Inorganic–organic hybrid materials based on functionalized silica and carbon: A comprehensive understanding toward the structural property and catalytic activity difference over mesoporous silica and carbon supports

Inorganic–organic hybrid materials based on functionalized silica and carbon were synthesized by anchoring molybdovanadophosphoric acid (H₅[PMo₁₀V₂O₄₀] · 32.5H₂O) onto amine-functionalized SBA-15, ethane-bridged SBA-15 and mesoporous carbon, respectively. Small angle X-ray diffraction, N₂ sorption analysis, HRTEM, SEM, FT-IR, CP-MAS NMR were used to diagnose the mesoporous structure of inorganic–organic hybrid materials. The structural integrity of molybdovanadophosphoric acid has been found to be retained after immobilization over mesoporous materials. These inorganic–organic hybrid materials were tested in the environmentally friendly oxidation of 2-methylnaphthalene (2MN) with 30% aqueous hydrogen peroxide. Molybdovanadophosphoric acid containing mesoporous organosilica hybrid material (ethane-bridged SBA-15) exhibited higher catalytic activities in the oxidation of 2MN to give a clean product 2-methy-1,4-naphthoquinone (menadione vitamin K3 precursor), because of the improved hydrophobicity of the material. The correlation between structural properties and catalytic activities of these hybrid materials has been well addressed in our present studies.     

Degradation of phenolic aqueous solutions by high frequency sono-Fenton systems (US–Fe2O3/SBA-15–H2O2)

The aim of this work is to establish the influence of different ultrasonic frequencies ranging from 20 to 1142 kHz on the efficiency of the US/Fe₂O₃/SBA-15/H₂O₂ (sono-Fenton) system. The frequency of 584 kHz has been established as the optimum ultrasonic irradiation for the degradation of aqueous phenol solutions by the sono-Fenton system and the effect of different variables, such as hydrogen peroxide concentration or catalyst loadings in the reaction was studied by factorial design of experiments. Catalyst loadings of 0.6 g/L and hydrogen peroxide concentration, close to the stoichiometric amount, show high organic mineralization, accompanied by excellent catalyst stability in a wide range of concentrations of aqueous phenol solutions (0.625–10 mM). Additionally, the catalyst can be easily recovered by filtration for reuse in subsequent reactions without appreciable loss of activity. The coupling of US (584 kHz)/Fe–SBA-15/H₂O₂ at room temperature is revealed as a promising technique for wastewater treatment. Additionally, a new sono-Fenton variant, the so-called latent remediation has also been studied, using ultrasonic irradiation only as pretreatment for 15 min in an attempt at reducing the cost of the degradation process. It has been observed that latent remediation provides TOC degradation of around 21% after 15 min sonication followed by 6 h silent reaction while the typical sono-Fenton reaction affords 29% TOC reduction after 6 h sonication.     

Rapid synthesis of La–Ce–silica mesoporous SBA-15-type material via microwave technique

La–Ce–silica mesoporous SBA-15-type material has been rapidly synthesized using microwave technique and characterized by XRD, FT-IR, DRS, and low temperature N₂ adsorption–desorption measurement. The results show the La and Ce were successfully incorporated into the framework of SBA-15 molecular sieve and the synthesized material not only retains the hexagonal order and physical properties of purely siliceous SBA-15 but also possesses high surface area and narrow pore-size distribution. Further, the obtained material La–Ce–SBA-15 was used as catalyst support to load active metal Pt for CO oxidation reaction. The results of experiment indicate that the catalytic activity of Pt/La–Ce–SBA-15 is higher than that of the Pt/SBA-15 and Pt/La/Ce/SBA-15.     

Heterogenized Molybdovanadophosphoric Acid on Amine-Functionalized SBA-15 for Selective Oxidation of Alkenes

Mono-vanadium substituted molybdovanadophosphoric acid has been immobilized on amine-functionalized SBA-15 and characterized by different techniques. Small angle X-ray scattering (SAXS) analysis and SEM technique provide evidence for the structural integrity of the amine-functionalized SBA-15 and for the molybdovanadophosphoric acid immobilized sample. Diffuse reflectance UV–vis, ³¹P, ⁵¹V-NMR and FT-IR data confirm the incorporation of molybdovanadophosphoric acid onto the amine-functionalized SBA-15. The textural properties of these materials were studied by nitrogen sorption studies. Oxidation of selected substrates, norbornene, cyclooctene, cyclohexene and styrene with aqueous hydrogen peroxide was carried out with the immobilized molybdovanadophosphoric acid catalyst (heterogenized) and the results were compared with that of the neat molybdovanadophosphoric acid catalyst (homogeneous). The selectivity of the desired products was higher with the immobilized catalyst. The immobilized catalyst could be separated after the reaction and the reusability of the catalyst has also been demonstrated.     

