In-situ synthesis and catalytic activity of ZSM-5 zeolite

ZSM-5 zeolite has been hydrothermally synthesized in-situ on the external surface of calcined kaolinite in the presence of n-butylamine. This supported zeolite was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectroscopy and N₂ adsorption. Several synthesis variables were systematically investigated, including SiO₂ to Al₂O₃ ratio, pH, crystallization time, and crystallization temperature. After mixing the ZSM-5 with a Fluid Catalytic Cracking (FCC) catalyst, catalytic performance was evaluated by cracking vacuum gas oil (VGO) in a micro-fixed bed reactor. ZSM-5 addition was favorable for the production of light olefins by catalytic cracking of VGO.     

Wet oxidation of wastewater containing hydrocarbons by novel supported Pd catalysts

Pd catalysts supported on TiO₂, ZrO₂, ZSM-5, MCM-41 and activated carbon were used in catalytic wet oxidation of hydrocarbons such as phenol, m-cresol and m-xylene. It was found that the Pd/TiO₂ catalyst was highly effective in the wet oxidation of hydrocarbon. The activities of catalysts with various hydrocarbon species, catalyst support, oxidation state of catalyst performed in a 3-phase slurry reactor show that reaction on Pd surface is more favorable than that in aqueous phase and that the active site is oxidized Pd in catalytic wet air oxidation of hydrocarbons. Based on the experimental results, a plausible reaction mechanism of wet oxidation of hydrocarbons catalyzed over Pd/TiO₂ catalyst was proposed. This catalyst is superior to other oxide catalysts because it suppressed the formation of hardly-degradable organic intermediates and polymer.     

Transesterification of Refined Sunflower Oil to Biodiesel Using a CaO/ZSM-5 Powder Catalyst

The production of biodiesel from refined sunflower vegetable oil over basic CaO/ZSM-5 catalysts was investigated. Several catalysts with various loadings of CaO on ZSM-5 were prepared, calcined at 800 °C, and characterized by N₂ adsorption-desorption, X-ray diffraction, Fourier transform infrared spectroscopy, and CO₂-temperature-programmed desorption techniques. Calcined catalysts were tested in the transesterification reaction and reaction conditions were optimized by varying the catalyst-to-oil ratio and reaction time. The most active catalyst was the CaO/ZSM-5 catalyst with a 35 wt % loading which gave the highest fatty acid methyl ester yield. The high catalytic activity was attributed to the active basic sites generated following CaO addition. Furthermore, the catalyst demonstrated stability against the leaching process.     

Screening of Catalysts for Acrylonitrile Decomposition

The catalytic decomposition of acrylonitrile over various metal components (Mg, Ca, Mn, Fe, Co, Ni, Cu, Zn, Ga, Pd, Ag, and Pt) supported on several metal oxides (Al₂O₃, SiO₂, TiO₂, ZrO₂, and MgO) and ZSM-5 was studied. The most promising catalyst was Cu-ZSM-5, which exhibited 100% conversion and at least 80% N₂ selectivity above 350 °C.     

Reduction of NO by CO on Cu/ZrO2/Al2O3 catalysts: Characterization and catalytic activities

ZrO₂, γ-Al₂O₃ and ZrO₂/γ-Al₂O₃-supported copper catalysts have been prepared, each with three different copper loads (1, 2 and 5 wt%), by the impregnation method. The catalysts were characterized by nitrogen adsorption (BET), X-ray diffraction (XRD), temperature programmed reduction (TPR) with H₂, Raman spectroscopy and electronic paramagnetic resonance (EPR). The reduction of NO by CO was studied in a fixed-bed reactor packed with these catalysts and fed with a mixture of 1% CO and 1% NO in helium. The catalyst with 5 wt% copper supported on the ZrO₂/γ-Al₂O₃ matrix achieved 80% reduction of NO. Approximately the same rate of conversion was obtained on the catalyst with 2 wt% copper on ZrO₂. Characterization of these catalysts indicated that the active copper species for the reduction of NO are those in direct contact with the oxygen vacancies found in ZrO₂.     

