苯加氢催化剂Pd/MCM—41催化性能的研究

对负载型催化剂Pd/MCM—41进行了透射电镜及N2吸附表征。结果表明,金属Pd主要以纳米粒子的形式负载在分子筛表面,MCM—41的基本结构未被破坏。将Pd/MCM—41用于苯加氢反应,研究了反应温度和反应压力对催化活性的影响。结果表明,随着反应温度、反应压力的增加,苯的转化率得到有效提高。     

Preparation and characterization of Pd/Si-MCM-41 with high hydrogenation activity

The pure silica mesoporous molecular sieve MCM-41 was synthesized under hydrothermal conditions. Pd/Si-MCM-41 was prepared by the incipient wetness impregnation of pure silica MCM-41 with PdCl₂ as precursor. The samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), nitrogen adsorption–desorption isotherms at 77 K, inductively coupled plasma (ICP) spectroscopy measurements. The formation of Pd particles reduced the crystalline character of Si-MCM-41, but the structure of Si-MCM-41 framework was retained. The designed Pd/Si-MCM-41 mesoporous material was used as catalysts for hydrogenation of rosin, and showed excellent catalytic performance. Such outstanding catalytic performance should be attributed to the proper size of Pd particles and its high dispersion.     

Iron, cobalt or nickel substituted MCM-41 molecular sieves for oxidation of hydrocarbons

A series of mesoporous Fe-MCM-41, Co-MCM-41 and Ni-MCM-41 catalysts with different quantity of the metal incorporated in the framework were synthesized and characterized (as-synthesized samples and those after reaction) by X-ray diffraction pattern (XRD), N₂ adsorption–desorption, transmission electron microscopy (TEM), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) techniques. The effect of the incorporated metal on the MCM-41 surface hydroxyl groups has been evidenced. The catalytic activity and selectivity of these catalysts in liquid phase oxidation of 1-hexene, styrene and benzene with hydrogen peroxide were studied. The structure and morphology of the catalysts before and after reaction were also compared. The results show a high activity and selectivity of catalysts having higher Co content to benzaldehyde from styrene or phenol from benzene, and a low activity of all prepared catalysts in the oxidation of the 1-hexene. The activity and efficiency of H₂O₂ increases with the metal content and depend on the reaction parameters such as temperature, molar ratio of the reactants and the solvent, and the nature of the reactor.     

Hydroisomerization of model FCC naphtha over sulfided Co(Ni)–Mo(W)/MCM-41 catalysts

Deep hydrodesulfurization (HDS) of gasoline generally brings about the saturation of olefins and leads to the serious octane number losses. Conversion of linear olefins to branched ones followed by hydrogenation to isoalkanes would minimize such octane number losses. In this work, MCM-41-supported Co–Mo, Ni–Mo and Ni–W catalysts were prepared by the incipient wetness impregnation method, and compared with an industrial Co–Mo/γ-Al₂O₃ catalyst. The surface acidities were measured by the techniques of microcalorimetry and infrared spectroscopy for the adsorption of ammonia, and probed by the reaction of conversion of isopropanol. The isomerization and hydrogenation of 1-hexene as well as the HDS of thiophene were studied by using model FCC naphtha. It was found that the sulfidation enhanced significantly the surface Brønsted acidity that favored the skeletal isomerization of 1-hexene under the HDS conditions. Since the isomerization and hydrogenation of 1-hexene are the two competition reactions, the catalysts with relatively lower hydrogenation activity may have higher selectivity to the isomerization reactions. The Co–Mo/MCM-41 showed the high selectivity to the skeletal isomerization reactions due to its strong surface Brønsted acidity and the relatively low hydrogenation activity. On the other hand, the Ni–Mo/MCM-41 exhibited high hydrogenation activity and therefore low selectivity to the isomerization reactions although it possessed quite strong surface Brønsted acidity. The Ni–W/MCM-41 exhibited the low activity for the HDS of thiophene and isomerization of 1-hexene due to the poor dispersion of active metals.     

