Utilization of mesoporous molecular sieves synthesized from natural source rice husk silica to Chlorinated Volatile Organic Compounds (CVOCs) adsorption

The adsorption of trichloroethylene (TCE), tetrachloroethylene (PCE), and carbon tetrachloride was studied over our synthesized mesoporous material, MCM-41, from rice husk silica source, abbreviated as RH-MCM-41. More than 99% silica for RH-MCM-41 synthesis was extracted from rice husk under refluxing in HBr solution and then calcined at 873 K for 4 hours. RH-MCM-41 possessed surface area around 750-1,100 m²/g with a uniform pore size with an average diameter of 2.95 nm, narrow range of pore distribution and somewhat hexagonal structure, similar to properties of parent MCM-41. The adsorption of CC1₄ to RH-MCM-41 was stronger than that of TCE and PCE. The adsorption capacity of RH-MCM-41 for CVOCs (chlorinated volatile organic compounds) was higher than commercial mordenite and activated carbons.     

The nature of low temperature deactivation of CoCr2O4 and CrOx/γ-Al2O3 catalysts for the oxidative decomposition of trichloroethylene

The CoCr₂O₄ and CrO_x/γ-Al₂O₃ catalysts were used for the oxidative decomposition of trichloroethylene (TCE). Both catalysts showed an initial deactivation at low temperatures around 280 °C, mainly due to the dissociative adsorption of reactant TCE. This was confirmed by the temperature programmed oxidation of TCE where the carbon oxides were formed up to a temperature below 300 °C. Possible changes in the oxidation state of chromium species were observed with XANES and ESR. During the oxidation reaction at low temperatures, the Cr(VI) species were reduced to Cr(III) species, which seemed to be coupled with TCE adsorption. At higher temperatures, however, the Cr(VI) species appeared again and the catalytic activity was completely recovered.     

2-吡啶甲醛功能化SBA-15介孔材料的制备及其对Cr(Ⅲ)离子的吸附

通过席夫碱反应将2-吡啶甲醛成功嫁接到氨基化的SBA-15介孔分子筛上，本文获得了一种新型功能化SBA-15吸附剂（N-SBA-15）。采用傅里叶变换红外光谱、X射线衍射、元素分析、扫描电子显微镜、透射电子显微镜、X射线光电子能谱、热重分析和氮气吸附-脱附等手段对N-SBA-15的表面官能团、形貌、孔道结构和表面化学性质进行了详细的表征分析。利用N-SBA-15对水溶液中的Cr(Ⅲ)进行了吸附实验，其最大吸附容量为84.3mg/g。动力学分析和等温吸附研究结果表明，N-SBA-15对Cr(Ⅲ)的吸附过程符合准二级动力学模型和Langmuir模型。吸附热力学分析表明，该吸附过程是自发的吸热过程（?G<0、?S>0、?H>0）。吸附机理分析表明该吸附过程主要是由N-SBA-15表面有机官能团与Cr(Ⅲ)的配位作用实现的。而且，N-SBA-15吸附剂经过5次吸附-脱附测试，仍然对Cr(Ⅲ)具有较高的吸附容量。     

Cooperative effect of crystallization temperature and NaF addition in the formation process and hydrothermal stability of MCM-48 mesoporous molecular sieve

The hydrothermal stability of MCM-48 was conveniently and effectively improved by increasing the crystallization temperature and directly adding NaF to the synthesis gel. The crystallization temperature varied from 373 K to 403 K. The influences of NaF addition, crystallization temperature and crystallization time on the formation process and hydrothermal stability of MCM-48 were systematically studied here to solve the problem of poor reproducibility. Results from XRD patterns indicated that the crystallization temperature and crystallization time were very critical factors for the improvement of the hydrothermal stability besides NaF addition. The formation process of MCM-48 was significantly accelerated and the pore structure ordering was also greatly improved by increasing the crystallization temperature and F⁻/Si ratio. A high hydrothermally stable MCM-48 mesoporous molecular sieve was obtained after being crystallized at 393 K for 36 h in the presence of NaF, which endured the hydrothermal treatment in boiling water at least for 4 days. However, only an amorphous product was obtained when the crystallization temperature was further increased to 403 K. Results from Si MAS NMR, N₂ adsorption isotherms, TEM, Raman spectra and XRD patterns manifested that the improved stability of MCM-48 was attributed to the high silicates condensation degree and the excellent pore structure ordering. The possible reason for the successful formation of hydrothermally stable MCM-48 sample by controlling the crystallization temperature, time and F⁻/Si ratio was explained here.     

