MCM-41负载钨磷杂多酸催化剂的性能研究

制备并表征MCM-41负载H~3PW~1~2O~4~0(PW)催化剂.PW杂多酸在MCM-41上负载量高达70%(质量分数)时,XRD中仍未检测到其晶相峰.PW杂多酸与MCM-41载体的相互作用要比与SiO~2载体的强.PW杂多酸中的质子位是非常强的酸中心,它们对NH~3的微分吸附热在160-180kJ/mol的范围.与PW杂多酸相比,PW/MCM-41催化剂的酸中心强度变弱并且分布不均匀,其酸量和酸中心分布可以通过改变PW杂多酸的负载量来调节.PW/MCM-41是一类适合于中强酸和弱酸催化反应的新型固体酸催化剂。     

SiO2负载磷钨杂多酸催化的甲苯与乙酸酐酰化反应

以SiO2负载12-磷钨酸（PW）为催化剂，对甲苯与乙酸酐(AA)的酰化反应进行了研究。采用XRD、BET、TGA和NH3-TPD等对PW/SiO2催化剂进行了表征。结果表明，PW负载量及焙烧温度对PW/SiO2的酸性、PW在SiO2上的分散状态以及酰化催化活性有明显的影响。PW的负载量40%（按质量计）、焙烧温度300℃制备的PW(40%)/SiO2催化剂，其PW在载体表面的分散度好，酸量及酸强度适宜，对甲苯与乙酸酐的酰化反应具有较高的催化活性。在130℃，催化剂/乙酸酐（质量比）2.2时，催化反应效果最佳。     

介孔二氧化硅负载磷钨杂多酸催化合成聚四氢呋喃

采用浸渍法制备了介孔二氧化硅(SiO2)负载的磷钨杂多酸(PW12)催化剂(PW12/SiO2),其物化性质和表面酸强度经BET,IR,TG-DTG和Hammett指示剂法表征.以PW12/SiO2催化四氢呋喃开环聚合合成聚四氢呋喃(PTHF),考察了PW12的负载量[w(PW12)]和焙烧温度对催化剂活性的影响.实验结果表明,在w(PW12)为35.0%,于230 ℃焙烧活化3 h的条件下制备的催化剂(35Cat)活性最高.以35Cat为催化剂,用量占反应物总质量的15.0%时,PTHF收率达60.2%.     

HMCM-56分子筛负载磷钨酸催化苯酚与异丙醇烷基化反应

采用浸渍法制得了负载量不同的PW/MCM-56分子筛催化剂,并用X射线衍射(XRD)、NH_3化学吸附表征了催化剂的结构,在自制反应装置上完成苯酚与异丙醇烷基化反应,以此评价负载磷钨酸的MCM-56分子筛的催化活性。表征结果显示,磷钨酸能很好地分散在HMCM-56分子筛的表面,强酸中心酸强度有所增加,过高的负载量降低酸量及酸强度。实验结果表明,PW/MCM-56分子筛催化剂活性随着负载量的增加有所提高,负载量为10%的PW/MCM-56分子筛催化剂上,在温度220℃,异丙醇与苯酚进料配比0.8,空速为3.0 h~(-1)的条件下,苯酚转化率最高,对、邻异丙基苯酚总选择性接近80%。     

高镍负载量Ni/SiO2和低镍负载量Ni-Ce/SiO2催化CO甲烷化的比较研究

采用等体积浸渍法制备了高镍负载量的13%Ni/SiO₂(13Ni/Si)催化剂和低镍负载量的7%Ni-2%Ce/SiO₂(7Ni-2Ce/Si)催化剂.通过N₂物理吸附、XRD、FT-IR、TEM、H₂-TPR/TPD等技术对催化剂进行表征,在连续流动微反装置上考察了催化剂的CO甲烷化活性.结果表明,在7Ni-2Ce/Si催化剂中NiO、CeO₂和SiO₂之间产生的相互作用,改变了Ni-O-Si键的化学环境,促进了氧化镍物种的分散和还原,进而提高了催化剂的活性比表面积,同时在催化剂表面形成了新的中等强度的CO吸附中心.与高镍负载量的13Ni/Si催化剂相比,低镍负载量的7Ni-2Ce/Si表现出更高的CO吸附能力和甲烷化活性.常压下,在CO体积分数1%和空速7 000 h^-1的反应条件下,低镍负载量的7Ni-2Ce/Si催化剂上CO完全甲烷化最低温度为230 ℃,比高镍负载量的13Ni/Si低了30 ℃.     

