Selective hydroxylation of phenol employing Cu–MCM-41 catalysts

We studied the oxidation reaction of phenol in aqueous and acetonitrile media under mild conditions, employing Cu-modified MCM-41 mesoporous catalysts. The stability of the catalysts under reaction conditions was confirmed by XRD, UV–VIS and FTIR techniques. Results obtained indicate that the selective oxidation of phenol with H₂O₂ by a radical substitution mechanism produces three main reaction products: catechol, hydroqinone and benzoquinone.     

Synthesis of Fe-MCM-48 and its catalytic performance in phenol hydroxylation

Highly ordered Fe-MCM-48 was synthesized by a mixed templation method under low molar ratio (0.17:1) of mixed surfactants to silica and characterized by XRD, ²⁹Si-MAS NMR, ESR, and UV-Visible. Its catalytic activity and selectivity was studied for phenol hydroxylation using H₂O₂ (30%). The substituting element (Fe³⁺) is partially incorporated into the framework position forming a new type of active site which raises the phenol conversion to 43.6% and the diphenol (the mixture of catechol (CAT) and hydroquinone (HQ)) selectivity to 97.7%.     

助剂掺杂对Fe—MCM-41在环己烷氧化反应中催化性能的影响

z以硅酸钠为硅源，十六烷基三甲基溴化铵为模板剂，硝酸铁为金属源，水热法直接合成Fe—MCM-41，再辅以助剂co和cr形成双金属掺杂的介孔材料，采用XRD、N2吸脱附、TG—DTA、FTIR、ICP对材料的结构和物化性质进行表征。以乙腈为溶剂，H2O2为氧化剂，考察所制备的材料对环己烷氧化的催化活性和选择性的影响。结果表明，与Fe—MCM41的催化性能相比，FeCo—MCM41会使环己烷的转化率下降，但环己醇的选择性增加；而FeCr—MCM41会使环己烷的转化率和环己酮的收率增加。     

煤系高岭土制备Fe-MCM-41介孔分子筛及其氨选择性催化还原NOx

以煤系高岭土、十六烷基三甲基溴化铵（CTAB）、硝酸铁等为原料,通过水热法合成不同Fe含量的六方介孔分子筛Fe-MCM-41。通过傅里叶变换红外光谱、N2吸附脱附、高分辨透射电子显微镜对催化剂进行表征,并以氨为还原剂研究其选择性催化还原NO活性以及反应条件（包括Fe掺量、反应温度、空速、氨氮比和O2浓度等）对催化性能的影响。结果表明,Fe成功进入MCM-41介孔材料的骨架内,Fe-MCM-41介孔分子筛BET比表面积为980.2～596.8 m2/g,孔容积为0.95～0.60 cm3/g,平均孔径在3.90～3.45 nm。随着铁掺杂量的增加,介孔结构的有序度下降。当n(Fe)/n(Si)=0.05、空速为5000 h?1,Fe-MCM-41催化剂在350 ℃反应时NO转化率最高,可达90.7%;且当氨氮比为1.1和O2含量为2.5%时,催化剂能保持较高的活性。     

Effects of pore structure of post-treated TS-1 on phenol hydroxylation

The present study reports the effects of crystal size of TS-1 (micrometer sized umTS1 and nanometer sized nmTS1) and the post-treatment (TPAOH and NaOH treatment) on the porous structure and the catalytic performances of TS-1 in phenol hydroxylation. TPAOH post-treatment generates hollow crystal and increases the surface area of umTS1 without changing its pore structure. In contrast, NaOH treatment selectively dissolves framework silica to form mesopore and modify microporous structure through which hierarchical material is constructed with agglomerated crystals. The umTS1 sample gives a much lower conversion and lower selectivity of dihydroxylbenzenes (DHB) than the nmTS1 sample. Its activity can be greatly improved by TPAOH post-treatment exhibiting a comparable catalytic activity and DHB selectivity with the nmTS1 sample. Furthermore, successive post-treatment by TPAOH following with NaOH can generate micropores larger than the pore size of TS-1. The higher titanium content and faster diffusivity associated with the successive post-treatment significantly improve the catalytic performance of TS-1.     

铁基沸石类催化剂催化苯酚羟基化制备苯二酚的研究

铁基沸石分子筛催化苯酚直接羟基化制备苯二酚反应,具有原料低廉、反应条件温和、合成路线简单和过程绿色环保等优势,近些年来逐渐成为研究的热点.主要分析苯酚羟基化反应中诱导期、催化活性、选择性和稳定性等与铁基沸石催化剂结构性质之间的关系.比较苯酚羟基化反应的各种机理.探讨反应温度、反应时间、溶剂、催化剂用量、过氧化氢与苯酚物...     

CuO-containing MCM-48 as catalysts for phenol hydroxylation

The CuO–MCM-48 catalysts prepared by wet impregnation technique were originally used as the catalysts, with high phenol conversion and diphenol selectivity, for phenol hydroxylation with hydrogen peroxide. Furthermore, the optimized reaction conditions over these catalysts for phenol hydroxylation were acquired.     

