Enhanced selectivity to benzaldehyde in the liquid phase oxidation of benzyl alcohol using nanocrystalline ZSM-5 zeolite catalyst

In the present paper, nanocrystalline hierarchical ZSM-5 zeolites were successfully synthesized by the hydrothermal method in the presence of tetrapropylammonium hydroxide as a single template with the gel composition of 58SiO₂:Al₂O₃:20TPAOH:1,500H₂O. The prepared zeolite catalysts were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, Nitrogen adsorption–desorption (BET), scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HR-TEM) techniques. The formation of pure and highly crystalline ZSM-5 zeolite phase is confirmed by XRD. The IR vibration band at 550 cm^?1 is assigned to the double 5-rings of MFI-type zeolites. N₂ adsorption–desorption isotherms showed that the synthesized product had high BET surface area and possessed composite pore structures with both micro and mesopores. The catalytic performance of hierarchical ZSM-5 zeolite was investigated in the selective oxidation of benzyl alcohol (BzOH) with hydrogen peroxide (H₂O₂) under mild conditions. The results showed that the conversion of BzOH and the selectivity to benzaldehyde were about 94 and about 99 % respectively, when using 0.08 g ZSM-5 catalyst with acetonitrile as the solvent and H₂O₂ as the oxidant at 90 °C. This catalyst can be retrieved and reprocessed for five times without a significant loss in its activity and selectivity.     

Hydroisomerization of n-hexadecane over Brønsted acid site tailored Pt/ZSM-12

Hydroisomerization of n-hexadecane is performed over ZSM-12 framework having tailored Brønsted acidity to investigate the effect in terms of product selectivity and yield. For this purpose, pure phase of ZSM-12 (bulk molar ratio Si/Al ~ 60) has been synthesized using TEABr as a structure directing agent. The framework Brønsted acidity is tailored with group II elements (M) viz. Ca, Ba and Mg, by means of ion-exchange method. The samples so prepared have been characterized for phase purity, textural parameters, morphology by employing powder X-ray diffraction, nitrogen adsorption–desorption isotherm measurement at 77 K, and scanning electron microscopy technique, respectively. Similarly, % metal exchange is estimated using inductively coupled plasma technique. The quantification of Brønsted acidity for H⁺–M⁺⁺–ZSM-12 samples has been estimated by means of ammonia temperature programmed desorption (NH₃-TPD) and Fourier transform infrared spectroscopy of ammonia (NH₃-FTIR). The well characterized H⁺–M⁺⁺–ZSM-12 samples were loaded with Platinum (Pt, 0.5 wt%) and subjected to hydroisomerization of n-hexadecane using an up-flow fixed bed reactor to verify the effect of process parameters like temperature and WHSV. Pt/H⁺–Ba²⁺–ZSM-12 with tailored Brønsted acidity in the range of about 25 % demonstrated the optimum performance among all the catalysts with an increased isomer selectivity and yield (89.2 and 80.3 %, respectively) by about 4 wt% at a conversion level of about 90 % compared to Pt/H⁺–ZSM-12 framework at 568 K. Such enhancement in isomer selectivity and yield is found to be significant from commercial application point of view. Based on the obtained trend, the potential benefits of implementation of Pt/H⁺–Ba²⁺–ZSM-12 (bulk molar ratio Si/Al ~ 60) framework for cold flow property improvement of ‘bio-ATF’ have been envisaged.     

A new method to construct hierarchical ZSM-5 zeolites with excellent catalytic activity

Desilicication and dealuminzation with weak alkaline solution and acid liquor is an effective way to construct hierarchically mesoporous without damaging its crystallinity and preserving its acidity in ZSM-5 zeolites. We investigated the influence of the concentration of NaAlO₂, treatment time, temperature and the concentration of HCl on the crystallinity of ZSM-5 and characterized the products with XRD, SEM, XRF, BET, NH₃-TPD, etc. The results showed that the appropriate concentration of NaAlO₂ solutions extract selectively silicon from the framework of the zeolites while a small portion of aluminum would patch some parts of vacancies produced by the removal of silicon, then the HCl would dealuminize to maintain the SiO₂/Al₂O₃ ratios, which preserved the crystallinity of ZSM-5 perfectly. Furthermore, the micro-reaction activity tests displayed that the obtained products had higher catalytic than the parent zeolites because of their optimized hierarchical micro-mesoporous.     

