Non-oxidative conversion of methane to aromatics over modified Mo/HZSM5 catalysts

The effects of HZSM5 Si/Al ratio, cobalt additive and HCl-acidified pretreatment on methane conversion and selectivity to aromatics have been investigated for non-oxidative conversion of methane to aromatics. The HZSM5 (E) with low Si/Al ratio (Si/Al=20) has better methane conversion and benzene selectivity than HZSM5 (D) (Si/Al=55). The synergistic effect is exhibited in 3% Mo-1% Co-HCl/HZSM5 (E) catalyst, on which a high methane conversion of 10.7% can be achieved, in comparison with 5.3% methane conversion on 3% Mo/HZSM5 (E). The catalysts have been characterized by XPS and the reaction mechanism is discussed.     

Non-oxidative methane conversion into aromatics on mechanically mixed Mo/HZSM-5 catalysts

The catalyst prepared by the physical mixing of powder MoO₃ and HZSM-5 exhibits a better performance for methane conversion at high Mo loading compared with those prepared by the impregnation method. The specific surface area is larger for physically mixed samples than that for impregnated samples with the same Mo loading. The preferential orientation of MoO₃ crystallite is along the (0 k 0) axis, while the (0 2 1) plane is exposed preferentially by MoO₃ to impregnated HZSM-5. Both hcp β-Mo₂C and fcc α-Mo₂C can be formed on physically mixed samples, while only hcp β-Mo₂C is found on the impregnated samples under the same reaction condition.     

重芳烃轻质化技术进展

重芳烃是生产轻芳烃的重要资源,重芳烃轻质化涉及加氢脱烷基、歧化和烷基转移等反应。TAC-9、ATA-11、Transplus等有代表性的国内外重芳烃轻质化反应工艺具有各自的优势与不足,未来重芳烃轻质化工艺技术发展应针对重芳烃轻质化反应的特点,开发以小颗粒、大孔径的分子筛作催化剂活性组元,增产附加值高的二甲苯。     

Interconversion of light olefins—aromatics over zeolite catalysts

Improved yield in light olefins and aromatics from methanol conversion was observed on Zn and Mn loaded ZSM-5 zeolite—asbestos catalysts. The best results in terms of conversion into hydrocarbons were obtained with a Zn content not exceeding 0.6% wt/wt. The light olefins/aromatics ratio in the products varied with the Mn content in the catalyst, the cumulative light olefinic and aromatic production being kept constant at a high value.     

重芳烃轻质化工艺和催化剂研究进展

介绍了国内外有关重芳烃轻质化反应及催化剂和比较有代表性的工艺技术路线。重点阐述了催化加氢脱烷基和烷基转移反应特点和有关催化剂的研究以及国内外主要工艺发展现状。认为,重芳烃轻质化发生的反应所用催化剂多属于酸型,开发以小颗粒、大孔径以及良好抗积炭性能的固体酸催化剂,尤其是催化加氢脱烷基和烷基转移反应催化剂,对提高C⁺₉重质芳烃利用价值和增产附加值高的二甲苯和苯有着重要意义。     

Steam reforming of n-hexadecane over noble metal-modified Ni-based catalysts

Steam reforming of n-hexadecane, a main constituent of diesel, over noble metal-modified Ni-based hydrotalcite catalyst was carried out in a temperature range of 700–950 °C, at an atmospheric pressure with space velocity of 10,000–100,000 h⁻¹ and feed molar ratio of H₂O/C = 3.0. The catalysts were prepared by a co-precipitation and dipping methods. The noble metal-modified Ni-based hydrotalcite catalyst displayed higher resistance for the sintering of active metal than the Ni-based hydrotalcite catalyst prepared by the conventional method. It was found that the Rh-modified Ni-based catalysts showed high resistance to the formation of carbon compared to Ni-based catalysts. The results suggest that Rh-modified Ni-based catalyst can be applied for the steam reforming (SR) reaction of diesel.     

