Synthesis of the nanosized MCM-22 zeolite and its catalytic performance in methane dehydro-aromatization reaction

A novel and facile synthesis method based on the combination of self-assembly and in-situ crystallization is developed for the preparation of nanosized MCM-22 zeolites (simplified as MCM-22-NZ hereafter) of about 40 nm, where the cationic polymer, PDDA, was added to play a role of protecting agent to avoid the synthesis colloids self-aggregation. MCM-22-NZ was characterized by XRD, TEM, DLS, NH₃-TPD, XRF, TG and N₂ adsorption analysis. The catalytic activity of MCM-22-NZ in methane dehydro-aromatization (MDA) reaction was also studied. Mo/HMCM-22-NZ showed better methane conversion, higher benzene yield and more considerable durability of the catalyst as compared to the conventional microsized catalyst.     

Study on attrition of spherical-shaped Mo/HZSM-5 catalyst for methane dehydro-aromatization in a gas-solid fluidized bed

As a potential methane efficient conversion process,non-oxidative aromatization of methane in fluidized bed requires a catalyst with good attrition resistance,especially in the states of high temperature,long-time rapid movement and chemical reaction.Existing evaluation methods for attrition resistance,such as ASTM D5757 and Jet Cup test,are targeted for fresh catalysts at ambient temperature,which cannot well reflect the real process.In this study,spherical-shaped Mo/HZSM-5 catalyst prepared by dipping and spray drying was placed in a self-made apparatus for attrition testing,in which the catalyst attrition under differ-ent system temperatures,running time and process factors was investigated with percent mass loss (PML),particle size-mass distribution (PSMD) and scanning electron microscope (SEM).Carbon deposition on the catalyst before and after activation,aromatization and regeneration was analyzed by thermogravimetry(TG),and the attrited catalysts were evaluated for methane dehydro-aromatization (MDA).The results show that the surface abrasion and body breakage of catalyst particles occur continuously,with the increase of system temperature and running time,and make the PML rise gradually.The process factors of activation,aromatization and regeneration can cause the catalyst attrition and carbon deposits,which broaden the PSMD in varying degrees,and the carbon-substances on catalysts greatly improve their attrition resistance at high temperature.Catalyst attrition has a certain influence on its catalytic performance,and the main reasons point to particle breakage and fine powder escape.     

NH_4与Pt改性的HZSM-5催化剂上2-甲基萘与甲醇的择形甲基化反应(英文)

Shape-selective methylation of 2-methylnaphthalene (2-MN) was carried out over NH4F and Pt modified HZSM-5 (SiO2/Al2O3 83) catalysts in a fixed-bed down-flow reactor using methanol as methylating agent and 1,3,5-trimethylbenzene (1,3,5-TMB) as a solvent. Pt promoted HZSM-5 catalysts showed low concentration of coke-like polycondensed aromatics, NH4F modification decreased non-shape-selective acid sites. After Pt and NH4F co-modification, both conversion of 2-MN and selectivity to 2,6-DMN were improved. 6%NH4F/0.5%Pt/HZSM-5 catalyst exhibited 13.8% of 2-MN conversion with 6.2% of 2,6-DMN yield after 7 h time on stream (TOS), and 2,6-/2,7-DMN ratio of 1.7 after 10 h of TOS.     

水热处理磷改性HZSM-5催化剂的研究

以催化裂化轻汽油馏分为原料,以水热处理磷改性HZSM-5为催化剂,在小型固定床反应装置上考察了水热处理改性方法制备催化剂的催化裂解性能。通过对HZSM-5分子筛催化剂水热处理,调变其酸性,达到多产丙烯的目的。确定催化剂改性最佳条件为：水热处理温度650 ℃,处理时间2 h,处理空速2 h^-1。HZSM-5水热处理后,明显改善催化剂的水热稳定性和活性,提高丙烯选择性。     

