Alkaline hydrothermal zeolites synthesized from high SiO2 and Al2O3 co-disposal fly ash filtrates

A co-disposal reaction was used wherein fly ash (FA) was reacted with acid mine drainage (AMD), to collect filtrates for zeolite synthesis. Raw fly ash as well as fly ash leached with HCl were subjected to the same alkaline hydrothermal zeolite synthesis conditions, as for the co-disposal filtrates, in order to evaluate the zeolitic material obtained. The Si and Al contents of the fly ash (FA) filtrates were used as precursor species for the alkaline hydrothermal conversion of the fly ash filtrates into zeolites. These filtrates were then analysed by XRF spectrometry for quantitative determination of SiO₂ and Al₂O₃. The [SiO₂]/[Al₂O₃] ratio obtained in the filtrates range from 1.4 to 2.5. The [SiO₂]/[Al₂O₃] ratio was used to predict whether the fly ash filtrates could successfully be converted into faujasite zeolitic material by the adopted synthesis procedures. If the [SiO₂]/[Al₂O₃] ratio is higher than 1.5 in the co-disposal filtrates, it favours the formation of faujasite. The zeolite synthesis included an alkaline fusion of the co-disposal filtrates, followed by aging for 8 hours and hydrothermal conversion by crystallisation at 100 °C. Different variables were investigated during the synthesis of zeolite to ascertain their influence on the end product. These variables include adding different amounts of deionised water to the FA-related starting material, using different compositions of FA related starting material and different FA:NaOH ratios in fusing the starting material.     

预成型高岭土干胶转化合成NaY型分子筛

通过干胶转化法制备了整体式NaY分子筛,采用XRD、SEM及XRF分析表征原料及产物,系统考察了合成体系的n（SiO₂）/n（Al₂O₃）、n（Na₂O）/n（SiO₂）、水量、晶化温度和晶化时间对整体式NaY分子筛制备的影响。结果表明,合成体系n（SiO₂）/n（Al₂O₃）=7.5时,骨架硅铝比（二氧化硅与氧化铝物质的量比）最大为6.12;n（Na₂O）/n（SiO₂）逐渐增大,整体式NaY分子筛结晶度逐渐升高,当n（Na₂O）/n（SiO₂）增至0.35时,会导致P型分子筛的生成;晶化温度从90 ℃逐渐增至120 ℃时,整体式NaY分子筛结晶度也随之升高;在110 ℃下晶化20 h,产物的结晶度达到98%并趋于稳定。干胶转化制备整体式NaY分子筛必须有水的参与,n（H₂O）/n（SiO₂）为4.2左右对反应物的成型及整体式NaY分子筛的晶化较为适宜。     

An anionic framework aluminophosphate |(CH2)6N4H3·H2O|[Al11P12O48] and computer simulation of the template positions

A new aluminophosphate compound |(CH₂)₆N₄H₃·H₂O|[Al₁₁P₁₂O₄₈] (denoted AlPO-CJB2) with a three-dimensional open framework and an Al/P ratio of 11/12 has been synthesized solvothermally by using hexamethylenetetramine as a template. It was characterized by X-ray powder diffraction, inductively coupled plasma, elemental (CHN), and thermogravimetric analyses, and the structure was determined by single-crystal X-ray diffraction analysis. AlPO-CJB2 crystallizes in the trigonal space group R-3c with a=14.088(2) Å, c=42.199(9) Å, and Z=6. Its structure features two new kinds of cages, i.e., cage 1, 4¹²4³6⁶8⁶ and cage 2, 4¹²6¹². The two cages alternate along the [0 0 1] direction forming an infinite column by sharing a common snowflake-like chiral motif, which is constructed from an AlO₆-centered six four-membered rings. The title compound is constructed from strictly alternating Al polyhedra (AlO₄ and AlO₆) and P tetrahedra (PO₄) via bridging oxygen atoms, and presents a new type of stoichiometry with an Al/P ratio of 11/12 in the aluminophosphate family. Computer simulation was used to determine the possible positions of the organic template within the cages.     

