不同硅铝比HZSM-5分子筛对合成气一步法制二甲醚的影响

采用固定床高压反应装置,以工业用（CuO／ZnO／Al2O3）作为甲醇合成催化剂,四种不同硅铝比（硅铝比为25、38、50和150）的HZSM-5作为甲醇脱水催化剂,二者机械混合制备出一步法合成二甲醚双功能催化剂。考察了催化剂中脱水组分（HZSM-5分子筛）的硅铝比对二甲醚合成反应的影响,并通过BET、XRD和NH,-TPD等手段对催化剂进行表征。结果表明,一步法合成二甲醚催化剂中脱水组分HZSM-5的最佳的硅铝比为50。     

The effect of Si/Al ratio and copper exchange level on isothermal kinetic rate oscillations for N2O decomposition over Cu-ZSM-5: a transient FTIR study

Kinetic rate oscillations in the decomposition of N₂O over Cu-ZSM-5 were studied over a series of catalysts with varying Si/Al ratios and copper exchange levels. Oscillations were observed to occur over all catalysts with Si/Al≥29 and exchange level >100%, including excessively-exchanged catalysts with Cu/Al>1.0. FTIR spectroscopy showed that the same monodentate nitrate species was present under reaction conditions for all catalysts displaying oscillatory behavior, and that the coverage of this species was correlated to the gas phase oscillations. Catalysts with low Si/Al ratios did not show oscillation due to a combination of factors: (1) additional actives sites exist on these catalysts (possibly Cu ion pairs) that stabilize additional nitrate species, (2) the nitrate species desorb at a lower temperature compared to the other zeolite catalysts, and (3) the formation of nitrate on these catalysts was shown to be an order of magnitude slower than on the catalysts which show oscillations. FTIR-based kinetic studies of nitrate formation verified that the most critical reaction occurs between N₂O and extra lattice oxygen in order to form NO, which is converted rapidly to surface nitrate. FTIR also identified a possible intermediate in the formation of nitrate at 1537 cm⁻¹ that has been assigned to monodentate nitrite on Cu²⁺ ions.     

Decomposition of NO over Cu-AITS-1 zeolites

H-AITS-1 zeolite with Si/Ti = 50 and Si/Al = 50 was employed in preparing catalyst samples by ion-exchange and impregnation with a copper nitrate solution to obtain 0.24–1.15 wt.% and 1.5, 2 and 2.5 wt.% Cu loading, respectively. The catalytic properties for the NO decomposition were compared with that of Cu-ZSM-5 (Si/Al = 25 with 2 wt.% Cu loading) and similarity was found between the AITS-1 based samples and Cu-ZSM-5. Due to the higher acidity, the activity at 500°C per total copper atoms (an apparent turnover frequency, TOF) was significantly higher over Cu based AITS-1 samples being 2–3 × 10⁻³ s⁻¹ as compared to 1 × 10⁻³ s⁻¹ measured on Cu-ZSM-5. For the ion-exchanged Cu-AITS-1 there was an increase in TOF with increasing copper content, whereas on the impregnated samples a decrease in TOF was found. On all catalysts there was a maximum in the NO conversion at 500–550°C. The amount of NO per copper atom measured by temperature programmed desorption (TPD) was about the same as that on Cu-ZSM-5 and the features of the TPD were also similar. At the first contact of the catalyst at 500°C with the 2 vol% NO/Ar gas a transient N₂O formation and a considerable delay in the O₂ formation was observed. This could, however, be reproduced only on fresh catalyst, while all further transients showed different but reproducible features using the same sample.     

Effect of copper precursors on the catalytic performance of Cu-ZSM-5 catalysts in N2O decomposition