Comparing two new routes for benzene hydroxylation

The vapour phase hydroxylation of benzene to phenol by two different methods has been investigated. In the first, a mixture of oxygen and hydrogen using a Pd membrane tubular reactor with and without second catalyst was used. Hydrogen dissociated on the palladium layer and reacted with oxygen to give active oxygen species, which reacted with benzene to produce phenol. The slow step in the overall reaction is the formation of usable hydrogen peroxide. Using a second catalyst changed the productivity, and conversion of benzene was increased by changing the length and diameter of porous reactor tubes. Low phenol productivity and selectivity was observed and showed that hydroxylation of benzene using a Pd membrane reactor is a far from economic method. In the second, selective oxidation of benzene with N₂O on iron zeolite of different SiO₂/Al₂O₃ composition, with concentration of iron rating from 50 to 2000 ppm was investigated. The effects of temperature, reactant mole ratio, and contact time were investigated. Phenol was formed with near 97% selectivity and average productivity of 5 mmol g⁻¹ h⁻¹.     

Synthesis, characterization of bimetallic Sn-Zn-MCM41 and its catalytic performance in the hydroxylation of phenol

A series of Sn-Zn modified-MCM41 has been synthesized by direct hydrothermal method and characterized using ICP, XRD, TG/DTA, FT-IR, HRTEM and N_2-adsorption techniques. Catalytic performances of the obtained materials were evaluated in the hydroxylation of phenol with H₂O₂. Results indicated that all the samples exhibited typical hexagonal arrangement of mesoporous structure with high surface area and the heteroatoms were probably incorporated into the framework of MCM41. Catalytic tests revealed that the bimetallic incorporated materials were effective catalysts in the hydroxylation of phenol. The conversion of phenol could be reach to 56.8% for the catalysts with Sn: Zn: Si = 2.69: 4.57: 100 (molar ratio) under the optimized reaction conditions. Moreover, the materials containing Sn and Zn exhibited higher catalytic activity than monometallic Sn and Zn modified MCM41.     

Performances of Fe-[Al, B]MFI catalysts in benzene hydroxylation with N2O The role of zeolite defects as host sites for highly active iron species

The catalytic performances of Fe-[Al, B]MFI zeolites in benzene hydroxylation with N₂O are studied as a function of the nature of the T atom (Al, B) and compared with the characterization of the nature of iron species determined by UV–vis diffuse reflectance spectroscopy. The results indicate that the mechanism for generation of iron species highly active in this reaction is the creation of hydroxyl nests in the zeolite framework due to framework to extra-framework migration of the T atom. The process is favoured when B is present as T atom, but occurs also in the case of Fe and Al as T atoms. Iron atoms migrate to these zeolite defect sites forming highly active Fe³⁺ isolated species in square pyramidal or highly distorted octahedral coordination. The process occurs during the catalyst pre-treatment as well as during the initial half an hour of time on stream, leading to an increase in the phenol productivity during this step. A model of these active sites is presented. The effect of the silica source in the preparation of these catalysts is also reported.     

Efficient isomerization of safrole by amino-grafted MCM-41 materials as basic catalysts

Design of base catalyst featuring large mesoporous surfaces allows performing base-catalysed reactions in the fields of production of perfumes. Post-synthesis grafting of organotrialkoxysilanes has effectively been applied to incorporate active organic functional groups onto the mesoporous silica surfaces. The novelty of our study is the use of mesoporous materials with different chemical compositions: silicate (MCM-41), aluminosilicate (AlMCM-41; Si/Al = 64) and niobosilicate (NbMCM-41; Si/Nb = 64) and consequently, different acidity, as supports for three aminopropylalkoxysilanes (APMS), [3-(2-aminoethylamino) propyl]trimethoxysilane (2APMS) and 3-[2-(2-aminoethylamino) ethylamino]propyltrimethoxysilane (3APMS). Isomerization of safrole to the corresponding thermodynamically stable isosafrole has been carried out on these amino-grafted MCM-41 materials. Maximum conversion of around 85% with a cis/trans ratio of 1/9 at 433 K in DMF as solvent was obtained. Isomerization is strongly dependent on the nature of the support and changed in the following order: APMS/AlMCM-41 > APMS/NbMCM-41 ? APMS/MCM-41. The nature of the amine chain is also responsible of the activity. The order of activity is APMS/AlMCM-41 > 2APMS/AlMCM-41 > 3APMS/AlMCM-41.     

Preparation of spherical MCM-41 molecular sieve at room temperature: Influence of the synthesis conditions in the structural properties

A rapid and facile synthesis route to obtain mesoporous MCM-41 silica at room temperature under basic conditions using as template cetyltrimethylammonium bromide (CTAB) is reported. The synthesis variables such as reaction time, molar ratios of CTAB/TEOS and H₂O/ethanol in the initial gel composition were studied. Samples were characterized by X-ray diffraction, nitrogen adsorption–desorption analyses, scanning electron microscopy and transmission electron microscopy. It was found that reaction conditions affect the quality of the MCM-41 silica. This silica can be prepared at short periods of time, and it exhibited a uniform size and spherical morphology.     

