and catalytic performance of metal-incorporated SAPO-34 for chloromethane transformation to light olefins

SAPO-34 and MeAPSO-34s (MeCo, Mn, Fe) molecular sieves have been synthesized and used as catalysts for chloromethane transformation to light olefins. The influences created by metal incorporation are characterized with XRD, XRF, SEM, NMR, TG and H₂-TPR. The synthesized MeAPSO-34s have the same CHA topology structure, while metal incorporation gives rise to the increase of unit cell parameter and crystalline particle size. The coexistence of metal species in the synthesis starting gel has effect on the Si substitution into AlPO framework. Co, Mn or Fe incorporation generates a negligible difference on the chemical shift in ³¹P and ²⁷Al MAS NMR. ²⁹Si MAS NMR study has demonstrated that metal incorporation favors the Si island formation, predicting the stronger acidity. The reducibility of metal species in the synthesized MeAPSO-34s has been investigated by H₂-TPR with the comparison of metal-impregnated SAPO-34. Two weight losses in TG analysis from template decomposition in diluted oxygen suggest different chemical location of template molecules in the molecular sieves. For MeAPSO-34, more template removal occurrence at high temperature range indicates stronger template-framework interaction and stronger acidity than SAPO-34 after calcinations. All the SAPO-34 and MeAPSO-34 molecular sieves are very active and selective catalyst for light olefins production. Metal incorporation improves the catalyst life and favors the ethylene and propylene generation. These catalytic properties enhancements are possibly related to the mechanism of chloromethane conversion with deposited coke species as reaction center.     

C<Subscript>2</Subscript>H<Subscript>6</Subscript>/CO<Subscript>2</Subscript> oxidative dehydrogenation (ODH) reaction on nanostructured CrAPSO-34 catalyst: One-pot hydrothermal vs. conventional hydrothermal/impregnation catalyst synthesis

A series of Cr incorporated SAPO-34 catalysts varying in Cr content and a Cr supported SAPO-34 catalyst were prepared by one-pot hydrothermal and incipient-wetness impregnation methods, respectively. The synthesized materials were characterized by XRD, FESEM, TEM, BET, EDX dot mapping, TPD-NH₃ and FTIR, and tested in ethane dehydrogenation with CO₂ reaction. The incorporation of Cr³⁺ into the SAPO-34 framework and impregnation of Cr species were proved by TEM technique. With increase in the incorporated Cr content, smaller cubic crystals and amorphous particles were obtained. However, the extra-framework species probably appeared. Chromium impregnation led to micropore blockage and surface coverage partly, resulting in morphology change somewhat, significant decrease of surface area and acidity as evidenced by FESEM, TEM, BET and TPD-NH₃ analysis. However, one-pot synthesis not only preserved the structure of SAPO-34 but also allowed higher surface area, more effective surface acidity and better chromium dispersion to be achieved, features that account for superior catalytic performance and stability of directly synthesized Cr rich catalyst. The Cr incorporated SAPO-34 catalyst containing rich amount of Cr exhibited the best catalytic activity, showing 38% ethylene yield at 700 °C even after 5 h on-stream operation.     

Characterization of AlPO4-based molecular sieves and methanol conversion to light olefins

Of the AlPO₄-based molecular sieves, A1PO₄, SAPOs, and MeAPOs of different pore sizes were prepared at 100-200°C by a hydrothermal crystallization method. This study was purposed to maximize the yield of light olefins through methanol conversion. Crystal structure was confirmed by means of XRD and SEM, and acidity was examined by TPD and IR of adsorbed ammonia on the catalysts. It was found that SAPO-34 exhibited more than 90% selectivity for light olefins such as ethylene, propylene, and butylene due to shape selectivity through small pores, although it had a strong acidity. MeAPO-34 exhibited slightly lower selectivity for light olefins than SAPO-34 and different product distribution, depending on the electronegativity of the metal in its framework. SAPO17 and SAPO-44, which have the same pore size with SAPO-34 but different pore structure from SAPO-34, showed less selectivity for light olefins than SAPO-34.     