Catalysts based on zeolite ZSM-23 for isodewaxing of a lubricant stock

Granular Pt/(ZSM-23-γ-Al₂O₃) catalysts with different platinum and zeolite contents have been synthesized with the aim of developing efficient isodewaxing catalysts for lowering the pour point of lubricants and diesel fuels. Their physicochemical properties have been studied by X-ray diffraction, temperature-programmed desorption of ammonia, and low-temperature nitrogen adsorption/desorption. The effects of catalyst composition and process conditions (1.0–3.0 MPa, 220–400°C) on the outcomes of the isodewaxing of the 280°C-EBP lubricant fraction isolated from the hydrocracking product of vacuum gas oil have been investigated. The highest yields of products with the same pour points have been obtained with a 0.30 wt % platinum catalyst supported on the 20 wt % zeolite ZSM-23 + 80 wt % γ-Al₂O₃ material. An analysis of the basic performance characteristics of the isodewaxing catalysts based on zeolite ZSM-23 and dewaxing catalysts based on zeolite ZSM-5 has demonstrated that the catalysts based on ZSM-23 ensure higher yields of dew-axed products than the laboratory and commercial catalysts based on ZSM-5.     

Synthesis of sulfated ZrO2/MWCNT composites as new supports of Pt catalysts for direct methanol fuel cell application

Sulfated zirconia supported on multi-walled carbon nanotubes as new supports of Pt catalyst (Pt–S-ZrO₂/MWCNT) was synthesized with aims to enhance electron and proton conductivity and also catalytic activity of Pt electrocatalyst in terms of larger concentrations of ionizable OH groups on surfaces. Fourier transform infrared spectroscopy analysis shows that the sample surfaces were modified with sulfate. Transmission electron microscopy results show that the Pt and sulfated ZrO₂ particles dispersed relatively uniformly on the surface of the multi-walled carbon nanotube. X-ray diffraction shows that S-ZrO₂ and Pt coexist in the Pt–S-ZrO₂/MWCNT composites and S-ZrO₂ has no effect on the crystalline lattice of Pt. Pt–S-ZrO₂/MWCNT catalyst was evaluated in terms of the electrochemical activity for methanol electro-oxidation using cyclic voltammetry, steady-state polarization experiments and electrochemical impedance spectroscopy technique at room temperature. Pt–S-ZrO₂/MWCNT catalyst show higher catalytic activity for methanol electro-oxidation compared with Pt catalyst on non-sulfated ZrO₂/MWCNT support and commercial Pt/C (E-TEK).     

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.     

Activity and Selectivity of a Nanostructured CuO/ZrO2 Catalyst in the Steam Reforming of Methanol

Steam reforming of methanol for production of hydrogen can be carried out over copper based catalyst. In the work presented here, the catalytic properties of a CuO/ZrO₂ catalyst (8.5wt%) synthesised by a templating technique were investigated with respect to activity, long term stability, CO formation, and response to oxygen addition to the feed. The results were obtained using a fixed bed reactor and compared to a commercial methanol synthesis catalyst CuO/ZnO/Al₂O₃. It is shown that, depending on the time on stream, the temporary addition of oxygen to the feed has a beneficial effect on the activity of the CuO/ZrO₂ catalyst. After activation, the CuO/ZrO₂ catalyst is found to be more active (per copper mass) than the CuO/ZnO/Al₂O₃ system, more stable during time on stream (measured up to 250h), and to produce less CO. Structural characterisation by means of X-ray powder diffraction (XRD) and X-ray absorption spectroscopy (XAS) reveals that the catalyst (as prepared) consists of crystalline, tetragonal zirconia with small domain sizes (about 60Å) and small/disordered crystallites of CuO.     

