Enhancing the Deactivation Durability of Nano-sized HZSM-5 for Aromatization by Adjusting its Ratio of Lewis／BrФnsted Acid Sites

Ratio of Lewis/BrФnsted acid sites (C1/Cb) on the surface of nano-sized HZSM-5 was successfully manipulated by means of steaming and acid leaching. Significant enhancement of the deactivation durability of nano-sized HZSM-5 in the aromatization of fluid catalytic cracking (FCC) gasoline olefins seems to be closely related to the increase of Lewis/BrФnsted acid sites ratio.     

Dual-Bed Catalytic System for Direct Conversion of Methane to Liquid Hydrocarbons

A dual-bed catalytic system is proposed for the direct conversion of methane to liquid hydrocarbons. In this system, methane is converted in the first stage to oxidative coupling of methane (OCM) products by selective catalytic oxidation with oxygen over La-supported MgO catalyst. The second bed, comprising of the HZSM-5 zeolite catalyst, is used for the oligomerization of OCM light hydrocarbon products to liquid hydrocarbons. The effects of temperature (650-800℃), methane to oxygen ratio (4 10), and SiO2/Al2O3 ratio of the HZSM-5 zeolite catalyst on the process are studied. At higher reaction temperatures, there is considerable dealumination of HZSM-5, and thus its catalytic performance is reduced. The acidity of HZSM-5 in the second bed is responsible for the oligomerization reaction that leads to the formation of liquid hydrocarbons. The activities of the oligomerization sites were unequivocally affected by the SiO2/Al2O3 ratio. The relation between the acidity and the activity of HZSM-5 is studied by means of TPD-NH:j techniques. The rise in oxygen concentration is not beneficial for the C5 selectivity, where the combustion reaction of intermediate hydrocarbon products that leads to the formation of carbon oxide (CO CO2) products is more dominant than the oligomerization reaction. The dual-bed catalytie system is highly potential for directly converting methane to liquid fuels.     

Effects of P content in a P/HZSM-5 catalyst on the conversion of ethanol to hydrocarbons

A series of P/HZSM-5 catalysts prepared by impregnation method were used for ethanol conversion to lower olefins. The catalysts were characterized by X-ray diffraction (XRD), NH3-temperature-programmed desorption (NH3-TPD) and N2 adsorption-desorption measurements. It was found that the P/HZSM-5 catalysts showed high activity and selectivity toward light olefins. The selectivities of propylene and butylene can be improved with the introduction of phosphorus (P). When the content of P reached 3.0 wt%, more than 18.9% propylene in the gaseous products was obtained over the P/HZSM-5 catalyst at 450 ?C. The introduction of P modified the strong Br?nsted acid sites of the original HZSM-5 catalysts and P/HZSM-5 catalysts could resist coke formation and showed good stability.     

Non-oxidative dehydro-oligomerization of methane to higher molecular weight hydrocarbons at low temperatures

The non-oxidative dehydro-oligomerization of methane to higher molecular weight hydrocarbons such as aroma tics and C2 hydrocarbons in a low temperature range of 773-973 K with Mo/HZSM-5,Mo-Zr/HZSM-5 and Mo-W/HZSM-5 catalysts is studied.The means for enhancing the activity and stability of the Mo-containing catalysts under the reaction conditions is reported.Quite a stable methane conversion rate of over 10% with a high selectivity to the higher hydrocarbons has been obtained at a temperature of 973 K.Pure methane conversions of about 5.2% and 2.0% have been obtained at 923 and 873 K,respectively.In addition,accompanied by the C2-C3 mixture,tht- methane reaction can be initiated even at a lower temperature and the conversion rate of methane is enhanced by the presence of tne initiator of C2-C3 hydrocarbons.Compared with methane oxidative coupling to ethylene,the novel way for methane transformation is significant and reasonable for its lower reaction temperatures and high selectivity to the desired prod     

Methylation of 2-methylnaphthalene with methanol to 2,6-dimethylnaphthalene over HZSM-5 modified by NH4F and SrO

The methylation of 2-methylnaphthalene (2-MN) into 2,6-dimethylnaphthalene (2,6-DMN) was investigated over the solid acid catalysts.The results show that HZSM-5 modified by NH_4F has better catalytic performance than parent HZSM-5 due to the decrease in the acidity.When NH_4F/HZSM-5 is further modified by SrO,its catalytic activity decreases due to the decrease in the total acid amount and acidic strength.As a result,the comprehensive modification of NH_4F and SrO leads to the increase in the 2,6- DMN selectivity (2,6-DMN to DMN),up to 64.8% when 2-MN conversion is 10%.We calculated the ESP charge by density functional theory and the results show that the 6-position in 2-MN has higher ESP charge value than 7-position.The formation of 2,6-DMN is favored energetically as compared to that for 2,7-DMN.This suggests during the alkylation of 2-MN inside the ZSM-5 channel,the formation of 2,6-DMN is favored electronically than that of 2,7-DMN.Hence,lowering the acidity of catalyst is a key factor to obtain high selectivity of 2,6-DMN.     