Effect of the activation procedure on the performance of Mo/H-MFI catalysts for the non-oxidative conversion of methane to aromatics

The effect of pre-treatment on the performance of Mo/H-MFI zeolite catalysts applied to the non-oxidative conversion of methane to aromatics has been investigated. It is demonstrated that catalyst performance depends on activation conditions. Activation of the Mo-oxide/H-MFI precursor with an n-butane/hydrogen mixture results in higher catalyst stability and benzene selectivity which are tentatively attributed to the formation of the -MoC_1−x carbide, with f.c.c. structure as revealed by XRD.     

C10+重质芳烃轻质化工艺技术研究

为解决重质芳烃难以处理的问题,开发了一种C10+重质芳烃轻质化工艺.以某炼厂生产的C10+重质芳烃和新鲜氢气为原料,在工业侧线装置上进行性能评价.在优化操作条件下,C10+重质芳烃经轻质化工艺流程处理后可转化为混合芳烃和C7轻烃及以下组分,其中混合芳烃质量约占产物质量的57％,混合芳烃中以C8—C10芳烃为主,且主要为...     

B-ZSM-5酸调控及催化褐煤热解挥发分制轻质芳烃研究

在不同碱性条件下水热合成了B-HZSM-5 （B-H5）催化剂用于原位催化褐煤热解挥发分制备轻质芳烃。通过X射线衍射仪、扫描电子显微镜、氨气程序升温脱附仪和N₂物理吸附脱附表征了合成条件对分子筛的形貌、酸性和质构特征的影响。在强碱性条件下合成的分子筛表面更光滑、结晶度更高,Na-xB-H5（合成过程加碱）弱酸明显增强。与母体H5相比,Na-xB-H5骨架硼形成的B—OH—Si提供更多的弱酸位点能够吸附乙烯丙烯等中间产物,增加甲基化和烷基化速率。在具有较高的结晶度、丰富的酸位点和微孔/介孔的Na-0.69B-H5（硼添加量为0.69 g）上得到了最高烷基苯产率11.4 mg/g。而过量引入硼则会使骨架Al流失,强弱酸比例减少,抑制芳构化反应,降低轻质芳烃产率。通过骨架硼的引入调控分子筛酸性为褐煤催化热解提高轻质芳烃产率提供了新思路。     

重芳烃轻质化研究进展

综述重芳烃轻质化技术的研究进展,重芳烃轻质化技术包括针对侧链的脱烷基技术、烷基转移技术和针对双环芳烃的选择性加氢开环技术,介绍脱烷基和烷基转移催化剂与工艺及选择性加氢开环催化剂,分析贵金属和非贵金属催化剂各自的优势与不足。概述各种轻质化工艺及组合工艺,未来重芳烃轻质化工艺技术发展应针对单环芳烃和双环芳烃的不同加工路线,对单环和双环芳烃选择分离,采用多种轻质化技术配套形成高效组合工艺,提高重芳烃综合利用效益。     

Characterization of surface carbon formed during the conversion of methane to benzene over Mo/H-ZSM-5 catalysts

During the conversion of methane to benzene in the absence of oxygen over a 2 wt% Mo/H-ZSM-5 catalyst at 700°C, three different types of surface carbon have been observed by X-ray photoelectron spectroscopy: adventitious or graphitic-like C (284.6 eV), carbidic-like C (282.7 eV), and hydrogen-poor sp-type C (283.2 eV), where the C 1s binding energies for the respective forms of carbon are given in parentheses. Pretreatment of the catalyst at 700°C in CO also resulted in a strong signal at 283.2 eV; thus, the species responsible for this signal appears to be different from the usual aromatic-type coke. The coke with dominantly sp hybridization is concentrated on the external surface of the zeolite and is responsible for the gradual deactivation of the catalyst. This revised version was published online in July 2006 with corrections to the Cover Date.     