HZSM-5型分子筛催化合成2-乙酰噻吩

用固体酸催化剂HZSM-5型分子筛代替液体磷酸催化合成2-乙酰噻吩,探讨了反应时间、反应温度、催化剂质量对该反应的影响。采用正交实验法优化的工艺条件是:反应温度为95℃,反应时间为2.5 h,催化剂质量为2.5 g(约占原料质量的3.5%)。最优工艺条件下2-乙酰噻吩的收率为90.60%。产物通过色谱-质谱联用仪分析可知:产品2-乙酰噻吩的质量分数约为98.28%,副产物主要是少量的3-乙酰噻吩。该实验中,固体催化剂可以回收、再生和重复使用,给出的收率几乎与新鲜的催化剂相同。     

HZSM-5型分子筛绿色催化合成7-羟基-4-甲基香豆素

首次以HZSM-5分子筛为催化剂,以间苯二酚和乙酰乙酸乙酯为原料,在无溶剂条件下合成了标题化合物。实验结果表明:HZSM-5分子筛对Pechmann反应有很高的催化活性,具有催化剂用量(0.3 g/0.1 mol间苯二酚)少、产率较高(达96.7%)、后处理简单和无污染、可重复循环利用(循环使用5次产率高达90%以上)等优点。HZSM-5分子筛催化合成标题化合物反应的最佳条件为:V(间苯二酚)∶V(乙酰乙酸乙酯)=1∶1,催化剂用量0.3 g/0.1 mol间苯二酚,反应1.5 h,反应温度约105℃。     

Interaction between ammonium heptamolybdate and NH4ZSM-5 zeolite: the location of Mo species and the acidity of Mo/HZSM-5

Mo/HZSM-5 catalysts show high reactivity and selectivity in the activation of methane without using oxidants. Mo/HZSM-5 catalysts with Mo loading ranging from 0 to 10% were prepared by impregnation with an aqueous solution of ammonium heptamolybdate (AHM). The samples were dried at 393 K, and then calcined at different temperatures for 4 h. The interaction between Mo species and NH₄ZSM-5 zeolite was characterized by FT-IR spectroscopy, differential thermal analysis (DTA) and temperature programmed decomposition (TPDE) and NH₃-TPD at different stages of catalyst preparation. The results showed that if Mo/HZSM-5 catalysts were calcined at a proper temperature, the Mo species will interact with acid sites (mainly with BrØnsted acid sites) and part of the Mo species will move into the channel. The Mo species in the form of small MoO₃ crystallites residing on the external surface and/or in the channel, and interacting with BrØnsted acid sites may be responsible for the methane activation. Strong interaction between Mo species and the skeleton of HZSM-5 will occur if the catalyst is calcined at 973 K. This may lead to the formation of MoO ₄ ^2– species, which is detrimental to methane activation.     

Dehydrogenation and aromatization of methane in the absence of oxygen on Mo/HZSM-5 catalysts before and after NH4OH extraction

A phosphorus-modified electrolytic silver catalyst was prepared and used as catalyst in the oxidative dehydrogenation of glycoto glyoxal. The yield of glyoxal was observed as high as 82% at 98% conversion for the Ag-P catalyst, while 62% at 89% conversion for the pure electrolytic silver. The formation of the surface compounds between the phosphorus additives and the silver surface was demonstrated by means of XPS and SEM. It caused the decrease of the surface concentration of atomic oxygen species, and restrained the decomposition and total oxidation of adsorbed glycol to C₁ products.     

焙烧温度对HZSM-5分子筛催化1-丁烯齐聚性能的影响

考察焙烧温度对HZSM-5分子筛催化剂结构及1-丁烯齐聚性能的影响,采用XRD、SEM和NH3-TPD对催化剂进行表征。结果表明,升高焙烧温度,对HZSM-5分子筛催化剂的晶相和晶粒尺寸没有影响,催化剂中弱酸与强酸的酸强度和酸量均随焙烧温度的升高逐渐减弱。在催化剂晶粒尺寸一定条件下,催化剂酸性对催化剂的齐聚性能有较大影响,焙烧温度500℃时,C5+收率和C10+选择性最佳。     

HZSM-5型分子筛催化乙醇溶液脱水制备乙烯的工艺

以稀乙醇溶液为原料、自制分子筛HZSM-5为催化剂,催化脱水制备乙烯.考察了硅铝比、反应温度、质量空速及乙醇的质量浓度对该反应的影响,得到了较优化的反应工艺条件为:催化剂为HZSM-5(硅铝比30)分子筛,ρ(乙醇)为100~200 g/L,质量空速为2~6 h-1,反应温度为300℃.乙醇的转化率可达99%,乙烯的选择性达99%以上.     