Synthesis,characterization and catalytic properties of mesoporous MCM-48 containing zeolite secondary building units

Mesoporous aluminosilicate MCM-48 containing zeolite secondary building units in the pore wall has been synthesized in alkaline media with a two-step procedure. The aluminosilicate precursors comprising zeolite secondary building units were first synthesized by carefully controlling reaction conditions and then were assembled using cotemplates of gemini surfactant [C₁₈H₃₇N(CH₃)₂(CH₂)₃N(CH₃)₂C₁₈H₃₇]²⁺ (18-3-18) and triethanolamine (TEA). X-ray Diffraction (XRD) patterns of the as-made samples indicated that highly ordered mesostructured MCM-48 was formed. Transmission Electron Microscopy (TEM) images further verified the formation of MCM-48 with uniform cubic pore channel system having the pore opening diameter of about 25 Å. Compared with the conventionally synthesized MCM-48, the as-synthesized MCM-48 sample showed an adsorption band at 520 600 cm^-1 in its FT-IR spectrum, which was assigned to five-membered ring vibration from zeolite structure. This suggested the presence of zeolite building units in the pore wall. N2 adsorption data showed that the material had a much higher specific surface area (1 200 m₂/g) than the conventional MCM-48(1 100 m₂/g). Finally, the catalytic performance of the as-made MCM-48 was evaluated by hydrogenation dealkylation reaction of heavy aromatic hydrocarbons. Catalytic results showed that the as-made MCM-48 catalyst exhibited higher conversion than the conventional MCM-48 catalyst. The as-made mesostructured MCM-48 may have a potential catalytic application in the conversion of bulky molecules.     

氨基功能化介孔硅吸附剂的制备及其对铬(Ⅲ)的吸附行为

采用3-氨丙基三甲氧基硅烷（APTMS）对SBA-15介孔硅进行改性,获得氨基功能化介孔硅吸附剂（NH₂-SBA-15）,从而赋予其螯合重金属离子的能力。利用XRD、SEM、TEM、EDX、TGA、BET和XPS等手段对吸附剂的表面形貌、孔道结构、元素分布和表面化学性质进行了表征。研究了NH₂-SBA-15吸附剂对水溶液中铬(Ⅲ)的吸附性能,分析了吸附动力学、吸附热力学和再生性能。结果表明,SBA-15吸附剂经过氨基功能化后,其原有的结晶结构没有明显变化,且对铬(Ⅲ)的吸附性能显著提高。NH₂-SBA-15对铬(Ⅲ)的吸附行为符合Langmuir等温吸附模型和拟二级吸附动力学方程。NH₂-SBA-15对铬(Ⅲ)的吸附过程主要依靠其表面—NH₂与铬(Ⅲ)的配位螯合作用,且为吸热过程。经过5次循环利用后,NH₂-SBA-15对铬(Ⅲ)的吸附率仍然保持在92%以上。该氨基功能化介孔硅吸附剂在吸附铬(Ⅲ)方面具有潜在的应用前景。     

Chromium catalysts supported on mesoporous silica for ethylene tetramerization: Effect of the porous structure of the supports

Supported chromium catalysts were prepared by loading Cr(acac)₃ and N-isopropyl bis(diphenylphosphino)amine (PNP) onto methylaluminoxane-modified MCM-41 and SBA-15. The structure of supported catalysts was characterized and the influence of the pore structure of supports on the reactivity for ethylene tetramerization was investigated. The results revealed that the chromium was immobilized on the mesoporous silica in different supported patterns, which was affected by the pore size of the supports and affected catalyst performance. The highest selectivity toward 1-octene was provided by the SBA-15-supported Cr(acac)₃/PNP catalyst, and this value was higher than that of the homogeneous analogs.     