Alkynes Hydrogenation over Pd-Supported Catalysts

The liquid-phase stereoselective hydrogenation of phenyl alkyl acetylenics at 298 K and atmospheric pressure on Pd-supported catalysts has been studied. The catalysts were prepared by impregnation of Pd(acac)₂ precursor (1 wt% of Pd) on different siliceous substrates such as amorphous SiO₂, mesoporous MCM-41 and silylated MCM-41. The poisoning effect of lead incorporation on the supported palladium was also studied. All the catalysts displayed high selectivity to cis-alkene isomer, with Pd/MCM-41 being the most active catalyst. Deliberately adding lead to the base, palladium catalysts underwent changes in the selectivity to cis-alkene isomer and a significant drop in the activity. All the solids were characterized by nitrogen adsorption–desorption isotherms at 77 K, TGA, TPR, H₂ and CO chemisorption, XRD, XPS, and TEM.     

Methanol synthesis over Pd/SiO2 with narrow Pd size distribution prepared by using MCM-41 as a support precursor

All silicious MCM-41 was investigated as a support or a support precursor for Pd/SiO₂ and prepared catalysts were tested for methanol synthesis from CO and H₂. The methods of Pd loading on the MCM-41 were impregnation, seed impregnation and chemical vapor deposition (CVD). For both impregnations, most Pd existed outside of the pore as large particles, and only a small part of Pd was inserted into the pore of MCM-41 retaining the initial structure. On the contrary, in the catalyst prepared by CVD method, the MCM-41 structure was completely destroyed to become amorphous SiO₂. Yet the average Pd particle size in this catalyst was smaller and its distribution was narrower than those of the catalysts prepared by impregnation methods. In the methanol synthesis from CO hydrogenation the catalyst prepared by CVD showed higher methanol selectivity than other MCM-41-derived catalysts. This result was considered to be due to the more uniform distribution of the Pd particle size.     

A simple method to prepare highly active and dispersed Ni/MCM-41 catalysts by co-impregnation

A simple method for preparing highly active and dispersed supported metal catalysts was developed by co-impregnation. Compared with conventional wetness impregnation, addition of moderate ethylene glycol into the metal nitrate aqueous solution could enhance interaction with MCM-41 surface, resulting in formation of very small NiO particle size (3.5 nm) and high dispersion of the active phase. The Ni/MCM-41 catalysts using co-impregnation exhibited excellent catalytic performance for low temperature hydrogenation of naphthalene with 100% conversion at 55 °C, which could rival the activity of commercial Raney Ni catalyst. The obtained catalysts were characterized by XRD, TEM, TG-DSC, FT-IR, BET and TPR.     

Effect of surface Na+ or K+ ion exchange on hydrodesulfurization performance of MCM-41-supported Ni–W catalysts

Ni–W hydrodesulfurization (HDS) catalysts supported on MCM-41 synthesized from two different silica sources (sodium silicate hydrate and tetraethylorthosilicate) as well as on Na⁺ or K⁺ ion exchanged MCM-41 were prepared. These catalysts were used to investigate the influence of the surface properties of MCM-41 on the performance of HDS catalysts with DBT as the model molecule. The XRD and N₂ adsorption results indicated that the MCM-41 prepared from tetraethylorthosilicate (MCM-41(T)) exhibited the best structural properties. The mesostructure of MCM-41 synthesized from sodium silicate (MCM-41(S)) remained after ion exchange with Na₂C₂O₂ and K₂C₂O₂. Both pyridine FT-IR and Hammett indicators showed that only MCM-41(S) possessed some Brönsted and Lewis acid sites. Ni–W/MCM-41(S) showed the highest HDS and hydrogenation activities. The introduction of Na⁺ and K⁺ strongly inhibited the hydrogenation activity of Ni–W/MCM-41(S) but enhanced its hydrogenolysis activity. UV–vis and TPR studies indicated that the introduction of Na⁺ and K⁺ into MCM-41(S) may lead to the segregation of surface Ni species and may hinder the reducibility of the supported Ni–W oxides. Spillover hydrogen, which is “trapped” by Na⁺ and K⁺, may play an important role in the HDS activity and selectivity of Ni–W catalysts.     