Catalytic conversion of methane to benzene over Mo/ZSM-5

Dehydroaromatization of methane to benzene occurs over a 2 wt% Mo/ZSM-5 catalyst at 700C under non-oxidizing conditions. Following an initial induction period, during which CH₄ reactant reduces the original Mo⁶⁺ ions in the zeolite to Mo₂C and deposition of coke occurs, a benzene selectivity of 70% at a CH₄ conversion of 8–10% could be sustained for more than 16 h. X-ray photoelectron spectroscopy and X-ray powder diffraction measurements indicate that the reduced Mo is highly dispersed in the channels of the zeolite. Initial activation of CH₄ reactant occurs on Mo₂C sites, leading to the formation of C₂H₄ as the primary product. The latter then undergoes subsequent oligomerization reactions on acidic sites of the zeolite to form aromatic products.     

Dimethyl ether conversion to light olefins over the SAPO-34/ZrO2 composite catalysts with high lifetime

The SAPO-34/ZrO₂ composite catalysts using ZrO₂ as a binder were prepared and their performance was investigated for the dimethyl ether to olefins (DTO) reaction. The composite catalysts showed higher catalytic lifetimes than the free SAPO-34 catalyst, while maintaining high selectivity toward light olefins. This suggests that the binder-filled space between the SAPO-34 crystals can provide additional diffusion paths for mass transfer. In the SAPO-34/ZrO₂ composite catalysts with different ZrO₂ contents, the SAPO-34(11 wt%)/ZrO₂ composite catalyst showed the highest catalytic lifetime. It can be concluded that ZrO₂ is one of the best binders for the preparation of SAPO-34/binder composite catalysts.     

甲醇制芳烃反应中ZSM-5催化剂改性技术

芳烃是种重要的化工原料,在众多领域得到广泛应用。随着甲醇生产技术的成熟,甲醇制芳烃工艺已经成为现阶段非石油路线合成轻质芳烃的重要途径。目前,甲醇制芳烃工艺中常用的催化剂为ZSM-5分子筛,但仍需对分子筛进行合适的后处理改性操作如调变分子筛酸性、活性中心位点和孔道结构等,以提高芳烃收率及特定产品的选择性。综述了甲醇制芳烃反应中ZSM-5分子筛催化剂负载法、碱处理法、酸处理法和水热处理法等改性技术研究进展,以期达到工业化要求,最终实现甲醇制芳烃工艺的工业化发展。     

新型非常规天然气直接催化转化制芳烃催化剂的研究

近年来,常规天然气供应紧张,因此非常规天然气的开发利用显得尤为重要。甲烷无氧芳构化作为非常规天然气的直接转化方式之一,由于其工艺流程简单、芳烃选择性集中、产物附加值高等特点,一直受到广大科研工作者的关注。为提高甲烷转化率及甲苯和二甲苯等产物的选择性,通过一步浸渍法制备了0.189%Mg/8%Mo/HZSM-5（以质量分数计）催化剂,在700 ℃、101 kPa条件下通过将甲烷无氧芳构化反应与芳烃烷基化反应耦合,其中甲醇作为烷基化试剂与甲烷以共进料的方式进入反应体系,将甲烷的转化率提升至27.45%、甲苯和二甲苯的选择性分别达到28.29%和24.65%,并且8 h内催化剂未出现活性减弱,实现了反应的高效稳定运行。     

Conversion of methane to benzene over Mo2C and Mo2C/ZSM-5 catalysts

The activation and dehydrogenation of CH₂ on Mo₂C and MO₂C/ZSM-5 have been investigated under non-oxidizing conditions. Unsupported Mo₂C exhibited very little activity towards methane decomposition at 973 K. The main reaction pathway was the decomposition of methane to give hydrogen and carbon with a trace amount of ethane. Mixing Mo₂C with ZSM-5 support somewhat enhanced its catalytic activity, but did not change the products of the reaction. A dramatic change in the product formation occurred on partially oxidized Mo2C/ZSM-5 catalyst; besides some hydrocarbons benzene was produced with a selectivity of 70–80% at a conversion of 5–7%. Carburization of highly dispersed MoO₃ on ZSM-5 also led to a very active catalyst: the conversion of methane at the steady state was 5–6% and the selectivity of benzene formation was 85%.This laboratory is a part of the Center for Catalysis, Surface and Material Science at the University of Szeged.     

