酸性沸石分子筛催化油酸异构化反应的研究

以酸性沸石分子筛催化油酸异构化制备支链油酸(ubc FA),并对产物加氢,得到C18饱和的支链脂肪酸(sbc FA)。采用气相色谱(GC)、气质联用(GC-MS)及核磁共振(NMR)技术对反应产物进行表征。研究了不同类型的酸性沸石分子筛对催化油酸异构化反应的活性差异,筛选出了对反应具有高活性高选择性的催化剂,最佳反应条件为:酸性丝光沸石分子筛6%(基于油酸质量),反应初压0.4 MPa,反应温度270℃,反应时间4 h。该反应条件下,油酸的转化率达98%,sbc FA的选择性达82%。     

酸性沸石分子筛催化油酸异构化反应的研究

以酸性沸石分子筛催化油酸异构化制备支链油酸(ubc FA),并对产物加氢,得到C18饱和的支链脂肪酸(sbc FA)。采用气相色谱(GC)、气质联用(GC-MS)及核磁共振(NMR)技术对反应产物进行表征。研究了不同类型的酸性沸石分子筛对催化油酸异构化反应的活性差异,筛选出了对反应具有高活性高选择性的催化剂,最佳反应条件为:酸性丝光沸石分子筛6%(基于油酸质量),反应初压0.4 MPa,反应温度270℃,反应时间4 h。该反应条件下,油酸的转化率达98%,sbc FA的选择性达82%。     

Theoretical studies of IM-12 zeolite for acidic catalysts

We theoretically investigate the properties of the IM-12 to address a catalyst for acidic conversion reaction of larger organic molecules. The acidic characteristics of the IM-12 are investigated by density functional theory (DFT) considering both the local density and generalized gradient approximations, LDA and GGA, respectively. Based on quantum mechanical (QM) calculation results, we find that the zeolite with Al element prefers the tetrahedral (T) sites, T4 and T6, when replacing Si in IM-12 framework. Isomorphously substituted IM-12 on the T4 and T6 sites by B, Al, and Ga is studied, respectively. Both of the sites give the Brönsted acidity order: B–IM-12 < Ga–IM-12 < Al–IM-12, which is the same as other zeolites. The calculated NH₃ adsorption energies are compared with the calculated and experimental results of H–[Al]MOR [M. Elanany, D.P. Vercauteren, M. Koyama, M. Kubo, P. Selvam, E. Broclawik, A. Miyamoto, J. Mol. Catal. A 243 (2006) 1; C. Lee, D.J. Parrillo, R.J. Gorte, W.E. Farneth, J. Am. Chem. Soc. 118 (1996) 3262]. Molecular dynamics (MD) results show that IM-12 zeolite allows the large molecules such as diisopropylbenzene (DIPB) and triisopropylbenzene (TIPB) to diffuse faster than those in MOR zeolite and IM-12 may have significant selectivity for TIPB over DIPB. We conclude that the IM-12 with Al impurity would be a good candidate for large organic molecule acidic conversion reaction.     

Reactivity of electrophilic oxygen species generated over mesoporous iron-containing catalysts

The vapour phase hydroxylation of toluene and epoxidation of propene and 1-butene with nitrous oxide over Fe/SBA-15 catalysts was experimentally investigated. Modification of these mesoporous catalysts by the addition of KCl resulted in a significant transfer from benzylic/allylic oxidation towards aromatic/vinylic oxidation by suppressing the reactivity of nucleophilic oxygen species. Analogous to the Fe/ZSM-5 system, highly dispersed iron species residing within the pore structure are responsible for generating the electrophilic oxygen species upon nitrous oxide decomposition. While substrate conversions are generally low (<4%), the catalysts offer phenolic/epoxide selectivities of 70% in an environmentally benign one-step reaction.     

高效烷氧基化催化剂

简述了高效烷氧基化催化剂 :碱土金属催化剂、聚碳酸单酯碱土金属盐、水滑石类含镁铝化合物、用Si4 、Ba2 改性氧化镁、用铁镍铈钇改性氧化镁、铝—镁复合氧化物、钛酸和 /或锆酸的酯等 ,并分别论述了它们的化学组成、制法及效果评价     

Transformation of hydrocarbons on zeolite catalysts

Catalytic processes on zeolites and catalytic characteristics of zeolites have been reviewed in the area of petrochemistry and refining.     

Oxidative dehydrogenation of propane on zeolite catalysts

Oxidative dehydrogenation of propane has been studied on zeolite Na-Y, stabilized zeolite Y (USY) and ZSM-5. The supports with the faujasite structure were modified with boron, gallium and indium oxides and Ca, Mg, Sn, and Sb cations. The samples containing simultaneously In₂O₃ and Ga₂O₃ in the USY support were compared. A detailed analysis of the zeolite catalysts performance in the title reaction has been carried out.     

