•Seed crystal was used to synthesize zeolite EMC-2 from organic-template-free system.•XRD patterns of EMC-2 matched well with the one synthesized by 18-crown-6 ether.•EMC-2 crystals preferentially grew along the <001> direction of seed crystals.EMT-type zeolite has been prepared by usage of seed directed method from an organic-template-free system (named as EMC-2-SOF). Powder X-ray diffraction (XRD) patterns verified that the diffraction patterns of EMC-2-SOF matched very well with EMC-2 synthesized using 18-crown-6 ether as template. EMT-type zeolite with complete diffraction patterns was prepared at high OH−/SiO2 ratio (more than 2.0) and low temperature (50 °C) for 3 days. It has been found that, without organic template, calcined EMC-2 (denoted as EMC-2-C) showed better directing effect than as-synthesized one for the synthesis of EMC-2-SOF. Besides, the variation of SiO2/Al2O3 molar ratio in original gel for synthesizing EMC-2-SOF was affected by OH−/SiO2 ratio. A best fit between the ratio of SiO2/Al2O3 and OH−/SiO2 has been achieved. At OH−/SiO2 = 2.0, the relative crystallinity of EMC-2-SOF first increased, then got to 100% at SiO2/Al2O3 = 50, and finally decreased with SiO2/Al2O3 ratio increasing. Meanwhile, by changing H2O/SiO2 ratio from 46.6 to 30, yield of EMC-2-SOF increased from 15.8 to 33.4 wt.%. A relationship of mutual compensation among three intensive parameters in preparing zeolites (alkaline, temperature and crystallization time) has been used to improve the crystallinity of EMC-2-SOF. When gels with SiO2/Al2O3 = 25, OH−/SiO2 = 2.0, H2O/SiO2 were crystallized at 55 °C for 12–20 h, all the samples had crystallinity above 100% with the yield over 25 wt.%.

•1,6-Hexamethylenediamine was used to investigate the state of small amine molecules in forming microporous metal phosphates.•The aggregates of small amine molecules not favors the formation of three dimensional frameworks.•Interaction of phosphates and individual amine molecule is the key to form large pores in metal phosphates or phosphites.A series of 1,6-hexamethylenediamine (1,6-HDA) solutions with different concentrations were prepared and used as the structure directing agents for the crystallization of microporous materials. The surface tension of these solutions has been measured to inspect the assembly behavior of 1,6-HDA molecules. It has been found that the surface tension of these solutions decrease with the increase of 1,6-HDA concentration, which is similar to what in surfactant CTAB (Cetyl trimethyl ammonium bromide) solutions. When they were used to direct the crystallization of aluminophosphites, zincophosphates, and aluminophosphates, it was found that at low concentration, 1,6-HDA molecules cannot affect the crystallization process, and three-dimensional frameworks without 1,6-HDA in it were obtained. When 1,6-HDA concentration increased, the surface tension of these solution decreased sharply, and 1,6-HDA containing three-dimensional (3-D) frameworks were formed. 1,6-HDA molecules retained in these structure were not in assembling state, but in independent state. At high 1,6-HDA concentration, the surface tension of the solutions changed slowly accompanying with the assembly of 1,6-HDA molecules. It always resulted in the formation of layered structures with the inorganic layers interleaved by composite layers of diprotonated 1,6-HDA. Formation of large-micropore containing 3-D frameworks mainly resulted from the interaction between inorganic framework and organic amine at proper ratio, not from the assembly of 1,6-HDA molecules. Otherwise, the aggregates of 1,6-HDA molecules favors the formation of layered materials.1,6-Hexamethylenediamine (1,6-HDA) solutions with different concentrations were used to investigate the state of small organic amine molecules for the formation of crystalline microporous metal phosphates. The conclusion that the aggregates of 1,6-HDA molecules not favors the formation of three dimensional frameworks has been obtained.

Triclinic AlPO4-34 arises from HF with fluoride ions located in the double Al–F–Al bridges. Previously, it has only been obtained in the presence of fluorine. In the present paper, a new synthetic method has been explored for the preparation of a microporous crystalline framework of triclinic AlPO4-34 avoiding the use of toxic HF acid. Fluoride-free triclinic AlPO4-34 (named as AlPO4-34FF) has been prepared by using a mixture of water and ethylene glycol as the mixing solvent. The effects of morpholine and ethylene glycol on the crystallization of AlPO4-34FF have been investigated by combining it with the model for constructing aluminum phosphate frameworks. It has been found that the stability of double Al–OH–Al bridges during crystallization is key for the formation of AlPO4-34FF. High morpholine concentration and a suitable ratio of ethylene glycol/water will regulate the extent of hydrolysis and condensation reaction to keep double Al–OH–Al bridges stable and play important roles in the crystallization. Meanwhile, the narrow crystallizing area for crystallizing AlPO4-34FF in mixing solvent has been understood by successfully using the quantitative relationship of 3 ethylene glycol molecules bonding to 4 water molecules in the mixing solvent. On this basis, fluoride-free crystallization of triclinic AlPO4-34 has been achieved in an aqueous system by limiting the water content in the gel to control the degree of hydrolysis and condensation of the reacting active species. Powder XRD patterns and single crystal refinement have verified the formation of this fluoride-free triclinic AlPO4-34 phase. A vibration band from diffuse reflectance FT-IR spectroscopy at 3640 cm−1 provides the information of a double Al–OH–Al bridge in triclinic AlPO4-34. Thermal analysis has shown that a double Al–OH–Al bridge is weaker than a double Al–F–Al bridge and led to the fluorine-free triclinic AlPO4-34 (space group P) to transform into AlPO4-34 (space group R) at lower temperatures.