介孔Fe2O3的化学沉淀法制备及其吸附性能

采用气-液化学沉淀法制备介孔Fe2O3纳米粒子。通过平衡实验,研究了Fe2O3对刚果红的吸附热力学和动力学性能。结果表明,Fe2O3对刚果红的吸附等温线符合Langmuir方程,且温度越高,吸附量越大。计算后得到的参数表明介孔Fe2O3对刚果红的吸附过程是一种自发的、吸热过程。同时,在6 h内,即可对35 mg/L刚果红溶液达到平衡,Fe2O3对刚果红的吸附动力学符合二级吸附动力学模型,主要以化学吸附为主。     

Synthesis, structural characterization and photocatalytic activity of Ti-MCM-41 mesoporous molecular sieves

This paper reports the applicability of hydrothermal synthesis in alkaline medium for preparation of Ti-containing mesoporous MCM-41 materials. The influence of different parameters was investigated, such as the Ti source, the molar ratio between Si and Ti and also the synthesis temperature. Structural analysis shows that the high specific surface area, large pore size and well ordered mesostructure, are partially retained in the titania containing materials. Modifying synthesis temperature, it was shown that MCM-41 isotherms are different for temperatures above or under 140°C. UV-VisDR spectroscopy was used to investigate the local environment of Ti sites. The obtained materials were evaluated for the photocatalytic degradation of Rhodamine 6G in aqueous medium. The best photocatalytic activity was found for the sample prepared at higher ageing temperature of 160°C, at which anatase particles were formed.     

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.     

Ni2P/Al-MCM-41催化剂的制备及其加氢脱硫性能

以硅酸钠为硅源、硫酸铝为铝源、十六烷基三甲基溴化铵（CTAB）作模板剂,采用共沸蒸馏与超声波分散技术相结合的方法制备了介孔分子筛Al-MCM-41。以Al-MCM-41为载体、硝酸镍和磷酸氢二氨为原料,采用超声波振荡、程序升温还原法制备了Ni₂P/Al-MCM-41催化剂,并对Al-MCM-41和Ni₂P/Al-MCM-41进行了傅里叶变换红外光谱、比表面积测定、X射线衍射、扫描电镜表征。考察了Ni₂P/Al-MCM-41催化剂对噻吩加氢脱硫的催化性能。结果表明：采用超声波制得的Al-MCM-41其比表面积、孔容和孔径明显高于常规搅拌制得的Al-MCM-41,共沸蒸馏制得的Al-MCM-41其比表面积、孔容和孔径高于未共沸蒸馏的Al-MCM-41;在反应时间为5 h、548 K、3.5 MPa条件下,Ni₂P/Al-MCM-41催化剂对噻吩加氢脱硫的转化率接近100%。     

Effect of pH in hydrothermal treatment of as-synthesized MCM-41 on wetting stability of resulting materials in aqueous solution

Effect of pH in aqueous media used in the hydrothermal treatment of as-synthesized MCM-41 on the structure and the wetting stability of the resulting materials was studied using XRD, TG-DTA and N₂ adsorption. The long-range structural order and the wetting stability of the mesoporous MCM-41 were improved through hydrothermal treatment of as-synthesized sample at around pH 7 without salt addition. The pH adjustment of aqueous media toward neutral is thought to shift the polymerization equilibrium of silica species around external surface of the micelles to a higher degree of condensation, and to reduce the electrostatic repulsion between the silicate–micelle composites. This leads to the further formation of Si–O–Si network within the silica walls of the mesoporous materials, resulting in the enhancement of the structural stability of MCM-41 samples.     

Selective catalytic reduction of NO with NH3 at low temperatures over iron and manganese oxides supported on mesoporous silica

A series of catalysts of iron–manganese oxide supported on mesoporous silica (MPS) with different Mn/Fe ratio were studied for low-temperature selective catalytic reduction (SCR) of NO with ammonia in the presence of excess oxygen. Effects of amounts of iron–manganese oxide and calcination temperatures on NO conversion were also investigated. It was found that the Mn–Fe/MPS with Mn/Fe = 1 at the calcination temperature of 673 K showed the highest activity. The results showed that this catalyst yielded 99.1% NO conversion at 433 K at a space velocity of 20,000 h⁻¹. H₂O has no adverse impact on the activity when the SCR reaction temperature is above 413 K. In addition, the SCR activity was suppressed gradually in the presence of SO₂ and H₂O, while such effect was reversible after heating treatment.     

Nd-Cr/Al_2O_3催化剂上苯直接氧化制苯酚的动力学研究

研究了苯直接氧化制苯酚反应的动力学行为。推测了Nd-Cr/Al2O3催化剂上过氧化氢氧化苯为苯酚的反应过程,建立了该反应动力学数学模型,模型很好的解释了实验结果。结果表明,在实验条件下,该羟基化反应对反应物苯、氧化剂过氧化氢和催化剂用量都是一级反应,反应的活化能为24.41 kJ/mol。