不同负载方式Fe/改性MCM-41催化剂的制备及其降解亚甲基蓝性能研究

以自制二元共聚物聚[苯乙烯—3-（甲基丙烯酰氧）丙基三甲氧基硅烷]改性MCM-41,并以其为载体分别采用浸渍负载活性金属、原位负载活性金属和NaBH₄还原负载活性金属的方式制备铁基异相催化剂。研究了3类催化剂降解亚甲基蓝的性能差异。结果显示,在3种催化剂中,浸渍负载活性金属制备的催化剂具有最好的催化活性,25 min时亚甲基蓝去除率为81.2%。同时采用XRD、TEM、FTIR、XPS、压汞测试等手段分析了催化剂具有优异性能的原因。表征结果表明:Fe与改性MCM-41间的相互作用及催化剂孔结构,两者的协同作用是催化剂具有优异性能的原因。     

Well-Dispersed Gallium-Promoted Sulfated Zirconia on Mesoporous MCM-41 Silica

Gallium-promoted sulfated zirconia (SZ) was confined inside pure-silica MCM-41 (abbreviated as SZGa/MCM-41), where the latter served as a host material. It was prepared by direct dispersion of metal sulfate in the as-synthesized MCM-41 materials, followed by thermal decomposition. The SZGa/MCM-41 catalysts were characterized by XRD, N₂ adsorption, HRTEM, DRIFT, NH₃-TPD, and TPR. The experimental results showed that the ordered porous host structure was still maintained in the catalyst. SZ was in meta-stable tetragonal phase and highly dispersed on the interior surface of MCM-41 even at a high loading of 50 wt%. Additionally, a small fraction of SZ nanoparticles on the external surface of MCM-41 was obtained. The catalytic activity of SZGa/MCM-41 was examined in n-butane isomerization. In comparison to SZ/MCM-41 without promoter, the catalytic activities of the Ga-promoted catalysts were greatly improved. The reason proposed for the higher activity of the Ga-promoted catalysts was that Ga enhances the oxidizing ability of the catalysts.     

Toluene hydrogenation over nickel-containing MCM-41 and Ti-MCM-41 materials

Nickel-containing MCM-41 and Ti-MCM-41 mesoporous materials with different amounts of nickel were prepared by one-pot, sol–gel synthesis. The properties of the nickel catalysts were studied by means of X-ray diffraction (XRD), N₂ physisorption, UV-Vis spectroscopy and temperature programmed reduction (TPR) methods. The catalysts have been tested in the gas phase hydrogenation of toluene. The formation of various nickel species due to the different metal-support interaction was assumed for both of the supports. Strong metal–support interaction was supposed when Ti-MCM-41 was used as a support. It has been shown that the reducibility and the catalytic activity of the catalysts is strongly influenced by the host.     

Synthesis of Ru-modified MCM-41 Mesoporous Material, Y and Beta Zeolite Catalysts for Ring Opening of Decalin

Ru modified MCM-41 mesoporous material, Y and Beta zeolites were synthesized, characterized and investigated in ring opening of decalin. Ru-MCM-41 catalysts were prepared using ion-exchange, impregnation and in situ synthesis methods. Ru-MCM-41, Ru-Y and Ru-Beta zeolite catalysts were characterized using XRD, SEM, EDXA, FTIR, XRF and nitrogen adsorption. Ru modification of MCM-41, Y and Beta zeolites did not influence the parent phase purity of materials. Microporous H-Beta and H-Y catalysts showed larger number of Brønsted acid sites than H-MCM-41 mesoporous material. Method of Ru introduction in MCM-41 was observed to influence conversion of ring opening of decalin and selectivity to ring opening products. Ru-MCM-41-IE catalyst prepared by ion-exchange method exhibited higher conversion of decalin than Ru-MCM-41-IMP and Ru-MCM-41-IS catalysts prepared by impregnation and in situ synthesis methods. Ru-MCM-41-IS catalyst prepared by in situ method showed higher selectivity to ring opening products than Ru-MCM-41-IE and Ru-MCM-41-IMP catalysts.     