Effect of ZrO2 content on the mechanical properties and microstructure of HAp/ZrO2 nanocomposites

This paper presents the effect of Zirconia (ZrO₂ =?0, 5, 10, 15, 20 and 25?wt%) on the mechanical properties and micro structural studies of Hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂) (HAp) nano composites. HAp and Zirconia nano composites of 20–40?nm were produced using High Energy Ball milling at 300?rpm for 1?h. X-ray diffraction studies showed that the crystallite and grain size gradually decreased with the increase in ZrO₂ content till 20?wt%, after which there was a sudden raise in both parameters. A dominant ZrO₂ phase was observed in X-ray diffraction studies of sintered samples. Mechanical properties were found to significantly improve on adding 20?wt% of ZrO₂ at 1200?°C. However, the addition of 25?wt% of ZrO₂ powder decreased the mechanical properties of HAp. The reduction could be due to the increase in grain size and dominant smaller particles of ZrO₂. The improved mechanical properties were correlated with the observed micro structural features.     

Interfacial reaction behavior and bonding mechanism between liquid Sn and ZrO2 ceramic exposed in ultrasonic waves

Ultrasound-assisted dipping of ZrO₂ ceramics into molten Sn solder was performed to realize the low-temperature joining of ZrO₂ ceramics in this study. Scanning electron microscopy with energy dispersive spectrometer, X-ray diffraction and X-ray photoelectron spectroscopy were employed to study the effects of ultrasonic vibration on the microstructure of Sn/ZrO₂ interface, and to elucidate the joining mechanism between Sn coating layer and ZrO₂ ceramic. Results showed that, after ultrasonically dipping in molten Sn for 1200 s, a pure Sn solder layer with a thickness of approximately 8–9 µm was coated on the ZrO₂ surface. The Sn coating layer exhibited excellent metallurgic bonding with ZrO₂ ceramic. A nano-sized ZrSnO₄ ternary phase, which was beneficial to the smooth transition of the lattice from Sn solder to ZrO₂ ceramic, was formed at the Sn/ZrO₂ interface. The formation of ZrSnO₄ interlayer was ascribed to the acoustic cavitation induced high-temperature reaction of Sn, O and ZrO₂ at the molten Sn/ZrO₂ ceramic interface. The tested average shear strength of ZrO₂/Sn/ZrO₂ joints was approximately 32 MPa, and the shearing failure mainly took place within the Sn solder layer.     

Influence of the different dechlorination time on catalytic performances of PtSnNa/ZSM-5 catalyst for propane dehydrogenation

Catalytic dehydrogenation of propane has recently received considerable attention because of the increasing demand for propene. Among several catalysts, PtSnNa/ZSM-5 catalyst is one of the most suitable ones. In this study, PtSnNa/ZSM-5 catalysts with different content of chlorine were prepared by changing the time of catalyst dechlorination. The obtained catalysts were characterized by X-ray fluorescence (XRF), XRD, nitrogen adsorption, ²⁷Al MAS NMR, NH₃-TPD, H₂ chemisorption and TPR. It was found that with the increase of treatment time, more framework aluminum atoms were removed from tetrahedral positions, leading to the loss of Sn species and the decrease of catalyst acidity. Meantime, the porous properties and the interactions between Pt and Sn of the catalysts changed remarkably, which was disadvantageous to the reaction. Compared with the dechlorinated catalysts, the fresh sample with suitable content of chlorine exhibited the best reaction activity and stability. The average yield of propene was about 30.4% over 45 h for the reaction of propane dehydrogenation at 590 °C. Finally, a model was proposed for the influence of dechlorinated treatment on catalytic properties of PtSnNa/ZSM-5 catalyst for propane dehydrogenation.     

