Effect of hydrothermal treatment temperature on FCC gasoline upgrading properties of the modified nanoscale ZSM-5 catalyst

Nanoscale HZSM-5 zeolite was hydrothermally treated with ammonia water at different temperatures and then loaded with La₂O₃ and ZnO. The parent and the modified nanoscale HZSM-5 catalysts were characterized by SEM, NH₃-TPD, IR and XRF. The performance of the modified HZSM-5 catalysts for FCC gasoline upgrading was evaluated in a fixed bed reactor in the presence of hydrogen. The results indicated that the modified catalyst which was hydrothermally treated at 400 °C exhibited excellent aromatization activity, isomerization activity and higher ability of reducing olefin content in FCC gasoline. Under the given reaction conditions, the olefin content in FCC gasoline could be decreased from 49.6 to 8.1 vol.%. The catalytic performance of the modified nanoscale ZSM-5 catalyst hardly changed within 300 h time on stream, and the research octane number (RON) of gasoline was preserved.     

Enhanced performance of methane dehydro-aromatization on Mo-based HZSM-5 zeolite pretreated by NH4F

Enhanced performance of methane dehydro-aromatization reaction (MDA) were achieved on a Mo-based HZSM-5 zeolite catalyst in which HZSM-5 were pretreated by a proper amount of NH₄F (Mo/HZ(F)). The results of NH₃-TPD and ²⁷Al MAS NMR demonstrated that the number of Brönsted acid sites decreased on the HZSM-5 zeolite and Mo/HZSM-5 catalyst after NH₄F treatment. TGA and TPO measurements showed that the Mo/HZ(F) catalysts were highly resistant to coke deposition, which resulted mainly from the elimination of the Brönsted acid sites after the pretreatment of the HZSM-5 zeolite with NH₄F.     

Characterization of an HZSM-5/MnAPO-11 composite and its catalytic properties in the synthesis of high-octane hydrocarbons from syngas

Zeolite HZSM-5 is known to be active for the catalytic conversion of methanol into hydrocarbons, but its strong acidity and narrow channels may lead to high selectivity to aromatics, thus decreasing the quality of synthesized gasoline. In this work, an HZSM-5/MnAPO-11 composite was prepared via hydrothermal synthesis, and the catalytic synthesis of high-octane gasoline from syngas was studied in flow-type fixed-bed reactors. The catalysts were characterized employing X-ray diffraction (XRD), N₂ adsorption-desorption, ammonia temperature-programmed desorption (NH₃-TPD), scanning electron microscopy (SEM), energy-diffusive X-ray spectroscopy (EDS), atomic absorption spectrophotometry (AAS), and Fourier transformed infrared spectroscopy (FT-IR). Compared with HZSM-5 and a mechanical mixture of HZSM-5 and MnAPO-11, the HZSM-5/MnAPO-11 composite showed the highest gasoline yield and iso-paraffin selectivity due to the presence of more mesopores and moderate acid sites. The results provide new perspectives on the synthesis and application of composite molecular sieves in the production of gasoline.     

Hydroconversion of n-octane over nanoscale HZSM-5 zeolites promoted by 12-molybdophosphoric acid and Ni

12-Molybdophosphoric acid (PMo), Ni and Ni–PMo loaded on nanoscale HZSM-5 zeolites were prepared and characterized by BET, IR, XRD, Py-IR, NH₃-TPD, TG and SEM. The hydroconversion of n-octane over various catalysts was investigated in order to obtain light isomers alkanes and aromatics products with high-octane-number. The acid amounts of the catalysts were modified after the loading of PMo and Ni, and its relation to the activity of the reaction was discussed. It is concluded that the stability of aromatization is improved, and the yield of light iso-alkanes is enhanced due to the introduction of PMo and Ni. The improved activity of n-octane hydroconversion over PMo and Ni loaded nanoscale HZSM-5 zeolites could be attributed to the increase of the acid amounts and the synergetic effect between Brønsted and Lewis acid sites.     