Properties and Characterization of Modified HZSM—5 Zeolites

Physicochemical and catalytic properties of phosphorus and boron modified HZSM-5 zeolites treated with 100% steam at 673K were investigated.The acidity and distribution of acidic sites were studied by infrared spectroscopy using pyridine as probe molecule and temperature programmed desortion (TPD) of ammonia.The structure of the samples was characterized by XRD,and the textural properties of the catalysts were determined by nitrogen isothermal adsorption-desorption measurements and scanning electron microscopy(SEM).The XRD results show that the modified samples have no novel crystalline phase,indicating a high dispersion of phosphorus and boron species.After treatment,the microporous volume and surface area of the samples markedly decrease,implying the bolockage of the channel.The nitrogen adsorption-desorption measurements suggest that the isothermal type of all samples is a combination of isothermal type Ⅰ and Ⅳ，and all hysteresis loops resemble the H4-type in the IUPAC classification.The total acidity of the modified samples,determined by pyrldine adsorption IR and TPD of ammonia,decreases in contrast to that of the parent HZSM-5.The conversion of n-heptane over P and B steammodified HZSM-5 is higher than that of P and B-modified HZSM-5 zeolites but lower than that of the parent HZSM-5.     

Formaldehyde intermediate participating in the conversion of methanol to aromatics over zinc modified H-ZSM-5

Metal-modified H-ZSM-5 has a high selectivity of aromatics in methanol to aromatics(MTA)reaction,which is often attributed to the metal promoting the aromatization of intermediate olefins.However,the effect of methanol dehydrogenation on aromatics formation over these catalysts is rarely studied.Here,we report that HCHO,which is formed by methanol dehydrogenation over Zn/H-ZSM-5 prepared by Zn impregnation,can participate in the synthesis of aromatics.Methanol conversion can produce more aromatics than olefins(propylene or ethylene)conversion over Zn/H-ZSM-5,indicating the conventional MTA pathway including methanol-to-olefins and olefins-to-aromatics is not complete.Moreover,an MTA mechanism including the conventional pathway and the methanol and HCHO coupling pathway is systematically proposed.     

Co-feeding with DME:An effective way to enhance gasoline production via low temperature aromatization of LPG

The aromatization of light alkenes in liquefied petroleum gas (LPG) with and without dimethyl ether (DME) addition in the feed was investigated on a modified ZSM-5 catalyst.The results showed that under the given reaction conditions the selectivity of alkenes to high-octane gasoline blending components was markedly enhanced and the formation of propane and butanes was greatly suppressed with the addition of DME.It was also found that the distribution of C5+ components was changed a lot with DME addition into the LPG feed.The formation of branched hydrocarbons (mainly C6 C8 i-paraffin) and multi-methyl substituted aromatics,which are high octane number gasoline blending components,was promoted significantly,while the content of n-paraffins and olefins in C5+ components was decreased obviously,indicating that in addition to the oligomerization,cracking,hydrogen-transfer and dehydrogenation-cyclization of alkenes,the methylation of the formed aromatics and olefins intermediates also plays an important role in determining the product distribution due to the high reactivity of surface methoxy groups formed by DME.And this process,in combination with the syngas-to-methanol/DME technology,provides an alternative way to the production of high-octane gasoline from coal,natural gas or renewable raw materials.     

Effects of Calcination Temperature on the Acidity and Catalytic Performances of HZSM-5 Zeolite Catalysts for the Catalytic Cracking of n-Butane

