Transformation of South African coal fly ash into ZSM-5 zeolite and its application as an MTO catalyst

This study presents a way of using South African coal fly ash by extracting metals such as Al and Fe with concentrated sulphuric acid, and then using the solid residue as a feedstock for the synthesis of ZSM-5 zeolite. The percentage of aluminium and iron oxides decreased from 28.0 ± 0.2% and 5.0 ± 0.1% in coal fly ash to 24.6 ± 0.1% and 1.6 ± 0.01% in the acid treated coal fly ash respectively. The fly ash-based zeolite ZSM-5 sample synthesised from the solid residue after extraction of Al and Fe, contained 62% of ZSM-5 zeolite pure phase with a number of Brønsted acid site density of 0.61 mmol per g_zeolite.By properly treating the as-prepared coal fly ash-based ZSM-5 zeolite, an active and selective methanol-to-olefins acid catalyst could be designed, leading to full methanol conversion during 15 h on stream. The optimised catalyst exhibited a cumulative methanol conversion capacity of 71 g(MeOH_converted)/g(catalyst) and a light olefin productivity of 21 g(C₂₌–C₄₌)/g(catalyst).     

Butene catalytic cracking to ethylene and propylene on mesoporous ZSM-5 by desilication

Mesopore ZSM-5 was prepared by alkali treatment of parent ZSM-5 zeolite and applied for butene catalytic cracking. The zeolite was treated in the NaOH solutions with different concentrations at 85 °C. XRD showed that the intrinsic MFI structure of ZSM-5 zeolite was preserved and corresponding crystallinity remained unchangeableness when ZSM-5 was treated with low concentration NaOH solutions. However, excessive NaOH led to the destruction of zeolite structure. The BET surface area increased obviously after desilication, and the N₂ adsorption/desorption curves indicated a number of mesopores generation. The experiment of butene catalytic cracking was carried out in a fixed-bed to investigate the influence of mesopores. The results showed that catalytic performances can be greatly improved through introducing the mesopores into parent ZSM-5 by alkali treatment. Highest yield of ethylene plus propylene were obtained when the treated concentration of NaOH solution is 0.1–0.2 M.     

Preparation of hierarchical mesoporous Zn/HZSM-5 catalyst and its application in MTG reaction

The hierarchical mesoporous Zn/ZSM-5 zeolite catalyst was prepared by NaOH treatment and Zn impregnation, and its application in the conversion of methanol to gasoline (MTG) was studied. N2 adsorption-desorption results showed that the mesopores with sizes of 2–20 nm in HZ5/0.3AT was formed by 0.3 M NaOH alkali treatment. The zeolite samples after modification were also characterized by XRF, AAS, XRD, SEM and NH3-TPD methods. Zn impregnated catalyst Zn/HZ5/0.3AT exhibited dramatic improvements in catalytic lifetime and liquid hydrocarbons yield. The selectivity of aromatic hydrocarbons was also improved after Zn impregnation. It is suggested that the mesopores of Zn/HZ5/0.3AT enhanced the synergetic effect of Zn species and acid sites and the capability to coke tolerance, which were confirmed by the results of catalytic test and TGA analysis, respectively.     

不同结构扩孔分子筛催化MTP反应行为及表面积炭物种表征

采用TEAOH溶液处理MFI结构ZSM-5分子筛、MWW结构MCM-22分子筛,NaOH溶液处理TON结构ZSM-22分子筛、CHA结构SSZ-13分子筛得到四种结构的扩孔分子筛。在反应温度480℃、反应压力0.1 MPa、甲醇与水质量比1∶1、甲醇质量空速1.5 h~(-1)的条件下,考察了四种扩孔分子筛的甲醇制丙烯(MTP)催化性能,并采用XRD、N_2吸附-脱附、NH_3-TPD、TG、UV-Raman和GC-M S等方法表征催化剂的物化性质及M TP反应2 h后的分子筛积炭性质。结果表明,四种分子筛扩孔改性后均出现介孔,其中,T-ZSM-5分子筛在MTP反应中寿命最长;T-MCM-22分子筛寿命次之且失活速率慢;而一维孔道结构N-ZSM-22分子筛和八元环尺寸较小的N-SSZ-13分子筛均失活迅速。受拓扑结构和孔道扩散的影响,MTP反应2 h后,分子筛积炭量增加的顺序为T-ZSM-5N-ZSM-22T-MCM-22N-SSZ-13且可溶焦分子质量随积炭量增加而增重,即从五甲基苯增重到菲、芘等多环芳烃。     

