Methane activation without using oxidants over Mo/HZSM-5 zeolite catalysts

The effect of Mo loading, calcination temperature, reaction temperature and space velocity on the catalytic performance of methane dehydrogenation and aromatization without using oxidants over Mo/HZSM-5 has been studied. The XRD and BET measurements show that Mo species are highly dispersed in the channels of the HZSM-5 zeolite, resulting from the interaction between the Mo species and the zeolite, which also leads to a decrease in its crystallinity. The Brønsted acidity, the channel structure and the state and location of Mo species in the zeolite seem to be crucial factors for its catalytic performance. It was found that 2% Mo/HZSM-5 calcined at 773 K showed the best aromatization activity among the tested catalysts, the methane conversion being 9% at 1013 K with the selectivity to aromatics higher than 90%. The experimental results obtained from the variation of space velocity gave evidence that ethylene is an initial product. On the basis of these results a possible mechanism for methane dehydrogenation and aromatization has been proposed in which both the heterolytic splitting of methane in a solid acid environment and a molybdenum carbene-like complex as an intermediate are of significance.     

正己烷在HZSM-5分子筛上的催化裂解研究

为筛选反应活性和烯烃选择性相对较高的催化剂用于研究吸热型碳氢燃料的催化裂解,以正己烷的催化裂解作为探针反应,探讨其在不同硅铝物质的量比HZSM-5［n(Si)∶n(Al)=25、36、100］分子筛上催化裂解的反应活性和产物分布。结果表明,正己烷在HZSM-5分子筛上的裂解转化率随温度的升高和分子筛中硅铝物质的量比的减小而增大;裂解产物中乙烯、丙烯和总烯烃的选择性均随裂解温度的升高和分子筛中硅铝物质的量比的增加而增加,在（300~550） ℃,HZSM-5［n（Si)∶n(Al)=36］上的总烯烃收率最高,芳烃含量随分子筛中硅铝物质的量比的增加而减小;基于裂解转化率、烯烃和芳烃收率等因素综合考虑,HZSM-5 n(Si)∶n(Al)=36］分子筛为优选催化剂。     

Methane Transformation using Light Gasoline as Co-Reactant over Zn/H-ZSM11

The catalytic conversion of methane (C1) to aromatic hydrocarbons (AH) such as benzene, toluene and xylenes (BTX) over a Zn/H-ZSM-11 catalyst using Light Gasoline (C5+C6) as co-reactant was studied. AH yields were as high as 30 %mol at 500 °C, w/f = 40 g h mol⁻¹ at C1 molar fraction = 0.20. The contact time and time-on-stream effects on the product distribution, were analyzed in detail in order to obtain information about the evolution of different species. The C1 conversion reached 36 mol% C using Zn/HZSM-11 with content of 2.13 mol of Zn²⁺ per cell unit.     

Aromatization of n-hexane over Ga,Mo and Zn modified H-ZSM-5 zeolite catalysts

n-Hexane aromatization was investigated at 500 °C on parent and metal (i.e. Ga, Mo and Zn) modified H-ZSM-5 zeolite catalysts. Conversion reached 88% over H-ZSM-5 and was stable. Addition of metal resulted in lower conversion (< 80%). Formation of aromatic compounds was favored on Ga/H-ZSM-5 (> 35%) and Zn/H-ZSM-5 (> 40%) while H-ZSM-5 and Mo/H-ZSM-5 showed higher cracking activity. Gallium and zinc favored aromatization. At 600 °C a decrease in activity with increasing TOS was observed. A decrease in aromatics selectivity was also observed. The aromatics selectivity with increase in TOS of Ga/H-ZSM-5 (43–27%) and Mo/H-ZSM-5 (35–27%) catalysts was higher than for Zn/H-ZSM-5 (46–7%).     

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.     

正己烷在Zn/HZSM-5上芳构化反应机理的探讨

比较了正己烷在HZSM-5、Al₂O₃和ZnO/Al₂O₃催化剂上的反应性能，探讨了锌含量和水热处理对Zn/HZSM-5芳构化性能的影响。发现B酸是芳构化反应不可缺少的活性中心，Zn-L因其氢解作用促进烃类的活化和脱氢，Al-L酸只是对正己烷有较弱的活化作用。提出了正己烷在Zn/HZSM-5上的芳构化反应机理。     

