Synthesis,characterization of Al-rich ZSM-12 zeolite and their catalytic performance in liquid-phase tert-butylation of phenol

Al-rich ZSM-12 zeolites were synthesized using N,N,N′,N′-tetraethylbicyclo[2.2.2]oct-7-ene-2,3:5,6-dipyrrolidinium diiodide as template under hydrothermal conditions. Their physico-chemical properties were characterized using XRD, ICP-AES, SEM, N₂ adsorption, ²⁷Al MAS NMR and NH₃-TPD. The results indicated that Al-rich ZSM-12 zeolites with low Si/Al ratios of 8–23 were successfully crystallized. Catalytic properties of the prepared zeolites were studied in the tert-butylation of phenol. Higher para selectivity was obtained on the Al-rich ZSM-12 zeolites compared with other types of zeolites.     

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.     

Iron exchanged ZSM-5 and Y zeolites calcined at different temperatures: activity in N2O decomposition

ZSM-5 and Y zeolites were modified with iron by an ion-exchange method and then calcined at 773, 873, 973 and 1,073 K. The obtained materials were characterized with respect to textural parameters (low-temperature N₂ sorption), structure (X-ray diffraction, UV–vis–DRS), redox properties (H₂-temperature programmed desorption, TPD) and surface acidity (NH₃-TPD). The obtained results have shown that the structure of zeolites influenced form, aggregation and content of the introduced iron species. In case of the FAU type structure characterized by wide pores (max. ring size, T-atoms—12) mainly iron in form of mononuclear Fe³⁺ cations and Fe _x ³⁺ O_y oligonuclear clustered species was found. On the other hand for the MFI type structure characterized by smaller pores (max. ring size, T-atoms—10) significant contribution of iron in the form of bulky Fe₂O₃ clusters located possibly on the outer surface of ZSM-5 was detected. Such significant differences in distribution of iron species is probably related to various mobility of iron species in the pore systems of both zeolites. The obtained materials were tested as catalysts in the process of N₂O decomposition. Calcination of zeolites at different temperatures influenced neither the properties nor the activity of the obtained catalysts.     

Catalytic performance of CeAPSO-34 molecular sieve with various cerium content for methanol conversion to olefin

A series of CeAPSO-34s with various cerium contents was synthesized and characterized by multiple techniques such as XRD, SEM, BET, ²⁹Si MAS NMR, NH₃-TPD and CO₂-TPD. NH₃-TPD spectra showed that a number of acid sites, especially those of strong acidity, is reduced with the increasing of Ce incorporation. Incorporation of metal ions gave rise to more silica-islands in the CeAPSO-34 framework. CO₂-TPD showed that basic sites on the surface of modified samples are due to the presence of Ce-containing species incorporation into the framework of CeAPSO-34 molecular sieves. The performance of the catalysts was studied in methanol to olefin reactions at 425 °C under the atmospheric pressure. The results showed that the incorporation of cerium ions had great effects on the structure and acidity of the molecular sieves. All SAPO-34 and MeAPSO-34 molecular sieves were the very active and selective catalyst for light olefins production. Cerium incorporation improved the catalyst lifetime and favored the ethylene and propylene generation. However, an excess Ce content resulted in an inferior catalytic performance and stability. Therefore, there existed optimal cerium content for a specific SAPO-34.     

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.     

Dimerization of isobutene over nickel modified zeolites to obtain isooctene

Ni/H Zeolites catalysts were prepared by impregnation, starting from HY-Zeolite, Hβ-Zeolite and H-mordenite with nickel precursor salts, NiCl₂, NiSO₄ and NiCO₃. The total number, NTSA, and the acid strength were found dependent on the nickel precursor salt. High catalytic activity, selectivity and stability of the modified zeolites in isobutene dimerization was attributed to the acidic properties of nickel modified zeolites. HY-Zeolite modified with NiCO₃ resulted more active and selective to dimerization reaction. The prepared catalysts were characterized by EDSX, SEM, and Adsorption/Desorption of N₂ at 77 K, NH₃ chemisorption and Ammonia Temperature-Programmed-Desorption (NH₃-TPD) and FT-IR of adsorbed pyridine. NH₃-TPD and isobutene adsorption revealed an acid sites a new distribution and apparition of acid sites not present in the protonated zeolites. Catalytic activity and reactor behavior were studied in a continuous downstream fixed bed reactor at 298 K, 27.6 kPa (4 psig), and WHSV = 0.27 h⁻¹.     