添加Sm对Pt /SBA-15催化苯完全氧化反应活性和热稳定性的影响

以Pt/SBA-15为催化剂,考察催化剂载体中添加Sm对于苯的完全氧化反应活性和热稳定性影响。采用了一种简便的记录起燃温度曲线和催化剂热稳定性评价方法,即向装载好催化剂的固定床反应器中持续通入恒定流量的反应气,逐步阶段性升高反应温度,同时在线检测出口尾气的浓度变化, 得到起燃温度曲线后,继续提高反应温度,然后恒定在某一设定的温度(如550℃)持续运行较长时间, 期间定时在线取样分析,如果有必要还可以连续考察降温情况下催化剂的反应活性情况。研究结果表明,几种催化剂低温活性次序为：Pt/SBA-15≈Pt/4%Sm₂O₃/SBA-15> Pt/Sm₂O₃> 4%Sm₂O₃/SBA-15,而对于高温稳定性则是Pt/4%Sm₂O₃/SBA-15> Pt/1.2%Sm₂O₃/SBA-15> Pt/SBA-15,Pt/Sm-SBA-15(SG)> Pt/SBA-15(SG)。总之,Sm的添加虽然未能提高Pt/SBA-15的低温催化活性,但是能明显提高催化剂在高温情况下活性的稳定性。1%Pt/4%Sm₂O₃/SBA-15同时具备较好的低温催化活性和高温稳定性,具有较好的应用前景。     

CoMo/Ti-SBA-15 catalysts for dibenzothiophene desulfurization

With a view to reducing the sulfur content in diesel fuels, novel desulfurization CoMo catalysts were supported on a Ti-loaded hexagonal mesoporous SBA-15 material. The Ti-SBA-15 substrates were synthesized using triblock copolymers as structure-directing agents. Catalytic activity was assessed in the model reaction of hydrodesulfurization (HDS) of dibenzothiophene (DBT), carried out in a batch reactor at T = 623 K and with a total hydrogen pressure of 3.1 MPa. The reaction proceeds via the direct desulfurization route (main route) and the hydrogenation (HYD) pathway. The incorporation of Ti into the SBA-15 afforded catalysts that were more active than the Ti-free counterpart, due to the enhancement of the DDS route in this reaction. This difference was explained in terms of a larger number of coordinately unsaturated sites (CUS) of the metal sulfide on Ti-loaded catalysts. Under steady-state conditions, the CoMoST20 catalyst with a Si/Ti ratio of 20 was the most active among the catalysts studied. Since this catalyst exhibited both Ti⁴⁺ ions incorporated into the SBA-15 framework and separate anatase TiO₂ clusters located on its surface, the activity enhancement on this sample was explained by the larger intrinsic activity of the “Co–Mo–S” phase located on these TiO₂ nanoparticles. The Ti-SBA-15 supports and the CoMo/Ti-SBA-15 catalysts were studied by N₂ adsorption–desorption isotherms, XRD, TEM, FTIR of adsorbed pyridine and NO, UV–vis DRS, TPR, micro-Raman and XPS spectroscopy.     

A simple co-impregnation route to load highly dispersed Fe(III) centers into the pore structure of SBA-15 and the extraordinarily high catalytic performance

Highly dispersed iron centers supported on SBA-15 were successfully prepared via a simple incipient wetness co-impregnation route by casting furfuryl alcohol (FA) solution of iron (III) acetylacetonate (Fe(acac)₃), which were used as carbon and iron sources, respectively, into the pore structure of SBA-15, followed by the subsequent removal of carbonized FA. Various techniques such as XRD, TEM, N₂ sorption, UV–vis, XPS and EPR, were employed to characterize the prepared catalysts. It was shown that both Fe₂O₃ nanoclusters and isolated iron species were present and highly dispersed onto the pore surface of SBA-15, due to the presence of abundant carbon source co-impregnated, with well-maintained, highly ordered and open mesoporous structure. A great number of acidities was introduced by the loading of Fe₂O₃, and the catalytic performance was tested on the Friedel–Crafts benzylation of benzene by benzyl chloride. Under the optimized reaction condition, the catalyst showed a superior catalytic performance with a 100% yield of monoalkylated product within 1.5 min at 60 °C. The catalyst demonstrated high reusability and stability, the yield of diphenylmethane was still higher than 90% after 6 runs. Moreover, the catalyst was still active at the temperature as low as 40 °C. Such a strategy is verified applicable to prepare other well-dispersed metal oxides, i.e. Mn_xO_y loaded into the pore structure of mesoporous materials.     