Selective production of propylene from methanol over high-silica mesoporous ZSM-5 zeolites treated with NaOH and NaOH/tetrapropylammonium hydroxide

The influence of alkaline treatments with NaOH and NaOH/TPAOH mixtures on the physicochemical properties and catalytic performance of high-silica ZSM-5 zeolites (Si/Al = 175) during the methanol-to-propylene (MTP) reaction have been investigated. It was found that alkaline treatment in an NaOH/TPAOH solution with TPAOH/(NaOH + TPAOH) = 0.4 ensures the formation of narrow and uniform intracrystalline mesoporosity without severely damaging the crystal structure and the intrinsic acidity of the zeolite, leading to the best catalytic performance, including the highest propylene selectivity (47.2) and P/E ratio (4.97) as well as the longest catalyst lifetime (80 h).     

Synthesis of double mesoporous core-shell silica spheres with tunable core porosity and their drug release and cancer cell apoptosis properties

In this work, we demonstrate a simple two-pot approach to double mesoporous core–shell silica spheres (DMCSSs) with uniform size of 245–790 nm, shell thickness of 41–80 nm and surface area and total pore volume of 141–618 m² g^?1 and 0.14–0.585 cc g^?1, respectively. First, solid silica spherical particles were synthesized by the Stöber method and used as a core. Second, a mesoporous shell could be formed around the silica cores by using an anionic surfactant and a co-structure directing agent. It was found that mesopores can be anchored within dense silica cores during mesoporous silica shell formation, synchronously the base group with surfactant assistant can etch the dense silica cores to re-organize new mesostructure, so that double mesoporous core–shell silica sphere (DMCSS) structure can be obtained by a single surfactant-templating step. The spherical size and porosity of the silica cores of DMCSS together with shell thickness can be tuned by controlling Stöber parameters, including the concentrations of ammonia, solvent and tetraethoxysilane and the reaction time. DMCSS were loaded with ketoprofen and thymoquinone, which are an anti-inflammatory and a potential novel anti-cancer drug, respectively. Both drugs showed controlled release behavior from the pores of DMCSS. Drug uptakes within DMCSS were ～27 and 81 wt.% for ketoprofen and thymoquinone, respectively. Furthermore, DMCSS loaded with thymoquinone was more effective in inducing cancer cell apoptosis than uncontained thymoquinone, because of the slow release of the drug from the mesoporous structure.     

Partially graphitic micro- and mesoporous carbon microspheres for supercapacitors

Partially graphitic micro-and mesoporous carbon microspheres(GMMCMs)were synthesized using hydrothermal emulsion polymerization followed by KOH activation and catalytic graphitization.The resulting GMMCMs show micro-and mesopores with a specifc surface area of 1113 m2/g,regular spherical shape with diameters of 0.5–1.0 mm and a partially graphitic structure with a low internal resistance of 0.34 V.The graphitic carbons as electrode for supercapacitor exhibit a fast ion-transport and rapid charge–discharge feature,and a high-rate electrochemical performance.The typical GMMCM electrode shows a specifc capacitance of 220 F/g at 1.0 A/g,and 185 F/g under a high current density of20.0 A/g in a 6 mol/L KOH electrolyte.     

The effect of FER zeolite acid sites in methanol-to-dimethyl-ether catalytic dehydration

In this paper, the effect of acidity of zeolites with FER framework was studied in the methanol dehydration to dimethyl ether reaction, by comparing catalysts with different Si/Al ratios(namely 8, 30 and60). The aim of this work was to investigate how the acid sites concentration, strength, distribution and typology(Br?nsted and Lewis) affect methanol conversion, DME selectivity and coke formation. It was found that the aluminium content affects slightly acid sites strength whilst a relevant effect on acid sites concentration and distribution(Br?nsted/Lewis) was observed as 24% of Lewis sites were found on Alrichest samples, whilst less than 10% of Lewis acid sites were observed on FER at higher Si/Al ratio. All the investigated catalyst samples showed a selectivity toward DME always greater than 0.9 and samples with the lowest Si/Al ratio exhibit the best performances in terms of methanol conversion, approaching the theoretical equilibrium value(around 0.85) at temperatures below 200 °C. Turnover-frequency analysis suggests that this result seems to be related not only to the higher amount of acid sites but also that the presence of Lewis acid sites may play a significant role in converting methanol. On the other hand, the presence of Lewis acid sites, combined with a high acidity, promote the formation of by-products(mainly methane) and coke deposition during the reaction. As final evidence, all the investigated catalysts exhibit very high resistance to deactivation by coke deposition, over 60 h continuous test, and a GC–MS analysis of the coke deposited on the catalyst surface reveals tetra-methyl benzene as main component.     