Five Cu-ZSM-5 catalysts were obtained by treating Na-ZSM-5(Si/Al ratio = 15) with aqueous solutions of different Cu precursors(CuCl_2, Cu(NO_3)_2, CuSO_4, Cu(CH_3COO)_2, and ammoniacal copper(II) complex ion). After being pretreated in flowing He at 500 ℃ to form active Cu+, these catalysts exhibited quite different activities in catalytic decomposition of N_2O. CZM-AC(II)(prepared by ammoniacal copper(Ⅱ) complex ion) with 9.4 wt% Cu content was the most active among these Cu-ZSM-5 catalysts, achieving almost complete N_2O conversion at 400 ℃.CZM-CA(prepared using Cu(CH_3COO)_2 as the Cu precursor) with 2.8 wt% Cu content was the second most active catalyst among these Cu-ZSM-5 catalysts, achieving almost complete N_2O conversion at 425 ℃. CZM-CC, CZMCN, and CZM-CS prepared by using Cu Cl_2, Cu(NO_3)_2, or CuSO_4 as the Cu precursor with similar Cu contents(≈ 1.7 wt%) were the least active among these Cu-ZSM-5 catalysts, achieving ca. 90% N_2O conversion at 500 ℃.XRD, ICP, SEM, TEM, EDX-mapping, and CO-IR experiments were conducted to characterize relevant samples.The superior activity of CZM-AC(Ⅱ) can be attributed to the high contents of total Cu+and dimeric Cu+among these samples. The influence of co-fed O_2 or H_2O on the catalytic performance of typical samples was also studied.     

NEURAL NETWORK MODELING OF TRANSITION METAL - ZEOLITE EXHAUST CATALYSTS

Recent research in automobile exhaust catalysts has addressed the substitution of platinum-group metals Pt, Pd and Rh by metals such as Cu, Co, Ag, Zn, Mn and Sr exchanged or impregnated on zeolites, TiO₂ or Zro₂ carriers. These catalysts have the potential of becoming good alternatives to the commercial three-way catalysts to convert pollutant hydrocarbons (HC), carbon monoxide (CO) and nitrogen oxides (NO_x). This paper describes a technique based on neural networks, to correlate the catalyst synthesis variables and resulting exhaust conversion. The optimum catalyst composition and operating conditions for a specified exhaust conversion are determined

A back-propagation algorithm was used to train the feed-forward neural network consisting of two hidden layers with 45 and 60 neurons in the first and second hidden layers respectively, with optimum values of the learning factor and momentum gain coefficient. The effects of the operating and compositional parameters on NO_x conversion by Cu-ZSM-5 were found. The optimum conversion was predicted for Si/Al atom ratio in the range 30-35, Cu-loading (in Cu-ZSM-5) of 1·1 - 1.2% of the zeolite weight, and an operating temperature of 650-675  K. The rare-earth metals (Ce, Cs and La) that act as promoters for three-way catalysts did not have a considerable effect on the exhaust conversion. The conversion increased by at least 10% when Co is used as a co-cation in Cu-ZSM-5.     

Turnover frequency for NO decomposition over Cu-ZSM-5 catalysts: insight into the reaction mechanism

In this letter we present a simple model useful to understand the relationship between the turnover frequency for NO decomposition over Cu-ZSM-5 catalysts (N _Cu), the number of Al atoms per unit cell of the ZSM-5 zeolite (p),and the copper loading expressed as percent of exchange (E). Our simple model is able to explain the literature data. We show that: (1) on catalysts with the highest activity (Cu exchange levelsE>90%),N _Cu increases withp (i.e. decreasing the Si/A1 ratio) indicating that the most active sites may contain two close copper ions; (2) at low Cu exchange levels (E<80%) the catalysts have lower activity and, moreover,N _Cu decreases withP, according to previous results of Iwamoto et al. (1986). The present results are also in agreement with the evidence that the redox couple Cu^2–/Cu^– play a key role in the reaction mechanism.Some of the ideas discussed in this letter were presented at the 2nd Italian national meeting on Science and Technology of Zeolites held in Modena, Italy, 6–8 October 1993.     

Catalytic properties and electronic structure of copper ions in Cu-ZSM-5

The effect of ion exchange conditions, such as Si/Al ratio, precursor copper salt, pH and concentration of the solution, on the catalytic activity in SCR of NO by propane and on the electronic state of copper ions in Cu-ZSM-5 has been studied. The NO conversion in NO SCR by C₃H₈ has been found to reach a maximum value at Cu/Al ratio about 0.37–0.4 and remain constant at higher Cu/Al.

ESR and UV–vis DR spectroscopy have been used to elucidate stabilization conditions of copper ions in Cu-ZSM-5 zeolites as isolated Cu²⁺ ions, chain copper oxide structures and square-plain oxide clusters. The ability of copper ions for reduction and reoxidation in the chain structures may be responsible for the catalytic activity of Cu-ZSM-5. These transformations of copper ions are accompanied by the observation of intervalence transitions Cu²⁺–Cu⁺ and CTLM of the chain structures in the UV–vis spectra.     