PEI-MCM-41吸附剂的制备及其CO_2吸附性能研究

使用不同方法合成了MCM-41,制备出具有不同骨架结构和内部孔道结构的介孔分子筛。通过XRD、高倍投射电镜、低温氮吸附/脱附等方法对样品进行了表征分析。用PEI对MCM-41分子筛进行改性,然后使用热重方法测定了其对CO2的吸附量。结果表明,使用硅酸钠和硫酸为原料制备的样品具有较大的比表面积和孔容,在该样品上负载50%PEI吸附量达到了269.3 mg/g,是同等条件下单纯PEI吸附量的3.4倍。说明将PEI负载在具有大比表面积和孔容的MCM-41介孔分子筛上,可以使PEI得到充分分散,并充分利用PEI分子上的氨基。     

Formation of Pd nanoparticles in surfactant-mesoporous silica composites and surfactant solutions

Highly dispersed palladium nanoparticles containing mesoporous silicas MCM-41 and MCM-48 were prepared by one-pot synthesis. The method consists of the simultaneous formation of CTA⁺ surfactant templating MCM-41 mesophase and CTA⁺ micelle-capped PdO, which was reduced by hydrogen to Pd metal with particle size ≈ 2 nm and was observed to stay inside the mesochannels of MCM-41 (pore size ≈ 3.8 nm) by TEM, XAS, and PXRD. During hydrothermal synthesis of Pd/MCM-48, Pd nanoparticles of average size ≈ 6–7 nm were deposited on the MCM-48 of pore size = 4 nm. The deposition is probably derived from ethanol reduction of Pd(II) complex generated from PdCl₂ precursor by hydrolysis of TEOS and C₁₂H₂₅(OCH₂CH₂)₄OH surfactant. The formation of Pd(0) from Pd(II) species in solid mesoporous silicas by hydrogen reduction was monitored by in situ XAS, and compared with the formation of Pd(0) from [PdCl₄]²⁻, [PdCl₃(H₂O)], and Pd(OH)₂ by sodium dodecyl sulfate surfactant and alcohol reduction in aqueous solutions.     

五乙烯六胺改性制备CO2吸附剂及其对模拟烟气中CO2捕集性能的研究（英文）

A novel solid support adsorbent for CO2 capture was developed by loading pentaethylenehexamine (PEHA) on commercial y available mesoporous molecular sieve MCM-41 using wet impregnation method. MCM-41 sam-ples before and after PEHA loading were characterized by X-ray powder diffraction, N2 adsorption/desorption, thermal gravimetric analysis and scanning electron microscope to investigate the textural and thermo-physical properties. CO2 adsorption performance was evaluated in a fixed bed adsorption system. Results indicated that the structure of MCM-41 was preserved after loading PEHA. Surface area and total pore volume of PEHA loaded MCM-41 decreased with the increase of loading. The working adsorption capacity of CO2 could be significantly improved at 60%of PEHA loading and 75 °C. The effect of the height of adsorbent bed was investigated and the best working adsorption capacity for MCM-41-PEHA-60 reached 165 mg·(g adsorbent)?1 at 75 °C. Adsorption/desorption circle showed that the CO2 working adsorption capacity of MCM-41-PEHA kept stable. ? 2014 The Chemical Industry and Engineering Society of China, and Chemical Industry Press. Al rights reserved.     

MCM-41介孔材料的合成条件和特性对吸附镉离子的影响

以气相氧化硅为硅源,十六烷基三甲基溴化铵(cetyl trimethyl ammonium bromide,CTAB)为模板剂,分别在碱性[氢氧化钠(NaOH),四乙基氢氧化铵,tetraethyl ammonium hydroxide,(C2Hs)4NOH(TEAOH)]和酸性介质条件[盐酸(HCl)]T水热合成了MCM-41有序介孔材料MCM-41-N,MCM-41-T和MCM-41-H.用X射线衍射、氮气吸附-脱附等手段对比分析了合成的3种MCM-41介孔材料的物相、比表面积、孔径、孔体积等,发现酸性介质中合成的介孔材料的孔径最大.在此基础上,利用MCM-41介孔材料对比研究了处理含镉离子(Cd2 )废水的效果和机理,确定了不同介孔材料用量、不同初始pH值条件下MCM-41介孔材料对水中Cd2 的吸附率和吸附量.结果表明:介孔材料用量相同时,溶液pH值的增大有利于提高3种MCM-41介孔材料对水中Cd2 的处理效果.在pH值从7.0到8.0的过程中,其吸附率有1个突变,MCM-41-T的Cd2 吸附率从35.65%提高到62.15%;MCM-41-N的从38.80%提高到69.40%;MCM-41-H的从50.22%提高到73.47%.孔径最大的MCM-41-H对Cd2 的吸附效果最佳,最大吸附率为89.56%,最大吸附容量为8.57 mg/g.吸附溶液pH值的大小和介孔材料的孔径尺寸是决定吸附量大小的关键因素,因此,重点应通过优化合成工艺提高介孔材料的孔径.     