Hydrogen production by steam gasification of polypropylene with various nickel catalysts

Several nickel-based catalysts (Ni/Al₂O₃, Ni/MgO, Ni/CeO₂, Ni/ZSM-5, Ni-Al, Ni-Mg-Al and Ni/CeO₂/Al₂O₃) have been prepared and investigated for their suitability for the production of hydrogen from the two-stage pyrolysis–gasification of polypropylene. Experiments were conducted at a pyrolysis temperature of 500 °C and gasification temperature was kept constant at 800 °C with a catalyst/polypropylene ratio of 0.5. Fresh and reacted catalysts were characterized using a variety of methods, including, thermogravimetric analysis, scanning electron microscopy with energy dispersive X-ray spectrometry and transmission electron microscopy. The results showed that Ni/Al₂O₃ was deactivated by two types of carbons (monoatomic carbons and filamentous carbons) with a total coke deposition of 11.2 wt.% after reaction, although it showed to be an effective catalyst for the production of hydrogen with a production of 26.7 wt.% of the theoretical yield of hydrogen from that available in the polypropylene. The Ni/MgO catalyst showed low catalytic activity for H₂ production, which might be due to the formation of monoatomic carbons on the surface of the catalyst, blocking the access of gaseous products to the catalyst. Ni-Al (1:2) and Ni-Mg-Al (1:1:2) catalysts prepared by co-precipitation showed good catalytic abilities in terms of both H₂ production and prevention of coke formation. The ZSM-5 zeolite with higher surface area was also shown to be a good support for the nickel-based catalyst, since, the Ni/ZSM-5 catalyst showed a high rate of hydrogen production (44.3 wt.% of theoretical) from the pyrolysis–gasification of polypropylene.     

The influence of different zeolitic supports on hydrogen production and waste degradation

The photocatalyst composition affects the chemical–physical properties and directly impacts photocatalytic activity, both in the hydrogen production and degradation of organic contaminants. In this work, the influence of zeolitic structures NaA, NaY, and ZSM-5 combined with a 10% active phase, TiO₂ catalyst doped with 1% copper, and cobalt cocatalysts was tested to mineralize the reactive blue dye (CI250) and to produce hydrogen by photocatalysis under ultraviolet radiation. The band gap energy was affected mainly by the cocatalyst, while the Brunauer-Emmett-Teller method (BET) area was affected by the zeolite structure as well as the X-ray diffraction (XRD). The most active catalyst was the Cu@TiO₂/NaY, which promoted a hydrogen production rate of 240 μmolH₂gcat⁻¹ using 10% ethanol (v/v) aqueous solution as a sacrificial agent and mineralization of 53% of the organic dye, followed by the catalysts impregnated on ZSM-5 zeolites, which had discolouration up to 50% and hydrogen evolution of 92.6 and 109.7 μmolH₂gcat⁻¹ for the catalyst doped with Cu and Co, respectively.     

Catalytic dechlorination of C5 compounds over metal-oxide/ZSM-5 catalysts

In this research, the dechlorination of 2-chloro-2-butene in C5 oil from the fluid catalytic cracking (FCC) process was performed through a catalytic reaction. Metal oxides were used as active materials and ZSM-5 was used as the supporting material for the catalysts; the metal was cobalt, iron, or manganese. After the preparation of three types of metal-oxide/ZSM-5 catalysts through the ion-exchange method, the activities and characteristics of each catalyst were evaluated. Through screening tests, the Co₃O₄/ZSM-5 catalyst was selected as the dechlorination catalyst, and the performance of catalysts containing different amounts of Co₃O₄ relative to ZSM-5 were tested.     

Low-temperature Oxidation of Carbon Monoxide on Co/ZrO2

A 10%Co/ZrO₂ catalyst prepared by impregnation was tested for its activity for the oxidation of CO to CO₂ in excess oxygen. Activity tests showed that conversion could be obtained at temperatures as low as 20 °C. Time-on-stream studies showed no loss of activity in these experiments, indicating that this catalyst is stable in the experimental oxidizing conditions. The activation energy for the CO to CO₂ oxidation reaction was calculated as E_a = 54 kJ/mol over this catalyst. Characterization of the material by thermogravimetric analysis, temperature-programmed techniques, X-ray photoelectron spectroscopy, and laser Raman spectroscopy indicate that Co₃O₄ is present on monoclinic ZrO₂ after the calcination of the catalyst.     