In the family of microporous aluminophosphate, AlPO4-9 is one of the members reported first in 1982. However, its structure and characteristics have not been known up to now, and this makes it a special member. In the present work, AlPO4-9 has been synthesized using piperazine as the structure-directing agent and the mixture of H2O and EG as the solvent. Structure refinement from single crystal X-ray diffraction data shows that AlPO4-9 is a material with the composition of C2H7Al5.50NO25P6. It crystallizes in the monoclinic space group C2/c (No: 15), with a = 24.230(5) Å, b = 14.026(5) Å and c = 16.197(3) Å, β = 119.87(4)°, V = 4773(2) Å3, Z = 8. The open-framework of AlPO4-9 is built of alternating corner-sharing PO4 tetrahedra and AlO4 tetrahedra (AlO6 octahedra) to construct a curved one-dimensional 8-ring channel system running along [1 0 1]. Meanwhile, the strict alternative of PO4 tetrahedra and AlO4 tetrahedra (AlO6 octahedra) results in a negative framework in AlPO4-9. Thermal stability has been determined on a thermal analyzer and by calcination. It reveals that AlPO4-9 framework is thermally stable and has a potential to be a catalytic material.Graphical abstractHighlights► Large single crystals of AlPO4-9 molecular sieves have been synthesized. ► Structure of AlPO4-9 has been obtained from the single crystal refined. ► Bronsted acid sites in the framework of AlPO4-9 are induced.

Morphology of AFO-topology molecular sieves has been identified from the large individual crystals of AlPO4-41 and SAPO-41, which were synthesized from three routes: (1) using H3PO3 as the phosphorus source; (2) the mixture of H3PO3 and H3PO4 being used as the phosphorus source; (3) an aluminophosphite NKX-2 used as the aluminum and phosphorus source, respectively. Shape clear large individual crystals of AlPO4-41 with the aspect ratio being 3.0 have been obtained from the in situ transformation of NKX-2. It has been found that H3PO3-containing systems not only favor the formation of AFO-structure molecular sieves, but also promote the growth of their large crystals. The crystal morphology of AlPO4-41 has been identified as octagonal prisms. Furthermore, SAPO-41 crystals with lower aspect ratio (being 0.25) have been obtained. It is notable that if silicon is incorporated in the AFO framework, further crystallization may be hindered, resulting in the formation of plate-like crystals just similar to what happened in AFI-structure. Besides, as the aspect ratio decreases, the diffraction intensities of planes in XRD patterns such as (1 0 0), (0 2 0) (2 1 0), and (1 3 0) decrease, whereas the intensity of (0 0 2) increases remarkably.Graphical abstractPerfect single crystals of AlPO4-41 have been obtained from the transformation of phosphorus valence route. Veil vestured on AFO-structure crystals has been uncovered with the octahedral prism morphology of AlPO4-41 and SAPO-41 crystals being discriminated.Research highlights► Large individual crystals of AFO-type molecular sieves have been obtained. ► Octagonal prisms morphology of AlPO4-41 and SAPO-41 crystal is discriminated. ► The transformation of phosphorus valence favor the growth of AlPO4-41 crystals.

SAPO-46 molecular sieve has been synthesized on a new one-step route by using phosphorous acid (H3PO3) or the mixture of H3PO3 and phosphoric acid (H3PO4) as the phosphorus source. It has been found that the pure phase of SAPO-46 could be obtained more conveniently from the H3PO3-containing gels at 200 °C. Meanwhile, SAPO-46 with higher crystallinity can be synthesized in a wide range of gel compositions, containing higher silica in the product. As the catalyst for the dehydration of methanol to dimethyl ether (DME), it has exhibited high selectivity for the formation of DME as well as the activity of methanol conversion. Raman and IR have been employed to characterize the initial gel and as-synthesized sample to investigate the formation of SAPO-46 and the one-template-multiple-structures phenomena in the new one-step route, where SAPO-41 or SAPO-46 can be formed according to silica concentration. The transformation of P(III) species in the initial gels to P(V) species during crystallization have been found. It may be the key role for the formation of SAPO-46 on the new route. Besides, the correlation between silica content and the structure type of crystalline products with di-n-propylamine as the template has also been obtained.The synthesis and catalysis of SAPO-46, which is synthesized as a pure phase from a one-step route in the presence of H3PO3 as the phosphorus source, have been described. It is used first as the catalyst for the formation of dimethyl ether from methanol with dimethyl ether selectivity 98.0% and higher conversion of methanol.