Synthesis of long zeolite-L crystals with flat facets

Synthetic conditions that produce long zeolite-L crystals in hexagonal columnar structures with flat basal and side planes were investigated. The gels with the molar compositions of Al₂O₃:SiO₂:K₂O:H₂O = a:b:c:d, where a = 1.3–2.0, b = 20–24, c = 10.2–10.5, and d = 1000–1400 and with Al₂(SO₄)₃ as the Al source produced zeolite-L with sharp edged hexagonal columnar structures and flat basal and side planes upon heating at 180 °C for 3 d. The crystal size, in particular the length, increased with increasing the SiO₂, H₂O, or Al₂O₃ content, but with decreasing the K₂O content. While the length increased, the width decreased upon increasing both Al₂(SO₄)₃ and H₂O contents, leading to the production of sharp-edged hexagonal columnar crystals. In the case where a = 1.7, b = 20, c = 10.9, and d = 1030, sharp edged hexagonal columnar crystals with the length up to 20 μm and the width of 2.3 μm were produced. When Al(OH)₃, a more commonly used Al source, was used instead of Al₂(SO₄)₃, crystals with blunt edges and round planes were produced. Furthermore, the size decreased with increasing the Al(OH)₃ content. While KCl and NaCl had a negligible effect on the morphology change, LiCl and MgCl₂ led to a dramatic decrease in size by 96% and 91%, respectively, even with in the presence of 0.2 and 0.001 equivalents, respectively, with respect to the amount of Al₂O₃ content. The addition of CaCl₂ led to the production of an unknown phase. The use of mixed base, i.e., the KOH and NaOH mixture in the mole ratio of 6:4.9, led to the formation of crystals whose one end was connected to a bundle of narrow and long crystals.     

无黏结剂ZSM-35沸石的制备与催化反应性能

考察了不同硅铝比无黏结剂ZSM-35沸石分子筛的合成条件及催化反应性能。以多种有机胺（乙二胺、环己胺、正丁胺）为模板剂,在SiO₂/Al₂O₃为30～40的情况下均可以水热合成无黏结剂ZSM-35沸石。在乙二胺模板剂体系中,ZSM-35合适的晶化温度为130～160℃。提高SiO₂/Al₂O₃至58时,在乙二胺和正丁胺模板剂体系下,合成产物易出现ZSM-5和石英相,而环己胺作为模板剂可以成功制备纯相的无黏结剂ZSM-35沸石。在SiO₂/Al₂O₃为72时,以乙二胺、环己胺、正丁胺为模板剂均难合成纯相ZSM-35沸石,易产生杂晶。在二甲苯异构化反应中,制备的ZSM-35沸石表现出比ZSM-5沸石更好的对二甲苯选择性和更低的二甲苯损失。     

New route for synthesizing Mn-silicalite-1

Mn-silicalite-1 (Mn_5.2Si_90.8O₁₉₂) was synthesized from Mn²⁺ ion-exchanged magadiite. The characteristics of Mn-silicalite-1 were investigated using electron spin resonance, synchrotron X-ray powder diffraction, IR spectroscopy and chemical analysis. The measurements indicate that Mn²⁺ ions replace Si in the silicalite-1 framework. The orthorhombic framework structure of calcined Mn-silicalite-1 has been determined. The space group is Pnma, with a=20.1017(3) Å, b=19.8826(4) Å, c=13.3758(3) Å.     