The influence of surface structure on the catalytic activity of alumina supported copper oxide catalysts. Oxidation of carbon monoxide and methane

X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and electron spin resonance (ESR) have been used to characterize a series of Cu/Al₂O₃ catalysts. The information obtained from surface and bulk characterization has been correlated with CO and CH₄ oxidation activity of the catalysts. For catalysts with Cu/Al atomic ratios 0.051, XPS data indicated that most of the Cu was present as a dispersed surface phase. ESR results showed that the ratio of isolated/interacting copper surface phase decreased with increasing Cu content. For catalysts with Cu/Al atomic ratio 0.077, large CuO crystallites were detected by XRD. XPS results indicated that Cu dispersion decreased with increasing Cu content. The turn over frequency (TOF) for CO oxidation increased with increasing Cu content. This has been attributed to an increase in the amount of crystalline CuO present in the catalysts. The TOF for CH₄ oxidation decreased with increasing Cu content up to Cu/Al = 0.051. This was paralleled by a significant decrease in the relative Cu ESR signal measured for the catalysts. We propose that the isolated Cu surface phase is more active for CH₄ oxidation than the interacting copper surface phase or crystalline CuO. CH₄ oxidation activities were similar for the catalysts with Cu/Al atomic ratio 0.077.     

High activity of copper-boralite in the reduction of nitric oxide with propane / oxygen

The activity of ZSM-5 and boralite zeolites (Na, H and Cu forms) in the reduction of nitric oxide with propane / oxygen is compared. Copper ion-exchanged boralite is more active than a corresponding Cu-ZSM-5 sample with the same MFI structure, Si/M (M = Al or B) ratio and copper content, showing that in copper-exchanged samples Brønsted acid sites do not play a key role in the reaction mechanism, in contrast to that found for samples without the exchanged transition metal.     

Promoting Xylene Production in Benzene Methylation using Hierarchically Porous ZSM-5 Derived from a Modified Dry-gel Route

Methylation of benzene is an alternative low-cost route to produce xylenes, but selectivity to xylene remains low over conventional zeolitic catalysts. In this work, a combined dry-gel-conversion and s...     

Effect of Si/Al ratio on performance of Pt–Sn-based catalyst supported on ZSM-5 zeolite for n-butane conversion to light olefins

The performance of Pt–Sn-based catalyst, supported on ZSM-5 of different Si/Al ratios were investigated for simultaneous dehydrogenation and cracking of n-butane to produce light olefins. The catalysts were characterized by number of physio-chemical techniques including XRF, TEM, IR spectra, NH₃-TPD and O₂-pulse analysis. Increase in Si/Al ratio of zeolite support ZSM-5 significantly increased light olefin's selectivity, while feed conversion decreases due to lower acidity of support. The results indicated that both the n-butane cracking and dehydrogenation activity to light olefin's over Pt–Sn/ZSM-5 samples with increasing Si/Al ratios greatly enhanced catalytic performance. The catalysts were deactivated with time-on-stream due to the formation of carbon-containing deposits. A coke deposition was significantly related to catalyst activity, while at higher Si/Al ratio catalyst the coke precursors were depressed. These results suggested that the Pt–Sn/ZSM-5 catalyst of Si/Al ratio 300 is superior in achieving high total olefins selectivity (above 90 wt.%). The Pt–Sn/ZSM-5 also demonstrates resistance towards hydrothermal treatment, as analyzed through the three successive reaction-regeneration cycles.     

正丁烷及丁烯-1在不同硅铝比ZSM-5分子筛上吸附的实验与模型

Four ZSM-5 zeolite catalysts with different Si/Al ratios for the catalytic cracking of C4 fractions to produce ethylene and propylene were prepared in this study.First,the adsorption isotherms of pure n-butane and butene-1 and their mixtures on these catalysts at 300K and p=0—100kPa were measured using the intelligent gravimetric analyzer.The experimental results indicate that the presence of Al can significantly affect the adsorption of butene-1 than that of n-butane on ZSM-5 zeolites.Then,the double Langmuir（DL）model was applied to study the pure gas adsorption on ZSM-5 zeolites for pure n-butane and butene-1.By combining the DL model with the ideal adsorbed solution theory（IAST）,the IAST-DL model was applied to model the butene-1（1）/n-butane（2）binary mixture adsorption on ZSM-5 zeolites with different Si/Al ratios.The calculated results are in good agreement with the experimental data,indicating that the IAST-DL model is effective for the present systems.Finally,the adsorption over a wide range of variables was predicted at low pressure and 300K by the model proposed.It is found that the selectivity of butene-1 over n-butane increases linearly with the decrease of Si/Al ratio.A correlation between the selectivity and Si/Al ratio of the sample was proposed at 300K and p=0.08MPa.     