Interaction of methane with surfaces of silica,aluminas and HZSM-5 zeolite. A comparative FT-IR study

Infrared investigations on the interaction of methane with silica, aluminas (, and ) and HZSM-5 zeolite have been carried out. At low temperature (173 K), methane adsorption was observed over these oxides and HZSM-5 zeolite. Our findings featured that the infrared inactive ₁ band (2917 cm^–1) of a gaseous methane molecule became active and shifted to lower frequencies (2900 and 2890 cm^–1) when it adsorbed on the surfaces of these adsorbents. Our results also demonstrate that hydroxyl groups played a very important role in methane adsorption over the acidic oxides and the HZSM-5 zeolite. When interaction between the hydroxyl groups and methane took place, the band shift of the hydroxyl groups varied with different oxides. The strength of the interaction decreased according to the following sequence, Si-OH-Al>Al-OH>Si-OH, which is in accordance with the order of their acidities. At higher temperatures, methane interacted quite differently with various oxides and HZSM-5 zeolite. It has been observed that the hydroxyl groups of silica, -alumina and HZSM-5 zeolite could exchange with CD₄ at temperatures higher than 773K, while those on -alumina could exchange at a temperature as low as 573 K. Another interesting observation was the formation of formate species over Al₂O₃ (both and ) at temperatures higher than 473 K. The formate species would decompose to CO₂, or produce carbonate at much higher temperatures. Formation of formate species was not observed over silica and HZSM-5 under similar conditions, -Al₂O₃ did not adsorb or react with methane in any case.     

Selective cracking of natural gasoline over HZSM-5 zeolite

This work presents a study on the catalytic cracking of natural gasoline (extracted from natural gas) over HZSM-5 zeolite. A factorial planning was carried out to evaluate the effect of temperature and W/F ratio on the cracking of natural gasoline, analyzing their effects on conversion and product distribution using an analysis based on surface response methodology. The process was optimized focusing on the maximization of the mass fractions and the production of specific products such as ethene, propene and butanes. The results have shown that the maximum selectivity and hourly mass production of ethene is obtained at high temperature (450 °C) and low catalyst weight to flow rate ratio (W/F) (7.2 to 8.2 g_cat h/mol). Maximum selectivity of propene is obtained at 350 °C and 7.0 g_cat h/mol, while the best condition for maximum mass production is found at 421 °C and 5.7 g_cat h/mol. The highest mass production of butanes is favored by high temperature (450 °C) and mid range W/F ratios (12.1 g_cat h/mol), while the highest selectivity is found at low temperature (350 °C).     

MgO沉积改性HZSM-12分子筛的结构表征与催化性能

采用化学液相沉积法用MgO对HZSM-12分子筛进行表面沉积改性,对改性分子筛的结构、酸性进行了表征,研究了改性HZSM-12分子筛对萘和甲醇烷基化的催化反应性能.结果表明MgO与HZSM-12分子筛的表面羟基发生作用,减少了分子筛的Bronsted酸中心,而产生了新的Lewis酸中心.用于催化萘和甲醇烷基化的反应结果表明,由于MgO沉积减少了HZSM-12分子筛的强酸中心,有效地提高了HZSM-12分子筛的抗积炭失活能力.     

