Catalytic Combustion of Methane over High Copper-Loading ZSM-5 Catalysts

Two series of Cu/ZSM-5 catalysts,loading from 5 to 20 wt% CuO,were prepared by the deposition-precipitation and impregnation methods,respectively.The catalysts prepared by the impreg- nation method showed better catalytic performances than those prepared by the deposition-precipitation method and the increase of copper loading favored methane conversion.20Cu(I)/ZSM-5 had the highest activity with T_(90%)of 746 K,and for 20Cu(D)/ZSM-5,T_(90%)was as high as 804 K.The characteriza- tion of X-ray diffraction(XRD),temperature-programmed reduction(TPR),temperature-programmed desorption(TPD),and X-ray photoelectron spectroscopy(XPS)revealed that the dispersion of cop- per species could be improved by using the deposition-precipitation method instead of the impregnation method,but the fraction of surface CuO,corresponding to active sites for methane oxidation,was larger on 20Cu(I)/ZSM-5 than 20Cu(D)/ZSM-5.The results of Pyridine-Fourier transform infrared spectrum (Py-FT-IR)showed that a majority of Lewis acidity and a minority of Brφnsted acidity were present on Cu/ZSM-5 catalysts.20Cu(I)/ZSM-5 presented more Lewis acid sites.The number of Lewis acid sites changed significantly with preadsorption of oxygen.Adsorption of methane and oxygen on acid sites was observed.The properties of Cu/ZSM-5 catalysts were correlated with the activity for methane oxidation.     

Synthesis and Characterization of ZSM-5/β Co-Crystalline Zeolite

ZSM-5/β co-crystalline zeolites with different content of ZSM-5 have been synthesized by adding different amount of ZSM-5 to the synthetic system of β zeolite with NaAlO2, silica sol as the source of aluminum and silica, respectively, and TEA as the template under controlled condition of the synthesis. The ZSM-5/β co-crystalline zeolite was studied by XRD, SEM, BET and NH3-TPD. The reaction activity of toluene alkylation was investigated with a mixture of toluene-methanol as the feedstock in a pulse micro-reactor over the ZSM-5/β co-crystalline zeolite. It is found that ZSM-5/β co-crystalline zeolite has two kinds of zeolite structure including ZSM-5 and β zeolite, not in the form of a physical mixture. The pore structure of ZSM-5/β co-crystalline zeolites is different from that for β zeolite, ZSM-5 and their physical mixture. In addition, the peaks of both high and low temperature desorption of ammonia over the ZSM-5/β co-crystalline zeolite shift 23 ℃ to lower temperatures and the acid amount of its strong acid is 3% more than the physical mixture. So the ZSM-5/β co-crystalline zeolite produces the highest content of xylene, which is 10.4% higher than the physical mixture. And the ZSM-5/β co-crystalline zeolite has better selectivity for toluene alkylation and weaker de-methylation than β zeolite, ZSM-5 and their physical mixture.     

Synthesis and Characterization of ZSM-5/β Co-Crystalline Zeolite

ZSM-5/β co-crystalline zeolites with different content of ZSM-5 have been synthesized by adding different amount of ZSM-5 to the synthetic system ofβ zeolite with NaAlO2, silica sol as the source of aluminum and silica, respectively, and TEA as the template under controlled condition of the synthesis. The ZSM-5/β co-crystalline zeolite was studied by XRD, SEM, BET and NH3-TPD. The reaction activity of toluene alkylation was investigated with a mixture of toluene-methanol as the feedstock in a pulse micro-reactor over the ZSM-5/β co-crystalline zeolite. It is found that ZSM-5/β co-crystalline zeolite has two kinds of zeolite structure including ZSM-5 and β zeolite, not in the form of a physical mixture. The pore structure of ZSM-5/β co-crystalline zeolites is different from that forβ zeolite, ZSM-5and their physical mixture. In addition, the peaks of both high and low temperature desorption of ammonia over the ZSM-5/β co-crystalline zeolite shift 23 ℃ to lower temperatures and the acid amount of its strong acid is 3% more than the physical mixture. So the ZSM-5/β co-crystalline zeolite produces the highest content of xylene, which is 10.4% higher than the physical mixture. And the ZSM-5/β co-crystalline zeolite has better selectivity for toluene alkylation and weaker de-methylation than β zeolite, ZSM-5 and their physical mixture.     