Recyclable Fenton-like catalyst based on zeolite Y supported ultrafine,highly-dispersed Fe2O3 nanoparticles for removal of organics under mild conditions

The active Fenton-like catalyst, obtained by highly dispersed Fe₂O₃ nanoparticles in size of 5 nm on the surface of zeolite Y, shows the excellent degradation efficiency to phenol higher than 90% under the mild conditions of room temperature and neutral solution, and the catalyst can be easily recovered with stable catalytic activity for 8 cycles.     

不同模板剂合成具有介微结构的ZSM-5分子筛及其甲醇制丙烯性能

分别采用四丙基氢氧化铵(TPAOH),十六烷基三甲基溴化铵(CTAB)和N-十八烷基-N'-己基-四甲基-1, 6-己二铵(C_18-6-6Br₂)作为模板剂,合成了具有不同介微结构的纳米ZSM-5分子筛(NZ),介孔ZSM-5分子筛(MZ)和纳米薄层ZSM-5分子筛(NSZ).对合成的样品进行X射线衍射(XRD),扫描电子显微镜(SEM), N₂吸附-脱附和氨程序升温脱附(NH₃-TPD)表征,并与传统微孔ZSM-5分子筛(CZ)对比.结果表明,样品的介孔孔容和外表面积大小的顺序为NSZ > MZ > NZ > CZ,强/弱酸之比的顺序为CZ > MZ > NZ > NSZ.在甲醇制丙烯(MTP)反应中,催化剂的介微结构特征影响MTP反应的产物选择性及稳定性,丙烯和总低碳烯烃选择性随着介孔孔容的增加而增加, NSZ样品具有最高的丙烯选择性(47.5%)及总低碳烯烃选择性(78.4%).此外,介孔的引入能适当延长催化剂的寿命,具有适宜酸性质的NZ样品的催化寿命最长(200 h).     

Catalyst optimization for enhanced propylene formation in the methanol-to-olefins reaction

ZSM-5 zeolites possessing different chemical compositions, acidities and crystal sizes, were synthesized and characterized by XRD, SEM and FTIR. Those as-prepared acid catalysts were tested in the conversion of methanol into light olefins at 673 K under atmospheric pressure. Propylene-to-ethylene ratios above 5 were achieved over ZSM-5 zeolite catalyst prepared via the fluoride route. This promising methanol-to-propylene (MTP) catalyst was designed both at the molecular scale, exhibiting low Brønsted acid site density, and at the microscopic level since large crystals (25 μm) with few defects were obtained. Aiming in a possible industrial application, the synthesis medium has to be seriously modified, thus avoiding harmful hydrofluoric acid use. Hydrochloric and phosphoric acids were therefore chosen as alternatives and resulted in the same ZSM-5 crystal morphologies and similar catalytic performance.     

Catalytic oxidation of volatile organic compounds (VOCs). Oxidation of o-xylene over Pd and Pt/HFAU catalysts

The transformation of o-xylene in low concentration (1 700 ppmv) into air was investigated over Pd and Pt/HFAU catalysts (framework Si/Al ratio equal to 17 and 100). Whatever the catalyst, o-xylene oxidation into CO₂ and H₂O is accompanied by the retention within the zeolite pores of heavy compounds (‘coke’). The relative significance of these reactions depends on the operating conditions (temperature, time-on-stream) and on the catalyst characteristics (Pd or Pt, Si/Al ratio). Over Pt and Pd/HFAU(17), time-on-stream has a positive effect on the xylene oxidation apparently related to the reducibility of Pd and Pt species during the reaction. The higher activity of Pt/HFAU catalysts can be attributed to its greater number of active species (especially Pt⁰). Those active species can be more rapidly formed than Pd⁰ by auto reduction during the calcination of Pt precursor. Whatever the metal, the higher the Si/Al ratio of the support, the faster the xylene oxidation and the lower the coke formation. This can be related to the higher proportion of reduced species (Pd⁰ and Pt⁰) formed on the more dealuminated catalyst but also to the hydrophobicity of the support. Indeed, the hydrophobicity of the zeolite play a positive role in the oxidation activity in presence of steam; the higher the Si/Al ratio of the zeolite, the faster the o-xylene oxidation. Thus a catalyst with a low platinum content supported on a hydrophobic zeolite (0.10 Pt/HFAU(100)) allows to oxidising totally o-xylene at 210 °C in presence of steam.     

