Ga2O3/HZSM-48 for dehydrogenation of propane: Effect of acidity and pore geometry of support

The catalytic performance of propane dehydrogenation over HZSM-48 supported Ga₂O₃ catalysts in the presence of CO₂ was investigated, and compared with that of HZSM-5 supported ones. The activity decreases with the increase of Si/Al ratio of catalyst support while the selectivity to propene shows a contrary trend. Ga₂O₃/HZSM-48 with Si/Al ratio of 130 has the best propene yield of 22%. HZSM-48 supported catalysts exhibit higher selectivities to propene than the HZSM-5 supported ones at similar propane conversion, due to their weak acid strength. However, their stabilities are not so good as those of the latters, owing to their more weak acid sites and unidimensional pore structures.     

Hβ/HZSM-5 Composite Carrier Supported Catalysts for Olefins Reduction of FCC Gasoline Via Hydroisomerization and Aromatization

In order to develop a novel catalyst system that has excellent olefin reduction ability for FCC gasoline without loss in research octane number (RON), different catalysts supported on single- and binary-zeolite carriers consisting of Hβ or/and HZSM-5 were prepared and their catalytic performances for FCC gasoline upgrading were assessed in the present investigation. Acidity measurements by pyridine-adsorbed Fourier transformed infrared spectroscopy (FTIR) showed that hydroisomerization and aromatization activities were closely related to the density of acid sites and the ratios of medium Lewis acidity and strong Br?nsted acidity to total acidity. Compared with the single HZSM-5 supported catalyst, the single Hβ supported catalyst was found to have much better olefin reduction performance, but the product RON still suffered from a loss of 1.6. Compared to the single-zeolite supported catalysts, the binary-zeolite Hβ/HZSM-5 supported catalysts with the mass ratio of Hβ to HZSM-5 at 6.6 offered much more stable activity and selectivity to arene, which played an important role in preserving gasoline RON.     

固体酸对二氧化碳加氢合成二甲醚催化剂性能的影响

以Cu-ZnO-Al2O3催化剂作为甲醇合成组分,以不同固体酸作为脱水组分,制备了一系列CO2加氢合成二甲醚的复合催化剂。研究表明CO2的转化率与固体酸的酸性无关,而取决于Cu-ZnO-Al2O3催化剂上甲醇的合成速率;二甲醚的选择性取决于固体酸的酸量和酸强度,脱水速率与固体酸的中/强酸有关。HZSM-5分子筛作为复合催化剂脱水组分时,二甲醚的收率最高;硅铝比对CO2转化率无影响,但可显著地影响二甲醚选择性;低硅铝比的HZSM-5更适合作为CO2加氢合成二甲醚复合催化剂的脱水组分。     

Dual effects of supported W catalysts for dehydroaromatization of methane in the absence of oxygen

The screening of a series of W-based catalysts on different supports i.e. HZSM-5, Hβ, USY and Al₂O₃ for the dehydroaromatization of methane (DHAM) revealed that HZSM-5 emerged as the best support. Next, the performance of W/HZSM-5 and W-H₂SO₄/HZSM-5 catalysts for the DHAM reaction was compared to study the effect of acidic treatment in the impregnation method. The results showed that the optimum activity of W-H₂SO₄/HZSM-5 catalyst exceeded that of W/HZSM-5 catalyst. Finally, the influence of Si/Al ratio in the W-H₂SO₄/HZSM-5 catalyst was studied and the catalyst with Si/Al ratio = 30 was found to be the most promising for the DHAM reaction. The remarkable activity of the catalyst is attributed to the presence of dual effects: suitable content of octahedral polymeric and tetrahedral monomeric tungstate species accompanied by proper amount and strength of acid sites in the catalyst.     

Realumination of dealuminated HZSM-5 zeolite by citric acid treatment and its application in preparing FCC gasoline hydro-upgrading catalyst

