Hydrothermal Conversion Of FAU Zeolite Research Articles

Synthesis of Phosphorus-Modified AFX Zeolite by the Hydrothermal Conversion of Tetraalkylphosphonium Hydroxide-Impregnated FAU Zeolite

Abstract Phosphorus-modified AFX zeolite was synthesized by the hydrothermal conversion of FAU zeolite, which was impregnated with tetraethylphosphonium hydroxide (TEPOH). For the optimization of the introduced phosphorus, we investigated the influence of the loaded amount of TEPOH on FAU zeolite and tested the combination of the starting materials, composed of phosphorus-free and TEPOH-impregnated FAU zeolites. The synthesis system, employing the combined starting materials, effectively incorporated phosphorus into AFX zeolite while the TEPOH-impregnated FAU zeolite was not effective as a solo starting material. X-ray diffractometry, N2 adsorption, and elemental analysis were employed to confirm the high purity of the AFX zeolite, obtained from the utilization of combined starting materials. Moreover, 13C and 31P magic angle spinning (MAS) NMR spectroscopy further revealed the modification of phosphorus in which the phosphorus species interacting with the zeolite framework was formed via the decomposition of tetraethylphosphonium (TEP) by calcination.

Synthesis of GME zeolite with high porosity by hydrothermal conversion of FAU zeolite using a dual-template method with tetraethylphosphonium and N,N-dimethyl-3,5-dimethylpiepridinium hydroxides

Highly crystalline gmelinite (GME) zeolites with Si/Al ratio of ~ 3 were successfully synthesized from FAU zeolites as the starting silica/alumina source using the dual-template method with a mixture of tetraethylphosphonium and N,N-dimethyl-3,5-dimethylpiepridinium cations as an organic structure-directing agent (OSDA). It was also found that the prepared GME zeolite exhibited high porosity when the as-made GME zeolite was K+ ion-exchanged and then calcined at 580 °C at 6 h to remove OSDAs in the zeolitic pores.

Phosphorus modified small-pore zeolites and their catalytic performances in ethanol conversion and NH3-SCR reactions

Small-pore zeolites, composed of 8-membered ring windows, exhibit high catalytic performances in the selective catalytic reduction of NOx with ammonia (NH3-SCR) and the light olefin production from methanol or ethanol (MTO or ETO). As these processes are performed at high reaction temperatures in the presence of steam, the enhancement of the thermal and hydrothermal resistances of zeolites is essential for the development of high-performance catalysts that retain their high catalytic activity and selectivity. This paper reports on the syntheses of phosphorus-modified small-pore zeolites with high thermal/hydrothermal stabilities, prepared by the hydrothermal conversion of FAU zeolite in the presence tetraalkylphosphonium cations as both organic structure directing agents and phosphorus modifying agents. Several phosphorus-modified small-pore zeolites with different framework structures and a controlled phosphorus modification degree were synthesized. Moreover, it was found that the phosphorus-modified small-pore zeolites exhibit a good catalytic activity and durability in the NH3-SCR and ETO processes even after severe thermal or hydrothermal treatment.

Facile synthesis of highly crystalline EMT zeolite by hydrothermal conversion of FAU zeolite in the presence of 1,1’-(1,4-butanediyl)bis(1-azonia-4-azabicyclo [2,2,2]octane) dihydroxide

Abstract Hydrothermal conversion of cubic (FAU) zeolite into hexagonal (EMT) zeolite using 1,1’-(1,4-butanediyl)bis (1-azonia-4-azabicyclo [2,2,2]octane) dihydroxide ([Dab-4]2+(OH)2) instead of 1,4,7,10,13,16-hexaoxacyclooctadecane (18-crown-6), a well-known organic structure-directing agent (OSDA) for the synthesis of EMT zeolite, was investigated. A systematic study concerning hydrothermal synthesis parameters such as H2O/SiO2, NaOH/SiO2, and [Dab-4]2+(OH)2/SiO2 ratios in the starting synthesis mixture, and temperature and time of synthesis revealed that pure, highly crystalline EMT zeolite can be easily obtained within a short crystallization period of 6 h.