Study of Mn incorporation into SAPO framework: Synthesis, characterization and catalysis in chloromethane conversion to light olefins

MnAPSO-34 molecular sieve has been synthesized with triethylamine as the template, characterized with XRD, XRF, ³¹P, ²⁷Al and ²⁹Si NMR and FT-IR techniques and compared with SAPO-34. The template decomposition and removal have been investigated with TG–DTG–DSC coupled with mass spectrometer. Mn incorporation generates a negligible difference on the chemical shift in ³¹P and ²⁷Al MAS NMR, while an effect on the intensity of resonance peaks is revealed. ²⁹Si MAS NMR study has demonstrated that Mn incorporation favors the Si island formation, which may give rise to the stronger acidic sites. The thermal analysis (TG–DSC) on template removal in a diluted oxygen atmosphere, leading to the formation of CO₂, NO and H₂O, showed, besides a low temperature endothermic weight loss due to the desorption of water, two weight losses (200–400 and 400–600 °C) for SAPO-34 and MnAPSO-34, suggesting two different chemical location environments of template molecules in these two molecular sieves. The quantity of template removed at higher temperature range is much higher in MnAPSO-34, indicating stronger template–framework interaction and stronger acidity after calcination. The acid difference caused by Mn incorporation has also been evidenced by ammonia adsorption evaluated by FT-IR. Chloromethane transformation was carried out over MnAPSO-34 and SAPO-34 and the catalytic performance showed that both molecular sieves are very active and selective catalyst for light olefins production. MnAPSO-34 demonstrated higher activity and light olefins selectivity.     

Improving SAPO-34 performance for CO2/CH4 separation and optimization of adsorption conditions using central composite design

ABSTRACT

SAPO-34 molecular sieves have a high adsorption capacity in separation of CO₂ from CO₂/CH₄ mixture. In this study, SAPO-34 was modified by different solutions at various operating conditions to enhance the removal of carbon dioxide from the methane gas. Modifications can change pore size and also Si/Al ratio in SAPO-34 and make changes in the acidity of the adsorbent via the ion exchange process. The effects of temperature and pressure on the separation were studied using the design of experiments. Finally, based on the results of the experimental optimization process applying central composite design (CCD) method, the highest yield of CO₂ separation from the methane gas (95%) was obtained when using P-SAPO-34 sample at 17.4°C and 4.6 bar.     

Adsorption of CO<Subscript>2</Subscript> and CO on H-zeolites with different framework topologies and chemical compositions and a correlation to probing protonic sites using NH<Subscript>3</Subscript> adsorption

Adsorption of CO₂ and CO at 25 °C has been conducted using commercially-available (Y, ZSM-5) and laboratory-synthesized (SSZ-13, SAPO-34) H-zeolites with different framework topologies and chemical compositions, and their textual and surface properties have been characterized by N₂ sorption and NH₃ adsorption techniques. All the zeolites were microporous, although ZSM-5 and SSZ-13 apparently showed a mesoporous sorption behavior due to the interparticle spaces. The zeolites had Si/Al values in the order of SSZ-13 (16.44) > ZSM-5 (16.08) ? Y (2.82) ? SAPO-34 (0.19). Regardless, high CO₂ adsorption capacity was obtained for SSZ-13 and SAPO-34 with a CHA framework. The FAU zeolite Y with the highest micropore volume showed less CO₂ adsorption than the CHA zeolites and the MFI-type ZSM-5 yielded the poorest performance. Probing acid sites in the H-form zeolites using NH₃ disclosed that these all contain both weak and strong acid sites with significant dependence of their strengths and amounts on the topology. The acid strength of the weak acid sites in the CHA zeolites was the weakest, which might allow a stronger interaction with CO₂. The H-zeolites gave CO₂/CO selectivity factors that were in the range of 4.61–11.0, depending on the framework topology.     

Synthesis, Characterization and Catalytic Activities of Mesoporous AlMSU-X with Wormhole-Like Framework Structure

Mesoporous AlMSU-X molecular sieves with high acidity have been prepared from preformed beta nanoclusters under strong acidic conditions in the presence of nonionic TX-100 as structure directors. These materials were characterized by XRD, HRTEM, N₂-adsorption, ²⁷Al MAS NMR, NH₃-TPD, IR-pyridine adsorption and catalytic cracking of cumene and 1,3,5-triisopropylbenzene. The experimental results showed that Al heteroatoms had been successfully incorporated into the framework structure of mesoporous MSU-X, and so-produced catalysts exhibited superior catalytic properties.     

Nanocrystalline Brookite-Type Titanium(IV) Oxide Photocatalysts Prepared by a Solvothermal Method: Correlation Between Their Physical Properties and Photocatalytic Activities

Mesoporous MSU-X alumina molecular sieves were synthesized through the neutral N⁰I⁰ assembly pathway using aluminum sec-butoxide as the precursor and a triblock poly(ethylene glycol)-poly(propylene glycol)-poly(ethylene glycol) as the structure-directing agent. Their surface acidity and basicity as well as textural properties were characterized by NH₃-TPD, CO₂-TPD, IR spectroscopy and N₂ adsorption methods. The materials are abundant in surface weak acid sites and weak-medium basic sites. They are more active than the commercial -Al₂O₃ catalyst for the CS₂ hydrolysis reaction, and the temperature of 90 conversion of CS₂ on the mesoporous alumina is 130K lower than that of -Al₂O₃.     