Revision of Charnell’s procedure towards the synthesis of large and uniform crystals of zeolites A and X

A critical replication and re-evaluation of Charnell’s procedure to the synthesis of zeolites A and X has been carried out, aiming at reliable protocols for preparation of large and uniform crystals of the respective zeolites in a scale of 50 g per batch. Triethanolamine, as an organic additive to the reacting sodium aluminosilicate hydrogel, increases the viscosity of the system, and reduces the reactivity of aluminium species towards nucleation and crystal growth through forming chelated complex compounds. The reactivity of silicate species has to be accordingly adjusted, by choosing proper source materials. Zeolite A crystals, which possess shapes of edge-truncated cubes, and sizes of 35–40 μm in edge-length, have been synthesized with a starting gel having the composition 1.7Na₂O:Al₂O₃:0.7SiO₂:165H₂O:6.1TEA in 2-l batch-size, using dissolved metallic aluminium and colloidal silica. The crystallization has been accomplished at 85 °C within 21 days. When the gel has a starting composition 2.3Na₂O:Al₂O₃:1.3SiO₂:300H₂O:10TEA (1-l batch), 70–80 μm large zeolite X crystals can be obtained at 85 °C in 35 days. Both starting gels are prepared at 0 °C, then quickly heated to the crystallization temperature.     

高硅铝比小晶粒NaY分子筛/高岭土复合物的合成及其催化裂化性能

以两种不同粒径的高岭土为原料,采用水热法合成了高硅铝比小晶粒NaY分子筛/高岭土复合物,通过XRD、SEM、晶粒度分析和N₂物理吸附等表征手段对复合物进行了结构和形貌表征。结果表明,与商品NaY相比,高岭土合成样品的结构稳定性和水热稳定性显著提高,以细化高岭土为原料合成样品的晶粒尺寸达310 nm,比表面积达807 m²·g^-1。以改性NaY分子筛/高岭土复合物为活性组分制备了催化裂化催化剂,采用NH₃程序升温脱附(NH₃-TPD)技术对其酸性特征进行了分析,并在小型微反装置上对其重油催化裂化性能进行了评价。研究结果发现,随着骨架硅铝比增大,催化剂表面酸中心强度增加,而酸量下降。采用细化高岭土合成的NaY分子筛/高岭土复合物的分子筛晶粒更小,催化剂酸中心数量以及催化裂化性能均大幅度提升。随着高温焙烧高岭土/偏高岭土质量比的增加,合成产物中的高岭土基质含量增加,催化剂表面酸中心强度下降。以原料高温焙烧高岭土/偏高岭土质量比为0.5,骨架硅铝比为6.1(摩尔比)的样品制备的催化剂,去柴重油转化率高达85.4%,同时有高达64.2%的汽油收率,表现出优异的重油催化裂化性能。     

超稳Y型分子筛的骨架硅铝比对甘油气相脱水反应的影响

以铵交换和高温水热处理法制备了不同硅铝比的超稳Y型分子筛（USY）,利用X射线衍射、扫描电镜、氮气吸附脱附和吡啶红外等技术对USY进行了表征。以USY为催化剂,考察了USY的骨架硅铝比对气相甘油脱水制丙烯醛的影响。X射线衍射和扫描电镜结果表明,铵交换和高温水热处理只是提高USY的硅铝比,相对结晶度略有降低,而对Y型分子筛的结构和形貌没有影响。氮气吸附-脱附和吡啶红外结果表明,随USY骨架SiO₂/Al₂O₃比提高,总酸量和B酸酸量逐渐降低,L酸酸量有所增多,介孔孔体积和平均孔径有所增大。气相甘油脱水反应结果表明,催化剂织构性质对甘油转化率和丙烯醛选择性的影响大于酸性的影响,因而SiO₂/Al₂O₃比为29的USY催化剂的反应性能最好,甘油转化率和丙烯醛收率分别达到了84.5%和51.8%。     

Oxidation state of palladium as a factor controlling catalytic activity of Pd/SiO2–Al2O3 in propane combustion

The oxidation state of palladium on SiO₂–Al₂O₃ used for propane combustion was examined by XPS and XRD, and the correlation of the catalytic activity with the oxidation state of palladium was systematically studied. The propane conversion over 5 wt% Pd/SiO₂–Al₂O₃ was measured in the range 1.0≤S≤7.2 (S is defined as [O₂]/5[C₃H₈] based on stoichiometric ratio). The propane conversion strongly depended on the S value and reached the maximum at S=5.5. The oxidation state of palladium also changed with the S value; palladium particles were more oxidized under the reaction mixture of higher S value. On the sample used for the reaction at S=5.5, both of metallic palladium and palladium oxide were found. It is concluded that partially oxidized palladium which has optimum ratio of metallic palladium to palladium oxide shows the highest catalytic activity in propane combustion.     