钾-钙双金属改性对HZSM-5分子筛催化甲醇制丙烯的影响

针对甲醇制丙烯反应体系,研究了不同金属、双金属改性的HZSM-5的催化性能。结果表明,钾改性提高了催化剂的稳定性和催化性能,当钾改性液的质量分数为2%时,改性效果最好,在此基础上,以2%K-HZSM-5作为不同钙负载的改性对象。结果表明,钾钙共同改性,具有较好的协同改性效果,大大提高了丙烯的选择性,有效的降低了乙烯和副产物的产率。     

HZSM-5沸石分子筛孔容与孔径的分子探针测定

对于ZSM-5沸石晶胞结构参数,目前只有静态的借助X光衍射法获得,本文着重用二甲苯的异构物等作分子探针,动态地估算了ZSM-5沸石分子筛的孔径和孔容,在实际应用中,更加具有实际意义。     

丁硫醚在Ce-HZSM-5分子筛上的转化反应研究

开发可降硫的催化剂和助剂,既可以降低汽油中硫化物含量,又不损失汽油收率、不降低汽油辛烷值已成为新的研究思路。作者以Ce改性的HZSM-5沸石为催化剂,在固定床微型反应器中研究了丁硫醚的催化转化反应。结果表明:Ce改性后的HZSM-5对丁硫醚的脱除具有较高的活性及稳定性;硫化氢的量得到上升,并趋于稳定;丁硫醚转化率明显提高,在350℃下,Ce3 交换量为1.51%时,丁硫醚基本完全转化;而丁硫醚的裂解副产物四氢噻吩(THT)的量有增大趋势。同时探讨了丁硫醚的反应历程,认为烷基硫醚类化合物裂解过程中,碳硫键的断裂生成类硫醇物种的一步是其裂解关键步骤。     

双金属Ni-Co/HZSM-5催化剂上甲烷二氧化碳重整反应

采用等体积浸渍法制备一系列双金属Ni-Co/HZSM-5催化剂,考察反应温度和Ni与Co质量比对甲烷二氧化碳催化重整性能的影响。采用BET和H2-TPR表征催化剂的孔结构和还原性能,结果表明,负载的活性组分均匀分散在HZSM-5载体孔道内。Ni与Co之间存在协同作用,促进了Ni-Co/HZSM-5催化剂的还原性能。单金属Co催化剂几乎对甲烷没有转化活性,双金属Ni-Co催化剂催化活性明显提高,Ni与Co质量比6∶4时,催化剂甲烷二氧化碳重整反应的催化活性和稳定性优于单金属Ni催化剂。     

Improvement of methane activation using n-hexane as co-reactant over Zn/HZSM-11 zeolite

Significance of effective conversion of methane (C₁) to more valuable compounds such as aromatics is studied using n-hexane (C₆) as co-reactant. AH yield was as high as 30 mol% C using the following reaction conditions: temperature, 500 °C; contact time w/f=30 g h mol⁻¹ and a C₁ molar fraction, X_C1:=(C₁/C₁ + C₆)=0.60, was achieved. The effect of the contact time, molar fraction, and time on stream was analyzed in order to obtain more information about different species evolution. The C₁ conversion reached at 50 mol% C using Zn/HZSM-11 with 2.13 mol Zn per cell unit.     

On the Enhanced Selectivity of HZSM-5 Modified by Chemical Liquid Deposition

The external surfaces and pore mouth regions of HZSM-5 samples with different crystal sizes were modified by chemical liquid deposition (CLD) with tetraethoxysilane (TEOS), which led to the passivation of unselective acid sites. The modification was found to be more effective for zeolite samples of larger crystal size. The diffusivity of o-xylene was substantially reduced after silylation, while the diffusivity of toluene hardly changed. Dealumination of the external surface of the zeolite crystals enhanced the silylation effects; this was related primarily to the removal of acid sites associated to extra-framework alumina. For the modified catalysts, a significant increase in the selectivity to p-xylene in the disproportionation of toluene was achieved.     

对硝基氯苯在HZSM-5沸石中的吸附和扩散行为研究

通过静态吸附实验,研究水体中对硝基氯苯在HZSM-5沸石中的吸附和扩散行为.研究结果表明,对硝基氯苯在HZSM-5沸石中的吸附等温线存在2个平台,其最大吸附量与温度无关.对硝基氯苯优先吸附在沸石孔道的交点位置,其吸附过程由内扩散控制.对硝基氯苯在HZSM-5沸石中的扩散性与温度和对硝基氯苯的吸附量密切相关,其扩散系数在高温与吸附量小于2 mol/u.c.时较高.