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.     

The catalytic performance of methylation of naphthalene with methanol over SAPO-11 zeolites synthesized with different Si content

A series of SAPO-11 zeolites with different Si contents were prepared by hydrothermally synthesized method. They were characterized by ICP, XRD, SEM, FT-IR, N₂ adsorption-desorption, NH₃-TPD and ²⁹Si MAS NMR, and evaluated by the methylation of naphthalene with methanol to 2,6-dimethylnaphthalene (2,6-DMN). According to XRD and SEM results, the crystallinity of SAPO-11 sample increased with increase of the Si content until the SiO₂/Al₂O₃ ratio was up to 0.2. However, a reduction in the crystallinity was observed with further increase of the Si content of the synthesis. N₂ adsorption-desorption results showed that all the samples possessed micropores and secondary mesopores. SAPO-11 sample with SiO₂/Al₂O₃ ratio of 0.2 exhibited the largest secondary mesopores size distributions. NH₃-TPD and ²⁹Si MAS NMR showed that the Si content was incorporated into the framework affecting not only the acid sites but also the acid strength of SAPO-11. SAPO-11 with SiO₂/Al₂O₃ ratio of 0.2 presented the high catalytic performances for the methylation of naphthalene, which was mainly attributed to the amount of secondary mesopores in the SAPO-11 zeolite.     

模板剂对SAPO-34分子筛性能的影响

采用XRD、SEM、NH3-TPD等方法研究了以三乙胺(TEA)、四乙基氢氧化铵(TEAOH)及二者的混合物为模板剂合成的产物的结构及物化性能,并以甲醇为探针分子,在固定床反应器上对合成产物在甲醇制取烯烃(MTO)反应中的催化性能进行了评价。结果表明,模板剂的种类及配比对所得产物的晶相结构、晶粒大小、酸强度、酸量以及催化性能有重要影响。双模板体系中,当n(TEAOH)/n(TEA)=0.037～0.186时,得到纯相SAPO-34分子筛;且当n(TEAOH)/n(TEA)=0.093时,得到的SAPO-34分子筛晶粒较小(1.0μm左右)且均匀,酸度适中,低碳烯烃(C2=～C4=)的选择性94.98%,催化寿命415min,较单独以TEA〔n(TEA)/n(Al2O3)=2.15〕或TEAOH〔n(TEAOH)/n(Al2O3)=2.0〕为模板剂合成的催化剂的低碳选择性(88.22%和89.29%)和寿命(170min和165min)均有明显提高,且积炭速率(0.016%/min)明显降低。     

模板剂对SAPO-34分子筛性能的影响研究

采用XRD、SEM、NH3-TPD等方法深入研究了以三乙胺(TEA)、四乙基氢氧化铵(TEAOH)及二者的混合物为模板剂合成的产物的结构及物化性能。并以甲醇为探针分子,在固定床反应器上对合成产物在甲醇制取烯烃(MTO)反应中的催化性能进行了评价。结果表明,模板剂的种类及配比对所得产物的晶相结构、晶粒大小、酸强度、酸量以及催化性能有重要影响。双模板体系中,当TEAOH/ TEA=0.037～0.186时,可以得到纯SAPO-34分子筛;且当TEAOH/TEA=0.093时,得到的SAPO-34分子筛晶粒较小(1.0μm左右)且均匀,酸度适中,低碳烯烃(C2=～C4=)的选择性94.98%,催化寿命415min,较单独以TEA(TEA/Al2O3=2.15)或TEAOH(TEA/Al2O3=2.0)为模板剂合成的催化剂的低碳选择性 (88.22%和89.29%)和寿命(170min和165min)均有明显提高,且积炭速率(0.016%/min)明显降低。     

Effect of phosphorus on acidity and catalytic performance of Al-MCM-41 for the selective conversion of ethyl mercaptan to ethylene and H<Subscript>2</Subscript>S

A series of phosphorus modified Al-MCM-41 molecular sieves with various P/Al ratios were prepared via impregnating method and tested in the selective transformation of ethyl mercaptan into ethylene and hydrogen sulfide. The resulting samples were characterized by a combination of X-ray diffraction, N₂ adsorption, ICP-OES, NH₃ -TPD, ²⁷Al and ³¹P MAS NMR spectroscopy. The experimental findings demonstrated that P modification can effectively increase the concentration as well as the strength of weak acid sites. Intermediate acid sites were gradually decreased with phosphorus addition, and the product distribution was found to vary with the acidity of the zeolites. Phosphorus content has strong influence on catalytic stability and ethylene selectivity. Upon P treatment, the amount of coke drastically decreased and the catalyst lifetime prolonged. The notable results could be useful for developing a viable process for removing ethyl mercaptan from natural gas.