Synergisms between matrices and ZSM-5 in FCC gasoline non-hydrogenating upgrading catalysts

This article describes a novel non-hydrogenating FCC gasoline upgrading catalyst system consisting of a kaolin/γ-Al₂O₃ binary-matrix and an active component zeolite HZSM-5. Different catalysts made from the different combinations of HZSM-5 with the three matrices (two kaolins and γ-Al₂O₃) or their binary mixtures were prepared and their catalytic performances were assessed in a continuously flowing fixed-bed reactor using FCC gasoline as feedstock. The results showed that compared with the single-matrix based HZSM-5 catalysts, the binary-matrix based HZSM-5 catalysts had much better catalytic performance. The characterization results of the acidity, specific area and pore structure properties of the catalysts revealed that the synergisms between the matrices and HZSM-5 in the acidity and pore distribution of the binary-matrix based catalysts accounted for their improved catalytic performance. Our results demonstrated that the non-hydrogenating catalyst system developed in the present investigation can convert olefins in FCC gasoline into aromatics that have higher research octane number (RON) and thus has potential application for FCC gasoline upgrading because of its excellent olefin reduction ability and RON preservability.     

Modification of acidity of Mo-Fe/HZSM-5 zeolite via argon plasma treatment

The NH₃-TPD characterization was conducted to confirm that the acidity of Mo-Fe/HZSM-5 zeolite could be selectively modified via the glow discharge plasma treatment. The plasma catalyst treatment could totally change the distribution of aromatic products with higher methane conversion compared to the untreated catalyst. Some polycyclic aromatics such as anthracene, pyrene and phenanthrene were also produced over the plasma treated catalyst, in addition to benzene, toluene and naphthalene, which were normally obtained over the untreated catalyst.     

Research on the Acidity of the Double-function Catalyst for DME Synthesis from Syngas

Two kinds of HZSM-5 zeolite (SiO₂/Al₂O₃ = 50,300) were introduced into the STD (syngas-to-DME) reaction and the double-function catalysts containing CuO/ZnO/Al₂O₃ and HZSM-5 were investigated by activity evaluation and NH₃-TPD. It was found that the acidity of HZSM-5 played a critical role in the performance of STD catalyst, and an appropriate acidic amount was required to obtain the best activity of STD catalyst; more and less acidic amount were both unfavorable for DME yield.     

Differences between ZSM-5 and ZSM-11 zeolite catalysts in 1-hexene aromatization and isomerization

ZSM-5 and ZSM-11 zeolites with high crystallinity are synthesized and tested in the aromatization and isomerization reactions of 1-hexene at 370 °C in a continuous flow fixed bed. The results indicate that ZSM-5 and ZSM-11 zeolites possess similar acid site amount and strength, and most of the acid sites belong to Brønsted acid. When the ZSM-5 and ZSM-11 zeolites were used as catalysts, the aromatics selectivity over ZSM-11 catalyst was higher than that over ZSM-5 catalyst in contrast to i-paraffins selectivity, maybe attributed to that the C₇ and C₈ aromatics have an easier exit from the ZSM-11 zeolite. Moreover, the decrease of particle size can present superior aromatics selectivity and less i-paraffins selectivity in the aromatization and isomerization of 1-hexene over the ZSM-11 catalyst.     

Performance of combined cobalt—nickel—zirconia and HZSM-5 catalyst systems for carbon monoxide hydrogenation

The synthesis of hydrocarbons via hydrogenation of carbon monoxide was investigated over cobalt—nickel—zirconia catalysts of various compositions in combination with zeolite HZSM-5 in “mixed bed” and “follow bed” arrangements. These combinations resulted in the formation of aromatics in amounts as high as 30-35 wt% under relatively mild operating conditions (1 atm, 250–280°C). Although the olefinicity of C₂ and C₃ fractions in the product stream was higher in the mixed bed compared to the follow bed arrangement, the selectivities to aromatics were comparable in the two bed arrangements. The aromatic selectivity was found to be sensitive to operating conditions. The formation of aromatics was favored at high HZSM-5/metal catalyst ratios, low space velocities and high reaction temperatures. The product distributions obtained using various metal/zeolite bifunctional catalysts have been discussed.     