This article describes a novel citric acid treatment method for realuminating dealuminated HZSM-5 zeolite and its application in enhancing the performance of the zeolite derived FCC gasoline hydro-upgrading catalysts. A series of modified HZSM-5 zeolites were prepared by streaming and/or acid treatments and the influences of the different modification methods on the acidity, pore structure and catalytic performance of the modified HZSM-5 zeolite supported catalysts were compared in the present investigation. The results showed that compared with the single HCl or citric acid treatment, the steaming treatment, and the steaming/HCl treatments, the citric acid treatment after steaming exclusively increased the amount of framework Al species due to its realumination effect on the steamed HZSM-5 zeolite. This realumination effect of the citric acid treatment could optimize the ratio of framework Al to extra-framework Al in the steamed HZSM-5 zeolite and thus greatly improve the acidity distribution and pore structure of the corresponding catalyst. The catalytic performance assessments of the different zeolite supported catalysts for FCC gasoline hydro-upgrading revealed that the catalyst supported on the steaming/citric acid treated HZSM-5 zeolite had balanced initial and long-term activities in hydrodesulfurization, hydroisomerization and aromatization, high liquid yield and improved gasoline road octane number. The superior catalytic performance of the catalyst could be closely related to its suitable ratio of framework Al to extra-framework Al achieved by the combinational use of the steaming dealumination and the citric acid realumination, fully demonstrating the effectiveness of the steaming and citric acid treatments in optimizing the physicochemical properties and catalytic performance of HZSM-5 zeolite supported catalysts.     

A novel catalyst system based on quadruple silicoaluminophosphate and aluminosilicate zeolites for FCC gasoline upgrading

To develop a novel catalyst system that has excellent olefin reduction capability for FCC gasoline without loss in octane number, different catalysts supported on multiple composite carriers consisting of SAPO-11, Hβ, HMOR and HZSM-5 were prepared and their catalytic performances for FCC gasoline upgrading were assessed in the present investigation. The pore structure and acidity of the catalysts were characterized by N₂ adsorption and pyridine adsorption FTIR, respectively. Based on the results obtained over the catalysts supported on binary-zeolite carriers (Hβ/HZSM-5, HMOR/HZSM-5 and SAPO-11/HZSM-5) using FCC gasoline as the feedstock, various multiple-zeolite supported catalysts were developed from different combinations of the binary-zeolite systems. It was found that the SAPO-11/HMOR/β/ZSM-5 quadruple composite zeolite supported catalyst gave higher liquid yield, improved gasoline RON, and lower coke deposit amount for the hydro-upgrading of FCC gasoline and thus can be considered as a potential catalyst system. A comprehensive analysis based on the catalytic activities and acidity measurements revealed that acid strength and acid type were two very important factors influencing hydroisomerization and aromatization activities, and the difference in catalyst acid strength determined which factor predominates.     

Preparation and characterization of zeolite catalysts for etherification reaction

Catalytic etherification of 2-naphthol with ethanol has been carried out over a series of solid-acid catalysts such as H-Beta, H-MOR and H-ZSM-5 using a flow-type reactor. H-Beta zeolite shows higher conversion and catalytic stability than other catalysts for the production of 2-naphthyl ethyl ether, which may be correlated to the amount and strength of acid sites. H-Beta zeolites with different Si/Al ratios show that conversion decreases with increasing Si/Al ratios. The NH₃-TPD profiles indicate that the weak acidity decreases more sharply with increase in Si/Al ratios, compared with the strong acidity. The influences of ethanol/2-naphthol molar ratios, reaction temperature, and space velocity with respect to catalytic activities are investigated for H-Beta zeolite in the present work.     

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.     

A Facile and Effective Method for the Distribution of Mo/HZSM-5 Catalyst Active Centers

Post-steaming treatment of Mo/HZSM-5 catalysts results in more molybdenum species migrating into and residing in the HZSM-5 zeolite channels. This is confirmed by XRF and XPS measurements. ¹H MAS NMR and ²⁹Si MAS NMR also demonstrate that the number of free Brönsted acid sites decreases in the Mo/HZSM-5 catalysts that underwent post-steaming treatment, compared to untreated Mo/HZSM-5 catalysts. As a result, the deactivation rate constant (k _d) on the Mo/HZSM-5 catalyst after post-steaming treatment for 0.5h is much smaller, and the catalyst therefore shows remarkable stability in the probe reaction of methane dehydro-aromatization. The results suggest that a more beneficial bi-functional balance between active Mo species for methane activation and acid sites for the following aromatization is developed over those Mo/HZSM-5 catalysts that have experienced post-steaming treatment for 0.5h, in comparison with the untreated Mo/HZSM-5 catalysts.     

Small-sized HZSM-5 zeolite as highly active catalyst for gas phase dehydration of glycerol to acrolein

The catalytic properties of nanocrystalline HZSM-5 catalysts with high Si/Al molar ratio (ca. 65) were investigated in the gas phase dehydration of aqueous glycerol. Compared with bulk HZSM-5, the small-sized catalyst exhibits greatly enhanced catalytic performance in glycerol dehydration even with very high GHSV (=1438 h^?1). Catalysts with different Si/Al ratios were studied, but it is difficult to separate the influence of Si/Al ratio from that of particle size. However, by varying the proton exchange degree for one mother batch of zeolite, a series of H_xNa_1–xZSM-5 catalysts with same particle size and different Brønsted acid site densities was prepared. The catalytic results for this series of samples show that high density of Brønsted acid sites favors the production of acrolein. Based on these results, small-sized HZSM-5 with high aluminum content appears to be most promising for gas phase dehydration of glycerol.     