n-Pentane isomerization over promoted SZ/MCM-41 catalysts

With metal sulfate as the precursor, the catalysts of sulfated zirconia on MCM-41, Al- and Ga-promoted sulfated zirconia on MCM-41 (named as SZ/MCM-41, ASZ/MCM-41 and GSZ/MCM-41, respectively) were prepared by direct dispersion in the as-synthesized MCM-41 materials, followed by thermal decomposition. The catalysts were characterized with various techniques such as XRD, FTIR, N₂ adsorption, NH₃-TPD, DRIFT, and TPR-MS. The ordered porous structure was still maintained in the catalysts. The addition of promoters helps to retard the phase transformation of ZrO₂ from tetragonal phase to monoclinic phase. Isomerization of n-pentane was investigated over the catalysts. In comparison to SZ/MCM-41, both promoted catalysts showed much improved catalytic activity and selectivity for isomerization of n-pentane. Moreover, the catalytical activities of both promoted catalysts for pentane isomerization remained steady over the period of 180 min while the activities of the unpromoted catalyst decreased in <120 min. Characterization of acidity showed no significant difference in strength distributions of the acid sites over the catalysts. The nature of acid sites in SZ/MCM-41 was affected by the presence of aluminum, but not affected by the presence of gallium. On the other hand, TPR study shows sulfur on GSZ/MCM-41 is much easier to reduce than SZ/MCM-41 and ASZ/MCM-41. The presence of gallium improved the redox capability provided by the sulfate ions in GSZ/MCM-41 catalyst. The causes for the promotion effects of Ga and Al are discussed.     

Hydrodesulfurization of Dibenzothiophene Over Ni-Mo Sulfides Supported by Proton-Exchanged Siliceous MCM-41

Strong acid sites on the surface of mesoporous MCM-41 were generated by ion-exchanging siliceous MCM-41 with dilute HNO₃ solution (0.5 M). The XRF determination indicates that most of the sodium cations contained in MCM-41 can be removed by the proton exchange, and dealuminization was observed during the proton exchange. The acidity of the mesoporous materials was characterized by means of NH₃-TPD and the Hammett indicators. It is revealed that new strong acid sites (-5.6 > H₀ > -8.2) were generated after the first 2 h of ion exchange and that the following ion exchanges had little effect on the acidic properties. XRD patterns of the mesoporous materials indicate that the structure of siliceous MCM-41 was improved by HNO₃ ion exchange. When Ni-Mo sulfides were supported on the prepared solid acid (H⁺-MCM-41), high performance in the hydrodesulfurization (HDS) of dibenzothiophene (DBT) was observed. However, the HDS activity was decreased while the selectivity of biphenyl (BP) was increased, when H⁺-Si-MCM-41 was ion exchanged with Na₂CO₃ aqueous solution. TPR profiles of the supported Ni-Mo oxides reveal that the acidic properties of the supports greatly influence the hydrogenation activities of the bimetallic oxides. The high performance of H⁺-MCM-41-supported Ni-Mo catalysts may be attributed to the enhanced hydrogenation activity. The introduction of Na cation into the support led to the decrease of the HDS activity due to the poor hydrogenation ability of the supported bimetallic oxides. The HDS activity is well correlated with the low H₂ consumption temperature in the TPR profiles.     

基于MCM-41的镍基甲烷化催化剂活性与稳定性

采用浸渍法分别以MCM-41,Al₂O₃和SiO₂ 为载体制备了不同镍负载量的甲烷化催化剂,并在连续流动固定床反应装置上对其甲烷化催化活性进行了评价。研究结果表明,与Ni/Al₂O₃和Ni/SiO₂相比,相同镍负载量的Ni/MCM-41催化剂具有更好的催化活性。同时研究了Ni含量对于Ni/MCM-41催化剂催化活性的影响,发现随着Ni含量的增加,CO转化率和CH₄收率逐渐升高,并且在Ni含量大于10%（质量分数）以后趋于稳定。在n（H₂）：n（CO）=3：1、反应压力1.5 MPa、反应温度350℃及质量空速12000 ml·h^-1·g^-1的反应条件下,10%Ni/MCM-41催化剂CH₄选择性达到94.9%,CO转化率接近100%。在100 h催化活性稳定性试验中,10%Ni/MCM-41催化活性无明显下降,表现出良好的催化活性稳定性。采用X射线衍射（XRD）、氮气物理吸附（BET）、热重分析（TG）及氢气程序升温还原（H₂-TPR）等技术手段对催化剂进行了表征,结果表明Ni颗粒大小是影响Ni/MCM-41催化剂催化活性的主要因素。     

新型MCM-22/MCM-41复合分子筛上FCC汽油降烯烃芳构化反应

采用纳米组装法合成MCM-22/MCM-41微孔/介孔复合分子筛,分别以H-MCM-22和H-MCM-22/MCM-41为催化剂,在固定床微反装置上对FCC汽油进行降烯烃芳构化的对比考察。结果表明,在反应时间2 h内,与MCM-22相比, MCM-22/MCM-41具有高的芳构化性能和持久的初始活性,复合分子筛汽油改质的产物中,芳烃体积分数由28.58%上升至51.1%,烯烃体积分数由34.04％降至5.8％。探讨了新型H-MCM-22/MCM-41复合分子筛用于FCC汽油改质的操作条件以及催化剂失活再生性能。结果表明,最佳反应条件为：反应温度400 ℃,压力2 MPa,空速3 h^-1。失活催化剂经过两次再生,降烯烃芳构化性能基本不变。     

