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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SAPO-34 supported Pt–Sn-based novel catalyst for propane dehydrogenation to propylene

The Pt–Sn-based catalyst was intensified using SAPO-34 as support for direct propane dehydrogenation to propylene. The catalyst was prepared by sequential impregnation method and characterized by XRF, BET, XRD, NH₃-IR, NH₃-TPD, H₂-TPR, HR-TEM and O₂-pulse coke analysis. NH₃-TPD, IR spectra and XRD results suggested that the doping of metals on SAPO-34 did not affect its acidic strength and structural topology of support, respectively. Propylene selectivity of 94% and total olefins selectivity greater than 97% was achieved using Pt–Sn/SAPO-34. The results were compared with Pt–Sn/ZSM-5 under identical conditions. The possible reasons for improvement were the larger surface area, shape selectivity and particular by suitable acidity of SAPO-34.     

A selective catalyst for methanol conversion into light olefin with a high propylene to ethylene ratio

MSU-S catalyst, assembled from ZSM-5 zeolite seed (MFI), was synthesized with silica to alumina ratio 55 and characterized by XRD, NH3-TPD, BET and FT-IR techniques. It was tested in a vertical fixed bed reactor for selective production of light olefins from methanol (MTO) at temperatures of 400, 450 and 500 °C and WHSV of 1, 5 and 25 h^?1. After thorough investigation, it was found that WHSV=5 h^?1 and temperature of 500 °C are the optimum conditions for maximum light olefin yield, which was 52% with propylene to ethylene ratio of 4.57. Acidity of MSU-S was promoted by incorporation of phosphotungusticacid (HPW) and a direct method to reach high HPW dispersion and thermal stability. Maximum light olefin yield was observed over HPW-MSU-S at the optimum reaction conditions to be nearly 60% with propylene to ethylene ratio of 4.3.     

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.     

Synthesis of Fe3O4-nanocatalysts with different morphologies and its promotion on shifting C5+ hydrocarbons for Fischer–Tropsch synthesis

The shape-defined Fe₃O₄ nanocatalysts such as spheres and polyhedrons prepared by a simple solvothermal method without calcination were applied in Fischer–Tropsch synthesis (FTS), which showed excellent catalytic activity and C₅⁺ selectivity compared to the traditional Fe catalyst. Especially, the Fe₃O₄ nanocatalyst with nanospheres (FNS) displayed higher catalytic activity and C₅⁺ selectivity (> 64%) than the Fe₃O₄ nanopolyhedrons (FNP). It was found that FNS was more favorable to the reduction and dispersion of iron species as well as formation of surface carbonaceous species (especially for χ-Fe₅C₂) compared to FNP, which provided more active sites for FTS and facilitated the product distribution shifting towards heavy hydrocarbons.     

Influence of ambient gas on microwave-assisted combustion synthesis of CuO–ZnO–Al2O3 nanocatalyst used in fuel cell grade hydrogen production via methanol steam reforming

The effect of different ambient gases for preparation of CuO-ZnO-Al₂O₃ nanocatalysts by the microwave assisted solution combustion method was studied. Air, nitrogen and carbon dioxide as the ambient atmospheres were injected during the solution combustion synthesis method. The fabricated nanocatalysts were characterized by various techniques such as XRD, FESEM, TEM, EDX, FTIR and BET analyses. It was understood that injection of nitrogen during synthesis of nanocatalysts led to high dispersion of Cu crystallites as the active sites for the steam methanol reforming reaction. Moreover, appropriate interaction between CuO and ZnO particles was achieved due to better morphology of the nanocatalyst synthesized by N₂ as the ambient gas than other samples. Finally, high methanol conversion with proper products selectivity were achieved by the nanocatalyst synthesized by injection of N₂ during the microwave assisted combustion synthesis method due to significant superiority in its physicochemical properties.     