The acidic modulations of a series of HZSM-5 catalysts were successfully made by calcination at different treatment temperatures, i.e. 500, 600, 650, 700 and 800 ℃, respectively. The results indicated that the total acid amounts, their density and the amount of B-type acid of HZSM-5 catalysts rapidly decreased, while the amounts of L-type acid had almost no change and thus the ratio of L/B was obviously enhanced with the increase of calcination temperature (excluding 800 ℃). The catalytic performances of modified HZSM-5 catalysts for the cracking of n-butane were also investigated. The main properties of these catalysts were characterized by means of XRD, N2 adsorption at low temperature, NH3-TPD, FTIR of pyridine adsorption and BET surface area measurements. The results showed that HZSM-5 zeolite pretreated at 800 ℃ had very low catalytic activity for n-butane cracking. In the calcination temperature range of 500-700 ℃, the total selectivity to olefins, propylene and butene were increased with the increase of calcination temperature, while, the selectivity for arene decreased with the calcination temperature.The HZSM-5 zeolite calcined at 700 ℃ produced light olefins with high yield, at the reaction temperature of 650 ℃ the yields of total olefins and ethylene were 52.8% and 29.4%, respectively. Besides, the more important role is that high calcination temperature treatment improved the duration stability of HZSM-5zeolites. The effect of calcination temperature on the physico-chemical properties and catalytic performance of HZSM-5 for cracking of n-butane was explored. It was found that the calcination temperature had large effects on the surface area, crystallinity and acid properties of HZSM-5 catalyst, which further affected the catalytic performance for n-butane cracking.     

ON THE ROLES OF Li IN Li-Pt/HZSM-5 CATALYSTS

Catalytic dehydrogenation of propane over alkali promoted Pt/HZSM-5 is investigated. Among the catalysts tested in this work, 1%Li-Pt/HZSM-5 exhibits a much better improvement in propene selectivity. Reactionpathway on the catalyst is postulated as a synergetic effect of reversed hydrogenspillover and controlled acidity of the catalyst. Another function of Li in thesuppressing of hydrogenolysis activity by Pt is also observed.     

温度和剂油比对汽油催化裂化脱硫的影响

Increasingly stringent regulations on environmental protection make gasoline desulfurization be a major concern for the present refineries. Accordingly, we proposed an original idea of sulfur reduction by catalytic cracking of FCC gasoline and simultaneously converting most sulfur of sulfides to H 2S. Some progress has been made in exploitation of the catalysts. In this paper, the effect of temperature and catalyst/oil ratio on the FCC gasoline desulfurization over two catalyst samples via catalytic cracking was discussed. The optimum temperature range is 400～420 ℃ for sulfur removal with relatively low cracking loss of gasoline. The highest sulfur removal percentage of 70% can be achieved with a liquid yield of more than 96%. The catalyst samples have higher desulfurization activity and selectivity for the sulfide cracking. In addition, both the gasoline yield and the sulfur content of the desulfurized gasoline decrease with the catalyst/oil ratio.     

Methane—the Promising Career of a Humble Molecule

Methane, CH4, here represents natural gas (NG) of which it is the main constituent. Routes ofchemical utilisation of NG — as opposed to energy usage — are discussed. A main step is the conversion of NG to synthesis gas, a mixture of CO and H2. Simple molecules derived from synthesis gas, like methanol,can be further reacted to longer-chained hydrocarbons like propylene and other olefins and even to gasoline and diesel.     

Modeling of Fischer-Tropsch Synthesis in a Slurry Reactor with Water Permeable Membrane

Fischer-Tropsch synthesis is an important chemical process for the production of liquid fuels and olefins. In recent years, the abundant availability of natural gas and the increasing demand of olefins, diesel, and waxes have led to a high interest to further develop this process. A mathematical model of a slurry membrane reactor used for syngas polymerization was developed to simulate and compare the maximum yields and operating conditions in the reactor with that in a conventional slurry reactor. The carbon polymerization was studied from a modeling point of view in a slurry reactor with a water permeable membrane and a conventional slurry reactor. Simulation results show that different parameters affect syngas conversion and carbon product distribution, such as the hydrogen to carbon monoxide ratio, and the membrane parameters such as membrane permeance.     

In改性Mo/HZSM-S催化剂上的甲烷芳构化反应性能

Dehydrogenation and aromatization of methane over Mo/HZSM-5 catalyst without adding oxygen were widely studied［1～3］. However, the existing problem of this route is the low yield of aromatics, owing to the high stability of methane. Recently, the introduction of the second metal species was believed to be a promising route to improve non-oxidative transformation of methane over Mo/HZSM-5 catalyst[4-7].     

