CARBON DIOXIDE METHANATION ON ORDERED MESOPOROUS CO/KIT-6 CATALYST

Mesoporous Co/KIT-6 and Co/SiO₂ catalysts were prepared via hydrogen reduction and were subsequently used in CO₂ catalytic hydrogenation to produce methane. The properties of the prepared Co/KIT-6 catalyst were investigated by low-angle X-ray diffraction, Brunauer-Emmett-Teller analysis, and transmission electron microscopy. The results indicate that the synthesized Co/KIT-6 catalyst has mesoporous structures with well-dispersed Co species, as well as higher CO₂ catalytic hydrogenation activities than that of the Co/SiO₂ catalyst. The Co/KIT-6 catalyst has a large specific surface area (368.9 m² · g^?1) and a highly ordered bicontinuous mesoporous structure. This catalyst exhibits excellent CO₂ catalytic hydrogenation activity and methane product selectivity; the CO₂ conversion and methane selectivity of the Co/KIT-6 catalyst at 280°C are 48.9% and 100%, respectively. The highly ordered, bicontinuous mesoporous structure of the Co/KIT-6 catalyst improves selectivity for the methane product.     

介孔二氧化硅KIT-6介观单晶微球的合成

以非离子表面活性剂［聚环氧乙烷（PEO）-聚环氧丙烷（PPO）-聚环氧乙烷三嵌段共聚物,P123］和阳离子聚电解质（聚二甲基二烯丙基氯化铵,PAC）形成的复合物胶束为模板,合成了具有球形形貌的介孔二氧化硅KIT-6介观单晶微球。通过扫描电镜（SEM）、透射电镜（TEM）、X射线衍射（XRD）、氮气物理吸附和热重分析（TGA）等手段对合成材料的形貌及孔结构进行了表征分析。结果表明,以有机复合物胶束为模板合成出的介孔KIT-6二氧化硅材料具有较规整的球形形貌,颗粒直径为2~3 μm,具有较大的比表面积和孔体积（747 m²/g和1.3 cm³/g）,介孔孔径为8.5 nm,且在整个颗粒内部介孔保持高度的有序排列。由于长链聚电解质PAC与硅源有着较强相互作用,样品可以在较高水热温度下（160 ℃）合成,有利于提升介观结构的稳定性。该合成方法对于介孔二氧化硅KIT-6单晶微球的合成及其在催化及吸附分离等领域的应用具有一定的启发意义。     

Structural modulation of cage-like mesoporous KIT-5 silica by post-synthesis treatments with ammonia and/or sulfuric acid

The post-synthesis structural modulation of cage-like mesoporous KIT-5 silica by the treatments with the ammonia solution of NH₄OH and/or the aqueous solution of H₂SO₄ was studied. While the NH₄OH-treated KIT-5 silicas generally have smaller unit cell parameters, smaller mesopore cage sizes and lower micropore volumes, the H₂SO₄ treatment gave materials with larger cage-like mesopores and pore entrances but very low micropore volumes. The effects of consecutive treatments with NH₄OH and H₂SO₄ on the structural properties of the treated KIT-5 silicas were also investigated.     

氨基功能化介孔分子筛KIT-1催化苯甲醛与丙二酸二乙酯缩合反应研究

采用后合成法将3-氨丙基三甲氧基硅烷嫁接在纯硅介孔分子筛KIT-1的孔道内外表面,制备出含氨丙基基团的介孔分子筛样品NH2-KIT-1,并用于苯甲醛和丙二酸二乙酯Knoevenagel缩合反应。利用傅里叶变换-红外光谱(FT IR)、X射线粉末衍射(XRD)、N2吸附-脱附和酸碱滴定等方法对样品的结构和表面碱含量进行了表征与测定。结果表明:氨丙基已成功嫁接在分子筛KIT-1表面,样品NH2-KIT-1仍保持了基体KIT-1的介孔结构和较高的比表面积、较大的孔容与孔径。表面碱含量为1.105 mmol/g样品(即30%NH2-KIT-1)在苯甲醛和丙二酸二乙酯Knoevenagel缩合反应中表现的催化活性最好,140℃反应12h,苯甲醛的转化率为66.5%,重复使用4次后,苯甲醛转化率下降到46.9%,表面碱含量下降到0.870mmol/g。催化剂活性下降的原因可能是分子筛表面活性基团-(CH2)3-NH2脱落造成的。     