MgO-modified VOx/SBA-15 as catalysts for the oxidative dehydrogenation of n-butane

VO_x catalysts supported on SBA-15 with and without MgO modification were prepared and characterized by N₂ adsorption–desorption, XRD, HRTEM, H₂-TPR, NH₃-TPD and XPS. Compared to the VO_x/SBA-15 catalyst, the VO_x/MgO/SBA-15 ones exhibit much higher C₄-olefins selectivity and yield in the oxidative dehydrogenation of n-butane. The enhanced performance can be attributed to the rise in VO_x reducibility as well as to the relatively lower acidity of the MgO-modified SBA-15 materials.     

One-pot Encapsulation of Pt Nanoparticles into the Mesochannels of SBA-15 and their Catalytic Dehydrogenation of Methylcyclohexane

Highly dispersed Pt nanoparticles have been confined in the mesochannels of SBA-15 silica by a simple “one-pot” co-assembly method. Metallic Pt can be encapsulated in the mesochannels by changing the amount of Pt ions in the starting materials. The catalytic performances of Pt–SBA-15 were evaluated for methylcyclohexane dehydrogenation. Compared with conventional supported Pt–SiO₂ catalysts, the Pt–SBA-15 catalysts show higher stability. TEM studies show that the confinement effect of ordered mesochannels of SBA-15 may restrict the further growth of Pt nanoparticles during the reaction.     

Effect of the preparation method on the structural stability and hydrodesulfurization activity of NiMo/SBA-15 catalysts

Defined hexagonal cylindrical pore structure SBA-15 material was synthesized as support for hydrotreating catalysts. The stability of the mesoporous material under acid and basic environments commonly used to prepare hydrotreating catalysts was investigated. The effects of the acid and basic treatments on the stability of SBA-15 and NiMo/SBA-15 catalysts were evidenced by different characterization techniques such as N₂ adsorption–desorption, X-ray diffraction (XRD), Raman Spectroscopy and high resolution transmission electron microscopy (HRTEM). Supported NiMo/SBA-15 catalysts prepared by pore volume co-impregnation in acidic, neutral and basic solutions of the Ni and Mo precursor salts were characterized to evaluate the textural and structural changes caused by the method of preparation. Characterization of the support after accelerated stability tests indicates large deterioration of the SBA-15 structural order at basic pH. The characterization results of oxide and sulfided catalysts indicate, for the catalysts prepared at high pH, an increasing presence of β–NiMoO₄ phase in the oxide catalysts, and a relatively lower population of MoS₂ in the sulfided catalysts. The activity of the different catalysts evaluated in the thiophene hydrodesulfurization reaction was higher for the catalysts prepared at low pH.     

Promotion effect of cerium and lanthanum oxides on Ni/SBA-15 catalyst for ammonia decomposition

CeNi/SBA-15 and LaNi/SBA-15 catalysts were prepared by deposition–precipitation (DP) method and characterized by N₂ physical adsorption, XRD, H₂-TPR, H₂-chemisorption and TEM. Their catalytic performances in the ammonia decomposition reaction were tested and compared with Ni/SBA-15 catalyst. Addition of cerium and lanthanum oxides to the Ni/SBA-15 catalyst caused some decrease of BET surface area and pore volume of the catalysts, but led to a promotion effect to their catalytic activity which was closely related to the ratio of Ce (La)/Ni. The highest conversion of ammonia could be obtained when the Ce (La)/Ni ratio was around 0.3. The promotion effect is more evident on CeNi/SBA-15(0.3) than on LaNi/SBA-15(0.3) catalyst under identical reaction conditions. The CeNi/SBA-15 and LaNi/SBA-15 catalysts show smaller nickel particle size and easier reducibility in comparison with the Ni/SBA-15 catalysts.     

