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《燃料化学学报》2021,(4)
采用三聚氰胺作为N源,N掺杂改性HZSM-5沸石分子筛后负载Mo活性金属组分,制备了一种用于甲烷无氧芳构化反应(MDA)的催化剂。采用XPS、N_2吸附-脱附、XRD、H2-TPR、TEM和NH3-TPD对催化剂性质和Mo金属组分状态进行了分析表征,并考察了催化剂的甲烷无氧芳构化反应催化性能。结果表明,HZSM-5经过N掺杂改性后,会在分子筛表面生成一层含氮基团,有序调控了分子筛的酸性位点;同时会诱导Mo金属组分在催化剂表面更好的锚定落位。此方法制备的Mo/HZSM-5-CN催化剂能有效提高MDA反应的甲烷转化率和芳烃选择性,减缓了积炭的生成,展现出更优良的催化性能。 相似文献
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利用天然气生产芳烃是一个有吸引力的课题,这个过程需要具有高性能活性位点的催化剂,以活化稳定的碳氢键.在甲烷直接转化方法中,将甲烷无氧脱氢芳构化(MDA)转化为高附加值芳烃(如苯、甲苯和萘)是甲烷增值的有效途径.本研究采用MoO3纳米带作为Mo源,微孔分子筛MCM-22作为载体制备双功能Mo基催化剂,结果表明MoO3纳米带高度分散在分子筛内部,与分子筛中Br?nsted酸中心结合形成有效活性中心,改善了甲烷无氧脱氢芳构化反应的催化活性,提高了催化剂的稳定性.在甲烷无氧脱氢芳构化反应测试中,当MoO3纳米带的负载量质量分数为6%时,N-Mo-HMCM-22催化剂催化的甲烷转化率达到14.1%,苯产率可达8.2%.本研究为合成高性能、稳定的MDA催化剂提供了一种更为简易的策略. 相似文献
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甲烷在Mo/HZRP-1催化剂上无氧脱氢芳构化反应 Ⅰ.Mo/HZRP-1催化剂的催化性能和积炭行为 总被引:1,自引:0,他引:1
用高硅含磷五员环沸石分子筛(商品代号HZRP-1)作为载体,制备了Mo/HZRP-1催化剂.与Mo/HZSM-5相比,Mo/HZRP-1对甲烷无氧脱氢芳构化反应也表现出较好的催化性能.实验过程中,在反应气中添加N2作为内标物,给出包括甲烷在Mo/HZRP-1上的结焦量、转化率及各产物选择性在内的总碳物料平衡计算结果.考察了不同Mo担载量对催化剂性能和积炭行为的影响;重点考察了不同温度焙烧后20%Mo/HZRP-1催化剂的性能和积炭行为.在反应的初始阶段,6%Mo/HZRP-1表现出很高的活性:反应进行30 min时,甲烷转化率为11%,芳烃选择性达81%,而催化剂的结焦选择性仅为12%.BET,NH3-TPD和催化反应等表征结果表明:Mo物种的数量和状态,分子筛的酸强度和酸量以及分子筛的孔道结构是决定甲烷无氧脱氢芳构化反应性能和积炭行为的关键因素. 相似文献
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甲烷无氧芳构化反应催化剂Mo/HZSM-5的H2-TPR研究 总被引:6,自引:0,他引:6
采用H2-TPR技术研究了不同方法制备的Mo/HZSM-5催化剂,并借助 1H MAS NMR等表征手段对Mo/HZSM-5催化剂还原过程中可能出现的6个TPR谱峰进行了详细归属,首次指认了分布于分子筛孔道内并与B酸性位相互作用的Mo物种的还原峰. 此外,还考察了各种Mo基催化剂在甲烷无氧芳构化反应中的催化性能. 结果表明,与B酸中心相互作用的Mo物种比其他形式的Mo物种具有更好的活性和稳定性. 相似文献
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不同方法制备的Mo/HZSM-5催化剂上甲烷的芳构化反应 总被引:8,自引:0,他引:8
采用机械混合、机械混合后焙烧和机械混合后微波处理等方法制备Mo/HZSM-5催化剂,并对催化剂上甲烷芳构化反应性能进行了考察.结果表明,与浸渍法相比,用机械混合法、固相反应法和微波法制备的催化剂,在保持甲烷转化率不变的前提下,能明显提高芳烃选择性并减少积炭的生成;不同方法制备的Mo/HZSM-5催化剂上Mo物种的落位不同,机械混合法、固相反应法和微波法使Mo物种较多地落位于分子筛外表面.结合反应结果可以得出,落位于分子筛外表面的Mo物种对甲烷芳构化反应更为有利,而且明显减少积炭的生成. 相似文献
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Mo/HZSM-5催化剂上甲烷芳构化反应行为的改善-催化剂制备因素及反应物添加剂的考察 总被引:1,自引:0,他引:1
考察了6Mo/HZSM-5催化剂的不同制备因素对其甲烷芳构化反应性能的影响,包括甲烷气氛下以不同的程序升温速率(从600℃到700℃)预还原催化剂,及采用热溶液(70~80℃)浸渍制备催化剂等方法.在t=700℃,P=0.1MPa,SV=1500mL/(g-cat·h)的反应条件下,发现适当的程序升温速率预还原和热溶液浸渍制备等方法可以改善6Mo/HZSM-5催化剂的甲烷芳构化反应性能,提高催化剂的反应活性及稳定性.同时还考察了1.5%二甲醚作为反应物添加剂在不同反应温度、不同Mo担载量的HZSM-5催化剂上的甲烷芳构化反应性能,并与CO2,H2O的反应结果进行了对比.实验结果表明,在P=0.1MPa,SV=1500mL/(g-cat·h)的反应条件下,较高的反应温度及适量增加催化剂Mo担载量有利于进一步改善1.5%二甲醚/甲烷共进料情况下的芳构化反应行为;反应6h后催化剂的TEM照片显示,二甲醚与甲烷共进料改变了催化剂上积碳的形貌. 相似文献
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表面性质对甲烷芳构化Mo基催化剂反应性能的影响 总被引:1,自引:0,他引:1
研究了不同载体对Mo基催化剂反应性能的影响,发现对于在无氧条件下的甲烷芳构化反应,分子筛酸性,结构和金属氧化物的存在这3个因素是至关重要的,考察了作为第2组分的Zn,W,Cu,Cr,Ni5种元素对Mo/HZSM-5反应性能的影响,发现第2组分的添加均在不同程度上提高了催化剂的甲烷芳构化活性和选择性,异丙醇分解反应的结果表明,Zn,W,Cu的加入,增加了催化剂的脱氢中心强度,Cr,Ni的加入,增加了催化剂的酸中心强度,酸中心和脱氢中心的加强有利于甲烷芳构化反应。 相似文献
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High activity and high formation selectivity for aromatics in the dehydrocondensation reaction of methane were realized only on selected catalysts. The requisites of a metal and a zeolite support as the selected catalyst were described. However, the catalytic activity steadily declined even on the selected catalysts with time on stream because of coke accumulation. A stable catalytic activity was obtained when CO2 or CO was added into methane feed due to effective removal of coke from the catalyst surface by CO or CO2. The route from methane to aromatics and the formation process of active phase of catalyst were discussed. 相似文献