钨含量对W/SiO2/Al2O3催化剂上1-丁烯自歧化反应的影响

采用浸渍法制备了一系列钨负载量不同的W/SiO₂/Al₂O₃ 催化剂. 采用X 射线衍射(XRD)、激光拉曼(Raman)光谱、紫外-可见(UV-Vis)光谱、氢气程序升温还原(H₂-TPR)和氨程序升温脱附(NH₃-TPD)等技术对催化剂进行了表征. 实验结果表明: 钨的负载量对催化剂上氧化钨物种的分散程度、还原性以及催化剂的酸性有非常重要的影响. 对该类催化剂上1-丁烯自歧化反应进行了详细考察, 结果表明: 当钨的质量分数为6.0%时,W/SiO₂/Al₂O₃催化剂表现出最佳的歧化活性和稳定性. 原因在于6.0%的钨负载量可以使催化剂上氧化钨物种具有中等程度的分散性、合适的还原性, 并且使催化剂具有一定程度的酸性, 这些因素有利于在催化剂上形成烯烃歧化活性位.     

负载型P-Mo-V/SBA-15催化剂上的甲烷选择氧化反应

以磷钼钒杂多酸(H₅PMo₁₀V₂O₄₀)为前驱体、介孔SBA-15为载体, 采用浸渍法制备不同负载量的P-Mo-V氧化物催化剂. 在甲烷选择氧化反应中, 考察了负载量、反应温度、空速等对甲烷转化率和产物选择性的影响. 结果表明, 催化剂对甲烷选择氧化制甲醛具有较高活性, 甲烷转化率随负载量的增大和反应温度的升高而提高, 甲醛的选择性随负载量的增大先升后降. 反应温度为640 ℃、空速为48300 L•kg^－1•h^－1、氧化物负载量w＝2.89%时, 甲醛的时空产率最高(295 g•kg_cat^－1•h^－1). 多种表征表明, 氧化物负载量w≤2.89%时, P-Mo-V氧化物在载体介孔孔道内以高分散形式存在. 催化剂的酸性和氧化还原性质与负载量相关, NH₃-TPD和H₂-TPR的测试结果表明, 较弱的酸性位和较低还原温度的活性组分有利于甲烷选择氧化制甲醛.     

Ir/ZrO2催化剂对甲烷催化燃烧性能的研究

采用浸渍法制备了ZrO₂为载体负载Ir的催化剂(Ir/ZrO₂), 考察了催化剂的CH₄催化燃烧性能. 采用X射线衍射(XRD), 拉曼光谱(Raman), X射线光电子能谱(XPS), 氢气程序升温还原(H₂-TPR)等技术对催化剂的结构和Ir物种的存在形式进行了表征. 结果表明, Ir/ZrO₂催化剂中Ir是以IrO₂形式存在的, Ir/ZrO₂催化剂的CH₄燃烧表观活性随着Ir负载量的增加而提高, 并且催化剂表现出较高的催化活性和良好的反应稳定性. 在低Ir负载量(≤1%)时, CH₄燃烧的转换频率(TOF)随着Ir粒子的增大而提高|然而高Ir负载量(≥1%)时, TOF随着Ir粒子的增大保持不变.     