Liquid-phase degradation of polyethylene wax over mordenite catalysts with different Si/Al molar ratios

The catalytic liquid-phase degradation of polyethylene wax into fuel oil was studied using mordenite catalysts with various Si/Al molar ratios prepared by dealumination. The total yield of gas and liquid products showed a volcano plot along the Si/Al molar ratio of mordenite. No significant change was observed in the composition of the liquid product for all catalysts used in this study. Fast deactivation was anticipated on the mordenite catalysts with low Si/Al molar ratios such as 5 and 10, due to pore blocking by the carbon deposited on the external surface of the zeolite. A high activity and a long catalyst life were obtained on the mordenite catalyst with a Si/Al molar ratio of 12.     

不同硅铝比ZSM-5负载铁基催化剂二氧化碳加氢性能

CO₂加氢在铁基催化剂上直接制取高附加值化学品是实现其资源化利用的重要途径。通过等体积浸渍法制备了不同硅铝比（25,70,150）的ZSM-5负载的铁基催化剂,考察硅铝比对铁基催化剂上CO₂加氢性能的影响。结果表明,随着硅铝比的升高,催化剂活性先升高后降低,最优化硅铝比为70。CO₂-DRIFTS和CO₂-TPD结果显示,硅铝比为70的ZSM-5载体制备的催化剂具有较多且较强的表面碱性位,促进CO₂分子的活化解离。通过H₂-TPR、XRD、Raman等表征揭示了催化剂结构的演变过程。还原后催化剂的活性金属以单质Fe形式存在,反应过程中单质Fe向Fe₃O₄和FeC_x物种转化。不同硅铝比配位环境影响Fe与C的相互作用,影响FeC_x的生成,从而影响CO₂加氢的活性和选择性。     

N-烷基-N-甲基咪唑系列离子液体中ZSM-5分子筛催化环已烷氧化反应

Heterogeneous oxidation of cyclohexane by tert-butyl hydroperoxide (TBHP) was carried out over ZSM-5 catalysts with different Si/Al ratios in ionic liquids and organic molecular solvents. Higher yield and selectivity of the desired products were found in ionic liquids than in molecular solvents. The conversion of cyclohexane exhibits a decrease from 15.8% to 10.8% with the increase of Si/Al ratio of the HZSM-5 catalyst, and all the catalysts exhibit good selectivity of monofunctional oxidation products at around 97%. The activity of catalyst is found strongly de-pendent on the alkyl chain length of ionic liquid.     

有序介孔材料Al-FDU-12的合成及其加氢精制应用

采用原位合成法合成了不同硅铝原子比（Si/Al=50、40、30、20、10）的Al-FDU-12介孔材料,进一步浸渍镍钼活性金属制备了催化剂。通过小角X射线衍射（XRD）、广角XRD、N₂吸附-脱附、扫描电镜（SEM）、透射电镜（TEM）和紫外等表征手段对材料及催化剂做了相应的表征,并且考察了不同硅铝比的NiMo/Al-FDU-12催化剂在催化裂化柴油中的加氢脱硫脱氮性能。结果表明,FDU-12介孔材料孔径、孔容以及比表面积大,活性金属分散度高。铝改性后的NiMo/Al-FDU-12催化剂加氢脱硫、脱氮活性得到显著提高。当反应条件为温度350℃、氢油体积比600、压力5.0MPa、质量空速（WHSV）1.0h^-1、硅铝比20时,催化剂的加氢脱硫脱氮活性最高,脱硫率可达98.9%,脱氮率可达95.3%。在相同反应条件下,工业催化剂催化柴油加氢脱硫、脱氮率低于NiMo/AF-20以及NiMo/AF-10催化剂。因此,铝改性后的FDU-12材料具有良好的工业应用前景。     

Production of Middle Distillate Through Hydrocracking of Paraffin Wax Over NiMo/SiO2-Al2O3 Catalysts: Effect of Solvent in the Preparation of SiO2-Al2O3 by a Sol–Gel Method