Synergic effect of Pd/γ-alumina and Cu/ZSM-5 on the performance of NO x storage reduction catalyst

NO _x reduction with a combination of catalysts, Pd catalyst, NO _x storage reduction (NSR) catalyst and Cu/ZSM-5 in turn, was investigated to elucidate for the high NO _x reduction activity of this catalyst combination under oxidative atmosphere with periodic deep rich operation. The catalytic activity was evaluated using the simulated exhaust gases with periodically fluctuation between oxidative and reductive atmospheres, and it was found that the NO _x reduction activity with this catalyst combination was apparently higher than that of the solely accumulation of these individual activities, which was caused by the additional synergic effect by this combination. The Pd catalyst upstream of the NSR catalyst improved NO _x storage ability by NO₂ formation under oxidative atmosphere. The stored NO _x was reduced to NH₃ on the NSR catalyst, and the generated NH₃ was adsorbed on Cu/ZSM-5 downstream of the NSR catalyst under the reductive atmosphere, and subsequently reacted with NO _x on the Cu/ZSM-5 under the oxidative atmosphere.     

Characterization and oxidation states of Cu and Pd in Pd–CuO/ZnO/ZrO2 catalysts for hydrogen production by methanol partial oxidation

Copper and zinc oxide based catalysts prepared by coprecipitation were promoted with palladium and ZrO₂, and their activity and selectivity for methanol oxidative reforming was measured and characterized by N₂O decomposition, X-ray absorption spectroscopy, BET, X-ray photoelectron spectroscopy, X-ray diffraction, and temperature programmed reduction. Addition of ZrO₂ increased copper dispersion and surface area, with little effect on activity, while palladium promotion significantly enhanced activity with little change of the catalytic structure. A catalyst promoted with both ZrO₂ and palladium yielded hydrogen below 150 °C. EXAFS results under reaction conditions showed that the oxidation state of copper was influenced by palladium in the catalyst bulk. A palladium promoted catalyst contained 90% Cu⁰, while the copper in an unpromoted catalyst was 100% Cu¹⁺ at the same temperature. Palladium preferentially forms an unstable alloy with copper instead of zinc during reduction, which persists during reaction regardless of copper oxidation state. A 100-h time on stream activity measurement showed growth in copper crystallites and change in copper oxidation state resulting in decreasing activity and selectivity. A kinetic model of the reaction pathway showed that palladium and ZrO₂ promoters lower the activation energy of methanol combustion and steam reforming reactions.     

Microstructures formed by secondary growth of fired ZSM-5 seed crystals

Oriented ZSM-5 seed crystals on an α-Al₂O₃ porous substrate were hydrothermally treated in a raw sol. The ZSM-5 membranes were fabricated via secondary growth of the seed crystals. For some samples, the seed-applied substrate was fired at 300 or 600 °C before the secondary growth in order to enhance adhesion between the substrate and the seed crystals. The influence of the firing on the subsequent secondary growth of the seed crystals was examined by XRD, SEM, and TEM. The TEM images of the sample fired at 300 °C showed that the resulting membrane was continuous, and in the membrane, large ZSM-5 particles were distributed in a porous matrix. The ZSM-5 particles were slightly smaller than the used seed crystals. HR-TEM observations showed that the porous matrix is comprised of ZSM-5 micro-crystals, and the part adjacent to the large ZSM-5 crystals has the same crystallographic orientation as the large crystals. The TEM images of the sample fired at 600 °C showed that the resulting layer is comprised of particles with a core-shell structure. The core consisted of ZSM-5 micro-crystals, whereas the shell was composed of large ZSM-5 rod-like crystals. It is inferred that the formation of these interesting microstructures is related to the degradation of the template agent, NPr₄OH, in the seed crystals by firing at 300 and 600 °C. The part including no template is dissolved by a hydrothermal treatment, and the dissolved species is re-crystallized via reaction with a template agent in the used raw sol, resulting in the formation of interesting microstructures.     

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.