Cr负载V2O5-WO3/TiO2催化剂的低温NH3-SCR脱硝活性

采用浸渍法制备了一系列不同Cr负载量的CrO_x-V₂O₅-WO₃/TiO₂催化剂, 研究了Cr改性对该催化剂脱硝活性及抗硫性能的影响. 结果表明, Cr的引入使V₂O₅-WO₃/TiO₂催化剂的低温NO_x去除效果和抗硫性能显著提升. Cr的负载量为3%(以Cr₂O₃计算质量分数)时, 催化剂具有最佳的低温脱硝活性和N₂选择性. 结构表征结果表明, 改性催化剂中Cr元素主要以Cr³⁺形式存在, Cr的引入使催化剂的氧化性能明显提升, 并使表面弱酸位点、 强酸位点和催化剂表面吸附氧数量增多. XPS分析结果表明, Cr能使催化剂中V⁵⁺/V⁴⁺比例降低, 促进催化剂中自由电子的迁移. In situ DRIFTs表征结果显示, Cr的引入能促进NO与吸附在Brönsted酸位点上的NH₃在低温条件下反应, 从而使催化剂具有更好的低温脱硝活性. UV-Vis光谱分析结果表明, CrO_x负载量提高会显著增加高价态Cr的烧结聚集. 同时, 提出了一种选择性催化还原(SCR)反应中Cr-V协同催化的机理.     

铈钛混合氧化物负载磷钨酸吸附-分解NOx性能

通过软化学途径合成了铈钛混合氧化物(CeO2-TiO2)载体材料,并分别通过等体积浸渍法和机械研磨法负载磷钨酸(H3PW12O40)。采用FTIR、XRD、SEM和BET比表面积测定对CeO2-TiO2及负载型多酸催化剂进行了表征;考察了负载量、负载方法、吸附温度等因素对催化剂吸附NOx效率的影响;选取吸附性能最佳的催化剂进行了NOx催化分解实验,探讨了NOx吸附-分解机理。结果表明:相对于等体积浸渍法,机械研磨法更适合此类载体负载H3PW12O40,其NOx吸附效率均高于H3PW12O40及载体本身;在0~60%的负载量范围内,随着H3PW12O40负载量的增加,负载型催化剂吸附NOx的效率呈先升后降趋势,负载量为40%时NOx吸附效率最佳,达90%;吸附过程中NOx与催化剂活性组分H3PW12O40发生作用,生成NOH+;H3PW12O40二级结构中结晶水对催化剂吸附NOx有重要作用;当温度从150℃升至450℃时,被吸附的NOx发生分解,分解产物的组成与N2的收率均受升温速率的影响,升温速率越快,N2收率越高。向吸附分解NOx后的催化剂床层通入含有水蒸气的空气,可有效补充NOx分解过程中H3PW12O40失去的结晶水,从而恢复催化剂优良的NOx吸附分解性能,实现催化剂的有效再生利用。     

Hydroisomerization of n-heptane over bimetal-bearing H3PW12O40 catalysts supported on dealuminated USY zeolite

The bimetal-bearing (CePt or LaPt) 12-tungstophosphoric acid (H₃PW₁₂O₄₀ (PW)) catalysts supported on dealuminated USY zeolite (DUSY) were prepared by impregnation and characterized by XRD, BET, IR, and H₂-chemisorption. Their catalytic activities were tested in the hydroisomerization of n-heptane with a continuous atmospheric fixed-bed reactor. After the steam treatment combined with the acid leaching, as well as the supporting with PW and the bimetals, the DUSY support retains the Y zeolite porosity and the PW well keeps its Keggin structure in catalysts. The doping of Ce into the catalysts enhances the dispersion of Pt on the catalyst surface. The Pt-bearing PW catalysts doped with Ce or La, especially Ce, exhibit much higher catalytic activity and selectivity than the catalysts without dopants at lowered reaction temperatures. At the optimal reaction conditions, i.e., the reaction temperature of 250°C and WHSV of 1.4 h^?1, the catalyst with a Pt loading of 0.4%, PW loading of 10% and a molar ratio of Ce to Pt of 15:1 shows a conversion of n-heptane of 70.3% with a high selectivity for isomerization products of 94.1%.     