Catalytic Cracking of Heavy Olefins into Propylene, Ethylene and Other Light Olefins

Hybrid catalysts developed for the thermo-catalytic cracking of liquid hydrocarbons were found to be capable of cracking C₄ ⁺ olefins into light olefins with very high combined yields of product ethylene and propylene (more than 60 wt%) and C₂–C₄ olefins (more than 80 wt%) at 610–640 °C, and also with a propylene/ethylene weight ratio being much higher than 2.4. The olefins tested were heavier than butenes such as 1-hexene, C₁₀ ⁺ linear alpha-olefins (LAO) or a mixture of LAO. The hydrogen spillover effect promoted by the Ni bearing co-catalyst, contributed to significantly enhancing the product yield of light olefins and the on-stream stability of the hybrid catalyst.     

Enhanced Production of C2–C4 Olefins Directly from Synthesis Gas

An attempt made for the selective production of C₂–C₄ olefins directly from the synthesis gas (CO + H₂) has led to the development of a dual catalyst system having a Fischer–Tropsch (K/Fe–Cu/AlOx) catalyst and cracking (H-ZSM-5) catalyst operate in consecutive dual reactors. The flow rate (space velocity) and H₂/CO molar ratio of the feed have been optimized for achieving higher CO conversions and olefin selectivities. The selectivity to C₂–C₄ olefins is further enhanced by optimizing the reaction temperature in the second reactor (cracking), where the product exhibited 51% selectivity to C₂–C₄ hydrocarbons rich in olefins (77%) with a stable time-on-stream performance in a studied period of 100 h.     

Nb–TiO2 supported platinum nanocatalyst for oxygen reduction reaction in alkaline solutions

Platinum based nanocatalyst at home made Nb–TiO₂ support was synthesized and characterized as the catalyst for oxygen reduction reaction in 0.1 mol dm⁻³ NaOH, at 25 °C. Nb doped TiO₂ catalyst support, containing 5% of Nb, has been synthesized by modified acid-catalyzed sol–gel procedure in non-aqueous medium. BET and X-ray diffraction (XRD) techniques were applied for characterization of synthesized supporting material. XRD analysis revealed only presence of anatase TiO₂ phase in synthesized support powder. Existence of any peaks belonging to Nb compounds has not been observed, indicating Nb incorporated into the lattice.Nb–TiO₂ supported Pt nanocatalyst synthesized, using borohydride reduction method, was characterized by TEM and HRTEM techniques. Platinum nanoparticles distribution, over Nb doped TiO₂ support, was quite homogenous. Mean particle size of about 4 nm was found with no pronounced particle agglomeration. Electrochemical techniques: cyclic voltammetry and linear sweep voltammetry at rotating disc electrode were applied in order to study kinetics and estimate catalytic activity of this new catalyst for the oxygen reduction reaction in alkaline solution. Two different Tafel slopes were found: one close to −90 mV dec⁻¹ in low current density region and other approximately −200 mV dec⁻¹ in high current density region, which is in good accordance with literature results for oxygen reduction at Pt single crystals, as well as Pt nanocatalysts in alkaline solutions. Similar specific catalytic activity (expressed in term of kinetic current density per real surface area) of Nb(5%)–TiO₂/Pt catalyst for oxygen reduction reaction in comparison with the carbon supported platinum (Vulcan/Pt) nanocatalyst, was found.     

Glycerol Hydrogenolysis to 1,2-Propanediol by Cu/ZnO/Al2O3 Catalysts

The effect of preparation methods on the Cu/ZnO/Al₂O₃ catalyst structure and catalytic activity on liquid glycerol hydrogenolysis to 1,2-propanediol has been investigated. The physicochemical properties of the catalysts were characterized by BET, XRD, TG/DTA, NH₃-TPD and TPR. The experimental results showed that the catalyst prepared by an oxalate gel–coprecipitation had the highest activity. At 200 °C and 400 psi hydrogen pressure, the glycerol conversion and 1,2-propanediol selectivity catalyzed by the Cu/ZnO/Al₂O₃ catalyst prepared via oxalate gel–coprecipitation were 92.3 and 94.5 % respectively. It was found that the 1,2-propanediol selectivity was dependent on hydrogen pressure and the un-desired by-products were mainly due to the side reactions caused by the presence of the intermediate acetol.