(CH3CH[NH3]CH2NH3)1/2·ZnPO4, a zincophosphate analogue of aluminosilicate zeolite thomsonite

The synthesis and structure of (CH₃CH[NH₃]CH₂NH₃)_1/2·ZnPO₄, an organically templated zincophosphate (ZnPO) analogue of aluminosilicate zeolite thomsonite (THO), are described. The ZnPO framework is built up from an alternating, vertex-sharing, network of ZnO₄ and PO₄ groups (d_av(Zn–O)=1.944 (8) Å, d_av(P–O)=1.535 (9) Å, θ_av(Zn–O–P)=130.5°) involving distinctive 4=1 secondary building units. The 1,2-diammonium propane cations are highly disordered in the [0 0 1] 8-ring channels. Crystal data: (CH₃CH[NH₃]CH₂NH₃)_1/2·ZnPO₄, M_r=198.42, orthorhombic, space group Pncn (no. 52), a=14.119 (6) Å, b=14.136 (5) Å, c=12.985 (5) Å, V=2591 (3) ų, Z=10, R(F)=0.057, R_w(F)=0.061 (for a twinned crystal).     

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.     

Preparation and crystal structure of RUB-18 modified for synthesis of zeolite RWR by topotactic conversion

The systematic study on the synthetic route of the siliceous zeolite RWR with a small 8-MR straight channel by topotactic conversion of crystalline layered silicate RUB-18 was carried out by using several topotactic precursors obtained from Na-RUB-18. Intermediate layered structures of topotactic precursors were designed by intercalation of amine molecules and acid treatment. Crystal structures of two kinds of TMAOH intercalated RUB-18s (TMA-RUB-18-poly1 and TMA-RUB-18-poly2) and their acidified TMA-RUB-18 were determined by ab initio structure analysis using X-ray powder diffraction data. The layered structure of TMA-RUB-18-poly1 and TMA-RUB-18-poly2 had tetragonal symmetry of space group P4₂/nmc, and the lattice parameters were estimated to be a = 7.4121 Å, c = 22.615 Å for TMA-RUB-18-poly1 and a = 7.3718 Å, c = 29.342 Å for TMA-RUB-18-poly2. Two silicate layers were involved in a unit-cell and TMA⁺ cations were intercalated in the interlayer. The layer stacking sequence was completely different from that of Na-RUB-18. Structure of acidified TMA-RUB-18 had also tetragonal symmetry of space group I4₁/amd and lattice parameters a = 7.4722 Å, c = 37.242 Å with four silica layers. Stacking sequence in acidified TMA-RUB-18 was similar to that of Na-RUB-18 although a large shrinking of interlayer distance (ca. 2.0 Å) was observed. In the acidified TMA-RUB-18, one-dimensional pseudo pore was constructed by semi-circular geometry derived from the framework structure and stabilized by formation of hydrogen bonding between the terminal silanol groups, which faced each other with atomic distance d(O–O) of ca. 2.5 Å. By the dehydration–condensation of silanol groups during careful calcination, zeolite RWR could be successfully prepared from the acidified TMA-RUB-18.     

Hydrodesulfurization over noble metals supported on ZSM-5 zeolites

Pt/HZSM-5 showed high and stable catalytic activity for the hydrodesulfurization of thiophene at 400°C and its catalytic activity was higher than that of commercial CoMo/Al₂O₃ catalyst. Pt/HZSM-5 zeolite was not poisoned by hydrogen sulfide in the hydrodesulfurization of thiophene and hydrocracking of hydrocarbons. The catalytic activity of Pt/HZSM-5 decreased with increase of SiO₂/Al₂O₃ ratio in HZSM-5. The Brønsted acid site of HZSM-5 and spillover hydrogen formed on Pt particle in Pt/HZSM-5 catalyst play an important role for the hydrodesulfurization of thiophene.     