Zn-Co bimetallic supported ZSM-5 catalyst for phosgene-free synthesis of hexamethylene–1,6–diisocyanate by thermal decomposition of hexamethylene–1,6–dicarbamate

A set of mono-and bimetallic(Zn-Co) supported ZSM-5 catalysts was first prepared by PEG-additive method. The physicochemical properties of the catalysts were investigated by FTIR, XPS, XRD, N_2adsorption-desorption measurements, SEM, EDS and NH3-TPD techniques. The physicochemical properties showed that the Zn Co_2O_4 spinel oxide was formed on the ZSM-5 support and provided effectual synergetic effect between Zn and Co species for the bimetallic catalyst. Furthermore, bimetallic supported ZSM-5 catalyst exhibited weak, moderate and strong acidic sites, while the monometallic supported ZSM-5 catalyst showed only weak and moderate or strong acidic sites. Their catalytic performances for thermal decomposition of hexamethylene–1,6–dicarbamate(HDC) to hexamethylene–1,6–diisocyanate(HDI) were then studied. It was found that the bimetallic supported ZSM-5 catalysts,especially Zn-2Co/ZSM-5 catalyst showed excellent catalytic performance due to the good synergetic effect between Co and Zn species, which provided a suitable contribution of acidic sites. HDC conversion of 100% with HDI selectivity of 91.2% and by-products selectivity of 1.3% could be achieved within short reaction time of 2.5 h over Zn-2Co/ZSM-5 catalyst.     

CeAlPO-5分子筛催化剂上二苯基甲烷选择性氧化生成二苯甲酮(英文)

Selective oxidation of diphenylmethane to benzophenone requires active and selective catalysts. The framework incorporation of cerium in AlPO-5 molecular sieves creates active cerium sites in isolation. These active sites are responsible for selective oxidation. Cerium incorporated AlPO-5 with different Al/Ce ratios were synthesized, and the vapor phase oxidation of diphenylmethane in air over these catalysts was studied at 250, 275, 300, 325, and 350 °C. The diphenylmethane conversion and selectivity for benzophenone were more than 90%. CeAlPO-5(25) was found to be more active than other catalysts. The stability of the catalyst was verified by the time on stream study which indicated steady diphenylmethane conversion and benzophenone selectivity. Hence framework incorporated CeAlPO-5 molecular sieves are stable and active catalysts for the selective oxidation of diphenylmethane.     

Improved Performance of W／HZSM-5 Catalysts for Dehydroaromatization of Methane

The dehydroaramatization of methane over W-supported ZSM-5 with varying degrees of Li^ ion-exchanged catalysts was studied with and without oxygen at 1073 K and atmospheric pressure.Catalyst activity and stability were found to be influenced by the catalyst acidity related to BrSnsted acid sites and by the presence of oxygen in the feed. The NH3-TPD and FTIR-pyridine results demonstrated that partially exchanged of H^ ions by Li^ into the W/HZSM-5 catalysts could be used to control the amount of strong acid sites on the catalyst surface. Without oxygen, the 3WHLi-Z (5:1) catalyst that has strong acid sites equal to nearly 74% of the original strong acid sites in the parent HZSM-5 exhibited the highest methane conversion and selectivity towards aromatics. However, the catalyst deactivated in a five hour period. In the presence of oxygen, the catalyst activity and stability could be improved further.The results of this study revealed that a suitable amount of strong Bronsted acid sites as well as oxygen addition in the feed increased the catalyst activity and stability. The 3WHLi-Z(5:1) catalyst exhibited improved performance in the dehydroaromatization of methane.     

Dealuminated ZSM-5 Zeolite Catalyst for Ethylene Oligomerization to Liquid Fuels

Ethylene oligomerization using ZSM-5 zeolite was investigated to study the role of Bronsted acid sites in the formation of higher hydrocarbons. The oligomerization of olefins, dependent on the acidity of ZSM-5 zeolite, is an important step in the conversion of natural gas to liquid fuels. The framework Si/Al ratio reflects the number of potential acid sites and the acid strength of the ZSM-5 catalyst. ZSM-5 with the mole ratio SiO2/Al2O3 equal to 30 was dealuminated for different periods of time according to the acidic ion-exchange method to produce ZSM-5 with various Si/Al ratios. The FT-IR analysis revealed that the integrated framework aluminum band, non-framework aluminum band, and silanol groups areas of the ZSM-5 zeolites decreased after being dealuminated. The performance of the dealuminated zeolite was tested for ethylene oligomerization. The results demonstrated that the dealumination of ZSM-5 led to higher ethylene conversion, but the gasoline selectivity was reduced compared to the performance     