Effect of calcination temperature on the oxidation of benzene with ozone at low temperature over mesoporous α-Mn2O3

Highly ordered mesoporous α-Mn₂O₃ was synthesized from cubic mesoporous silica (KIT-6) via nano-casting method. The mesoporous α-Mn₂O₃ thus obtained was calcined at 200-500 °C, and characterized using XRD, N₂ sorption and temperature-programmed reduction (TPR). The calcination temperature did not significantly affect the BET surface areas, mesopore sizes, pore structures and crystallinities of the mesoporous α-Mn₂O₃ materials. The mesoporous α-Mn₂O₃ calcined at 300 °C showed the highest catalytic activity due to its high reduction ability revealed from the TPR analysis. However, the catalytic activity was negligible without ozone. In addition, the selectivity to CO₂ was about 90% and this seems to be an advantage of mesoporous α-Mn₂O₃ for removing benzene using ozone.     

超枝化固体胺吸附分离烟气中二氧化碳

采用浸渍方法将四乙烯五胺（TEPA）负载到KIT-6介孔硅材料孔道表面上合成超枝化固体胺KIT-6(TEPA),并对其吸附CO₂性能进行研究。结果表明,随着温度的升高,KIT-6(TEPA)的CO₂吸附量呈增长趋势,343 K时获得最大吸附量（3.1 mmol·g^-1）。继续升高温度吸附量则呈下降趋势。KIT-6(TEPA)吸附CO₂过程以化学吸附为主,化学吸附量占总吸附量的97.2%以上（323相似文献   

Solvent-free infiltration method for mesoporous SnO2 using mesoporous silica templates

Mesoporous tin oxide (SnO₂) materials, exhibiting high surface areas, crystalline frameworks and various mesostructures, were successfully obtained by a facile solvent-free infiltration method from mesoporous silica templates. Various kinds of mesoporous silica materials, such as KIT-6 (bicontinuous 3-D cubic, Ia3d), SBA-15 (2-D hexagonal, p6mm), SBA-16 (3-D cubic with cage-like pores, Im3m) and spherical mesoporous silica (disordered), were utilized as the hard templates. Tin precursor (SnCl₂ · 2H₂O, m.p. 310–311 K) was infiltrated spontaneously within the mesopores of silica templates by melting the precursor at 353 K without using any solvent. The heat-treatment of SnCl₂-infiltrated composite materials at 973 K under static air conditions and subsequent removal of silica templates by using HF result in the successful preparation of mesoporous SnO₂ materials. The mesostructures as well as the morphologies of mesoporous SnO₂ materials thus obtained were very similar with those of the mesoporous silica templates. The mesoporous SnO₂ materials exhibit high surface areas of 84–121 m²/g as well as high pore volumes in the range of 0.22–0.35 cm³/g. The present solvent-free infiltration method is believed to be a simple and facile way for the preparation of mesoporous materials via nano-replication from mesoporous silica templates.     

Disordered mesoporous KIT-1 as a support for hydrodesulfurization catalysts

MoO₃ and NiO were supported on KIT-1, a new disordered mesoporous molecular sieve. MoO₃ is homogeneously dispersed as a monolayer on the support, whereas NiO tends to form small crystallites in the mesoporous channels. KIT-1 supported MoO₃ and/or NiO catalysts exhibit higher catalytic activities for thiophene hydrodesulfurization than similar MCM-41 and NaY zeolite supported catalysts, because the three-dimensional disordered network of short channels in KIT-1 reduces the risk of blockage in the catalysts and facilitates the transport of reactant and product molecules. This revised version was published online in July 2006 with corrections to the Cover Date.     