Synthesis of polyaniline/mesoporous carbon nanocomposites and their application for CO<Subscript>2</Subscript> sorption

Ordered mesoporous carbons (OMC), were synthesized by nanocasting using ordered mesoporous silica as hard templates. Ordered mesoporous carbons CMK-1 and CMK-3 were prepared from MCM-48 and SBA-15 materials with pore diameters of 3.4 nm and 4.2 nm, respectively. Mesoporous carbons can be effectively modified for CO₂ adsorption with amine functional groups due to their high affinity for CO₂. Polyaniline (PANI)/mesoporous carbon nanocomposites were synthesized from in-situ polymerization by dissolving OMC in aniline monomer. The polymerization of aniline molecules inside the mesochannels of mesoporous carbons has been performed by ammonium persulfate. The nanocomposition, morphology, and structure of the nanocomposite were investigated by nitrogen adsorption-desorption isotherms, Fourier Transform Infrared (FT–IR), X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and thermo gravimetric analysis (TGA). CO₂ uptake capacity of the mesoporous carbon materials was obtained by a gravimetric adsorption apparatus for the pressure range from 1 to 5 bar and in the temperature range of 298 to 348 K. CMK-3/PANI exhibited higher CO₂ capture capacity than CMK-1/PANI owing to its larger pore size that accommodates more amine groups inside the pore structure, and the mesoporosity also can facilitate dispersion of PANI molecules inside the pore channels. Moreover, the mechanism of CO₂ adsorption involving amine groups is investigated. The results show that at elevated temperature, PANI/mesoporous carbon nanocomposites have a negligible CO₂ adsorption capacity due to weak chemical interactions with the carbon nanocomposite surface.     

Characterization of acidic property of sulfo-group functionalized microporous and mesoporous silica by adsorption microcalorimetry

Sulfo-group functionalized microporous and mesoporous silica based-on a MCM-41 framework which showed solid acid property were synthesized and characterized by adsorption microcalorimetry. Both the sulfo-functionalized microporous and mesoporous silica (Micro-SO₃H and Meso-SO₃H) were prepared by the oxidation of thiol group (–SH) included mesoporous silica which was obtained through the hydrolysis and co-condensation of tetramethoxysilane (TMOS) and mercaptopropyl trimethoxysilane (MPTMS). The samples have an ordered two-dimensional hexagonal pore array similar to that of MCM-41 as depicted from the XRD patterns. Nitrogen adsorption also shows that both microporous and mesoporous silica have pore characteristics similar to MCM-41, i.e. high surface area and high pore volume. However, pore regularity, surface area and pore volume decreased as the MPTMS loading increased. Solid-state ²⁹Si NMR indicated that the sulfo groups were successfully incorporated into both microporous and mesoporous silica frameworks. This sulfo-functionalized porous silica have high NH₃ uptakes and high differential heats of NH₃ adsorption, suggesting the presence of strong acidic sulfo groups on the silica surface. Acid catalyses of the samples were characterized by the isomerization reaction of but-1-ene to cis, trans-but-2-ene.     