The effect of FER zeolite acid sites in methanol-to-dimethyl-ether catalytic dehydration

In this paper, the effect of acidity of zeolites with FER framework was studied in the methanol dehydration to dimethyl ether reaction, by comparing catalysts with different Si/Al ratios(namely 8, 30 and60). The aim of this work was to investigate how the acid sites concentration, strength, distribution and typology(Br?nsted and Lewis) affect methanol conversion, DME selectivity and coke formation. It was found that the aluminium content affects slightly acid sites strength whilst a relevant effect on acid sites concentration and distribution(Br?nsted/Lewis) was observed as 24% of Lewis sites were found on Alrichest samples, whilst less than 10% of Lewis acid sites were observed on FER at higher Si/Al ratio. All the investigated catalyst samples showed a selectivity toward DME always greater than 0.9 and samples with the lowest Si/Al ratio exhibit the best performances in terms of methanol conversion, approaching the theoretical equilibrium value(around 0.85) at temperatures below 200 °C. Turnover-frequency analysis suggests that this result seems to be related not only to the higher amount of acid sites but also that the presence of Lewis acid sites may play a significant role in converting methanol. On the other hand, the presence of Lewis acid sites, combined with a high acidity, promote the formation of by-products(mainly methane) and coke deposition during the reaction. As final evidence, all the investigated catalysts exhibit very high resistance to deactivation by coke deposition, over 60 h continuous test, and a GC–MS analysis of the coke deposited on the catalyst surface reveals tetra-methyl benzene as main component.     

Dealuminated ZSM—5 Zeolite Catalyst for Ethylene Oligomerization to Liquid Fuels

Ethylene oligomerization using ZSM-5 zeolite was investigated to study the role of Broensted acid sites in the formation of higher hydrocarbons,The oligomeriztion of olefins,dependent on the acidity of ZSM-5 zeolite ,is an important step in the conversion of natural gas to liquied fuels,The framework Si/Al ratio reflects the number of potential acid sites and the acid strength of the ZSM-5 catalyst,ZSM-5 with the mole ratio SiO2/Al2O3 equal to 30 was dealuminated for different periods of time according to the acidic ion-exchange method to produce ZSM-5 with various Si/Al ratios,The FT-IR analysis revealed that the integrated framework aluminum band,non-framework aluminum band,and silanol groups areas of the ZSM-5 zeolites decreased after being dealuminated,The performanc of the dealuminated zeolite was tested for ethylene oligomerization.The results demonstrated that the dealumination of ZSM-5 led to higher ethylene conversion,but the gasoline selectivity was reduced compared to the performance of a ZSM-5 zeolite ,The characterization results revealed the amount of aluminum in the zeolitic framework,the crystallinity of the ZSM-5 zeolite,and the Si/Al ration affected the formation of Broensted acid sites,The number of the Broensted acid sites on the catalyst active sites is important in the olefin conversion to liquied hydrocarbons.     

Effect of external surface of HZSM-5 zeolite on product distribution in the conversion of methanol to hydrocarbons

The external surface of HZSM-5 zeolite was passivated by liquid siliceous deposition and by acidic sites poisoning with lepidine, respectively. Then methanol-to-hydrocarbons （MTH） reaction was investigated over the above as-prepared catalysts and the dissoluble coke on these used catalysts was analyzed by GC-MS, to study the role of the external surface of HZSM-5 in the catalytic reaction. Comparison with the experi- mental results based on parent ZSM-5 showed that the product distribution of MTH reaction was obviously influenced by the external surface. Evidences were listed as follows： （1） the final product on parent HZSM-5 showed higher aromatic selectivity, lower olefin selectivity, lower ra- tio of C2/C3＋ aliphatics and higher ratio of C3/C4＋ aliphatics than the reaction mixture produced by the sole catalysis of acidic sites in HZSM-5 channel; （2） a little of pentamethylbenzene and hexamethylbenzene in the product on parent HZSM-5, was produced via multi-methylation of methylbenzene on the external surface. The above conclusion may also be suitable for MTH reaction over other zeolites with 10-ring channel.     