Catalytic stepwise pyrolysis of packaging plastic waste

In this paper the combination of catalytic and stepwise pyrolysis is explored. A mixture of polyethylene (PE), polypropylene (PP), polystyrene (PS), poly(ethylene terephthalate) (PET) and poly(vinyl chloride) (PVC), which resembles real municipal plastic waste, has been pyrolysed in a 3.5 dm³ semi-batch reactor at 440 °C for 30 min using a ZSM-5 zeolite as catalyst. A low temperature (300 °C) dechlorination step has been carried out both with and without catalyst. It has been proved that the application of such dechlorination step gives rise to a 75 wt% reduction of chlorine in the liquid fraction. However, such step has a negative influence on the catalyst, which loses some catalytic activity. The optimum procedure in terms of quality and chlorine content of the products is the combination of first a low temperature step without catalyst, and second the catalytic pyrolysis step.     

Preparation of novel magnetic hollow mesoporous silica microspheres and their efficient adsorption

Ordered mesoporous aluminas with high surface areas (up to 783 m²/g), large pore volumes (up to 0.82 cm³/g) and the presence of complementary micropores (up to 0.17 cm³/g) are synthesized with Pluronic® F127 or P123 triblock copolymers in a one-pot synthesis of metal alkoxide, template and cosolvent molecules such as 1,3,5-trimethylbenzene or 1,3,5-triisopropylbenzene in an acidic ethanol solution at 15 °C. Materials are characterized by nitrogen adsorption analysis, small-angle X-ray diffraction and transmission electron microscopy.     

Availability and interconnectivity of pores in mesostructured ZSM-5 zeolites by the adsorption and diffusion of mesitylene

Probing the mesopore architecture in mesoporous zeolites is of importance for large scale applications of the materials. In this work, the adsorption and diffusion of mesitylene with larger molecule size in mesoporous ZSM-5 zeolites were carried out, in order to acquaint the availability and interconnectivity of mesopores in zeolite crystals. The comparisons of the shape of adsorption isotherms and the mesopore volume calculated from mesitylene and N₂ adsorption in mesoporous ZSM-5 zeolites with different mesoporosities can be used to discriminate two cases of mesopores: accessible mesopores connected to external surface of the zeolite crystals and non-accessible meso-voids that are occluded in the microporous matrix. Furthermore, the effective diffusivity and activation energy of mesitylene in mesoporous ZSM-5 extracted from ZLC desorption curves as a function of mesopore volume calculated from mesitylene adsorption reveal the enhancement of mesopore interconnectivity to molecule diffusion in zeolite crystals.     

CO tolerant Pt/WC methanol electro-oxidation catalyst

Platinum supported on WC (Pt/WC) catalyst (20 wt.% Pt) was synthesized as a new methanol electro-oxidation catalyst. Particle size of 7.5 nm was obtained from X-ray diffraction results and a uniform distribution of particles was observed by transmission electron microscopy. In cyclic voltammetry (CV) measurement, the reduction peak potential of PtO increased from 0.72 V in commercial Pt/C to 0.76 V in Pt/WC. By combining the CV and CO stripping results, spill-over of H⁺ from Pt to WC was observed. Electrochemically active surface area calculated from the desorption area of H⁺ were 11.2 and 5.74 m²/g catalyst for Pt/WC and Pt/C, while those obtained from the desorption area of CO were 4.42 and 6.40 m²/g catalyst, respectively. CO electro-oxidation peak potential greatly decreased from 0.80 V in Pt/C to 0.68 V in Pt/WC. The reaction of WC with water to produce WC–OH could lower to CO electro-oxidation peak potential. Specific activity for methanol electro-oxidation increased from 144 mA/m² in Pt/C to 188 mA/m² in Pt/WC.     