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High activity and high formation selectivity for aromatics in the dehydrocondensation reaction of methane were realized only on selected catalysts. The requisites of a metal and a zeolite support as the selected catalyst were described. However, the catalytic activity steadily declined even on the selected catalysts with time on stream because of coke accumulation. A stable catalytic activity was obtained when CO2 or CO was added into methane feed due to effective removal of coke from the catalyst surface by CO or CO2. The route from methane to aromatics and the formation process of active phase of catalyst were discussed. 相似文献
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Wen-Hua Chen Shing-Jong Huang Chiun-Shen Lai Tseng-Chang Tsai Huang-Kuei Lee Shang-Bin Liu 《Research on Chemical Intermediates》2003,29(7-9):761-772
The effects of binder, coking and regeneration on the acid properties of H-mordenite zeolite during toluene disproportionation reaction (TDP) have been investigated by solid-state 31P-MAS-NMR of various adsorbed phosphorous probe molecules in conjunction with elemental analysis by ICP-MS technique. A series of fresh, spent and regenerated mordenite-based commercial catalysts were examined and the results were also compared with binder-free H-mordenite zeolite and unformulated γ-alumina binder. It is found that parent H-mordenite zeolite possessed only Brønsted acidity, which is responsible for the observed catalytic activity. In contrast, the γ-Al2O3 binder exhibited only Lewis acidity and plays a minor role during the catalytic reaction. While the amount of strong Brønsted acid sites decreased rapidly during initial coking, it reached a plateau at a total coke content of ca. 7 wt%, corresponding to ca. 80% decrease in total acidity. That the catalyst remained active even under deep coke deposition (>7 wt%) condition indicated catalytic activity may be invoked by subsequent coking taking place on the external surface rather than intracrystalline channels of the zeolite catalyst. Furthermore, upon catalyst regeneration treatment, ca. 75% of the total acidity could be effectively recovered. 相似文献
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以碳黑为第二模板剂在氟离子体系中一步水热合成了多级结构MCM-22分子筛组装体(简称为MCM-22-FC)。考察了碳黑和氟离子对MCM-22分子筛形貌和催化性能的影响。MCM-22-FC分子筛是由大量片状晶体交错生长形成的组装体结构,其中MCM-22的片层结构更薄,在其固有的微孔中存在的晶间孔呈现大孔和介孔的特征。MCM-22-FC负载Mo后得到的Mo/MCM-22-FC催化剂在甲烷无氧芳构化反应(MDA)中提高了苯收率和芳烃选择性,并且提高了催化剂的寿命。通过氨气程序升温脱附(NH3-TPD)表征,吡啶红外(Py-IR)表征,结合热重(TG)分析,得出的结论是Mo/MCM-22-FC在MDA中优越的催化性能是由于氟离子进入到分子筛骨架当中,形成具有拉电子效应的结构单元,从而提高了分子筛的Brönsted酸量,较多的Brönsted酸性位将更多的Mo物种迁移至分子筛孔道内部,形成更多的MoCx或MoOxCy活性物种以及更有利于大分子产物扩散的MCM-22薄片层的结构。少量过剩的Brönsted酸性位在成型后保留在Mo/HMCM-22-FC催化剂活性中心抑制了积碳的形成,也有助于改善芳烃的选择性。 相似文献
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Bonan Liu Liam France Chen Wu Zheng Jiang Vladimir L. Kuznetsov Hamid A. Al-Megren Mohammed Al-Kinany Saud A. Aldrees Tiancun Xiao Peter P. Edwards 《Chemical science》2015,6(9):5152-5163