Skeletal Isomerization of n-Pentane over Platinum-Promoted Tungstophosphoric Acid Supported on MCM-41

Skeletal isomerization of n-pentane in the presence of hydrogen has been studied over Pt-promoted H₃PW₁₂O₄₀ (TPA)/MCM-41 bifunctional catalyst. A series of solid acid catalysts with different loading amount of TPA and Pt were prepared and characterized by XRD, FT-IR and XPS. The optimal catalytic activity of Pt-TPA/MCM-41 was observed with 2% Pt and 30% TPA. According to the cracked products distribution, this is typical of a monomolecular bifunctional metal-acid mechanism. Further, catalysts with different combination of noble metals (Pt, Pd and Ru), heteropoly acids (HPAs) (TPA, tungstosilicic acid (TSA), and molybdophosphoric acid (MPA)) and supports (MCM-41, SBA-1 and SiO₂) were also synthesized and their catalytic performances were compared.     

Synthesis, Characterization of Ag/MCM-41 and the Catalytic Performance for Liquid-phase Oxidation of Cyclohexane

Nano-scale silver supported mesoporous molecular sieve Ag/MCM-41 was directly prepared by one-pot synthesis method. The prepared sample was characterized by XRD, TEM, and N₂ sorption. The results showed that the sample of Ag/MCM-41 had no appreciable incorporation of silver into the mesoporous matrix of MCM-41 with good crystallinity, and silver nanoparticles were dispersed inside or outside of the channels in the mesoporous host. The catalytic performance of the sample for the cyclohexane liquid-phase oxidation into cyclohexanone and cyclohexanol by oxygen in the absence of solvents without inducing agents was investigated. The 83.4% selectivity to cyclohexanol and cyclohexanone at 10.7% conversion of cyclohexane was obtained over Ag/MCM-41 catalyst at 428 K for 3 h. The turn over numbers (TONs) of Ag/MCM-41 was up to 2946. The catalytic activity of Ag/MCM-41 was also compared with Ag/TS-1 as well as Ag/Al₂O₃. The results indicated that Ag/MCM-41 showed superior activity to both Ag/TS-1 and Ag/Al₂O₃. A calcined Ag/MCM-41 was found to be an efficient catalyst for the cyclohexane oxidation into cyclohexanol and cyclohexanone using oxygen as oxidant.     

Pd/Ni-MCM-41制备及其对苯甲醛加氢的催化性能

以十六烷基三甲基溴化铵为模板剂,正硅酸乙酯为硅源,MCM-41为载体,碱性条件下,合成Pd/Ni-MCM-41。通过XRD、HR-TEM、FT-IR和BET等对Pd/Ni-MCM-41进行表征。Pd/Ni-MCM-41的比表面积为(444.32～621.69) m^2·g(-1),孔容为(0.54～0.69) cm^3·g^(-1),孔径分布均匀,主要集中在(2～4) nm。将Pd/Ni-MCM-41用于苯甲醛加氢制备苯甲醇反应中,Ni质量分数6%时,在反应温度100℃和反应压力0.20 MPa条件下反应2 h,苯甲醛转化率65.1%,苯甲醇选择性为100%。     

Preparation of sulfated alumina supported on mesoporous MCM-41 silica and its application in esterification

New types of mesoporous SA/MCM-41 solid acid catalysts were prepared by loading sulfated alumina (SA) on MCM-41. The prepared catalysts were characterized by XRD, IR, N₂ physisorption, elemental analysis, FT-IR of adsorbed pyridine and NH₃-TPD. The esterification of acetic acid with n-butanol and citric acid with n-butanol were used as model reactions to test the catalytic activities and reusability of the SA/MCM-41 solid acid catalysts. Compared with SA catalyst, SA/MCM-41 catalysts exhibited higher catalytic performances, which were attributed to their high BET surface area and large pore volume. Moreover, 20SA/MCM-41 solid acid catalyst showed excellent reusability in both esterifications.