Preparation of bisphenol-A over zeolite catalysts

The reaction of phenol and acetone to give bisphenol-A (4,4-isopropylidenediphenol) has been investigated using zeolite as catalysts. The zeolites are less active and selective than the cation-exchange resin, Amberlyst-15.     

Realumination of zeolite Y under acidic conditions

Dealuminated zeolites Y were treated with aqueous solutions of various acids and ammonium salts to investigate the realumination behavior under acidic conditions. From the results of ²⁷Al MAS NMR, ²⁹Si MAS NMR and FT-IR measurements, it was found that a part of non-framework aluminum species in the dealuminated zeolite Y is effectively reinserted into the zeolite framework in CH₃COONH₄ and C₆H₅COONH₄ aqueous solutions. Pyridine adsorption experiments also revealed that most of incorporated aluminum species generate tetrahedrally coordinated framework aluminum species, namely Brönsted acid sites. Although the realumination also proceeded in H₂SO₄ and CH₃COOH aqueous solutions, large amounts of incorporated aluminum species were not necessarily responsible for generation of Brönsted acid sites. Framework connected aluminum species, presumably as 3-fold-coordinated Lewis acidic framework aluminum species, were mainly generated. In the TEM image of the realuminated zeolite Y, needle-like crystals with ca. 25–80 nm in length were observed, which are probably due to AlOOH generated from non-framework aluminum species.     

合成MTBE的分子筛催化剂研究述评

分子筛催化剂是一种具有择形功能的绿色化学催化剂。自20世纪80年代以来,国内外用分子筛催化剂进行合成甲基叔丁基醚的研究已经开展了许多工作。本文对此作了综述。     

Isomerization of n-hexane over nickel-loaded zeolite catalysts

The isomerization of n-hexane to branched-chain isomers was studied over various zeolite supports containing nickel between 1 to 5 wt%. NaA, NaY, CaY and Zeolon 900H were loaded with nickel by an impregnation technique. It was observed that at a nickel content of about 2.5 wt%, all the catalysts showed maximum activity for isomerization. A catalyst containing 1 wt% Ni/CaY gave the maximum selectivity among all the catalysts studied. Increasing the nickel loading beyond 2.5 wt% Ni with CaY and Zeolon 900H led to more hydrocracking. No major change in the activity and selectivity of Ni/NaA catalysts was observed beyond 2.5 wt% Ni, whereas the activity of Ni/NaY catalysts remained almost constant over the range of nickel content studied. A catalyst containing 2.5 wt% Ni on Zeolon 900H gave the maximum yield of isomers at 643°K. The apparent activation energy of the reaction was found to be 48.6 kJ/mol for 1 wt% Ni on Zeolon 900H catalyst.     

Role of zeolite structure on NO reduction with diesel fuel over Pt supported zeolite catalysts

A highly desirable selective catalytic reduction (SCR) of NO with real life diesel fuel over Pt supported zeolites with different topologies (Pt-ZSM-5, Pt-FER, Pt-MOR and Pt-BEA) is studied under simulated exhaust conditions. The catalysts are characterized by CO chemisorption, NH₃-TPD and TGA. The NO conversion ability of these catalysts has been correlated with zeolite structure and acidity. Pt-MOR is found to be the most active catalyst, 90% NO conversion at 300 °C, however Pt-FER showed highly desirable low temperature window, 77% NO conversion below 260 °C. Over ZSM-5, BEA and Y with three dimensional pore structures extensive carbonaceous deposits are observed by TGA which are detrimental to NO conversion. On the other hand, FER zeolite having one dimensional pore structure did not allow extensive coke formation resulting in a highly desired low temperature NO conversion. The results suggest that, NO reduction mainly take place near the zeolite pore opening, which is in reasonable agreement considering the long and bulky molecules in diesel fuel.     

不同沸石分子筛催化剂上萘与异丙醇的烷基化反应

考察了USY、Hβ、HMCM-22、HM、HZSM-5等5种沸石分子筛在萘与异丙醇烷基化反应中的催化性能,并用XRD和NH3-TPD等手段对催化剂的物化性质进行了表征。实验结果发现,沸石分子筛的酸性质和孔结构是影响其活性和选择性的主要因素,以弱酸和中强酸为主的酸性中心以及十二元环开放的孔道有利于提高催化剂活性,而与目标产物2,6-二异丙基萘的分子直径接近的一维孔道有利于其选择性的提高。     

Interparticulate coke formation during hydrocarbon cracking on zeolite catalysts

A thermogravimetric study of coking of various C₆–C₇ hydrocarbons on HY and REY zeolites was performed using a Cahn microbalance modified to allow in-situ measurements of catalyst weight changes during reaction under flow conditions. Mass transfer effects during the reaction were found to play an important role in the coking process of the static catalyst bed. The results indicate that catalytic coke can form in the void space between zeolite particles in such a way as to deter molecular diffusion through the catalyst bed.     