Direct synthesis of vanadium incorporated three-dimensional KIT-6: A systematic study in the oxidation of cyclohexane

The direct synthesis of three-dimensional (3-D) cubic V-KIT-6 was prepared using a Pluronic P123 triblock copolymer as the structure directing agent and n-butanol as the co-surfactant. The material obtained therein showed a very high specific surface area 1000 m²/g with pore diameters that could be tuned within a narrow size distribution of 5.7–6.0 nm. After calcination, Raman and UV–vis analysis revealed the presence of V⁵⁺ species in a highly dispersed state with much less crystalline V₂O₅ formation. ⁵¹V-NMR analysis showed that the vanadium species interacted directly with the silica framework in an almost symmetrical tetrahedral environment. NH₃-TPD analysis for V-KIT-6 showed a wide distribution of acid sites at temperatures ranging from 200 to 800 °C. The calcined V-KIT-6 materials showed excellent catalytic activity in the direct oxidation of cyclohexane using dilute aqueous H₂O₂ as the oxidant.     

Direct synthesis of CeO2/SiO2 mesostructured composite materials via sol–gel process

A series of CeO₂/SiO₂ mesostructured composite materials was synthesized by sol–gel process using Pluronic P123 as template, tetraethylorthosilicate as silica source and hexahydrated cerium nitrate as precursor under acid condition. The as-synthesized materials with Ce/Si molar ratio ranging from 0.03 to 0.3 were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), laser Raman spectroscopy (LRS), and N₂ adsorption. Characterization revealed that all samples possess ordered hexagonal mesoporous structure similar to SBA-15 and possess high surface area, large pore volume and uniform pore size. The fact that cerium species are present as highly dispersed CeO₂ nanocrystals in hexagonal matrix was confirmed by XRD combined with high-resolution TEM and selected area electron diffraction (SAED) analysis. Introduction of ceria to silica matrix can cause a distortion of hexagonal ordering structure and decrease pore diameter and increase the wall thickness of mesopores. Moreover, it can be found that this sol–gel route is a feasible, effective and simple method for templating synthesis of CeO₂/SiO₂ composite materials.     

CeO2-ZnO/KIT-6催化剂在光催化吸附脱硫中的应用

光催化吸附脱硫技术在油品脱硫领域引起了极大的关注,具有高光催化活性和有机硫化物吸附能力的双功能材料的开发是关键。首次合成了3D介孔二氧化铈-氧化锌/KIT-6（CeO₂-ZnO/KIT-6）催化剂,并应用于二苯并噻吩（DBT）的光催化吸附脱硫。通过X射线衍射（XRD）、氮气吸附-脱附和透射电子显微镜（TEM）等手段对催化剂进行表征,并研究了催化剂在光照下对DBT的转化性能。实验结果表明,在没有额外添加氧化剂（例如氧气、过氧化氢或有机氧化剂）的情况下,CeO₂-ZnO/KIT-6具有很好的光催化脱硫能力,当二氧化铈质量分数为10%、氧化锌质量分数为15%时,催化剂CeO₂-ZnO/KIT-6对DBT的转化率可达90%,最大吸附量（以硫计）为8.1 mg/g。无氧化剂体系对于燃料的后续处理非常有利,并且可以明显降低脱硫成本。     

Dispersion measurement of heteropoly acid supported on KIT-1 mesoporous material

Heteropoly acid (HPA) catalysts supported on KIT-1 mesoporous material were prepared with different loadings and characterized using XRD, UV–VIS and N₂ adsorption. Supported HPA was dispersed mainly on the inner surface of pores, resulting in the disappearance of XRD peaks. The diffraction peaks of HPA from the KIT-1 mesoporous material loaded with HPA of 41 wt% was very weak compared to those of physical mixtures of HPA and mesoporous material. The remaining adsorption amount of 1-butene on the supported HPA catalysts revealed the exposed amount of HPA molecules, which is useful in determining the HPA dispersion. HPA dispersion of supported HPA catalysts was useful to interpret their catalytic activity in the skeletal isomerization of 1-butene.     