A series of MoO3/H-ZSM-5 (Si/Al = 25) catalysts were prepared via calcination at a lower-than-usual temperature (400 °C) and subsequently evaluated in the methanol-to-hydrocarbon reaction at that same temperature. The catalytic properties of those catalysts were compared with the sample prepared at the more conventional, higher temperature of 500 °C. For the lower temperature preparations, molybdenum oxide was preferentially dispersed over the zeolite external surface, while only the higher loading level of MoO3 (7.5 wt% or higher) led to observable inner migration of the Mo species into the zeolite channels, with concomitant partial loss of the zeolite Brønsted acidity. On the MoO3 modified samples, the early-period gas yield, especially for valuable propylene and C4 products, was noticeably accelerated, and is gradually converted into an enhanced liquid aromatic formation. The 7.5 wt% MoO3/H-ZSM-5 sample prepared at 400 °C thereby achieved a balance between the zeolite surface dispersion of Mo species, their inner channel migration and the corresponding effect on the intrinsic Brønsted acidity of the acidic zeolite. That loading level also possessed the highest product selectivity (after 5 h reaction) to benzene, toluene and xylenes, as well as higher early-time valuable gas product yields in time-on-stream experiments. However, MoO3 loading levels of 7.5 wt% and above also resulted in earlier catalyst deactivation by enhanced coke accumulation at, or near, the zeolite channel openings. Our research illustrates that the careful adoption of moderate/lower temperature dispersion processes for zeolite catalyst modification gives considerable potential for tailoring and optimizing the system''s catalytic performance. 相似文献
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Zhibing Shen Ming Ke Pei Yu Shida Liu Zhaozheng Song Qingzhe Jiang 《Transition Metal Chemistry》2012,37(6):587-593
A series of molybdenum-modified Ni/Al2O3 catalysts were prepared, and their catalytic activities and stabilities for thioetherification of mercaptans and di-olefins in fluid catalytic cracking (FCC) naphtha were investigated. The sulfided catalyst samples were characterized by a range of physical techniques. The results showed that the addition of Mo to Ni catalysts could improve the degree of dispersion of Ni species in the carrier, inhibit the formation of NiAl2O4 crystallites, enhance the presulfidation degree of the metals, and change the chemical environment and electronic structure of Ni. These effects could significantly improve the activity of the Ni/Al2O3 catalysts for thioetherification in FCC naphtha. Furthermore, addition of a small amount of Mo improved the di-olefin selective hydrogenation ability of the Ni/Al2O3 catalyst and significantly reduced coke formation during the reaction. 相似文献
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《Journal of Energy Chemistry》2017,26(3):368-372
CeO_2 supports were prepared by calcination or precipitation method and 5% MoO_3/CeO_2 catalysts were prepared by incipient-wetness impregnation method. The catalytic performance of the 5% MoO_3/CeO_2 catalysts toward sulfur-resistant methanation was investigated. The results showed that the Mo/Ce-1 catalysts with CeO_2 support prepared by calcination method exhibited the best sulfur-resistant methanation activity and stability with CO conversion as high as 75% while the Mo/Ce-3 catalysts the poorest. The supports and catalysts were characterized by N_2-adsorption–desorption, temperature-programmed reduction(TPR), X-ray diffraction(XRD), Raman spectroscopy(RS) and scanning electron microscope(SEM). The results indicated that the saturated monolayer loading MoO_3 on Ce-3 support was lower than 5% and there were some crystalline MoO_3 particles on the surface of the Mo/Ce-3. The preparation method of CeO_2 had a big influence on the specific surface area, the crystalline of CeO_2, and the catalytic performance of the corresponding Mo-based catalyst for sulfur-resistant methanation. 相似文献