Modified Beta Zeolite as Catalyst for Fries Rearrangement Reaction

Modified beta zeolites were applied as catalysts for the Fries rearrangement reaction. The properties of the modified zeolites were characterized by NH₃-TPD, n-hexane and 1,2,4-trimethylbenzene adsorption. Modification with SiO₂ did not block the pores of the beta zeolite but reduced the number of acid sites on the surface. However, when the beta zeolite was modified with Ce₂O₃, the number of acid sites determined by NH₃-TPD increased, which indicated that new acid sites are created by the interaction of cerium oxide and zeolite. Modified beta zeolites and H-beta were applied as catalysts for the Fries rearrangement of phenol acetate. Reaction over H-beta has low selectivity and the catalyst is easily deactivated. SiO₂ modification of the catalyst increases the selectivity of the reaction but decreases the conversion. Ce₂O₃-modified beta zeolites show higher catalytic activity and rearrangement selectivity in the reaction than other catalysts. The stability of the catalyst is also improved after Ce₂O₃ modification. About 70% selectivity and 60-80% conversion can be achieved over 16 wt% Ce₂O₃-modified beta zeolite.     

改性HZSM-5对甲醇制汽油反应性能的影响

对HZSM-5分子筛改性是提高甲醇制汽油反应催化性能的有效方式,分别用非金属、稀土金属及水热处理对HZSM-5分子筛催化剂进行改性,考察改性方法对HZSM-5分子筛酸性、孔径和比表面积等性质的影响,同时对改性HZSM-5分子筛催化剂催化甲醇制汽油的汽油收率和芳烃含量等指标进行比较。结果表明,经La改性的催化剂可明显提高汽油收率,水热处理的催化剂反应产物汽油中的均四甲苯含量大幅增加。改性催化剂对反应的影响可一定程度验证相关理论。     

Characterization and catalytic application of MnCl2 modified HZSM-5 zeolites in synthesis of aromatics from syngas via dimethyl ether

The conversion of syngas to aromatics via dimethyl ether was investigated over MnCl₂ modified HZSM-5 zeolites. The results demonstrated that 2%MnCl₂ modified HZSM-5 (SiO₂/Al₂O₃ = 38) exhibited higher p-xylene selectivity than other catalysts and further decreased 1,2,4,5-tetramethylbenzene selectivity. The CO conversion was obviously increased after 5%MnCl₂ modification to HZSM-5. The catalysts were characterized by XRD, BET, XPS, FT-IR, NH₃-TPD, SEM, element analysis and O₂-TPO. The loading amount of MnCl₂ affected the adsorption and reaction of DME molecules on zeolites. Appropriate amount of MnCl₂ introduction could adjust the acidity and pore volume of HZSM-5 to increase p-xylene selectivity and CO conversion.     

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.     

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.     

Conversion of light paraffins for preparing small olefins over ZSM-5 zeolites

The conversion of C₃-C₉ paraffins to small olefins over ZSM-5 zeolite is investigated. The small olefins are primary products and are usually converted into other more stable secondary products such as aromatics on the ZSM-5 zeolites. Thermally treated HZSM-5, K/HZSM-5 and Ba/HZSM-5 catalysts were developed and favourable oxidative conditions were introduced for the conversion process to maximize selective conversion of light paraffins to small olefins at the relatively low temperature of 873 K. The role of K and Ba is to minimize bimolecular hydrogen transfer reactions and enhance the dehydrogenation activity of the catalysts. Meanwhile, the oxygen in the gas phase is effective to improve the olefin selectivity and yield. C₂-C₄ olefin selectivities of 70.4 and 66.8% have been obtained for propane andn-hexane feed-stocks, respectively, at a temperature of 873 K.     

Transformation of methanol to gasoline range hydrocarbons using HZSM-5 catalysts impregnated with copper oxide

Various CuO/HZSM-5 catalysts were studied in a fixed bed reactor for the conversion of methanol to gasoline range hydrocarbons at 673 K and at one atmospheric pressure. The catalysts were prepared by wet impregnation technique. Copper oxide loading over HZSM-5 (Si/Al=45) catalyst was studied in the range of 0 to 9 wt%. XRD, BET surface area, metal oxide content, scanning electron microscopy (SEM) and thermogravimetric (TGA) techniques were used to characterize the catalysts. Higher yield of gasoline range hydrocarbons (C₅-C₁₂) was obtained with increased weight % of CuO over HZSM. Effect of run time on the hydrocarbon yields and methanol conversion was also investigated. The activity of the catalyst decreased progressively with time on-stream. Hydrocarbon products’ yield also decreased with the increase in wt% of CuO. Relatively lower coke deposition over HZSM-5 catalysts was observed compared to CuO impregnated HZSM-5 catalyst.     