Aqueous treatment of single-walled carbon nanotubes for preparation of Pt–Fe core–shell alloy using galvanic exchange reaction: Selective catalytic activity towards oxygen reduction over methanol oxidation

We have demonstrated a new, cost effective synthesis of single-walled carbon nanotube supported Pt–Fe core–shell alloy catalyst (Pt–Fe/SWNT) for the direct methanol fuel cell using galvanic exchange reaction. The Pt–Fe/SWNTs have shown much larger Pt active surface area (150 m²/g-Pt) than the commercial catalyst (54 m²/g-Pt). Furthermore, four-fold enhancement of catalytic activity of the Pt–Fe/SWNTs for oxygen reduction reaction (ORR) has been observed. This catalyst has also demonstrated its tolerance to methanol in ORR.     

Synthesis of mesoporous hollow carbon hemispheres as highly efficient Pd electrocatalyst support for ethanol oxidation

The synthesis procedure of the highly mesoporous hollow carbon hemispheres (HCHs) using glucose as carbon source and solid core mesoporous shell silica (SCMSS) as template and the formation mechanism of the HCHs have been presented. The HCHs show an ultrahigh surface area of 1095.59 m² g^?1 and an average mesopore size of 9.38 nm. The hemispherical structure with large mesopores also results in the improvement in the mass transfer and therefore more concentrated ethanol solution can be used to increase the energy density. The additional advantage of the HCHs compared to the hollow carbon spheres is that they can provide the similar surface area at reduced volume. The current densities of ethanol oxidation on Pd nanoparticles supported on HCH (Pd/HCH) electrocatalyst are three times as many as on Pd/C at the same Pd loadings.     

多级孔ZSM-5分子筛的合成及其在甲醇脱水制二甲醚反应中的应用

以四丙基氨为微孔模版剂,阳离子高分子聚合物为介孔模版剂,合成了具有多级介孔的ZSM-5分子筛,并用于甲醇气相脱水合成二甲醚.结果表明,加入阳离子高分子聚合物后,合成的HZSM-5分子筛样品既保持了其MFI典型结构,又呈现了多级介孔特征;随着阳离子高分子聚合物模板剂加入量的增加,其多级介孔特征更为明显.具有多级介孔的HZSM-5分子筛表现出比常规微孔HZSM-5分子筛高的反应稳定性和二甲醚选择性,这主要是由于其织构和酸性的双重作用.     

Exploring meso-/microporous composite molecular sieves with core-shell structures

A series of core–shell‐structured composite molecular sieves comprising zeolite single crystals (i.e., ZSM‐5) as a core and ordered mesoporous silica as a shell were synthesized by means of a surfactant‐directed sol–gel process in basic medium by using cetyltrimethylammonium bromide (CTAB) as a template and tetraethylorthosilicate (TEOS) as silica precursor. Through this coating method, uniform mesoporous silica shells closely grow around the anisotropic zeolite single crystals, the shell thickness of which can easily be tuned in the range of 15–100 nm by changing the ratio of TEOS/zeolite. The obtained composite molecular sieves have compact meso‐/micropore junctions that form a hierarchical pore structure from ordered mesopore channels (2.4–3.0 nm in diameter) to zeolite micropores (≈0.51 nm). The short‐time kinetic diffusion efficiency of benzene molecules within pristine ZSM‐5 (≈7.88×10^?19 m² s^?1) is almost retainable after covering with 75 nm‐thick mesoporous silica shells (≈7.25×10^?19 m² s^?1), which reflects the greatly opened junctions between closely connected mesopores (shell) and micropores (core). The core–shell composite shows greatly enhanced adsorption capacity (≈1.35 mmol g^?1) for large molecules such as 1,3,5‐triisopropylbenzene relative to that of pristine ZSM‐5 (≈0.4 mmol g^?1) owing to the mesoporous silica shells. When Al species are introduced during the coating process, the core–shell composite molecular sieves demonstrate a graded acidity distribution from weak acidity of mesopores (predominant Lewis acid sites) to accessible strong acidity of zeolite cores (Lewis and Brønsted acid sites). The probe catalytic cracking reaction of n‐dodecane shows the superiority of the unique core–shell structure over pristine ZSM‐5. Insight into the core–shell composite structure with hierarchical pore and graded acidity distribution show great potential for petroleum catalytic processes.