Preparation and Characterization of Polysiloxane@CeO2@PMMA Hybrid Nano/Microspheres via In Situ One-Pot Process

In this study, polysiloxane@CeO₂@PMMA microspheres were successfully synthesized by controllable one-pot process, in which CeO₂ nanoparticles were stabilized in the surface of PMMA nano/microsphere using an in situ precipitation method. The core–shell structure of the synthesized product were confirmed by FT-IR, XRD and electronic microscope analysis. The size of polysiloxane@CeO₂@PMMA nano/microspheres were about 550 nm via microscopy analysis. Moreover, the novel hybrid nanocomposites eliminated the yellowish coloration problem of CeO₂ and had good dispersibility. In addition, the transmittance of the multifunctional films based on polysiloxane@CeO₂@PMMA microspheres owned good transmittance of visible light and can block harmful UV rays, which can be attributed to nano-CeO₂ accession. Hence, such green synthesized route can be considered as a simple common method for preparing UV-shielding multifunctional materials.     

Synthesis and Characterization of Platinum Impregnated Zn-ZSM5 Nanocatalysts for Xylene Isomerization Reactions

The influence of zinc to the synthesis of ZSM-5 nanocatalysts (Si/Al?=?24) was investigated in xylene isomerization reactions. Pt was doped through partial vacuum impregnation method on both the parent and Zn-ZSM-5. The synthesized nanocatalyst were characterized by ICP, BET, XRD, FE-SEM, XPS, ²⁷Al MAS NMR, FTIR, NH₃-TPD, and TG analysis. The concentration of weak acid sites of ZSM-5 nanocatalyst slightly decreased while that of strong acid sites increased with the addition of Zn to the nano zeolite structure. Reducing weak acidity resulted in lower coke formation and remarkable catalytic stability in Zn-ZSM-5 nanocatalysts. The precence of Pt on the Zn-containing ZSM-5 illustrated simultaneous high PX yield and high catalytic stability. (0.1 wt%)Pt/(0.8 wt%) Zn-ZSM-5 as an active and stable nanocatalyst for xylene isomerization reactions demonstrated high PX yield (32.6 wt%), high level of EB conversion (68%) and low xylene loss (2.1%).

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Hierarchical ZSM-5 catalytic performance evaluated in the selective oxidation of styrene to benzaldehyde using TBHP

Hierarchical ZSM-5 catalysts with different Si/Al ratios (20, 60 and 100) were hydrothermally synthesized. The prepared samples were studied by several techniques, including X-ray diffraction (XRD), X-ray fluorescence (XRF) analysis, Fourier transform infrared (FTIR) spectroscopy, N₂ adsorption–desorption, high resolution transmission electron microscopy (HR-TEM), high resolution scanning electron microscopy (HR-SEM), and differential scanning calorimetry (DSC) technique. The average crystallite size and crystallinity decreases with increasing Si/Al ratio, which is confirmed by XRD. FTIR analysis further confirms the formation of ZSM-5 by the presence of characteristic bending, stretching and framework vibration. The HR-TEM images showed that all the samples having disc-like nanostructures are assembled by many primary nanocrystals. The as-synthesized ZSM-5 zeolites are thermally stable, which is confirmed by DSC. The catalytic activity of ZSM-5 zeolites was evaluated in the selective oxidation of styrene using tertiary-butyl hydroperoxide (TBHP) as the oxidant. Among the catalysts, ZSM-5(60) catalyst showed significantly higher yield of benzaldehyde at optimum conditions. The catalyst was recovered and recycled three times without a significant loss in activity and selectivity.     