The in situ decomposition of tetraethylene-pentamine, triethylenetetramine, or diethylenetriamine has been controlled to direct the synthesis of three open-framework cobalt−zinc phosphates, CoZnPO4-I, CoZnPO4-II, and CoZnPO4-III. These phosphates can be synthesized as the intergrowth from a single gel at 200 °C in the presence of diethylenetriamine with propylamine as the assistant organic additive. Structure analysis reveals that species encapsulated in the structures of CoZnPO4-I, CoZnPO4-II, and CoZnPO4-III are ammonium, ethylenediaminum, and diethylenetriaminum, respectively, which can be attributed to the in situ decomposition of diethylenetriamine molecules during the crystallization procedure. It has been found that the presence of second organic amine redound to controlling the decomposition of these linear polyamines, such as diethylenetriamine, to form these three CoZnPO4 materials from a single gel. Pure phase of CoZnPO4-I, CoZnPO4-II, and CoZnPO4-III have also been obtained by varying assistant amines, crystallizing at a lower temperature, or using other linear polyamines, such as triethylenetetramine or tetraethylene-pentamine instead of diethylenetriamine as the main organic additives. Single-crystal X-ray diffraction analysis has shown that CoZnPO4-I is a novel metal phosphate. It crystallizes in hexagonal space group p63 (No.173), with a = 10.7207(5) Å, c = 8.7241(8) Å, V = 868.36(10) Å3, and Z = 4. Its three-dimensional framework can be considered as the stacking of six-ring sheet with the combination of UDUDUD (U, upward; D, downward) and UUUDDD linkages in the proportion 1:3. Its negative framework is charge-compensated by NH4+ cations, which are encapsulated in 694(6) cage of the structure. CoZnPO4-II crystallizes in the tetragonal system, space group P42bc (No. 106), with a = b = 14.694(2) Å, c = 8.936(2) Å, V = 1929.4(6) Å3, and Z = 8, possesses DFT topology, and is built of ZnO4 (or CoO4), and PO4 tetrahedra with ethylenediaminum cation resided in the 8-member ring channels to compensate the negative framework charge. The three-dimensional architecture of CoZnPO4-III crystallizes in the trigonal system, space group R̅ (No. 148), with a = 13.5393(8) Å, c = 15.0443(10) Å, γ = 120°, V = 2388.3(3) Å3, and Z = 3, is built up of ZnO4(or CoO4), PO4 tetrahedra, and CoO6 octahedra with diethylenetriaminums encapsulated in the channels.

In the report, H3PO3 was used in place of H3PO4 as the phosphorus source to synthesize chabazite structure silicoaluminophosphate (SAPO) molecular sieves, SAPO-34, SAPO-44, and SAPO-47. It has been found that the directing effects of organic bases have met with a competition coming from the alternation of phosphorus source. For example, using H3PO4 as the phosphorus source, morpholine and triethylamine are two well known organic bases for directing the formation of SAPO-34. However, when H3PO3 or the mixtures of H3PO3 and H3PO4 are used as the phosphorus source, the directing product has changed from SAPO-34 to SAPO-47. Raman investigation has shown that there are some P(III) species in the intermediates for crystallizing SAPO-47. It means that chabazite structure SAPO molecular sieves are formed from a new route containing the transformation of P(III) to P(V) species. Meanwhile, the host–guest interactions between organic bases and SAPO framework have been studied and used to discuss why SAPO-47 is the preferable crystallizing product in the presence of H3PO3. Moreover, the competitive effect of phosphorus source H3PO3 on the synthesis of SAPO-47 has met its limitation when employing cyclohexylamine as the structure-directing agent. It has shown that no matter using H3PO3 or the mixture of H3PO3 and H3PO4 as the source of phosphorus, SAPO-44 is always the crystallizing product.

The pure phase of AlPO4-41 molecular sieve has been synthesized in a new reproducible route by using Phosphorous acid (H3PO3) or the mixture of H3PO3 and phosphoric acid (H3PO4) as the phosphorus source. It was found that gels containing H3PO3 favor the formation of AlPO4-41. Raman and IR investigation showed that P(III) species has transformed to P(V) species after crystallization. AlPO4-41 has been obtained as a high crystallinity pure phase in a wide range of gel compositions. When the mixed phosphorus source of H3PO3 and H3PO4 were used, the crystallization of AlPO4-41 was accelerated.