     

Glycerol Hydrogenolysis to 1,2-Propanediol by Cu/ZnO/Al2O3 Catalysts

The effect of preparation methods on the Cu/ZnO/Al₂O₃ catalyst structure and catalytic activity on liquid glycerol hydrogenolysis to 1,2-propanediol has been investigated. The physicochemical properties of the catalysts were characterized by BET, XRD, TG/DTA, NH₃-TPD and TPR. The experimental results showed that the catalyst prepared by an oxalate gel–coprecipitation had the highest activity. At 200 °C and 400 psi hydrogen pressure, the glycerol conversion and 1,2-propanediol selectivity catalyzed by the Cu/ZnO/Al₂O₃ catalyst prepared via oxalate gel–coprecipitation were 92.3 and 94.5 % respectively. It was found that the 1,2-propanediol selectivity was dependent on hydrogen pressure and the un-desired by-products were mainly due to the side reactions caused by the presence of the intermediate acetol.     

Evaluating the Catalytic Performances of SAPO-34 Catalysts for the Oxidative Dehydrogenation of Ethane

Acid silicoaluminophosphate SAPO-34 catalysts with a chabasite-related (CHA) structure were tested for the oxidative dehydrogenation of ethane in the temperature range 550-700 °C achieving very interesting catalytic performances (about 70% C₂H₄ selectivity at 45% ethane conversion) which were related to both Lewis and Brønsted acid sites, as found by a NH₃-TPD study.     

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.     

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.     

Effect of tungsten loading on zirconia impregnated MCM-41 and its catalytic activity on transesterification reaction

WO₃/ZrO₂ weight % (WO₃/ZrO₂ = wt% = 4/22, 8/22, 15/22, 15/30 and 15/40) was impregnated on Si-MCM-41. The crystalinity, textural property, surface feature and surface acidity of the materials were characterized by XRD, N₂-physisorption isotherm (BET), NH₃-TPD, Laser-Raman and XRF. The XRD and BET results revealed that the materials were hexagonally ordered mesoporous (pore size = 2.58–3.07 nm) materials. High angle XRD showed the presence of tetragonal ZrO₂ (crystallite size L = 14.88 nm) and monoclinic ZrO₂. The catalytically active t-ZrO₂ was stabilized by increasing wt% of WO₃. Raman spectra confirmed the presences of crystalline WO₃ along with t-ZrO₂ and m-ZrO₂ which was not detected by high angle XRD. WO₃ restrict the phase transfer from metastable t-ZrO₂ to thermodynamically favoured m-ZrO₂. NH₃-TPD results indicated the presence of weak acid sites and it increased with an increase in tungsten loading on mesoporous materials. There was no appreciable increase in acid sites by increasing ZrO₂. The catalytic activity was studied on transesterification of diethyl oxalate diester with various alcohols in liquid phase system under autogeneous pressure. When the t-ZrO₂ phase increases the selectivity of diester also increases. However the optimum metal oxide loading on Si-MCM-41 was with 15 % WO₃/22 % ZrO₂/Si-MCM-41. Hence the materials can be a convenient and suitable acid catalyst for transesterification.     

Boosting the antimicrobial and Azo dye mineralization activities of ZnO ceramics by enhancing the light-harvesting and charge transport properties