Enhancing the Production of Light Olefins by Catalytic Cracking of FCC Naphtha over Mesoporous ZSM-5 Catalyst

The enhanced production of light olefins from the catalytic cracking of FCC naphtha was investigated over a mesoporous ZSM-5 (Meso-Z) catalyst. The effects of acidity and pore structure on conversion, yields and selectivity to light olefins were studied in microactivity test (MAT) unit at 600 °C and different catalyst-to-naphtha (C/N) ratios. The catalytic performance of Meso-Z catalyst was compared with three conventional ZSM-5 catalysts having different SiO₂/Al₂O₃ (Si/Al) ratios of 22 (Z-22), 27 (Z-27) and 150 (Z-150). The yields of propylene (16 wt%) and ethylene (10 wt%) were significantly higher for Meso-Z compared with the conventional ZSM-5 catalysts. Almost 90% of the olefins in the FCC naphtha feed were converted to lighter olefins, mostly propylene. The aromatics fraction in cracked naphtha almost doubled in all catalysts indicating some level of aromatization activity. The enhanced production of light olefins for Meso-Z is attributed to its small crystals that suppressed secondary and hydrogen transfer reactions and to its mesopores that offered easier transport and access to active sites.     

Preparation and characterization of equimolar SiO2–Al2O3–TiO2 ternary aerogel beads

Crack-free mesoporous equimolar SiO₂–Al₂O₃–TiO₂ ternary aerogel beads have been synthesized and characterized. Silica sol, alumina sol, and titania sol were synthesized individually to prevent the formation of inhomogeneous structure due to the different hydrolization and polymerization rate of individual precursor. After mixing these three types of acidic sols, SiO₂–Al₂O₃–TiO₂ ternary beads were prepared by the ball dropping method. The ternary aerogel beads were typically mesoporous, showing high surface area (305 m² g^?1), large pore volume (1.32 cm³ g^?1), and high surface acid amount (0.884 mmol NH₃ g^?1). Moreover, the acid sites of the ternary aerogel beads showed higher thermal stability than those of binary aerogel beads. Gradient drying (GD), supercritical drying (SD), ambient drying (AD), extended aging (EA) and hydrophobic modifying drying (HM) have been employed to investigate the effects of drying method on the characteristics of the aerogel beads. The surface areas of the ternary aerogel beads obtained by different drying methods decrease in the sequence EA > HM > GD > SD > AD. The ternary aerogel beads have been characterized by scanning electron microscopy, nitrogen adsorption, X-ray powder diffraction, Fourier-transform infrared spectroscopy (FTIR), solid-state NMR, temperature-programmed desorption measurements, pyridine adsorption FTIR, and differential scanning calorimetry.     

Oxidative dehydrogenation of n-butane over bimetallic mesoporous and microporous zeolites with CO2 as mild oxidant

Oxidative dehydrogenation of n-butane was tested using carbon dioxide as a mild oxidant over bimetallic Cr–V supported catalysts (MCM-41, ZSM-5, MCM-22 and mesoZSM-5). The textural properties of the catalysts were measured by means of XRD, N₂ adsorption, SEM-EDX, Raman, H₂-TPR, pyridine FT-IR, NH₃ and CO₂-TPD techniques. The metal content of Cr and V was maintained around 1.2 and 2.8 wt% for the catalytic test in packed bed reactor at different temperatures (525–600 °C) for 180 min. 1.2Cr2.8 V/MCM-41 and 1.2Cr2.8 V/ZSM-5 exhibited maximum conversion of 14 and 13.1 %, respectively at 10 min and 600 °C. Significantly, high butenes selectivity was observed over MCM-41 (86.27 %) than ZSM-5 support (58.1 %). The mesoporosity in ZSM-5 had a negative impact on conversion level (7.1 %) but improved the butenes selectivity slightly. 1.2Cr2.8 V/M-22 showed the highest cracking ability leading to overall reduced butenes selectivity (57.9 %). The study shows that over all catalysts, n-butane conversion is independent of CO₂ conversion. 1.2Cr2.8 V/M-22 showed highest CO₂ conversion in the range 2.35–2.2 % between 525 and 550 °C. The apparent activation energies of dehydrogenation and cracking reaction over the four catalysts were evaluated. The ratio of conversion to coke weight per cent over the four catalysts are observed in the following order: 1.2Cr2.8 V/M-41 > 1.2Cr2.8 V/Z-5 > 1.2Cr2.8 V/mesoZ-5 > 1.2Cr2.8 V/M-22.     