The oxidation of carbon monoxide over the palladium nanocube catalysts: Effect of the basic-property of the support

The nanocatalysts of Pd nanocubes supported on SiO₂, TiO₂ and MgO were prepared and the CO oxidation activities over the three catalysts were evaluated. The acid–basic properties of the support materials were determined using the temperature-programmed desorptions of NH₃ (NH₃-TPD) and CO₂ (CO₂-TPD). The CO adsorptions over the three catalysts were investigated by the diffuse reflectance infrared Fourier transform (DRIFT). It was found that the Pd/MgO catalyst showed the strongest ability to adsorb CO molecules and performed best for CO oxidation.     

Modified Beta Zeolite as Catalyst for Fries Rearrangement Reaction

Modified beta zeolites were applied as catalysts for the Fries rearrangement reaction. The properties of the modified zeolites were characterized by NH₃-TPD, n-hexane and 1,2,4-trimethylbenzene adsorption. Modification with SiO₂ did not block the pores of the beta zeolite but reduced the number of acid sites on the surface. However, when the beta zeolite was modified with Ce₂O₃, the number of acid sites determined by NH₃-TPD increased, which indicated that new acid sites are created by the interaction of cerium oxide and zeolite. Modified beta zeolites and H-beta were applied as catalysts for the Fries rearrangement of phenol acetate. Reaction over H-beta has low selectivity and the catalyst is easily deactivated. SiO₂ modification of the catalyst increases the selectivity of the reaction but decreases the conversion. Ce₂O₃-modified beta zeolites show higher catalytic activity and rearrangement selectivity in the reaction than other catalysts. The stability of the catalyst is also improved after Ce₂O₃ modification. About 70% selectivity and 60-80% conversion can be achieved over 16 wt% Ce₂O₃-modified beta zeolite.     

Effects of the Nitridation of Y and USY Zeolites on their Catalytic Activity for the Base Catalyzed Knoevenagel Condensation

This contribution reports on the preparation, physicochemical characterization and catalytic performances of nitrided zeolites in the Knoevenagel condensation reaction. These basic materials were prepared by subjecting one Y zeolite (Si/Al ratio of 2.6) and two ultrastable Y zeolites (Si/Al ratio of 13 and 37) to nitridation, i.e., treatment with ammonia at high temperature. Both the amount and the chemical nature of incorporated nitrogen species were controlled by the nitridation temperature. Namely, an increase of the temperature induces an increase of the nitrogen content and the appearance of nitrogenous species in the following order of increasing temperature: NH₄ ⁺, adsorbed NH₃, –NH₂, >NH and >N–. The nitridation occurred practically in the same manner whatever the Si/Al ratio of the starting material. However, from a catalytic point of view different behavior was observed. No direct correlation was found with the nitrogen content of the samples. Nitrided zeolites were found to exhibit catalytic activity as long as the zeolitic framework was maintained.     

Dehydrogenation of ethylbenzene and propane over Ga2O3–ZrO2 catalysts in the presence of CO2

Ga₂O₃–ZrO₂ catalysts were prepared by a coprecipitation method. The catalysts were characterized by XRD, Raman, DRS, XPS, SEM, EDX, IR, NH₃-TPD, CO₂-TPD and N₂ adsorption methods. Dehydrogenation of ethylbenzene and propane in the presence of CO₂ over these catalysts has been investigated and compared. Ga₂O₃–ZrO₂ catalysts exhibit different catalytic behavior for the two dehydrogenation reactions.     

TiO2 photocatalyst for degradation of organic compounds in water and air supported on highly hydrophobic FAU zeolite: Structural,sorptive, and photocatalytic studies

Preparation of highly hydrophobic FAU zeolite has been achieved by a two-step preparation method that comprises predealumination treatment using concentrated mineral acids and subsequent calcination treatment. The hydrophilic/hydrophobic character of the zeolites was estimated by detailed adsorption measurements using water and toluene molecules as adsorbates, which showed the strict hydrophobic nature of the prepared FAU zeolites. By means of TG, FT-IR, and ²⁹Si MAS NMR analyses, it was concluded that the enhancement in hydrophobicity originates from the healing of silanol defect sites and the formation of a refined silica surface with fewer adsorption sites. Thus-prepared FAU zeolite, with high crystallinity, structural and thermal stability, and hydrophobicity, significantly improved the photocatalytic degradation rates of 2-propanol in water and acetaldehyde in air on TiO₂ when it was used as a catalyst support. A distinct correlation was found between the hydrophobicity of zeolites and photocatalytic activity of the supported TiO₂.     