Alkylation of hydroquinone with tert-butanol over AlSBA-15 mesoporous molecular sieves

A series of AlSBA-15 catalysts with different pore size and different Si/Al ratio were prepared and characterized by N₂ adsorption and NH₃-temperature programmed desorption (NH₃-TPD) methods. Their catalytic behaviors for the alkylation of hydroquinone with tert-butanol were studied and compared with that of HZSM-5, HY, HAlMCM-41. It is found that the catalytic activity correlates well with the amount of medium-strong acid sites on the surface of the catalysts, and the selectivity towards 2-tert-Butylhydroquinone has some connection with the pore size of the catalysts. The reusability of the catalyst depends on its hydrothermal stability, which needs to be improved for the AlSBA-15 catalysts.     

酸性催化剂催化异丙醇脱水制丙烯反应

对HZSM-5及Zn改性HZSM-5、SAPO-34、MCM-41和磷钨酸负载MCM-41分子筛催化剂进行表征,评价固定床反应器中催化异丙醇脱水反应.Zn改性HZSM-5可有效调节催化剂的酸性,提高催化剂选择性,酸性较弱的SAPO-34与Al2O3质量比为5:1混合组成的SAPO-34催化剂和MCM-41分子筛也表现出...     

n(硅)∶n(铝)对HZSM-5分子筛膜催化裂解性能的影响

采用二次生长法在不锈钢管内壁上制备了不同n(硅)∶n(铝)的HZSM-5分子筛膜.采用XRD、SEM和原位吡啶吸附红外光谱对样品的结构和酸性质进行了表征,以超临界正十二烷的催化裂解为模型反应对样品的催化性能进行了评价.随着n(硅)∶n(铝)的增加,HZSM-5交织生长程度变大并且Brφnsted酸量逐渐减少.低n(硅)∶n(铝)的分子筛膜表面具有较高的Brφnsted酸量,在反应的初始阶段存在活性的快速下降行为.适当增加分子筛膜的n(硅)∶n(铝),可以减缓反应初始阶段的活性下降速度,从而明显提高HZSM-5分子筛膜的催化活性.但过高的n(硅)∶n(铝)使分子筛膜表面的酸量大幅减少、致密性增加,不利于裂解反应.n(硅)/n(铝)为125的HZSM-5分子筛膜具有最高的反应活性和初始活性稳定性.     

Tailoring acidity of HZSM-5 nanoparticles for methyl bromide dehydrobromination by Al and Mg incorporation

Three kinds of HZSM-5 nanoparticles with different acidity were tailored by impregnating MgO or varying Si/Al ratios. Both the textural and acidic properties of the as-prepared nanoparticles were characterized by nitrogen adsorption-desorption measurements, X-ray diffraction (XRD), scanning electron microscopy (SEM), ammonia temperature-programmed desorption (NH₃-TPD) and Fourier transform infrared spectroscopy (FTIR or Py-FTIR). It was found that the intensity of Lewis acid sites with weak strength was enhanced by impregnating MgO or reducing Al concentration, and such an enhancement could be explained by the formation of Mg(OH)⁺ or charge unbalance of the MgO framework on the surface of HZSM-5 support. The effect of HZSM-5 nanoparticles'' acidity on methyl bromide dehydrobromination as catalyst was evaluated. As the results, MgHZ-360 catalyst with the highest concentration of Lewis acid sites showed excellent stability, which maintained methyl bromide conversion of up 97% in a period of 400 h on stream. Coke characterization by BET measurements and TGA/DTA and GC/MS analysis revealed that polymethylated naphthalenes species were formed outside the channels of the catalyst with higher acid intensity and higher Brønsted acid concentration during the initial period of reaction, while graphitic carbon formed in the channels of catalyst with lower acid intensity and higher Lewis acid concentration during the stable stage.     