Self-assembled HPW/silica–alumina mesoporous nanocomposite as catalysts for oxidative desulfurization of fuel oil

Mesoporous silica–alumina–polyoxometalate (HPW/SiO₂–Al₂O₃) nanocomposite materials with silica–aluminum molar ratios of 10–80 have been successfully synthesized by evaporation induced self-assembly method with non-ionic surfactant P123 as template agent. The surface areas and pore sizes of the obtained HPW/SiO₂–Al₂O₃ materials are in the range of 509–623 m² g^?1 and 3.6–3.8 nm, respectively, with different silica–aluminum molar ratios. The incorporated polyoxometalate clusters preserve their intact Keggin structure into the mesoporous frameworks. The Py–FTIR investigations indicate that the surface acidity of catalysts gradually increases with an increase in the percentage of aluminium, and the Lewis acidity sites are predominant. The nanocomposites were used as catalysts, and H₂O₂ as oxidant for oxidative desulfurization (ODS) of model fuel, which was composed of benzothiophene (BT), petroleum ether and benzene. The results show that the adsorption capacity and ODS performance of catalysts have close relationship with their surface acidity. An appropriate amount of Lewis acidity sites can contribute to the selective oxidation of the BT due to the preferential adsorption of BT on the catalyst surface, while the Brönsted acidity sites have a negative impact on the selective oxidation of the BT. As a result, the mesoporous HPW/SiO₂–Al₂O₃ with silica–aluminum molar ratio of 50 shows the highest selectivity for BT oxidation in the presence of benzene and has achieved the goal of desulfurization. In addition, the catalyst shows excellent reusing ability, which makes it a promising catalyst in ODS process.     

Yield of gasoline-range hydrocarbons as a function of uniform ZSM-5 crystal size

Uniform ZSM-5 nanocrystals were synthesized by a single-templating procedure. The samples were then characterized by a variety of physical techniques such as XRD, SEM, BET, ICP and TPD. The dehydration of methanol over synthesized ZSM-5 zeolite was studied in a fixed-bed continuous flow reactor at 370 °C and WHSV of 2.6 gg⁻¹ h under ambient pressure. The effect of crystal size of zeolite catalysts on product distribution in methanol dehydration reaction was investigated. Good correlation was observed between catalytic performance, product distribution and size of ZSM-5 crystals. It was found that the decrease in crystal size significantly influences light olefins (ethylene and propylene) and paraffins (C₁–C₄) selectivity in methanol dehydration reaction. Furthermore, nanocrystal ZSM-5 showed long-term catalytic stability compared with conventional ZSM-5 provided that the reaction activity is strongly dependent on the crystal size in methanol dehydration process. The results indicated that crystal size significantly affects the catalyst lifetime and hydrocarbon distributions in product stream. Based on the obtained results, it is concluded that the use of uniform ZSM-5 nanocrystals improves the yield of propylene and alkyl aromatics in methanol conversion reaction at mild conditions.     

Mesostructure controllable ZSM-5 single crystals supported Pd/transition metal oxides: efficient and reusable catalysts for selective oxidation under aerobic conditions

Pd and transition metal oxides functionalized ZSM-5 single crystals with b-axis aligned mesopores (ZSM-5-OM-PdO _x -MO _x ) were prepared. ZSM-5-OM support was obtained from crystallization of aluminosilicate gels in the presence of cationic polymers. Characterizations indicate abundant nanopores and highly crystalline degree of ZSM-5-OM-PdO _x -MO _x , and active species of Pd and transition metals were homogeneously dispersed into ZSM-5-OM, which showed unique interactions and enhanced ability for activating oxygen. Catalytic tests showed that ZSM-5-OM-PdO _x -MO _x were highly active and reusable catalysts for selective oxidation of alcohols under aerobic and solvent free condition, which were much better than those of Pd/transition metal oxides functionalized ZSM-5, mesoporous silica of SBA-15, and activated carbon catalysts.     