Isomerization of n-hexane over Platinum loaded zeolite catalysts

The isomerization of n-hexane over Pt-loaded Hβ, H-ZSM-5 and H-dealuminated mordenite was studied at temperatures lower than 573 K under atmospheric pressure. It was found that Pt loaded H β showed the highest activity and selectivity of these three catalysts. Namely, the conversion of hexane was 76 C-% and selectivities to dimethylbutanes, methylpentanes and cracking products were 19.4, 76.2 and 4.4 C-%, respectively, under the following conditions: reaction temperature, 548 K; W/ F, 5 g h mol⁻¹; molar ratio of hydrogen to n-hexane, 4. Pt/Hβ catalyst showed a good stability, because Hβ has acid sites with medium strength and three-dimensional large pores. We can adjust the balance between metallic sites and acid sites to obtain right catalyst which has the highest activity and the highest selectivity for the isomerization of hexane.     

Zn 助剂对WC/HZSM-5催化正己烷芳构化性能影响

以WC/HZSM-5为前驱体制备了一系列不同Zn含量的Zn-WC/HZSM-5催化剂,采用X射线衍射、扫描电子显微镜、N₂物理吸附、傅里叶变换红外光谱和热重分析等手段对Zn-WC/HZSM-5的晶相、形貌、比表面积、酸性质、积炭量等进行了表征,并研究了正己烷芳构化的催化性能,探究了助剂Zn与WC在反应过程中的作用。结果表明,Zn的引入可以提高催化剂的芳烃选择性和芳烃收率。当Zn负载量为1.5%(质量分数)时,所制备的Zn-WC/HZSM-5催化剂芳构化活性最佳,芳烃收率达到36.18%。Zn的引入不仅改变了WC/HZSM-5表面的酸性分布,而且可以减少WC/HZSM-5催化剂的积炭量。     

La/Zn/HZSM-5催化剂上的甲醇芳构化研究

Aromatization of methanol over co-impregnated La/Zn/HZSM-5 zeolite catalyst was studied.The selectivity of aromatics and BTX(benzene,toluene,and xylene)reached 64.0%and 56.6%,respectively,using La/Zn/HZSM-5 at 437°C,0.1 MPa and methanol WHSV(weight hourly space velocity)=0.8 h-1.Catalytic results showed that the La species was a very good promoter,increased selectivity of aromatics,and prolonged the catalyst lifetime on stream.The effects of the SiO2/Al2O3 ratio in zeolite,Zn and La loading,WHSV,reaction temperature, water content in the feed and H2 pretreatment of catalysts on the catalytic performance were studied in detail. Characterizations of the catalysts by thermogravimetric analysis(TGA),NH3-TPD(temperature programmed desorption),SEM(scanning electron micrograph),N2 adsorption-desorption,XRD(X-ray diffraction)and XRF (X-ray fluorescence),were carried out to understand the structure and discuss the aromatization performance of La/Zn/HZSM-5 zeolite catalyst.     

纳米Zn/HZSM-5分子筛催化丙烷芳构化

采用低温老化、高温晶化两步法在Na2O-Al2O3-SiO2-四丙基氢氧化铵(TPAOH)-H2O体系中水热合成了纳米ZSM-5分子筛。用BET、N2吸/脱附曲线和NH3-TPD等手段对负载Zn的纳米HZSM-5分子筛结构和酸性进行了表征。结果表明,与微米Zn/HZSM-5分子筛催化剂相比,所制备的纳米Zn/HZSM-5催化剂比表面积明显增大,总酸量和弱酸量增加;在丙烷芳构化反应中,纳米Zn/HZSM-5分子筛具有更佳的催化活性、稳定性和芳烃选择性。     

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).     

FCC汽油馏分在水热处理Zn/HZSM-5催化剂上的芳构化反应

制备了300 ℃、350 ℃、400 ℃和500 ℃不同水热处理温度下的Zn/HZSM-5催化剂，并用于FCC汽油馏分的芳构化反应。考察了水热处理温度对芳构化反应性能的影响，并与吡啶吸附红外光谱(FT-IR)相关联，研究了水热处理温度对催化剂表面酸性的影响。结果表明，水热处理Zn/HZSM-5的芳构化活性稳定性得以改善, 与未经水热处理的催化剂相比，400 ℃水热处理的Zn(2%)/HZSM-5催化剂芳构化反应36 h时，芳烃质量分数仍高达74.25%。随着水热处理温度的升高， B酸酸中心数在300～400 ℃变化不大，500 ℃显著减少，L酸酸中心数升高，400 ℃达到最大值后呈降低趋势，烯烃转化率、烷烃转化率和产品芳烃含量升高，水热处理400 ℃时均达到最大值，分别为83.62%、95.44%和92.23%，表明此时B酸中心和L酸中心比例协调性最佳。     

Upgrading of aspen poplar wood oil over HZSM-5 zeolite catalyst

Thermally fractionated components of an oil prepared by the liquefaction of aspen poplar wood have been upgraded using a HZSM-5 zeolite catalyst to yield products rich in benzene, toluene, xylenes and higher molecular weight aromatics. The effect of reactor temperatures on the relative abundance of these products has been studied.     