Conversion and in situ FTIR studies of direct NO decomposition over Cu-ZSM5

Copper ion-exchanged zeolites ZSM5 with SiO₂:Al₂O₃ molar ratios 33 and 53 have been subjected to activity tests for direct decomposition of NO (2000 ppm, GHSV 560–5400 h⁻¹). In situ infrared measurements were used to follow the reaction and surface and gas phase compositions. IR studies were also done in excess oxygen with rapid NO₂ formation in the gas phase.

A high level of overexchange of copper in the zeolite in combination with a low concentration of acid sites, concurrent with a high SiO₂:Al₂O₃ ratio, enhances the conversion of NO. A vibrational band at 1631 cm⁻¹ is observed below the light-off temperature and interpreted as a bridged nitrato group bound to Cu²⁺–O–Cu²⁺ dimers. This band disappears above the light-off temperature but the intensity below this temperature correlates with the catalytic activity. We interpret that these bridge bound nitrato groups act as siteblockers on the active sites for NO conversion and that a tentative reaction intermediate, N₂O₃, also binds in a bridge configuration to the same Cu²⁺–O–Cu²⁺ dimers.

A second nitrato group with unidentate coordination and vibrational bands at 1598/1575 cm⁻¹ probes isolated copper ions.

A third infrared band at 2130 cm⁻¹ confirms previous observations of -ions bound to the zeolite. We conclude that these species are coordinated to deprotonated and negatively charged sites on the zeolite and that these sites for adsorption are blocked by Cu²⁺ ion-exchange. The 2130 cm⁻¹ species appear to have no role in direct NO decomposition but the adsorption sites are crucial for the stability of the zeolite and intimately related to ion mobility in the lattice.

Prolonged immersion of the zeolite in dilute solutions of copper ions improves the catalyst performance by copper hydroxylation leading to enhanced formation of the above dimers.

A high SiO₂:Al₂O₃ ratio leads to more stable catalysts, particularly in combination with a modest overexchange of copper ions. Excessive amounts of copper escalates the deactivation of the Cu-ZSM5 catalyst through the migration and sintering of cupric oxide crystallites.     

Synthesis, structure and thermal properties of a novel 3D aluminophosphate UiO-26

The synthesis of a novel 3D aluminophosphate is described. The thermal properties of the material were investigated, and the existence of three high-temperature variants was revealed. The crystal structures of the as-synthesized material (UiO-26-as) and the material existing around 250°C (UiO-26-250) were solved from powder X-ray diffraction data. UiO-26-as with the composition [Al₄O(PO₄)₄(H₂O)]²⁻[NH₃(CH₂)₃NH₃]²⁺ crystallizes in the monoclinic space group P2₁/c (no. 14) with a=19.1912(5), b=9.3470(2), c=9.6375(2) Å and β=92.709(2)°. It exhibits a 3D open framework consisting of connections by PO₄ tetrahedra with AlO₄ tetrahedra, AlO₅ trigonal bipyramids and AlO₅(H₂O) octahedra forming two types of layers stacked along [1 0 0] and connected by Al–O–P bondings. The structure possesses a 1D 10-ring channel system running along [0 0 1], in which doubly protonated 1,3-diaminopropane molecules are located. UiO-26-250 with the composition [Al₄O(PO₄)₄]²⁻[NH₃(CH₂)₃NH₃]²⁺ crystallizes in the monoclinic space group P2₁/c with a=19.2491(4), b=9.27497(20), c=9.70189(20) Å and β=93.7929(17)°. The transformation to UiO-26-250 involves removal of the water molecule which originally is coordinated to aluminum. The rest of the structure remains virtually unchanged. The crystal structures of the two other variants existing around 400 (UiO-26-400) and 600°C (UiO-26-600) remain unknown.     