Propylene aromatization on Ga-MFI Zeolites

Propylene aromatization reaction was performed on various MFI type zeolites containing Ga species. The Ga was introduced into the zeolites by substitution (Ga-MFI), ion exchange (GIZ) and physical mixing (GPZ). A com-mercialized zeolite (PQZSM-5) was also used for comparison. The catalysts prepared were characterized by using XRF, XPS, surface area measurement, NH₃-TPD, and H₂-TPR. Through the Ga substitution, the acidity of the modified catalysts was decreased, and dehydrogenation and aromatization reactions occurred more easily. The lattice Ga did not react well with hydrogen contrary to the Ga located at the outside of the lattice. It was also found that Ga-MFI catalysts facilitate alkylation reactions. This paper is dedicated to Professor Wha Young Lee on the occasion of his retirement from Seoul National University     

Characterization of Modified Nanoscale ZSM-5 Zeolite and Its Application in the Olefins Reduction in FCC Gasoline

Nanoscale HZSM-5 zeolite was hydrothermally treated with steam containing 0.8 wt% NH₃ at 773 K and then loaded with La₂O₃ and NiO. Both the parent nanoscale HZSM-5 and the modified nanoscale HZSM-5 zeolites catalysts were characterized by TEM, XRD, IR, NH₃-TPD and XRF, and then the performance of olefins reduction in fluidized catalytic cracking (FCC) gasoline over the modified nanoscale HZSM-5 zeolite catalyst was investigated. The IR and NH₃-TPD results showed that the amount of acids of the parent nanoscale HZSM-5 zeolite decreased after the combined modification, so did the strong acid sites deactivating catalysts. The stability of the catalyst was still satisfactory, though the initial activity decreased a little after the combined modification. The modification reduced the ability of aromatization of nanoscale HZSM-5 zeolite catalyst and increased its isomerization ability. After 300 h onstream, the average olefins content in the gasoline was reduced from 56.3 vol% to about 20 vol%, the aromatics (C₇–C₉ aromatics mainly) and paraffins contents in the product were increased from 11.6 vol% and 32.1 vol% to about 20 vol% and 60 vol% respectively. The ratio of i-paraffins/n-paraffins also increased from 3.2 to 6.6. The yield of gasoline was obtained at 97 wt%, while the Research Octane Number (RON) remained about 90.     

Syngas production via combined oxy-CO2 reforming of methane over Gd2O3-modified Ni/SiO2 catalysts in a fluidized-bed reactor

In this research, Ni/SiO₂ catalyst was modified with different amount of Gd₂O₃ and characterized with temperature-programmed desorption of CO₂ (CO₂-TPD) and NH₃ (NH₃-TPD), temperature-programmed reduction with H₂ (H₂-TPR) and X-ray diffraction (XRD). It was found that Gd₂O₃-modified Ni/SiO₂ catalysts possessed higher CO₂ adsorption and activation ability due to the formation of surface carbonate species. H₂-TPR and XRD characterizations found that the strong interaction among nickel, Gd₂O₃ and SiO₂ took place, which improved the dispersion of Ni. Gd₂O₃-modified Ni/SiO₂ catalysts exhibited higher activity and stability for the combined oxy-CO₂ reforming of methane in fluidized-bed reactor. The H₂/CO ratio in produced syngas could be controlled via controlling reaction temperature and CO₂/O₂ ratio in feed.     

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.     

Improvement of CO2 adsorption on ZIF-8 crystals modified by enhancing basicity of surface

The imidazolate framework ZIF-8 samples were modified separately by using ammonia impregnation and thermal treatment in atmosphere of N₂ or H₂ in order to improve its adsorption property toward CO₂, and the modified samples A-ZIF-8, N-ZIF-8 and H-ZIF-8 were correspondingly available. The modified ZIF-8 samples were characterized, and the surface chemical properties of the ZIF-8 samples were determined separately by FTIR, CO₂-TPD, NH₃-TPD and H₂O-TPD. The isotherms of CO₂ on the modified ZIF-8 samples were measured. Results showed that after surface modification, the total amounts of basicity of the modified samples significantly increased, and followed the order: A-ZIF-8>H-ZIF-8>N-ZIF-8>O-ZIF-8. The uptakes of CO₂ increased proportionally with the basic groups on the surfaces of the ZIF-8 samples due to CO₂ being an acidic molecule. As a consequence of that, the CO₂ adsorption capacity of the samples followed the order: A-ZIF-8>H-ZIF-8>N-ZIF-8>O-ZIF-8. The amount adsorbed of CO₂ on the modified ZIF-8 sample by ammonia impregnation is the highest, having an increase.     