SBA-15固载磷钨酸催化剂的制备及催化合成叔丁基苯酚

以不同硅烷偶联剂改性的介孔分子筛SBA-15为载体、PW_(12)为催化剂,通过对SBA-15表面共价及非共价修饰制备磷钨酸@介孔分子筛/硅烷偶联剂复合催化剂PW_(12)@SBA-15/YSiX_3(YSiX_3=Apts、Atapts、Papts);并利用FT-IR、XRD、TEM、N_2吸附-脱附对其组成、结构及形貌进行表征。以改性SBA-15分子筛固载磷钨酸催化剂催化合成叔丁基苯酚为研究对象,考察不同硅烷偶联剂、反应温度、苯酚与叔丁醇物质的量比对催化合成叔丁基苯酚的影响,并获得合成叔丁基苯酚的最佳工艺条件,即反应温度145℃、n(苯酚)∶n(叔丁醇)=1∶2.5、重时空速2.2 h~(-1),该最佳反应条件下,PW_(12)@SBA-15/Apts催化剂催化合成叔丁基苯酚的催化活性最高,苯酚转化率为98.3%,2,4-二叔丁基苯酚选择性为57.3%.     

Mesoporous aluminosilicate catalysts from FAU precursor under mild acidic conditions and with Al in totally tetrahedral coordination

Al-SBA-15 mesoporous catalyst with strong Brönsted acid sites and Al stabilized in a totally tetrahedral coordination was synthesized from the addition of hydrothermally aged zeolite Y precursor to SBA-15 synthesis mixture under mildly acidic condition of pH 5.5. The materials possessed surface areas between 690 and 850 m²/g, pore sizes ranging from 5.6 to 7.5 nm and pore volumes up to 1.03 cm³, which were comparable to parent SBA-15 synthesized under similar conditions. As much as 2 wt.% Al was present?in the most aluminated sample that was investigated, and the Al remained stable in totally tetrahedral coordination, even after calcination at 550 °C. Calcined Al-SBA-15 showed high hydrothermal stability when treated with steam (20% v/v in nitrogen) at 650 °C for 2 h. Textural characteristics are maintained on steam treatment, and very little or no conversion of Al from tetrahedral to octahedral coordination resulted. The Al-SBA-15 mesoporous catalyst showed significant catalytic activity for cumene dealkylation, and activity increased as the amount of zeolite precursor added to the SBA-15 mixture was increased. The catalyst’s activity was not affected by the aging time of the precursor for up to the 24 h aging time investigated. This method of introducing Al and maintaining it in a total tetrahedral coordination is very effective, in comparison to other direct and post synthesis alumination methods reported.     

Liquid phase oxidation of 2-methyl pyridine to 2-pyridinecarboxylic acid over cobalt-doped SBA-3

Cobalt-doped SBA-3 was synthesized by cogellation method and was used as a catalyst for the oxidation of 2-methyl pyridine in acetic acid using aqueous hydrogen peroxide as oxidant. The catalyst exhibited very high substrate conversion (98%) and good product (2-pyridinecarboxylic acid) selectivity (93%). Fast hot catalyst filtration experiment proved that the catalyst acted as a heterogeneous one and it can be reused two times without losing its activity to a greater extent. The catalyst was characterized by X-ray diffraction, N₂ physisorption, diffuse reflectance UV–vis, and FT-IR.     

Platinum incorporated into the SBA-15 mesostructure via deposition-precipitation method: Pt nanoparticle size estimation and catalytic testing

We report the use of the deposition precipitation (DP) method for the functionalization of mesoporous silica SBA-15 with Pt. [Pt(NH₃)₄](OH)₂ was used as a platinum precursor. Experiments were performed at 90 °C, and urea was used to control the pH during precipitation. From the obtained pH profiles, an interaction between the support and the precipitating species is suggested. A general formula of the species is proposed to be [Pt^II(OH)_n] _s ^II-n . By Transmission electron microscopy (TEM) it is shown that the majority of Pt nanoparticles on SBA-15 reside in the range between 2 and 4 nm. However, particles in the range of 15 nm were also detected, which indicates that the precipitation does not occur exclusively within the channels of the SBA-15. The obtained material is compared to a reference catalyst, Pt/SBA-15, prepared by a conventional wet impregnation method. Here, larger Pt nanoparticles (4–6 nm) were detected. The catalysts were found to exhibit comparable activity in toluene hydrogenation in terms of turnover frequency based on CO chemisorption.     