Kinetic modelling of methylcyclohexane ring-opening over a HZSM-5 zeolite catalyst

A kinetic model is proposed in order to quantify product distribution in the ring-opening (using high hydrogen concentration in the reaction medium) of methylcyclohexane (MCH) over a catalyst based on HZSM-5 zeolite. The model is based on a reaction scheme proposed by Cerqueira et al. for methylcyclohexane cracking at atmospheric pressure, which has been modified in order to include the effect of hydrogen over the individual reaction steps. The experimental results used for estimating the kinetic constant were obtained in a fixed bed isothermal reactor in a wide range of conditions, i.e. 250–450 °C; WHSV = 0.5–10.5 h⁻¹ (τ = 0.095–2 g_cat h g_MCH⁻¹); pressure = 5–80 bar; H₂/MCH molar flow ratio = 4–79; conversion = 0–100%. The kinetic model proposed can be regarded as a basis for the proposal of models for ring-opening reactions of more complex naphthenic feedstock from a prior hydrogenation step involving aromatic refinery streams of secondary interest.     

Catalytic Activation of Methane Using n-Pentane as Co-reactant over Zn/H-ZSM-11 Zeolite

The catalytic conversion of methane (C1) into higher hydrocarbons using n-pentane (n-C5) as co-reactant over Zn/H-ZSM-11 zeolite material was studied. The aromatics yield was very high, achieving values of over 40 mol% at 500 °C and w/f = 30 g h mol_-1 with a C1/(C1+C5) molar fraction (XC1) = 0.30. Contact time and time-on-stream effects on the product distribution were analyzed in detail in order to obtain information about the evolution of different species. The C1 conversion was as high as 30 mol% without CO _x reaction products.     

Aromatization of propane over Zn/HZSM-5 catalysts prepared by chemical vapor deposition

Zinc was introduced into HZSM-5 by chemical vapor deposition (CVD) to investigate the catalytic properties of Zn/HZSM-5 for propane conversion. Irrespective of catalytic precursor or ion exchange method, protons were found to be replaced by Zn ions. However, Zn species in the zeolite were different depending on the precursors used. Although the addition of Zn decreased the intensity of the BrÕnsted acidity, it did not caused the apparent formation of Lewis acid sites unlike Ga/HZSM-5 catalysts. On Zn/HZSM-5, both Zn and protons intervene in propane activation step.     

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。     

Solid-state NMR studies of methanol-to-aromatics reaction over silver exchanged HZSM-5 zeolite

Solid-state NMR spectroscopy was used to study the conversion of methanol to aromatics (MTA) over silver exchanged HZSM-5 zeolites. It is the silver oxide rather than silver cation that plays a crucial role for the MTA reaction. The aromatic products (mainly toluene and benzene) are formed at the expense of the small alkanes (mainly propane and isobutane). AgZSM-5 zeolite calcined in air shows much higher activity and selectivity for the MTA conversion compared with AgZSM-5 zeolite calcined in vacuum or HZSM-5 zeolite. A possible reaction mechanism is proposed for the MTA conversion on the AgZSM-5 zeolite.     

偏三甲苯在改性HZSM-5分子筛上合成均四甲苯

采用离子交换制备了HZSM-5分子筛催化剂，用氟化铵溶液对其进行改性，并于不同温度下焙烧。研究了偏三甲苯-甲醇烷基化反应合成均四甲苯，考察了原料配比、反应温度和载气流量对烷基化反应的影响。     

The joint reaction of methanol and i-butane over the HZSM-5 zeolite

The effects of i-butane addition to methanol in MTP reaction were investigated over an in-house prepared HZSM-5 catalyst. It was observed that, propylene yield would be enhanced when i-butane fed to the reactor along with methanol. The rising growth of the propylene yield continued to peak on till the balance in thermal condition established. Similar trends have been observed when water was added to the mixture. The effect of WHSV with fixed water composition on product distribution was also studied. The optimum point where the highest amount of propylene yielded was shown to be high depended upon the temperature and residence time.