Synthesis of phosphorus-modified AFX zeolite using a dual-template method with tetraethylphosphonium hydroxide as phosphorus modification agent

Hydrothermal conversion of FAU zeolite was carried out in the presence of both 1,1'-(1,4-butanediyl)bis(1-azonia-4-azabicyclo[2,2,2]octane) (Dab-4) cation as a structure-directing agent and tetraethylphosphonium (TEP) cation as a phosphorus modification agent. By optimizing the synthesis parameters such as the TEPOH/SiO2, [Dab-4](OH)2/SiO2, NaOH/SiO2, and H2O/SiO2 ratios in the starting reaction mixtures, we successfully synthesized highly crystalline phosphorus-modified (P-modified) AFX zeolite with truncated hexagonal bipyramidal morphology. The P-modification of the AFX zeolite needed a TEP/(Dab-4+TEP) ratio higher than 0.9 because TEP cations have no structure-directing ability for the AFX phase. The obtained P-modified AFX zeolite with a Si/Al ratio of 5–6 and a P/Al ratio of 0.07–0.2 exhibited high thermal stability compared to the P-free one.

Incorporation of various heterometal atoms in CHA zeolites by hydrothermal conversion of FAU zeolite and their performance for selective catalytic reduction of NOx with ammonia

Heterometal atom incorporation in CHA aluminosilicate zeolites ([Al, M]-CHA, M = Fe, Ga, Sn) was successfully achieved by hydrothermal conversion of heterometal-incorporated FAU aluminosilicates ([Al, M]-FAU). X-ray powder diffraction (XRD), scanning electron microscopy, diffuse reflectance UV–vis spectroscopy, magic angle spinning NMR, and nitrogen adsorption measurements confirmed the formation of [Al, M]-CHA zeolites with heterometal atoms occupying homogeneously distributed tetrahedral coordination sites. The choice of hydrothermal conversion using [Al, M]-FAU was prompted by the inability to produce [Al, M]-CHA zeolites from amorphous hydrogels. The hydrothermal conversion of [Al, Fe]-FAU to [Al, Fe]-CHA was characterized by XRD, electrospray ionization mass spectrometry, and UV–vis spectroscopy. Analyses of liquid and solid phases during synthesis indicated that metal species present in the solid phase play an important role in the transformation process. We also investigated the effectiveness of Cu-loaded CHA zeolites for the selective catalytic reduction (SCR) of NOx by ammonia (NH3-SCR). Catalytic performance depended strongly on the kind and/or amount of heterometal atom in the [Al, M]-CHA zeolite. Although all fresh catalysts exhibited similar NO conversion efficiencies, there was a difference in NH3 conversion effectiveness at low reaction temperatures. Cu-loaded [Al, Ga]-CHA provided almost 100% NH3 conversion at 150 °C. The [Al, Sn]-CHA catalyst exhibited high stability even after hydrothermal treatment at 900 °C for 4 h. These results confirm hydrothermal conversion as an effective method for synthesizing heterometal-incorporated zeolite catalysts with high NH3-SCR performance.

Nanosized CHA zeolites with high thermal and hydrothermal stability derived from the hydrothermal conversion of FAU zeolite

Nanosized CHA zeolites approximately 100 nm in size with high thermal and hydrothermal stability were synthesized by hydrothermal conversion of FAU zeolites in the presence of N,N,N-trimethyl-1-adamantammonium hydroxide (TMAdaOH) as a structure-directing agent. The crystal size of CHA zeolites depended strongly on the silica/alumina source (FAU zeolite or amorphous aluminosilicate hydrogel) and the Si/Al ratio of starting material. An increase in the hydrothermal synthesis temperature enhanced the thermal stability of nanosized CHA zeolites without increasing the crystal size, and the structural framework of the nanosized CHA zeolites was maintained even after thermal treatment at 1000 °C for 1 h. The potential of nanosized CHA zeolites as solid acid catalysts and as catalyst supports was evaluated by the ethanol conversion reaction and the selective catalytic reduction (SCR) of NOx with NH3, respectively. A protonated nanosized CHA zeolite catalyst effectively produced propylene from ethanol by suppressing catalytic deactivation arising from carbonaceous deposition. A Cu-loaded nanosized CHA zeolite catalyst exhibited good performance for the NH3-SCR of NOx even after hydrothermal treatment at 900 °C for 4 h. The results indicate that hydrothermal zeolite conversion is very effective in producing nanosized CHA zeolites with high thermal and hydrothermal stabilities.