Efficient conversion of benzene and syngas to toluene and xylene over ZnO-ZrO2&H-ZSM-5 bifunctional catalysts

A series of ZnO-ZrO₂ solid solutions with different Zn contents were synthesized by the urea co-precipitation method, which were coupled with H-ZSM-5 zeolite to form bifunctional catalysts. As a new benzene alkylation reagent, syngas was used instead of methanol to realize the efficient conversion of syngas and benzene into toluene and xylene. A suitable ratio of ZnO-ZrO₂ led to the significant improvement in the catalytic performance, and a suitable amount of acid helped to increase the selectivity of toluene/xylene and reduce the selectivity of the by-products ethylbenzene and C₉⁺ aromatics. The highest benzene conversion of 89.2% and toluene/xylene selectivity of 88.7% were achieved over 10% ZnO-ZrO₂&H-ZSM-5 (Si/Al = 23) at a pressure of 3 MPa and a temperature of 450 ℃. In addition, the effect of the zeolite framework structure on product distribution was examined. Similar to the molecular dynamics of aromatic hydrocarbons, H-ZSM-5 zeolites comprise 10-membered-ring pores, which are beneficial to the activation of benzene; hence, the conversion of benzene is higher. H-ZSM-35 and H-MOR zeolites exhibited small eight-membered-ring channels, which were not conducive to the passage of benzene; hence, the by-product ethylbenzene exhibits a higher selectivity. The distance between the active centers of the bifunctional catalysts was the main factor affecting the catalytic performance, and the powder mixing method was more conducive to the conversion of syngas and benzene.     

Kinetic study of carbon nanotube synthesis over Mo/Co/MgO catalysts

The kinetics of carbon nanotube (CNT) synthesis by decomposition of CH₄ over Mo/Co/MgO and Co/MgO catalysts was studied to clarify the role of catalyst component. In the absence of the Mo component, Co/MgO catalysts are active in the synthesis of thick CNT (outer diameter of 7-27 nm) at lower reaction temperatures, 823-923 K, but no CNTs of thin outer diameter are produced. Co/MgO catalysts are significantly deactivated by carbon deposition at temperatures above 923 K. For Mo-including catalysts (Mo/Co/MgO), thin CNT (2-5 walls) formation starts at above 1000 K without deactivation. The significant effects of the addition of Mo are ascribed to the reduction in catalytic activity for dissociation of CH₄, as well as to the formation of Mo₂C during CNT synthesis at high temperatures. On both Co/MgO and Mo/Co/MgO catalysts, the rate of CNT synthesis is proportional to the CH₄ pressure, indicating that the dissociation of CH₄ is the rate-determining step for a catalyst working without deactivation. The deactivation of catalysts by carbon deposition takes place kinetically when the formation rate of the graphene network is smaller than the carbon deposition rate by decomposition of CH₄.     

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.     

Comparison of activities in selective catalytic reduction of NOx by C3H8 over Co/MFI, Fe/MFI, and H/MFI zeolite catalysts

The Co/MFI(SiO₂/Al₂O₃ = 30) were prepared by a precipitation method with NaOCl in alkali solutions exhibited high activities to N₂ at 250 °C for the selective catalytic reduction (SCR) of NO_x. These catalysts showed two UV–vis bands at 700 and 400 nm, indicating the presence of octahedral Co(III) as well as tetrahedral Co(II). The high SCR activity over such Co(III, II)/MFI(30) seems to come from Co(III)---O moieties. The Co(II)MFI(30) catalysts prepared from Co(II)Cl₂ exhibited low SCR activities due to the presence of tetrahedral Co(II) ions in MFI. Less CO formation occurred over Co/MFI catalysts. The Fe/MFI(30) catalyst exhibited high activity due to the presence of some Fe---O species in MFI but more amount of CO were produced during SCR. H/MFI(30) catalyst exhibited a good SCR activity. However, more amount of carbonaceous deposits were produced on it. The correlation between acid concentration and SCR activity was discussed over H/MFIs.