Characterization and Dehydrogenation Activity of SBA-15 and HMS Supported Chromia Catalysts

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Metal Nanoparticles Syntheses on Ionic Liquids Functionalized Mesoporous Silica SBA‐15

Supported metal nanoparticles hold great promise in heterogeneous catalysis as active and reusable catalysts for various organic transformations. Preparation methods of metal nanoparticles with excellent control over size, shape, and morphology on supports has significantly advanced to improve the performances of the resulting catalysts. Here, we aim to discuss the development of supported metal nanoparticles on mesoporous silica SBA‐15 in the presence of immobilized ionic liquids mostly based on examples from the previously reported results. This review highlights the preparation methods for size‐controlled syntheses and the immobilization of metal nanoparticles on solid supports, especially SBA‐15 by various techniques.     

Hydroisomerization of n-heptane over bimetal-bearing H3PW12O40 catalysts supported on dealuminated USY zeolite

The bimetal-bearing (CePt or LaPt) 12-tungstophosphoric acid (H₃PW₁₂O₄₀ (PW)) catalysts supported on dealuminated USY zeolite (DUSY) were prepared by impregnation and characterized by XRD, BET, IR, and H₂-chemisorption. Their catalytic activities were tested in the hydroisomerization of n-heptane with a continuous atmospheric fixed-bed reactor. After the steam treatment combined with the acid leaching, as well as the supporting with PW and the bimetals, the DUSY support retains the Y zeolite porosity and the PW well keeps its Keggin structure in catalysts. The doping of Ce into the catalysts enhances the dispersion of Pt on the catalyst surface. The Pt-bearing PW catalysts doped with Ce or La, especially Ce, exhibit much higher catalytic activity and selectivity than the catalysts without dopants at lowered reaction temperatures. At the optimal reaction conditions, i.e., the reaction temperature of 250°C and WHSV of 1.4 h⁻¹, the catalyst with a Pt loading of 0.4%, PW loading of 10% and a molar ratio of Ce to Pt of 15:1 shows a conversion of n-heptane of 70.3% with a high selectivity for isomerization products of 94.1%. Supported by the Natural Science Foundation of China (Nos. 20306011 and 20476046), the Ph. D. Program Foundation of Chinese University (20040291002), and the Ph. D. innovation Program Foundation of Nanjing University of Technology (BSCX200506)     

Silver Nanoparticles Supported on CeO2‐SBA‐15 by Microwave Irradiation Possess Metal–Support Interactions and Enhanced Catalytic Activity

Metal–support interactions (MSIs) and particle size play important roles in catalytic reactions. For the first time, silver nanoparticles supported on CeO₂‐SBA‐15 supports are reported that possess tunable particle size and MSIs, as prepared by microwave (MW) irradiation, owing to strong charge polarization of CeO₂ clusters (i.e., MW absorption). Characterizations, including TEM, X‐ray photoelectron spectroscopy, and extended X‐ray absorption fine structure, were carried out to disclose the influence of CeO₂ contents on the Ag particle size, MSI effect between Ag nanoparticles and CeO₂‐SBA‐15 supports, and the strong MW absorption of CeO₂ clusters that contribute to the MSIs during Ag deposition. The Ag particle sizes were controllably tuned from 1.9 to 3.9 nm by changing the loading amounts of CeO₂ from 0.5 to 2.0 wt %. The Ag nanoparticle size was predominantly responsible for the high turnover frequency (TOF) of 0.41 min^?1 in ammonia borane dehydrogenation, whereas both particle size and MSIs contributed to the high TOF of 555 min^?1 in 4‐nitrophenol reduction for Ag/0.5CeO₂‐SBA‐15, which were twice as large as those of Ag/SBA‐15 without CeO₂ and Ag/CeO₂‐SBA‐15 prepared by conventional oil‐bath heating.     