Indene epoxidation over immobilized methyltrioxorhenium on MCM-41 silica,fumed silica and aluminosilicate materials

The presented report focuses on the testing of heterogenized methyltrioxorhenium (MTO) in indene epoxidation. A range of mesoporous materials with different SiO₂/Al₂O₃ ratios, namely aluminosilicates type Siral and MCM-41 silica and fumed silica, were used as supports for immobilization of MTO. The tested support materials and prepared catalytic systems exhibited high surface area, well-defined regular structure and narrow pore size distribution of mesopores and therefore represent good quality catalysts for various reactions. The immobilized MTO on various supports was tested for the preparation of 1,2-epoxyindane using two forms of hydrogen peroxide as oxidation agents, namely aqueous solution of hydrogen peroxide and its anhydrous form, urea-hydrogen peroxide. The prepared catalysts were successfully used for the preparation of 1,2-epoxyindane with achieved 100 % selectivities to the desired product at high conversions of indene.     

Application of Mesoporous Metal Oxide Immobilized Gold–Palladium Nanoalloys as Catalysts for Ethanol Oxidation

Gold–palladium nanoalloys (AuPd) were synthesized by a dendrimer templating method and the as-prepared nanoalloys were immobilized on several reducible mesoporous metal oxides (MMOs). The MMOs of MnO₂, Co₃O₄ and CeO₂ exhibited low catalytic activity in gas-phase oxidation of ethanol. Upon immobilization of the AuPd nanoalloys the activity increased significantly, with high acetaldehyde selectivity at 120 °C. However, this activity increase from pure MMOs to AuPd/MMOs was accompanied by decrease in selectivity to acetaldehyde. One other interesting observation lies on the amount of gold in the nanoalloy. Increasing the ratio of Au:Pd in the nanoalloy from 1:1 to 10:1 lowered the activity by a factor of six but had a positive effect on selectivity. From this, we postulate dissociation absorption of molecular oxygen to the reactive oxides occurs more effectively on the Pd metal surface. With higher Au loading, the acetaldehyde selectivity remained above 90% even at higher reaction temperatures of 160 °C. This led to a postulation of quick desorption of acetaldehyde from the Au surface more than it does on the Pd surface.

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Facile synthesis and catalytic applications of micro-mesoporous molecular sieve ZK-1

A micro-mesoporous molecular sieve ZK-1 was synthesized at 170 °C by a facile one-step hydrothermal method. The structure of ZK-1 can be controlled by the crystallization time. ZK-1(I), the KIT-1 containing ZSM-5 building units in the pore walls, is formed during 2–6 h. ZK-1(II), A mixture of ZSM-5 and KIT-1, is formed after 8 h. The framework structure, porosity, morphology and acidity of the obtained materials were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, Transmission electron microscopy, N₂ adsorption, X-ray fluorescence, NH₃-temperature programmed desorption and ²⁷Al Magic angle spinning NMR spectroscopy. The samples exhibit good steam stability and better catalytic performances in the isomerization of o-ethyltoluene than KIT-1, suggesting their promising applications in the conversion of large molecules.     

Production of Propylene from Ethanol Over ZSM-5 Zeolites

In this work, we studied the conversion of ethanol to propylene over ZSM-5 zeolites. The catalytic performance of H-ZSM-5 (Si/Al₂ = 30, 80, and 280) and ZSM-5 (Si/Al₂ = 80) modified with various metals was investigated. H-ZSM-5(Si/Al₂ = 80) afforded high propylene yield, which indicates that a moderate surface acidity favored propylene production. Zr-modified ZSM-5(80) gave the highest yield (32%) of propylene at 773 K. Furthermore, the catalytic stability of the zeolite was improved by the modification of zirconium. The surface acidity and the presence of metal ions played important roles on the production of propylene.     