Factors controlling the selectivity of V2O5 supported catalysts in the oxidative dehydrogenation of propane

The surface properties of a series of V₂O₅ catalysts supported on different oxides (Al₂O₃, H–Na/Y zeolite, MgO, SiO₂, TiO₂ and ZrO₂) were investigated by transmission electron microscopy and FTIR spectroscopy augmented by CO and NH₃ adsorption. In the case of the V₂O₅/SiO₂ system TEM images evidenced the presence of V₂O₅ crystallites, whereas such segregated phase was not observed for the other samples. VO_x species resulted widely spread on the surface of Al₂O₃, H–Na/Y zeolite, MgO and SiO₂, whereas on TiO₂ and ZrO₂ they are assembled in a layer covering almost completely the support. Furthermore, evidences for the presence in this layer of V–OH Brønsted acid sites close to the active centres were found. It is proposed that propene molecules primarily produced by oxydehydrogenation of propane can be adsorbed on this acid centres and then undergo an overoxidation by reaction with redox centres in the neighbourhood. This features could account for the low selectivity of V₂O₅/TiO₂ and V₂O₅/ZrO₂ catalysts.     

硅锰渣复合粉煤灰水热合成NaA沸石及其表征

对硅锰渣进行高温煅烧预处理,并复合粉煤灰作为原料,采用水热法合成了结晶度良好的NaA沸石。研究了硅铝比(n(SiO₂)/n(Al₂O₃))、碱度(c(NaOH))、水热温度以及水热时间等条件对合成产物的影响。结果表明:在煅烧硅锰渣与粉煤灰以质量比为1∶1,n(SiO₂)/n(Al₂O₃)=2.2,反应温度为90 ℃,碱度为2 mol/L,反应时间为4 h的条件下即可合成结晶度良好且具备一定热稳定性的NaA沸石。相较于传统的以粉煤灰为原料合成NaA沸石,本实验掺入硅锰渣形成复合体系,为硅锰渣的资源化利用提供了新途径。     

New ceria-based catalysts for pollution abatement

In the present work, we describe the use of fluorite-structured solid solutions, based on mixtures of CeO₂/La₂O₃/Pr₂O₃, and similar systems, i.e. CeO₂/Ln₂O₃/Pr₂O₃ where Ln=Tb, Sm, and Gd as effective catalysts for methane combustion. Mixed lanthanide oxide doped ceria solid solutions were prepared using an evaporation method from nitrate precursors and were subsequently calcined to 1073 K. Sample characterisation was achieved using powder X-ray diffraction (PXRD) and temperature programmed reduction (TPR). PXRDs obtained subsequent to a 12 h calcination at 1073 K for 12 h all show peaks corresponding to a fluorite-based structure. There are no additional features suggestive of large-scale segregation or ordered superstructure formation. This was confirmed by Rietveld analysis which showed that the lattice possesses cubic nature with a=b=c=5.50 Å. Methane combustion tests show that the most effective catalysts are those lanthanide oxide doped ceria catalysts prepared with 5% Pr molar metal ratios. TPR experiments suggest PrO₂ is an essential component and both surface and bulk chemistries have important roles in catalytic activity.     

H-beta分子筛催化苯胺缩合制备二苯胺

对苯胺缩合生成二苯胺用H-beta分子筛催化剂进行研究,考察分子筛硅铝比和NH_4F改性对H-beta分子筛催化苯胺缩合反应的影响,采用NH_3-TPD和Py-IR对催化剂进行表征。结果表明,B酸是催化苯胺缩合的活性中心,低硅铝比与适当卤素处理均可提高B酸含量,有利于缩合反应。反应温度320℃,空速0. 2 h~(-1),0. 125 mol·L~(-1)的NH_4F溶液处理硅铝比为25的H-beta分子筛上,二苯胺的收率达到34. 68%。基于催化活性位点的研究,探讨了苯胺缩合反应机理。