n-Octane aromatization on Pt-containing non-acidic large pore zeolite catalysts

Platinum catalysts supported on the potassium-form of different large-pore zeolites (i.e. K-LTL, K-BEA, K-MAZ, and K-FAU) have been tested for n-octane aromatization at 500 °C. All catalysts were prepared by the vapor phase impregnation (VPI) method. It was found that the Pt/K-LTL catalyst exhibit a better aromatization performance than the other zeolite catalysts. However, due to secondary hydrogenolysis, the C8 aromatics produced inside the zeolite are converted to benzene and toluene. By contrast, a non-microporous Pt/SiO₂ catalyst did not present the secondary hydrogenolysis. Therefore, despite a lower initial aromatization activity, Pt/SiO₂ results in higher selectivity to C8 aromatics than any of the other zeolite catalysts. All fresh catalysts were characterized by hydrogen chemisorption and FT-IR of adsorbed CO. In addition, the residual acidity of the supports was analyzed by temperature programmed desorption (TPD) of ammonia. In agreement with previous studies, it was found that after reduction at either 350 or 500 °C, the Pt/K-LTL showed much higher Pt dispersion than other catalysts. It is known that the structure of L zeolite can stabilize the small Pt clusters inside the zeolite channel. By contrast, FT-IR indicated that a large fraction of platinum clusters were located outside the zeolite channels in the case of Pt/K-BEA and Pt/K-MAZ catalysts.     

分子筛催化C_9芳烃脱烷基的研究

将Bi、Ni、Mo、Pt分别负载在氢型ZSM-5、MOR、Y分子筛上,以异丙苯为模型化合物对分子筛催化加氢脱烷基性能进行评价,考察了不同金属的活性和分子筛结构。结果表明,不同分子筛载体上,不同金属脱烷基活性大小次序为:Pt>Mo>Ni>Bi;分子筛的孔结构可限制产物的形成,从而影响烷基转移反应和脱烷基反应二者的活性。此外,酸强度和密度的分布与金属同样重要,它们之间的平衡协同作用对催化剂的活性有着至关重要的作用。     

Isomerization of isobutyraldehyde to methyl ethyl ketone on zeolite catalysts

The isomerization of isobutyraldehyde (IBH) was studied over aluminium-free ZSM-5 zeolite catalysts with different boron content in the framework. The selectivity to methyl ethyl ketone (MEK) is high, ca. 83 wt%. With the increase of boron content, the conversion of IBH increased but the selectivity to MEK decreased. The effects of Na content, cation-exchange, 500°C-steam treatment and temperature on catalyst activity were investigated. It was observed that cation-exchange resulted in the decrease of conversion of IBH and increase of selectivity to MEK, but 500°C-steam treatment resulted in the decrease of selectivity to MEK.     

Studies on the synthesis of diacetyl over oxidation zeolite catalysts

Diacetyl (2,3-butanedione) synthesis from methyl ethyl ketone over oxidation zeolites using O₂ as oxidant was studied. Various zeolites with Fe, V and Ti as active sites were employed. VS-1, Ti-NCL, Ti-MCM-41 and FeBEA type materials were synthesized and characterized by BET, FTIR, XRD, pyridine adsorption and template desorption. The detailed study of the effect of reaction temperature, the effect of concentration of oxygen and the addition of water was realized. The most active catalyst was zeolites with V as oxidation center.     

Linear hexane isomerization over the natural zeolite based catalysts depending on the zeolite phase composition

A range of Pd-containing catalysts on the basis of mordenite–clinoptilolite rocks of different starting phase compositions is synthesized. Final phase composition and acidity of rocks change as the conditions of their dealumination are changed. The efficiency of catalysts synthesized is weakly influenced by change of mordenite component contents within 50–80%, and it is not inferior to the efficiency of the catalysts on the synthetic mordenite basis. The nature of active sites as trifunction ones and isomerization mechanism are proposed.     

Activity and stability of alumina zeolite nickel catalysts

The catalytic properties of nickel catalysts (50 wt.% of alumina and 50 wt.% of Ni,H-ZSM-5) were investigated and related to the amount of NiO (0–8 wt.%) and the method of nickel incorporation (8 wt.% NiO). Consideration was also given to the method by which zeolite and alumina were combined. The cracking properties of the catalysts increased when the amount of NiO was raised up to 4 wt.%. To decrease the content of aromatic hydrocarbons in the products it is necessary to raise the amount of NiO to a higher level than 4 wt.%. The catalyst prepared by peptisation of the mixture of zeolite and aluminium hydrogel (with ageing process) displayed reduced activity and stability because of the low susceptibility of NiO to reduction.