Uniform Terbium Coordination Polymer Microspheres: Preparation and Luminescence

Uniform terbium coordination polymer microsphere particles are synthesized via a facile solvothermal method, using 3-methyl benzoic acid (3-MeBAH) as ligand. The products were characterized by SEM, PXRD, EA, FT-IR, downconversion and upconversion luminescence. PXRD result confirms that sample 1 has one dimensional structure, which is constructed by dinuclear second building unit. The effect factors of reaction temperature and reaction time in synthesizing the uniform microsphere particles were investigated in detail. Downconversion luminescence research shows the sample 1 exhibits characteristic transitions at 488, 544, 585, 621 and 636 nm, which corresponding to the transitions of ⁵D₄ → ⁷F₆, ⁵D₄ → ⁷F₅, ⁵D₄ → ⁷F₄, ⁵D₄ → ⁷F₃ and ⁵D₄ → ⁷F₂ of Tb³⁺ respectively, and the strongest peak is at 544 nm. The absolute luminescence quantum yield of sample 1 is as high as 32.7 %. Furthermore, investigation indicates the upconversion luminescence of sample 1 is the two-photo absorption of the ligand.     

Airborne toluene degradation by using manganese oxide supported on a modified natural diatomite

The catalytic combustion of toluene over manganese oxide supported on natural diatomite has been investigated in the paper. The catalyst was prepared by the wet impregnation method and characterized by using the Brunauer Emmett Teller, field emission scanning electron microscopy, X-ray diffraction, X-ray fluorescence and temperature-programmed reduction analysis. The higher activity of the catalyst supported on diatomite for toluene oxidation was obtained at 12 wt% Mn loading. It was able to convert 90 % of toluene (T ₉₀) at 380 °C. The results indicated that the selectivity towards CO₂ was almost 100 % and no intermediates, such as CO or other hydrocarbons, were detected.     

Urothermal Synthesis of a New Cd(II)-Terephthalate: Synthesis,Structure, CO2 Adsorption and Luminescent Properties

A new Cd(II) compound, namely [Cd(pbdc)(e-urea)]_n (1 H₂pbdc = terephthalic acid, e-urea = ethyleneurea), has been synthesized by urothermal reactions of Cd(NO₃)₂, and H₂pbdc. Single crystal X-ray analysis reveals that it features a three-dimensional framework based on Cd(II)-carboxylate inorganic chains. The coordinated e-urea molecules are filled in the rhombic channels. Thermal analysis reveals that it can be stable up to 350 °C. The CO₂ adsorption and luminescent properties of compound 1 were also investigated.     

Co-conversion of methanol and n-hexane into aromatics using intergrown ZSM-5/ZSM-11 as a catalyst

The conversion of n-hexane and methanol into value-added aromatic compounds is a promising method for their industrially relevant utilization. In this study, intergrown ZSM-5/ZSM-11 crystals were synthesized and their resulting catalytic performance was investigated and compared to those of the isolated ZSM-5 and ZSM-11 zeolites. The physicochemical properties of ZSM-5/ZSM-11 intergrown zeolite were analyzed using X-ray diffraction, N₂ isothermal adsorption-desorption, the temperature-programmed desorption of ammonium, scanning electron microscopy, Fourier transform infrared spectra of adsorbed pyridine, and nuclear magnetic resonance of ²⁷Al , and compared with those of the ZSM-5 and ZSM-11 zeolites. The catalytic performances of the materials were evaluated during the co-feeding reaction of methanol and n-hexane under the fixed bed conditions of 400°C, 0.5 MPa (N₂), methanol:꞉n-hexane=7꞉:3 (mass ratio), and weight hourly space velocity=1 h^–1 (methanol). Compared to the ZSM-5 and ZSM-11 zeolites, the ZSM-5/ZSM-11 zeolite exhibited the largest specific surface area, a unique crystal structure, moderate acidity, and suitable Brønsted/Lewis acid ratio. The evaluation results showed that ZSM-5/ZSM-11 catalyst exhibited better catalytic reactivity than the ZSM-5 and ZSM-11 catalysts in terms of methanol conversion rate, n-hexane conversion rate, and aromatic selectivity. The outstanding catalytic property of the intergrown ZSM-5/ZSM-11 was attributed to the enhanced diffusion associated with its unique crystal structure. The benefit of using zeolite intergrowth in the co-conversion of methanol and alkanes offers a novel route for future catalyst development.