Effects of ZrO_2 on the Microstructure of a Mica Glass-ceramic

1 INTRODUCTION Glass-ceramic technology is based on the controlled nucleation and crystallization of glass, and glass-ceramics have several advantages over the conventional powder-processed ceramics. In addition to the easy flexibility of formation in t…     

Enhancement of Bio-based para-Xylene Selectivity in Catalytic Fast Pyrolysis of Cellulose Using a Surface-modified Mg/P/HZSM-5 Catalyst

With the growing consumption of oil, the production of /?-xylene(PX) from renewable biomass has gained significant attention recently. This work demonstrated that cellulose, a main component in lignocellulosic biomass, was directly converted into PX over the Mg/P surface-modified zeolites. The catalysts modified by the incorporation of P2O5 and MgO into HZSM-5(HZ) promoted the isomerization of zw-/o-xylenes to p-xylene. The PX selectivity was greatly enhanced using the modified zeolites due to the deactivation of external surface and the adjustment of pore entrance. In addition, the addition of methanol to cellulose was beneficial to increase the selectivity of xylenes due to the alkylation reactions and the Diels-Alder reactions between cellulose-derived furans and methanol-derived olefins. The highest PX yield of 10.7%(molar fraction) with a high PX selectivity in xylenes(97.1%) was obtained over the 10%Mg/5%P/HZ catalyst. The reaction pathway for the formation ofp-xylene was addressed according to the study of the key reactions and the characterization of catalysts.     

On QSAR Study of Stereoselectivity for Wittig Reaction

1INTRODUCTION Witting reaction is an important and well-known organic reaction.In this reaction system,phospho-nium ylides react with aldehydes or ketones to gene-rate olefins and phosphonium oxides.Obviously,the position of double bond in olefins is exactly the po-sition of carbonyl group in the reactants,so there are no other position isomers in products.Due to this advantage,Witting reaction has been widely used in organic synthesis[1].Witting reaction could introduce double bond to c…     

Characterization and Activity of Cr, Cu and Ga Modified ZSM—5 for Direct Conversion of Methane to Liquid Hydrocarbons

Direct conversion of methane using a metal-loaded ZSM-5 zeolite prepared via acidic ion exchange was investigated to elucidate the roles of metal and acidity in the formation of liquid hydrocarbons. ZSM-5 (SiO2/A12O3=30) was loaded with different metals (Cr, Cu and Ga) according to the acidic ion-exchange method to produce metal-loaded ZSM-5 zeolite catalysts. XRD, NMR, FT-IR and N2 adsorption analyses indicated that Cr and Ga species managed to occupy the alllmlnum positions in the ZSM-5 framework. In addition, Cr species were deposited in the pores of the structure. However, Cu oxides were deposited on the surface and in the mesopores of the ZSM-5 zeolite. An acidity study using TPD-NH3, FT-IR, and IR-pyridine analyses revealed that the total number of acid sites and the strengths of the BrSusted and Lewis acid sites were significantly different after the acidic ion exchange treatment.Cu loaded HZSM-5 is a potential catalyst for direct conversion of methane to liquid hydrocarbons. The successful production of gasoline via the direct conversion of methane depends on the amount of aluminum in the zeolite framework and the strength of the BrSnsted acid sites.     

Catalytic activity of phosphorus and steam modified HZSM-5 and the theoretical selection of phosphorus grafting model

The modification of HZSM-5 zeolite with phosphorus and steam has been studied. Results show that 1% phosphorus and steam modified HZSM-5 has the highest catalytic activity for n-heptane. Physicochemical and catalytic properties of 1% phosphorus and steam modified HZSM-5 zeolites have been investigated. The X-ray diffraction （XRD） results exhibit that there is considerable variation in the relative intensity of the individual diffraction peaks. The acidity of the samples decreases with an increase in the steaming temperature, which is determined by the IR of adsorbed pyridine and temperature programmed desorption （TPD） of ammonia. The oxidation state of phosphorus shown by XPS is ＋5, and a model for surface structure modification is proposed. The nitrogen adsorption isotherm for all samples is a combination of type I and type IV, all hysteresis loops resemble the H4-type. The density functional and cluster model methods have been invoked to select the phosphorus grafting model, and it was found that the phosphorus grafting model were more probable in the form of the terminal oxygen coordinating with aluminum.     

Low-temperature activation of methane over rare earth metals promoted Zn/HZSM-5 zeolite catalysts in the presence of ethylene

At low temperature of 723 K, methane can be easily activated in the presence of ethylene in the feed, and converted to higher hydrocarbons (C2–C4) and aromatics (C6–C10), through its reaction over rare metals modified Zn/HZSM-5 zeolite catalysts without undesirable carbon oxides formation. Methane can get 37.3% conversion over the above catalysts under low temperature, and the catalysts show a longer lifetime than usual metal supported HZSM-5 zeolite catalysts without adding any rare earth metals. The effects of methane activation over various rare earth metal promoted Zn/HZSM-5 catalysts on the products and influences of several reaction conditions such as temperature, catalyst lifetime and molar ratio of CH4/C2H4 have been discussed.