Effect of porous structure on the formation of active sites in manganese hosted in ordered mesoporous silica catalysts for environmental protection

Recently ordered mesoporous silicas have been considered as suitable catalyst supports due to their high surface area, well developed porous volume and tuned size, shape and topology of mesopores. Among them SBA-15 and KIT-6 are most promising and studied materials as host matrix of metal/metal oxide nanoparticles. Both structures are characterized with cylindrical mesopores which are 2D- and 3D-packed in the SBA-15 and KIT-6 silicas, respectively. The flexibility of the oxidation state of manganese ensures high oxygen storage capacity of its oxides and provokes their wide application as catalysts in various redox processes. The aim of the current investigation is to clear the effect of pore topology in SBA-15 and KIT-6 mesoporous silicas on the state of the hosted in them manganese oxide nanoparticles. The samples were obtained by incipient wetness impregnation of silicas with manganese nitrate and conventional SiO₂ was also used as a reference support. A complex of physicochemical techniques, such as nitrogen physisorption, X-ray diffraction, UV–Vis, XPS, FTIR and temperature-programmed reduction with hydrogen was used for samples characterization. The obtained modifications were tested as potential catalysts for environmental protection via total oxidation of VOCs (ethyl acetate) or hydrogen production from methanol as clean and effective alternative fuel. It was established that the porous structure of mesoporous silica supports influences in a complex way the catalytic behaviour of their manganese modifications, which is determined by the specificity of the reaction medium.     

Nitrous Oxide Reduction with Ammonia and Methane Over Mesoporous Silica Materials Modified with Transition Metal Oxides

Transition metal oxides (Cu, Cr and Fe) were deposited on various mesoporous silicas (MCM-48, SBA-15, MCF and x-MSU) by an impregnation method. Electron microprobe analysis, BET, UV-VIS-DRS and temperature programmed desorption of NH₃ were used for the characterization of the samples. The modified mesoporous silicas were tested as catalysts of the N₂O decomposition and the N₂O reduction using ammonia and methane. The Cu-containing samples presented the highest catalytic activity in the N₂O decomposition, while the Cr- and Fe-modified materials were more active in the reduction of nitrous oxide with NH₃ and CH₄. The type of the silica support strongly influenced the catalytic performance of the studied materials.     

One-pot synthesis of 5-hydroxymethylfurfural from glucose over zirconium doped mesoporous KIT-6

Zirconium doped mesoporous KIT-6 samples with different Si/Zr ratios were synthesized by the direct hydrothermal method. Various characterization techniques confirm that highly distributed ZrO₂ nanoparticles and multi-coordinated Zr⁴⁺ species are incorporated in the mesoporous composites. One-pot synthesis of 5-hydroxymethylfurfura(HMF) from glucose was examined in the presence of Zr-KIT-6(20) the molar ratio of Si to Zr is 20 under aqueous system. The effects of temperature, reaction time, catalyst dosage and biphasic solvent system on the conversion of glucose and the HMF yield were investigated. It was found that the glucose conversion and the HMF yield have been improved from 54.8% to 79.0% and from 19.5% to 34.5% in the biphasic MIBK-water system, respectively. Both the acidity of Zr-KIT-6(20) and the biphasic MIBK-water system are responsible for the improved performance of glucose dehydration to HMF.     

Alkali-treatment of ZSM-5 zeolites with different SiO2/Al2O3 ratios and light olefin production by heavy oil cracking

Four kinds of ZSM-5 zeolites with different SiO₂/Al₂O₃ ratios are alkali-treated in 0.2 M NaOH solution for 300 min at 363 K. Changes to the compositions, morphologies, pore sizes, and distributions of the zeolites are compared before and after alkali-treatment. The changes observed are largely influenced by the SiO₂/Al₂O₃ ratios with which the zeolites are synthesized. A possible mechanism of desilication during alkali-treatment is proposed. The SiO₂/Al₂O₃ ratio of zeolites is found to influence the yield of light olefins that use heavy oil as feedstock. Alkali-treated ZSM-5 zeolites produce higher yields of light olefins compared to either untreated zeolites or the industry catalyst CEP-1. It is believed that alkali-treatment introduces mesopores to the zeolites and improves their catalytic cracking ability. ZSM-5 zeolites with SiO₂/Al₂O₃ ratios of 50 also present superior selectivity toward light olefins because of their optimized hierarchical pores.     