Benzene Alkylation with Propane over Mo Modified HZSM-5

Benzene alkylation with propane has been studied over HZSM-5 loading 3.1–15.4 wt% Mo in continuous-flow microreactor under 350 °C and atmospheric pressure with the highest activity obtained at 6.7 wt% Mo loading. C_7–9 aromatics were obtained as main products while the total amount of benzene rings kept unchanged. i-Propylbenzene and n-propylbenzene are formed primarily, while toluene, ethylbenzene, and ethyl-toluene are formed secondly from the propylbenzenes. Catalytic performance of 6.7 wt% Mo/HZSM-5(38) partially poisoned by NH₃ shows that the strong acid sites play a crucial role in the alkylation. Low SiO₂/Al₂O₃ ratio of HZSM-5 in the Mo modified catalysts gives high propane conversion. Two hydrothermal treatment methods were applied to the 6.7 wt% Mo/HZSM-5(38) catalyst, caused decrease of propane conversion but result in different product distribution. A possible reaction mechanism concerning bifunctional active centers resulted from combination of loaded Mo species and strong acid centers on HZSM-5 is proposed.     

Hydrogenation of carbon dioxide by hybrid catalysts,direct synthesis of aromatics from carbon dioxide and hydrogen

Direct synthesis of aromatics from carbon dioxide hydrogenation was investigated in a single stage reactor using hybrid catalysts composed of iron catalysts and HZSM-5 zeolite. Carbon dioxide was first converted to CO by the reverse water gas shift reaction, followed by the hydrogenation of CO to hydrocarbons on iron catalyst, and finally the hydrocarbons were converted to aromatics in HZSM-5. Under the operating conditions of 350°C, 2100 kPa, and CO₂/H₅ = 1/2, the maximum aromatic selectivity obtained was 22% with a CO₂ conversion of 38% using fused iron catalyst combined with the zeolite. Together with the kinetic studies, thermodynamic analysis of the CO₂ hydrogenation was also conducted. It was found that unlike Fischer Tropsch synthesis, the formation of hydrocarbons from CO₂ may not be thermodynamically favored at higher temperatures.     

Conversion of n-Octene over Nanoscale HZSM-5 Zeolite

Transformation of n-octene has been investigated over nanoscale HZSM-5 at different reaction temperature and contact time. The results show that the main reaction was isomerization of n-octene over 200 °C. Hydrogen transfer reaction also occurred at 200 °C, but the products were alkanes and cycloolefins instead of aromatics. The aromatization was promoted by high temperature. The maximum selectivity of i-paraffins occurred between 300 and 350 °C. Propene, butene and pentene were the primary cracking products. These olefins were oligomerized and cracked to produce a wide distribution of olefins with different carbon atoms. These intermediates then were quickly transformed into aromatics and alkanes by hydrogen transfer over acid sites at high reaction temperature. Propane and butane can be transformed into methane and ethane at long contact time above 400 °C.     

碱处理改性对Zn/HZSM-5分子筛催化剂性能的影响

以不同浓度的NaOH溶液对HZSM-5分子筛进行碱处理改性后所得多级孔ZSM-5分子筛作为活性组分制备甲醇制芳烃催化剂,采用XRD、SEM、NH3-TPD和N2吸-脱附等手段对催化剂进行了表征,分别考察了碱处理改性对分子筛催化剂骨架结构、酸性质、孔结构以及催化性能的影响.结果表明,通过合适浓度的NaOH碱溶液处理后,HZSM-5分子筛在保持微孔骨架结构的同时,可以调变其晶内介孔孔道结构分布以及酸性质.随着NaOH碱溶液浓度升高,HZSM-5分子筛的酸量、介孔孔容、介孔表面积都增加、孔容分布变宽,催化剂的活性和稳定性等催化性能得以改善.HZSM-5分子筛碱处理改性适宜的NaOH溶液浓度为0.4 mol/L,改性后的催化剂芳烃收率由25.07％增加到32.22％,使用寿命由8d增加到16d,但NaOH溶液浓度超过0.6 mol/L后会严重破坏HZSM-5分子筛骨架结构,催化活性下降较快.