Mesoporous Ni-Al₂O₃ (XNiAl) catalysts with different Ni/Al atomic ratio (X) were prepared by a co-precipitation method for use in hydrogen production by steam reforming of liquefied natural gas (LNG). The effect of Ni/Al atomic ratio of mesoporous XNiAl catalysts on their physicochemical properties and catalytic activity for steam reforming of LNG was investigated. Physical properties of XNiAl catalysts did not show a consistent trend with respect to Ni/Al atomic ratio, while chemical properties of XNiAl catalysts strongly influenced by Ni/Al atomic ratio. Nickel species were highly dispersed on the surface of XNiAl catalysts through the formation of nickel aluminate phase or solid solution of nickel oxide and nickel aluminate phase. In the steam reforming of LNG, both LNG conversion and hydrogen composition in dry gas showed volcano-shaped curves with respect to Ni/Al atomic ratio. Nickel surface area of XNiAl catalysts was well correlated with LNG conversion and hydrogen composition over the catalysts. Among the catalysts tested, 0.8NiAl (Ni/Al = 0.8) catalyst with the highest nickel surface area showed the best catalytic performance.     

Heterogeneous carbonylation of methanol on rhodium introduced into faujasite-type zeolites

Zeolites X and Y with a Si/Al ratio from 1.1 to about 100 have been exchanged with a solution of [Rh(NH₃)₅Cl](OH)₂. The resulting catalysts with about 1 wt% Rh have been characterised by FT-i.r. structure determination (KBr), hydrogen chemisorption, and FT-i.r. spectroscopic investigation of adsorbed CO. Depending on the Si/Al ratio and the thermal pretreatment, different surface Rh carbonyls are formed during the interaction with CO. As shown by the i.r. spectra, two kinds of Rh dicarbonyls (type I on Rh/NaX, type II on Rh/US-Ex, both type I and II on Rh/NaY) are formed.

The carbonylation activity of the catalysts strongly depends on the Si/Al ratio of the zeolite supports. The formation of carbonylation products increases with decreasing Si/Al ratio (in the range of Si/Al=100 - 1.3/1.5). The maximum of the carbonylation activity is marked by the Si/Al ratio of 1.3 - 1.5. Active sites of the catalysts are formed preferably by pretreatment with air. The spectra of adsorbed CO allow a correlation for catalytic activity/ selectivity and the intensity of the i.r. bands at 2020 and 2100 cm⁻¹ due to the Rh dicarbonyl species (I). The in situ spectra at reaction conditions give support for the same mechanism as postulated for the liquid phase carbonylation on Rh complex catalysts.     

改性Cu-ZSM-11和Cu-ZSM-5分子筛催化分解一氧化氮性能

采用水热法合成法合成ZSM-11和ZSM-5分子筛,采用一步离子交换法制备了改性ZSM-11和ZSM-5系列催化剂。通过X射线衍射、电感耦合等离子体发射光谱和红外光谱对催化剂进行表征。结果表明:ZSM-5型催化剂负载的离子量高于ZSM-11型催化剂。催化剂中的共存离子Cu2+,Ce3+和Ni2+对两种类型分子筛振动所产生的影响不同,共存离子对ZSM-11的影响较大,表明2种类型分子筛骨架的结构存在差异。催化试验结果表明:Cu-ZSM-11催化剂催化稳定性高于Cu-ZSM-5催化剂。Ce3+和Ni2+改性的Cu-ZSM-11和Cu-ZSM-5催化剂的催化活性都有所提高,但Ce3+和Ni2+改性的Cu-ZSM-11催化剂的催化活性高于Cu-ZSM-11和对应的改性Cu-ZSM-5催化剂。随空速的增大,2种催化剂的催化活性先增大后减小,在空速约为0.6(g·s)/mL左右时达到最高活性。     

Synthesis of ethylbenzene by alkylation of benzene with diethyl oxalate over HZSM-5

Catalytic synthesis of ethylbenzene by alkylation of benzene with diethyl oxalate was carried out over HZSM-5 with Si/Al ratios from 50 to 250. The catalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), ammonia temperature-programmed desorption (NH₃-TPD) and pyridine IR techniques. As revealed by the results of NH₃-TPD and pyridine IR spectra, a significant decrease in acidic strength and the number of acidic sites is observed with increasing Si/Al ratio from 50 to 250. The benzene conversion and ethylbenzene selectivity increases obviously with increasing Si/Al ratio from 50 to 200. With a further increase in Si/Al ratios, a slight decrease in the conversion of benzene and selectivity for ethylbenzene is detected, indicating that a proper acidic strength was required in this reaction. In addition, the effects of temperature and feed ratio on the catalytic activity and product distributions are also investigated in this study.