ZSM-5分子筛骨架铝落位对甲醇转化制芳烃催化性能影响

采用水热合成法,在合成过程中通过添加矿化剂、尿素和改变硅源,制备了不同骨架铝落位的ZSM-5分子筛。通过SEM、XRD、BET、XRF、MAS NMR、NH_3-TPD和Py-FTIR等表征手段对分子筛的形貌、织构、骨架铝落位和酸性进行了系统研究,同时考察了不同ZSM-5分子筛催化剂甲醇制芳烃的催化性能。研究结果表明,制备的ZSM-5分子筛均具有结晶度高和形貌均一等特点,但在骨架铝落位和酸性方面存在显著差异。椭球状ZSM-5分子筛的骨架铝主要分布于直通孔道或正弦孔道中,并表现出较多的酸性位。块状分子筛中骨架铝主要落位在孔道交叉处,且具有较低的强酸量。在甲醇制芳烃反应中,骨架铝主要位于直通或正弦孔道并表现出较多酸性位的椭球状ZSM-5分子筛催化剂具有较高的活性稳定性和芳烃选择性。     

Stabilization of Extra-Large-Pore Zeolite by Boron Substitution for the Production of Commercially Applicable Catalysts

Stable extra-large-pore zeolites are desirable for industrial purposes due to their ability to accommodate bulky reactants and diffusion through channels. Although there are several extra-large pore zeolites reported, stable ones are rare. Thus, their stabilization is a feasible strategy for industrial applications. Here, an extra-large-pore zeolite EWT with boron substitution is presented, and the resulting zeolite B-RZM-3 increased the thermal stability from 600 °C in its silica form to 850 °C. The crystal structure, determined by combining continuous rotation electron diffraction (cRED) and powder X-ray diffraction (PXRD), shows that B atoms preferentially substitute the interrupted (HO)T(OT)₃ (Q³) sites and are partially converted into 3-coordination to relax framework deformation upon heating. After Al-reinsertion post-treatment, Al-B-RZM-3 shows higher ethylbenzene selectivity and ethylene conversion rate per mol acid site than commercial ZSM-5 and Beta zeolite in benzene alkylation reaction. Synthesizing extra-large-pore zeolite in borosilicate form is a potential approach to stabilize interrupted zeolites for commercial applications.     

不同形貌ZSM-5分子筛的合成及苯-乙醇烷基化反应性能

采用水热法制备了环状、薄片、类球状聚集体和小晶粒4种不同形貌和尺寸的纳米ZSM-5分子筛,用XRD、SEM、BET和NH3-TPD对所合成分子筛进行了表征,并考察分子筛形貌对苯和乙醇烷基化性能的影响。实验结果表明：在相同的硅铝比下,不同形貌的分子筛具有相似的弱酸峰强度,短b轴和中空结构的存在会降低分子筛的强酸峰强度,分子筛的强酸峰强度直接影响烷基化性能;分子筛颗粒形貌对催化烷基化性能有较大影响,四种形貌分子筛催化苯和乙醇烷基化性能优劣顺序为：薄片ZSM-5>环状ZSM-5>类球状团聚体ZSM-5>小晶粒ZSM-5。其中,具有薄片结构的H-ZSM-5分子筛在烷基化反应过程中表现出最佳的催化性能。综合对比结果表明：较低的强酸强度、较大的比表面积和孔容、较多的直形孔道占比下,分子筛的烷基化性能最佳,产物乙苯的选择性越高。     

甲醇芳构化中催化剂酸性对脱烷基、烷基化和异构化反应的影响

在Zn/P/ZSM-5催化剂上研究了甲醇、二甲苯、甲苯和甲醇等不同进料下芳烃产品分布随反应积碳的变化, 发现催化剂积碳对芳构化反应、脱烷基反应和烷基化反应的影响不同. 在不同硅铝摩尔比(Si/Al 比)和Zn负载量的Zn/P/ZSM-5 催化剂上进行甲醇转化, 考察催化剂酸性位点强度、密度和类型与芳烃收率和产品分布之间的关系, 发现当强酸位点酸密度下降时, 脱烷基反应最先被抑制, 其次是芳构化反应和异构化反应, 而烷基化反应却不受影响. 在Si/Al 比为14, 3% (w) Zn 负载量的Zn/P/ZSM-5 催化剂上可得到75%左右的芳烃收率, 二甲苯收率在35%左右, 具有重要的工业应用前景.     