碱改性介-微孔HZSM-5分子筛催化乙醇脱水制乙烯性能

对两种不同硅铝比的HZSM-5分子筛进行碱处理,制备介-微孔复合HZSM-5分子筛,研究乙醇脱水制乙烯的催化性能,并考察碱溶液浓度和处理温度对HZSM-5分子筛孔结构和表面酸性的影响。结果表明,适宜的碱处理条件有利于分子筛发生骨架脱硅和脱铝,从而形成介孔。碱处理对硅铝比低的HZSM-5分子筛酸性质影响明显,而硅铝比高的HZSM-5分子筛在碱处理过程中酸性质变化不明显,更易发生脱硅和脱铝而形成更多介孔。碱改性介-微孔HZSM-5分子筛催化剂使乙醇脱水制乙烯催化性能得到改善,尤其低温催化活性提高,这主要归功于碱处理中介孔的形成和表面酸性的调变。     

Ga2O3/HSSZ-13 for dehydrogenation of ethane: Effect of pore geometry of support

Dehydrogenation of ethane to ethylene in the presence of CO₂ was investigated over gallium oxide supported on HSSZ-13 with different Si/Al ratios. These catalysts exhibited higher activity as well as higher selectivity in comparison to HZSM-5 supported ones. 34% ethane conversion with 86.9% selectivity to ethylene could be obtained. The enhanced catalytic performance of Ga₂O₃/HSSZ-13 can be attributed to unique pore geometry of SSZ-13 support. However, the stability is not as good as that of Ga₂O₃/HZSM-5, owing to easy coking in channel with smaller pore-opening size.     

Catalytic cracking of isobutane over HZSM-5, FeHZSM-5 and CrHZSM-5 catalysts with different SiO<Subscript>2</Subscript>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> ratios

Several systems of HZSM-5, FeHZSM-5 and CrHZSM-5 zeolite catalysts with different ratios of SiO₂/Al₂O₃ (25,38,50,80, and 150) were prepared and they were characterized by means of X-ray diffraction (XRD), UV–Vis, NH₃-TPD and BET techniques. The results indicated that, compared with uncalcined HZSM-5 zeolites, the total acid amounts, acidic site density and acidic strength of HZSM-5, FeHZSM-5 and CrHZSM-5 zeolite catalysts obviously decreased, while those of weak acid amounts obviously enhanced with the decrease of SiO₂/Al₂O₃ molar ratio. When the ratio of SiO₂/Al₂O₃ is less than 50, the three systems of HZSM-5, FeHZSM-5 and CrHZSM-5 zeolite catalysts with same ratio of SiO₂/Al₂O₃ gave similar and high isobutane conversions. However, when the ratio of SiO₂/Al₂O₃ was equal to or greater than 80, these three systems of catalysts possessed different altering tendencies of isobutane conversions, thus their isobutene conversions were different. High yields of light olefins were obtained over the FeHZSM-5 and CrHZSM-5 zeolite catalysts with high ratio of SiO₂/Al₂O₃ (≥80). The ratio of SiO₂/Al₂O₃ has large effects on the surface area, and acidic characteristics of HZSM-5, FeHZSM-5 and CrHZSM-5 zeolites catalysts, and thus further affect their catalytic performances for isobutane cracking. That is the nature of SiO₂/Al₂O₃ ratio effect on the catalytic performances.     

高温水蒸汽处理对HZSM-5分子筛催化甲醇制丙烯的影响

考察不同硅铝比的HZSM-5分子筛催化剂和经过高温水蒸汽处理后的HZSM-5分子筛催化剂在甲醇制丙烯反应中的催化性能,考察温度和空速对催化反应的影响。结果表明,随着HZSM-5分子筛硅铝比的增加,产物中丙烯选择性增大,可能是分子筛的酸性降低所致;经过高温水蒸汽处理后的HZSM-5分子筛表面酸性降低,提高了催化剂的催化性能。在反应温度450 ℃和空速1.0 h^-1条件下,600 ℃高温水蒸汽处理后的催化剂HT-600的丙烯选择性从改性前的26.8%提高到33.5%。     

Suitable acidity of ZSM-5 for the isomerization of styrene oxide to phenylacetaldehyde

The effect of acidity of HZSM-5 (SiO₂/Al₂O₃ = 25–360) on isomerization of styrene oxide to phenylacetaldehyde was investigated under gas–phase free of solvents. The reaction was mainly catalyzed by the strong acid sites of HZSM-5 and catalyst lifetimes were affected by both acid strength and concentration. Trimerization of phenylacetaldehyde occurred at external acid sites, leading to a sharp decline in product selectivity. High Si/Al HZSM-5 (e.g., SiO₂/Al₂O₃ = 360), which contains weaker acid sites inside pores and trace amount of external acid sites, was found to be more effective with a higher stability and phenylacetaldehyde yield up to 95%.     

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.