Tungsten doped mesoporous SBA‐16 as novel heterogeneous catalysts for oxidation of cyclopentene to glutaric acid

Novel heterogeneous tungsten species in mesoporous silica SBA‐16 catalysts based on ship‐in‐a‐bottle methodology are originally reported for oxidizing cyclopentene (CPE) to glutaric acid (GAC) using hydrogen peroxide (H₂O₂). For all W‐SBA‐16 catalysts, isolated tungsten species and octahedrally coordinated tungsten oxide species are observed while WO₃ crystallites are detected for the W‐SBA‐16 catalysts with Si/ W = 5, 10, and 20. The specific surface areas and the corresponding total pore volumes decrease significantly as increasing amounts of tungsten incorporated into the pores of SBA‐16. Using tungsten‐substituted mesoporous SBA‐16 heterogeneous catalysts, high yield of GAC (55%) is achieved with low tungsten loading (for Si/W = 30, ~13 wt%) for oxidation of CPE. The W‐SBA‐16 catalysts with Si/W = 30 can be reused five times without dramatic deactivation. In fact, low catalytic activity provided by bulk WO₃ implies that the highly distributed tungsten species in SBA‐16 and the steric confinement effect of SBA‐16 are key elements for the outstanding catalytic performance.     

A study into Stille cross‐coupling reaction mediated by palladium catalysts deposited over siliceous supports bearing N‐donor groups at the surface

Mesoporous molecular sieve SBA‐15 and conventional silica gel were grafted with 3‐[2‐(diethylamino)ethylamino]propyl groups and used as supports for the preparation of deposited palladium catalysts, which were subsequently evaluated in Stille cross‐coupling reaction of aryl bromides. The highest conversions were achieved with the metal‐saturated catalyst resulting from the modified SBA‐15. Influence of various reaction parameters (solvent, additive, temperature, etc.) on the overall yield and selectivity was studied. Copyright © 2013 John Wiley & Sons, Ltd.     

Influence of Pore Structure on Catalytic Properties of Mesoporous Silica-supported Co-B Amorphous Alloys in Hydrogenation of Cinnamaldehyde to Cinnamyl Alcohol

Co‐B amorphous alloy catalysts supported on three kinds of mesoporous silica (common SiO₂, MCM‐41 and SBA‐15) have been systematically studied focusing on the effect of pore structure on the catalytic properties in liquid‐phase hydrogenation of cinnamaldehyde to cinnamyl alcohol (CMO). Structural characterization of a series of different catalysts was performed by means of N₂ adsorption, X‐ray diffraction, transmission electron microscopy, hydrogen chemisorption, and X‐ray photoelectron spectroscopy. Various characterizations revealed that the pore structure of supports profoundly influenced the particle size, location and dispersion degree of Co‐B amorphous alloys. Co‐B/SBA‐15 was found more active and selective to CMO than either Co‐B/SiO₂ or Co‐B/MCM‐41. The superior catalytic activity could be attributed to the higher active surface area, because most of Co‐B nanoparticles in Co‐B/SBA‐15 were located in the ordered pore channels of SBA‐15 rather than on the external surface as found in Co‐B/SiO₂ and Co‐B/MCM‐41. Meanwhile, the geometrical confinement effect of the ordered mesoporous structure of SBA‐15 was considered to be responsible for the enhanced selectivity to CMO on Co‐B/SBA‐15, inhibiting the further hydrogenation of CMO to hydrocinnamyl alcohol.     

Unraveling the Role of Site Isolation and Support for Semihydrogenation of Phenylacetylene

Intermetallic compounds (IMCs) composed of transition metals and post‐transition metals function as superior heterogeneous catalysts in comparison to their monometallic and bimetallic alloy counterparts. Rendering IMCs in their nanomaterial iterations further enhances their efficiency. Herein, we demonstrate the role of PdIn as well‐dispersed intermetallic nanoparticles (IMNPs) for the semihydrogenation of phenylacetylene selectively to styrene at ambient conditions. Higher selectivity of PdIn was explained with the help DOS calculations. We have explored the role of a few well‐known silica‐based supports such as SBA‐15 and MCM‐41, providing insight into how they affect catalysis. As an additional support we have explored previously reported JNC‐1, a mesoporous carbon material obtained via a templated strategy using SBA‐15. PdIn supported on SBA‐15 and JNC‐1 displayed the best dispersion, while also exhibiting the most catalytic activity due to the unique nature of the porous structure.