Thermodynamic Analysis on the Codeposition of SiC–Si3N4 Composite Ceramics by Chemical Vapor Deposition using SiCl4–NH3–CH4–H2–Ar Mixture Gases

A thermodynamic calculation on the chemical vapor deposition of the SiCl₄–NH₃–CH₄–H₂–Ar system was performed using the FactSage thermochemical software databases. Predominant condensed phases at equilibrium were SiC, Si₃N₄, graphite, and Si. The equilibrium conditions for the deposition of condensed phases in this system were determined as a function of the deposition temperature, dilution ratio (δ), and reactant ratios of CH₄/SiCl₄ and NH₃/SiCl₄. The CVD phase diagrams were used to understand the reactions occurring during the formation of Si–C–N from the gas species and determine the area of SiC–Si₃N₄. The concentration of condensed‐phase products was used to determine the deposition conditions of CVD SiC–Si₃N₄. The present work was helpful for further experimental investigation on CVD Si–C–N.     

Crucial Role of Weak Acid Sites for Catalytic Performance of Zeolites in Ethyl tert-butyl Ether Synthesis

Catalytic activity of different zeolites: H,NH₄-form of mordenite-containing rock (H-CMK) and H-Beta with a Si/Al ratio of 15–407 (H-ВЕА) in ethyl tert-butyl ether (ETBE) synthesis in a packed-bed flow reactor at 80–180°C and 1?MPa has been studied. Acid characteristics of zeolites were determined by stepwise (Quasi-Equilibrium) ammonia thermodesorption. Three types of acid sites of different strength has been found, which is marked as weak (E_NH3?=?60–75?kJ/mol), medium (E_NH3?=?86–123?kJ/mol), and strong (E_NH3?=?112–145?kJ/mol). The correlation between ETBE productivity and the concentration of weak acid sites has been found. Thereby, it was established that weak acid sites of zeolites are the active sites in ETBE synthesis.     

Hydroconversion of n-octane over nanoscale HZSM-5 zeolites promoted by 12-molybdophosphoric acid and Ni

12-Molybdophosphoric acid (PMo), Ni and Ni–PMo loaded on nanoscale HZSM-5 zeolites were prepared and characterized by BET, IR, XRD, Py-IR, NH₃-TPD, TG and SEM. The hydroconversion of n-octane over various catalysts was investigated in order to obtain light isomers alkanes and aromatics products with high-octane-number. The acid amounts of the catalysts were modified after the loading of PMo and Ni, and its relation to the activity of the reaction was discussed. It is concluded that the stability of aromatization is improved, and the yield of light iso-alkanes is enhanced due to the introduction of PMo and Ni. The improved activity of n-octane hydroconversion over PMo and Ni loaded nanoscale HZSM-5 zeolites could be attributed to the increase of the acid amounts and the synergetic effect between Brønsted and Lewis acid sites.     

Si/B/C/N/Al precursor-derived ceramics: Synthesis,high temperature behaviour and oxidation resistance

The Si/B/C/N/H polymer T2(1), [B(C₂H₄Si(CH₃)NH)₃]_n, was reacted with different amounts of H₃Al·NMe₃ to produce three organometallic precursors for Si/B/C/N/Al ceramics. These precursors were transformed into ceramic materials by thermolysis at 1400 °C. The ceramic yield varied from 63% for the Al-poor polymer (3.6 wt.% Al) to 71% for the Al-rich precursor (9.2 wt.% Al). The as-thermolysed ceramics contained nano-sized SiC crystals. Heat treatment at 1800 °C led to the formation of a microstructure composed of crystalline SiC, Si₃N₄, AlN(+SiC) and a BNC_x phase. At 2000 °C, nitrogen-containing phases (partly) decomposed in a nitrogen or argon atmosphere. The high temperature stability was not clearly related to the aluminium concentration within the samples. The oxidation behaviour was analysed at 1100, 1300, and 1500 °C. The addition of aluminium significantly improved the oxide scale quality with respect to adhesion, cracking and bubble formation compared to Al-free Si(/B)/C/N ceramics. Scale growth rates on Si/B/C/N/Al ceramics at 1500 °C were comparable with CVD–SiC and CVD–Si₃N₄, which makes these materials promising candidates for high-temperature applications in oxidizing environments.