Combined sorbent/catalyst media for destruction of halogenated VOCs

Several chromium modified zeolites have been developed and tested for their ability to physisorb chlorinated VOCs (CVOCs) at ambient and then catalytically destroy them at elevated temperatures (ca. 300°C). These dual function materials, which act as both sorbents and catalysts, are believed to be the key to implementing a new energy efficient process for the destruction of low concentration level CVOC streams. Data showing catalytic activity, sorptivity and other physical properties for Y and ZSM-5 zeolites based media are presented. A chromium exchanged ZSM-5 (Cr-ZSM-5) medium which showed superior performance catalytically (> 95% TCE and MeCl₂ destruction at 300°C) and adequate sorption capacity (0.074 g TCE/g sorbent, 0.064 g MeCl₂/g sorbent at 23°C in the presence of humid air) was chosen for subsequent dual function tests. These tests showed that ambient temperature fixed bed sorption of CVOCs followed by periodic heating of the upper portion of the bed to catalytic temperatures (ca. 35°C) with slow temperature ramping of the lower portion to desorb trapped CVOCs, produced a highly energy efficient cyclic process for their destruction. A Cr-ZSM-5 bed, which alternately stored and then destroyed CVOC from a humid 110 ppm TCE stream at a space velocity of 2400 h⁻¹, was shown to operate over a 1460 min cycle which required heating for only 7% of the time.     

Plasma-assisted catalysis total oxidation of trichloroethylene over gold nano-particles embedded in SBA-15 catalysts

The oxidative decomposition of trichloroethylene (TCE) in dry air was investigated in non-thermal plasma at atmospheric pressure and room temperature, both in the absence and in the presence of gold containing mesoporous silica (GMS) catalysts. In the absence of catalyst, TCE removal reached 100% for average powers dissipated in the plasma above 3 W, for a TCE concentration of 430 ppmv. Carbon monoxide and carbon dioxide were the major reaction products with CO₂ selectivity up to 25% and CO selectivity up to 70%. In the presence of gold containing mesoporous catalysts, the concentrations of CO and CO₂ increased as compared to those obtained with plasma alone. The GMS catalysts can dissociate ozone produced in plasma to oxygen radicals that decompose TCE. Among these catalysts, the one containing the least amount of Au (0.5% GMS) showed the best catalytic performance. In the presence of ozone generated in the plasma, isolated gold cations might play a critical role for the catalytic behavior.     

Hydrocracking of petroleum gas oil over NiW/MCM-48-USY composite catalyst

MCM-48-USY composite materials were prepared by coating USY zeolite by a layer of MCM-48 mesoporous material at different meso/microporous ratios (SiO₂/USY ratios of 0.1, 0.2, 0.3, 0.4, 0.5) and used as support for nickel and tungsten. The NiW/MCM-48-USY catalysts were prepared using the incipient wetness method. The prepared catalysts were characterized by TPD-TGA acidity, TGA thermal stability, BET surface area, pore volume, pore size, XRD, SEM and TEM and then tested for hydrocracking of petroleum gas oil at reaction temperature of 450 °C, contact time of 90 min and catalyst to gas oil ratio of 0.04. In all prepared samples, the catalyst activity and properties were improved with increasing SiO₂/USY ratio and found that maximum values of a total conversion and liquid product (total distillate fuels) were obtained at SiO₂/USY ratio of 0.5. Finally, the obtained results from hydrocracking of gas oil over composite MCM-48-USY catalysts were compared with those obtained over physically mixed USY and MCM-48 catalysts.     

The entrapment of UO2 in mesoporous MCM-41 and MCM-48 molecular sieves

A method based on direct template-ion-exchange was employed for the entrapment of UO₂²⁺ ions in MCM-41 and MCM-48 molecular sieves via swapping of cetyltrimethylammonium cations present in the mesoporous channels by the UO₂²⁺ ions in an aqueous solution. The samples were characterized by XRD, FT-IR, and ICP-AES techniques. The entrapment of UO₂²⁺ ions is facilitated by the large pore size vis-a-vis the high surfactant content in the as-synthesized host materials. A higher loading of UO₂²⁺ ions was achieved in MCM-48 as compared to MCM-41, which could be attributed to its three-dimensional pore system and higher surfactant-to-silica ratio. FT-IR results provide an evidence of a strong binding of UO₂²⁺ groups with the defect silica sites of mesoporous molecular sieves.     