Herein, we report the wet-chemical synthesis of a ferromagnetic nickel-doped ZnO (Zn_1-xNi_xO) nanocatalyst as a novel and visible-light-driven photocatalyst. Through X-ray diffraction, UV/Vis absorption, electronic studies, and current-voltage experiments, the effect of the ferromagnetic nickel dopant on the structural, optical, morphological, and electrical properties of the synthesized Zn_1-xNi_xO nanocatalyst was studied. The Ni-doping introduced the structural variation in the Zn_1-xNi_xO nanocatalyst, exhibiting a visible light-triggered optical band gap of 2.96 eV and an excellent current conductivity of 6.3 × 10⁻⁴ Sm⁻¹. Moreover, the synthesis of the Zn_1-xNi_xO catalyst at the nanoscale enhanced its surface energy, showing a robust affinity to stick with the dye and pathogenic microbes. The synergistic effects of all the mentioned features enable our Zn_1-xNi_xO nanocatalyst to efficiently generate and transport reactive oxygen species (ROS) under visible light illumination. Regarding antibacterial action, the as-synthesized Zn_1-xNi_xO nanocatalyst showed 1.7% higher activity against E. coli than that of the drug Ciprofloxacin. In addition, doped nanocatalysts mineralize almost 97% of the Allura red dye in just 80 min with a constant rate value of 0.036 min⁻¹. The impedance study and post-application XRD proposed that our Zn_1-xNi_xO nanocatalyst has good conductivity and structural stability. Applications studies show the unusual photocatalytic activity of as-synthesized Zn_1-xNi_xO nanocatalysts, which makes it a suitable candidate for industrial discharge treatment applications at the expense of solar light.     

超声制备锆基柱撑膨润土及其MTO催化性能

在超声波作用下,以钠基膨润土为原料、ZrOCl2?8H2O为锆源,制备了锆基柱撑膨润土（Zr-PILM）。结合XRD、BET、FTIR、SEM、吡啶吸附IR光谱等技术对柱撑膨润土进行表征,结果表明：Zr-PILM颗粒保留了较完整的层状和片状结构,层间距和比表面积增加。Zr-PILM的B酸和L酸总量都减少,形成了适宜催化甲醇制低碳烯烃反应的酸位点。超声法制备Zr-PILM用于甲醇制烯烃催化反应,在体积空速1.2 h－1、反应温度360 ℃时,甲醇的转化率达94.4%,低碳烯烃总选择性达到73.9%。     

K/LaFeMnO3 Perovskite-Type Oxide Catalyst for the Production of C2–C4 Olefins via CO Hydrogenation

LaBO₃ (B?=?Fe, Mn, and FeMn) perovskite-type oxides were prepared by sol–gel method and then used as catalysts in CO hydrogenation for light olefins. The catalysts were characterized using XRD, H₂-TPR, SEM, CO (CO₂)-TPD, and XPS. The results showed that the lattice oxygen migration and oxygen vacancies promoted oxygen mobility by doping Mn²⁺ at the B site, Moreover, the presence of manganese as a promoter in the catalyst increased olefin selectivity compared with the olefin selectivity of the catalyst containing iron at the B-site and exhibited resistance to carbon deposition; while reducing the metal elements. In CO hydrogenation, potassium-promoted LaFeMnO₃ catalysts afforded high catalytic activity and C₂⁼–C₄⁼ selectivity. An O/P value of 5.0 and a C₂⁼–C₄⁼ fraction of 54% were achieved for all hydrocarbons with low methane selectivity.

Graphic Abstract

     

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.     

Effect of Si/Al ratio on performance of Pt–Sn-based catalyst supported on ZSM-5 zeolite for n-butane conversion to light olefins

The performance of Pt–Sn-based catalyst, supported on ZSM-5 of different Si/Al ratios were investigated for simultaneous dehydrogenation and cracking of n-butane to produce light olefins. The catalysts were characterized by number of physio-chemical techniques including XRF, TEM, IR spectra, NH₃-TPD and O₂-pulse analysis. Increase in Si/Al ratio of zeolite support ZSM-5 significantly increased light olefin's selectivity, while feed conversion decreases due to lower acidity of support. The results indicated that both the n-butane cracking and dehydrogenation activity to light olefin's over Pt–Sn/ZSM-5 samples with increasing Si/Al ratios greatly enhanced catalytic performance. The catalysts were deactivated with time-on-stream due to the formation of carbon-containing deposits. A coke deposition was significantly related to catalyst activity, while at higher Si/Al ratio catalyst the coke precursors were depressed. These results suggested that the Pt–Sn/ZSM-5 catalyst of Si/Al ratio 300 is superior in achieving high total olefins selectivity (above 90 wt.%). The Pt–Sn/ZSM-5 also demonstrates resistance towards hydrothermal treatment, as analyzed through the three successive reaction-regeneration cycles.