Synthesis of LEV zeolite by interzeolite conversion method and its catalytic performance in ethanol to olefins reaction

The highly crystalline and pure LEV zeolite was obtained from the hydrothermal conversion of FAU zeolite as a crystalline aluminosilicate source in the presence of choline hydroxide. As LEV zeolite was not obtained from a conventional amorphous aluminosilicate gel, the advantage and uniqueness of the hydrothermal conversion of FAU zeolite was proven. The hydrothermal conversion of FAU zeolite into LEV zeolite depended significantly upon the Si/Al ratio of the starting FAU zeolite. Only the FAU zeolites with Si/Al ratios of 16–22 were converted into LEV zeolite. Most of all choline species as a SDA existed intact in zeolitic pores. As expected, the protonated LEV zeolite exhibited a good performance for conversion of ethanol to light olefins. The product yields were 35.8% of C 2H 4 and 34.4% of C 3H 6.

Synthesis of High-silica CHA Zeolite from FAU Zeolite in the Presence of Benzyltrimethylammonium Hydroxide

Abstract A highly crystalline and pure high-silica chabazite zeolite with a Si/Al ratio of ca. 17 was obtained by the hydrothermal conversion of FAU zeolite used as a crystalline Si/Al source in benzyltrimethylammonium hydroxide media.

Hydrothermal conversion of FAU zeolite into aluminous MTN zeolite

The hydrothermal conversion of FAU zeolite into aluminous MTN zeolite is described here. In the presence of both benzyltrimethylammonium hydroxide (BTMAOH) and sodium chloride (NaCl) the highly crystalline and pure MTN zeolites with Si/Al ratios of 21-23 could be obtained from the hydrothermal conversion of FAU zeolite. Based on powder XRD refinement and 13C CP/MAS NMR spectra, BTMA+ ions were not present in cages of the obtained zeolites, but TMA+ ions existed instead. It means that BTMAOH underwent degradation during the conversion. Moreover, the effects of Si/Al ratio of starting FAU zeolite, synthesis parameters (BTMAOH/SiO2 and H2O/SiO2 ratios) and the addition of alkali metal chlorides on the hydrothermal conversion of FAU zeolite into MTN zeolite are discussed. As compared to amorphous SiO2/γ-Al2O3, which produced impurity, the hydrothermal conversion of FAU zeolite showed a fast crystallization rate and a high selectivity to MTN zeolite formation. These phenomena indicate that the assembly of locally ordered aluminosilicate species coming from the decomposition or dissolution of FAU zeolite should be taking part in the conversion process.

An Insight into the Process Involved in Hydrothermal Conversion of FAU to *BEA Zeolite

The use of FAU zeolite as a starting material was found to enhance the crystallization rate of *BEA zeolite, suggesting that the dissolution of FAU zeolite provides locally ordered aluminosilicate species that assemble and evolve into *BEA zeolite. Here we show experimental findings that indicate the presence of such locally ordered aluminosilicate species in intermediate phases involved in the hydrothermal conversion of FAU zeolite into *BEA zeolite. On the basis of the previous fact that cetyltrimethylammonium (CTA+) cations seem to be able to preserve zeolitic fragments or seeds and retain them in the mesoporous framework, this method was applied to the characterization of the obtained intermediate phases. From the detailed characterization of mesoporous products, the different characteristics were found to be observed between intermediate phases. Namely, as the more disordered arrangement was found in the mesoporous products, the presence of evolved, locally ordered aluminosilicate species was strongl...

Hydrothermal conversion of FAU zeolite into RUT zeolite in TMAOH system

The highly crystalline and pure RUT (RUB-10) zeolite could be obtained from the hydrothermal conversion of FAU zeolite used as a crystalline Si/Al source in tetramethylammonium hydroxide (TMAOH) media. As compared to amorphous silica/Al(OH) 3 and amorphous silica/γ-Al 2O 3 sources, the crystallization rate for the formation of RUT zeolite was clearly faster when FAU zeolite was employed as the Si/Al source. Moreover, it was found that the hydrothermal conversion of FAU zeolite into RUT zeolite depended significantly upon the Si/Al ratio of the starting FAU zeolite. FAU zeolite could be hydrothermally converted into the highly crystalline and pure RUT zeolite under the following molar ratios: Si/Al = 17–28, TMAOH/SiO 2 = 0.2 and H 2O/SiO 2 = 3–7.