Evaluation of humic acid, chromium (VI) and TiO2 ternary system in relation to adsorptive interactions

Batch adsorption studies were carried out for the assessment of the adsorptive interactions of the system composed of humic acid, Cr(VI) and TiO₂. These were preceded by a thorough investigation of the effect of the chromium ion concentration on the adsorption of humic acid onto TiO₂. The adsorption equilibrium of total chromium, humic acid, and titanium dioxide in water were examined separately and in all combinations in order to distinguish the effects based on the interaction of the components. The adsorption data for the binary system as well as the ternary system were modeled with a simple Freundlich model and the model parameters were compared in terms of Cr(VI) and humic acid as expressed by Color₄₃₆ (color forming moieties) and UV₂₅₄ (UV absorbing centers) parameters.

In binary systems composed of Cr(VI) and TiO₂ no direct relationship could be assessed between adsorption capacity values (K_F) and changes in chromium ion concentration. Chromium ion and humic acid interactions were followed by UV-Vis spectra. A minor change irrespective of added chromium ion concentration was observed for Color₄₃₆ and UV₂₅₄ parameters of humic acid (<5%). However, a significant alteration was observed at 365 nm wavelength indicating the formation of chromate esters. In ternary systems comprising humic acid, Cr(VI) and TiO₂, increasing Cr(VI) concentration five-fold did not cause drastic changes in the adsorption capacity values in terms of Cr(VI) concentration. On the other hand, the adsorption capacity values for color forming moieties as well as for UV absorbing centers of humic acid exhibited a decreasing trend with respect to increasing chromium ion concentration.     

Al-MCM-48 as a potential hydrotreating catalyst support: I – Synthesis and adsorption study

The work has been focused on utilizing mesoporous alumina MCM-48 material as a potential hydrotreating catalyst support for light-cycle oil (LCO) and exploring its adsorption ability for large aromatics. A series of Al-MCM-48 samples with various Si/Al ratios was synthesized via a hydrothermal method and characterized with X-ray diffraction (XRD), nitrogen adsorption isotherms, solid NMR, etc. The adsorption equilibrium isotherms of typical aromatics in LCO such as diaromatic 1-methylnaphthalene on Al-MCM-48 and MCM-48 samples were studied by a standard gravimetric technique. Compared with parent MCM-48, Al-MCM-48 samples exhibited higher adsorption capacity and stronger adsorption affinity towards the addressed aromatic compounds. The incorporation of alumina into MCM-48 materials generated acid centers and more hydroxyl groups on the support surface, which can provide enhanced adsorption for the sorbate molecules and dispersion of active phases. It was found that the adsorption behaviors of the aromatic compounds in Al-MCM-48 samples were mainly governed by the acidity of the support. The balance between pore volume and acid strength of Al-MCM-48 can be adjusted by altering Si/Al ratio. The influence of incorporation of Al on the framework and adsorption properties of the materials has also been investigated.     

Mesoporous molecular sieve MCM-41 supported Co–Mo catalyst for hydrodesulfurization of petroleum resids

In this work, we explored the potential of mesoporous zeolite-supported Co–Mo catalyst for hydrodesulfurization of petroleum resids, atmospheric and vacuum resids at 350–450°C under 6.9 MPa of H₂ pressure. A mesoporous molecular sieve of MCM-41 type was synthesized; which has SiO₂/Al₂O₃ ratio of about 41. MCM-41 supported Co–Mo catalyst was prepared by co-impregnation of Co(NO₃)₂·6H₂O and (NH₄)₆Mo₇O₂₄ followed by calcination and sulfidation. Commercial Al₂O₃ supported Co–Mo (criterion 344TL) and dispersed ammonium tetrathiomolybdate (ATTM) were also tested for comparison purposes. The results indicated that Co–Mo/MCM-41(H) is active for HDS, but is not as good as commercial Co–Mo/Al₂O₃ for desulfurization of petroleum resids. It appears that the pore size of the synthesized MCM-41 (28 Å) is not large enough to convert large-sized molecules such as asphaltene present in the petroleum resids. Removing asphaltene from the resid prior to HDS has been found to improve the catalytic activity of Co–Mo/MCM-41(H). The use of ATTM is not as effective as that of Co–Mo catalysts, but is better for conversions of >540°C fraction as compared to noncatalytic runs at 400–450°C.