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《Journal of Energy Chemistry》2015,(3)
Long-term stability test of Mo/HZSM-5-N catalysts(HZSM-5-N stands for nano-sized HZSM-5) in methane dehydroaromatization(MDA)reaction has been performed with periodic CH4-H2 switch at 1033-1073 K for more than 1000 h.During this test,methane conversion ranges from 13% to 16%,and mean yield to aromatics(i.e.benzene and naphthalene) exceeds 10%.N2-physisorption,XRD,NMR and TPO measurements were performed for the used Mo/HZSM-5 catalysts and coke deposition,and the results revealed that the periodic hydrogenation can effectively suppress coke deposition by removing the inert aromatic-type coke,thus ensuring Mo/HZSM-5 partly maintained its activity even in the presence of large amount of coke deposition.The effect of zeolite particle size on the catalytic activity was also explored,and the results showed that the nano-sized zeolite with low diffusion resistance performed better.It is recognized that the size effect was enhanced by reaction time,and it became more remarkable in a long-term MDA reaction even at a low space velocity. 相似文献
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J. Agullo N. Kumar D. Berenguer D. Kubicka A. Marcilla A. Gómez T. Salmi D. Yu. Murzin 《Kinetics and Catalysis》2007,48(4):535-540
Low-density polyethylene (LDPE) catalytic pyrolysis was investigated over H-β-25, H-β-150, H-β-300, H-Y-12, H-Mordenite-20,
and H-Ferrierite-20 zeolite catalysts. The numbers denote the SiO2/Al2O3 molar ratios. The influence of the zeolite’s acidity on the transformation of LDPE was studied by varying the SiO2/Al2O3 molar ratios of the β zeolite. The influence of the zeolite structure was investigated by using the proton forms of Y, β,
Mordenite, and Ferrierite zeolites. The catalysts were characterized using X-ray powder diffraction patterns, nitrogen adsorption,
and FTIR spectroscopy with pyridine as the probe molecule. The large pore and least acidic H-β-300 catalyst showed the lowest
activity in the catalytic pyrolysis of LDPE. The H-β-25 catalyst, with higher acidity than H-β-300, showed higher activity
for LDPE pyrolysis than H-β-300, indicating the importance of strong acid sites for this reaction. The H-Ferrierite and H-Mordenite
catalysts, with small pores, showed the lowest effect on LDPE pyrolysis, although the catalysts were more acidic than H-β-25
and H-β-150, indicating that not only acidity but also the structure and pore size of zeolites are important for pyrolysis
of LDPE. However, the H-Y zeolite catalyst with large pores and cavities is not suitable for this reaction because of rapid
deactivation due to coke formation.
Published in Russian in Kinetika i Kataliz, 2007, Vol. 48, No. 4, pp. 570–575.
This article was submitted by the authors in English. 相似文献
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Co改性Mo/MCM-22催化剂上甲烷无氧芳构化及积炭研究 总被引:2,自引:0,他引:2
研究了Co的添加对Mo/MCM-22催化剂甲烷无氧芳构化反应性能的影响.发现用共浸渍法制备的Co/Mo摩尔比为0.2的催化剂具有较高的活性,而先浸渍Mo后浸渍Co的催化剂具有较好的稳定性.XRD实验表明,Co及Mo的氧化物均高度分散在分子筛表面,其担载降低了分子筛的衍射强度.不同接触时间下催化剂的反应结果表明,接触时间长,积炭选择性随接触时间增加而迅速增加;接触时间短,积炭选择性随接触时间增加而减少.积炭催化剂的TG研究表明,催化剂上的积炭主要有两种形式.低温积炭随反应时间增加而迅速增多,高温积炭的变化则较为缓慢.低温积炭可能是导致催化剂活化和失活的主要原因.高温积炭可能是一种大分子量的碳氢物种,位于MCM-22分子筛的“超笼”中,表明MCM-22有较大的容积炭能力. 相似文献