Use of mesoporous SBA-15 for nanostructuring titania for photocatalytic applications

SBA15–TiO₂ samples prepared by introducing titanium with a grafting method and having TiO₂ loadings below 15 wt.% have been characterized by XRF, XRD, IR, porosimetry, SEM, HRTEM, and UV–Visible diffuse reflectance. Differently from the samples reported in the literature characterized by a high TiO₂ loading, no evidences have been found for the presence of titania particles inside or outside the mesopores of SBA-15. Three different titanium species were instead evidenced to be present. The first two derive from the reaction of titanium with silanol groups in the corona area of inner SBA-15 walls leading to the formation of either TiO₄ tetrahedral sites (by reaction by hydroxyl nests of surface defect sites) and/or pseudo-octahedral surface sites anchored by two (or more) Si or Ti ions through bridging oxygens. The third species derives from the reaction of titanium in the regions with high sylanol density, e.g. in the micropores located in the corona of SBA-15 channels, leading to the formation of TiO₂-like nanoareas (probably Si-doped) with dimensions of around 1–2 nm maximum. The potential interest of these materials as photocatalysts, for the presence of a TiO₂-like nanoareas highly accessible by reactants, is discussed.     

Phase transition of mesoporous SiO<Subscript>2</Subscript> impregnated with an organic templating agent by post-synthetic microwave heating

Mesoporous silica SBA-15 samples were subjected to microwave heating for 10–40 min at 393 and 443 K after dry-impregnation with TPAOH (tetrapropylammonium hydroxide) to prepare a mesoporous material with zeolytically ordered pore walls. Physicochemical properties of the materials prepared were characterized by XRD, N₂ adsorption at 77 K, SEM, TEM, UV–vis and FT-IR spectroscopies. These investigations revealed that selective transformation of amorphous pore walls of SBA-15 to crystalline zeolytic phase is difficult to be achieved and a mixed phase of mesoporous silica/zeolite composite material was obtained, instead. Microwave heating time, temperature, TPAOH concentration, and hydrothermal stability of the mesoporous host materials tested (MCM-41, HMS, and SBA-15) were important factors to maintain the mesopore structure of the host materials during the post-synthetic microwave heating treatment.     

钾对丙烷脱氢催化剂性能的影响

考察助剂钾对氧化铝和介孔分子筛SBA-15载体体系的丙烷脱氢催化剂性能的影响,XRD、NH₃-TPD和铂分散度表征结果表明,钾对两种体系催化剂的影响完全不同,在氧化铝体系中,钾助剂降低催化剂酸性,提高催化剂性能,而在SBA-15载体体系中,钾的引入使催化剂中铂的分散度大大降低,从而使催化剂活性降低,不利于反应。     

SBA-15固载酸性离子液体催化酯化反应性能

为了减少离子液体用量及解决催化剂分离问题,采用键合法制备了以SBA-15为载体的固载化离子液体催化剂[C₃SO₃HCP]HSO₄/SBA-15,通过FT-IR、TG、XRD、BET和TEM分析了催化剂的结构和稳定性。并将其应用于催化丁二酸酐和乙醇的酯化反应。结果表明:[C₃SO₃HCP]HSO₄被成功固定在SBA-15上,且具有较高的热稳定性和催化活性,克服了非均相催化剂活性不高与均相催化剂难以分离的不足。在催化剂用量为反应物总质量的5%、n(C₄H₄O₃):n(C₂H₅OH)=1:3,反应温度80℃;反应时间4 h、带水剂用量为反应物总质量的30%的条件下,酯收率达93.7%,且该催化剂循环使用8次后,仍具有较高的催化活性。此外,还考察了以[C₃SO₃HCP]HSO₄/SBA-15为催化剂催化合成系列酯也获得了较高的酯收率,且易于与产物酯分离。     

Steam reforming of ethanol over Pt–Ni Catalysts

A parametric study was conducted over Pt–Ni/δ-Al₂O₃ to explore the effect of Pt and Ni contents on the ethanol steam reforming characteristics of the bimetallic catalyst. Experiments with catalysts having 0.2–0.3 wt%Pt and 10–15 wt%Ni contents indicated that the best ethanol steam reforming performance is achieved over 0.3 wt%Pt–15 wt%Ni/δ-Al₂O₃. Kinetics of ethanol steam reforming was studied over this catalyst in the 673–823 K interval using differential and integral methods of data analysis. A power-function rate expression was obtained with reaction orders of 1.01 and −0.09 in ethanol and steam, respectively, and the apparent activation energy of ethanol steam reforming over 0.3 wt%Pt–15 wt%Ni/δ-Al₂O₃ was calculated as 59.3 ± 2.3 kJ mol⁻¹.