Vanadium-loaded carbon-based monoliths for on-board NO reduction: Influence of nature and concentration of the oxidation agent on activity

A series of polymeric carbon-coated monoliths oxidized with either concentrated or 2N HNO₃, H₂O₂ or H₂SO₄ and subsequently loaded with 3 wt.% vanadium were prepared. The influence of the different oxidation treatment conditions on the SCR (selective catalytic reduction) catalytic activity, texture and chemical surface properties were studied. Similar pore distribution and pore volumes were observed for the four oxidized samples, indicating that surface modification of carbon supports has been successfully made without disrupting the original textural structures of activated coated monoliths. The surface chemistry created by the oxidation treatments has two effects on the catalytic activity. One of these is that higher surface acidity results in higher NO reduction up to a certain extent. The highest acidities seem to promote a sufficiently strong NH₃ adsorption on the surface such that the lack of efficient desorption decreases the overall NO conversion efficiency. The other effect is that a low surface acidity does not seem to promote vanadium dispersion and fixation, thereby also resulting in decreased NO reduction efficiency.     

Porous polymers prepared via high internal phase emulsion polymerization for reversible CO2 capture

A series of porous polymers with different pore volumes, pore sizes, and crosslinking densities were synthesized by high internal phase emulsion (HIPE) polymerization. The crosslinked polymerized HIPEs (polyHIPEs) were formed by the copolymerization of 4-vinylbenzyl chloride and divinylbenzene using water droplets in conventional or Pickering HIPEs as the templates. These porous materials were further modified by quaternization and ion exchange to introduce quaternary ammonium hydroxide groups. The resulting polyHIPEs were utilized as sorbents for reversible CO₂ capture from air using the humidity swing. The effect of pore structure on the CO₂ adsorption and desorption processes was studied. The polyHIPEs containing large pores and interconnected porous structures showed improved swing sizes and faster adsorption/desorption kinetics of CO₂ compared to a commercial Excellion membrane with similar functional groups.     

The preparation of V2O5/TiO2 catalyst supported on the ceramic filter candle for selective reduction of NO

In order to prepare the catalytic filters based on V₂O₅/TiO₂ for the removal of NO_x and participate simultaneously from the flue gas stream, the experimental study was carried out. The effective method to support TiO₂ layer in the pore of the commercial ceramic filter element was developed. TiO₂ layer was supported on the filter element by three methods; impregnation with Ti solution, sol-gel dip coating and sol-gel centrifugal coating. As the model test to check the catalytic activity, NO reduction in the oxidizing stream was investigated. The catalytic filter prepared by applying the centrifugal force showed the best NO conversion more than 90% when the face velocity was 0.02 m/sec. This was a very promising result for the application of catalytic filter for the flue gas control at high temperature. The supporting methods by the impregnation and dip coating were not recommended because the TiO₂ layer was concentrated in the exterior layer of the filter element. Presented at the Int’l Symp. on Chem. Eng. (Cheju, Feb. 8–10, 2001), dedicated to Prof. H. S. Chun on the occasion of his retirement from Korea University     

Stable carbon dioxide reforming of methane over modified Ni/Al2O3 catalysts

CO₂ reforming of methane was studied over modified Ni/Al₂O₃ catalysts. The metal modifiers were Co, Cu, Zr, Mn, Mo, Ti, Ag and Sn. Relative to unmodified Ni/Al₂O₃, catalysts modified with Co, Cu and Zr showed slightly improved activity, while other promoters reduced the activity of CO₂ reforming. Mn-promoted catalyst showed a remarkable reduction in coke deposition, while entailing only a small reduction in catalytic activity compared to unmodified catalyst. The catalysts prepared at high calcination temperatures showed higher activity than those prepared at low calcination temperature. The Mn-promoted catalyst showed very low coke deposition even in the absence of diluent gas and the activity changed only slightly during 100 h operation. This revised version was published online in July 2006 with corrections to the Cover Date.