ZSM-5催化丙烯芳构化反应构效关系及反应特性

甲醇两步制芳烃反应中低碳烯烃芳构化反应稳定性优异,为分析其内在机制,制备了不同硅铝比(n_SiO2/n_Al2O3)及Zn负载量的ZSM-5催化剂,以丙烯芳构化为模型反应,分析ZSM-5表面酸性对低碳烯烃芳构化反应性能的影响规律,并探究反应微观特性。发现当硅铝比由150降至75时,增加的酸密度促进了烯烃氢转移芳构化过程,使芳烃选择性由31.0%增至34.4%,但丙烯直接参与的氢转移过程也被强化,使丙烷产物选择性由28.2%增至36.0%。引入Zn助剂可将部分Br?nsted酸转变为ZnLewis酸,强化烯烃脱氢芳构化过程,使芳烃选择性进一步显著增加到62.4%。丙烯芳构化过程中芳烃烷基化深度比甲醇芳构化过程低,提升总芳烃选择性的同时,也明显抑制了难溶性积碳的形成,使反应稳定性明显提升。由此得出,甲醇两步制芳烃过程中甲醇制低碳烯烃过程对甲醇的预先消耗,抑制了低碳烯烃芳构化反应芳烃产物的深度烷基化,是该反应表现出优异稳定性的重要原因。     

ROLE OF Ga AND Pt-Ga IN THE CONVERSION OF PROPANE OVER Ga/HZSM-5 AND Pt-Ga/HZSM-5

为获得较高的Ｃ２选择性，在加水（水蒸气）条件下，研究了添加ＣａＯ对甲烷氧化偶联Ｌａ２Ｏ３催化剂的影响。发现ＣａＯ的添加提高了Ｌａ２Ｏ３催化剂的活性，同时水的添加明显地提高了催化剂的Ｃ２选择性。在加水条件下，Ｌａ２Ｏ３－ＣａＯ催化剂获得了较好的结果，其ＣＨ４转换率为２０％，Ｃ２选择性超过８０％。利用ＸＲＤ和ＸＰＳ技术对催化剂进行了表征，并对加水和不加水条件下的催化剂性能与结构变化的关系进行了讨论     

碱金属化合物改性ZSM-5沸石的择形催化作用

经碱金属化合物改性的HZSM-5分子筛,能提高甲苯烷基化生成对二甲苯的选择性,降低二甲苯异构化活性。改性后沸石的表面总酸度下降,酸强度减弱,孔结构变化不明显。     

Ethylene Dehydroaromatization over Ga-ZSM-5 Catalysts: Nature and Role of Gallium Speciation

Bifunctional catalysis in zeolites possessing both Brønsted and Lewis acid sites offers unique opportunities to tailor shape selectivity and enhance catalyst performance. Here, we examine the impact of framework and extra-framework gallium species on enriched aromatics production in zeolite ZSM-5. We compare three distinct methods of preparing Ga-ZSM-5 and reveal direct (single step) synthesis leads to optimal catalysts compared to post-synthesis methods. Using a combination of state-of-the-art characterization, catalyst testing, and density functional theory calculations, we show that Ga Lewis acid sites strongly favor aromatization. Our findings also suggest Ga(framework)–Ga(extra-framework) pairings, which can only be achieved in materials prepared by direct synthesis, are the most energetically favorable sites for reaction pathways leading to aromatics. Calculated acid site exchange energies between extra-framework Ga at framework sites comprised of either Al or Ga reveal a site-specific preference for stabilizing Lewis acids, which is qualitatively consistent with experimental measurements. These findings indicate the possibility of tailoring Lewis acid siting by the placement of Ga heteroatoms at distinct tetrahedral sites in the zeolite framework, which can have a marked impact on catalyst performance relative to conventional H-ZSM-5.     

Ethylation and disproportionation of ethylbenzene over substituted AFI type molecular sieves

The vapour and liquid phase ethylation of ethylbenzene was performed over AlPO₄-5 and its substituted counter parts. The results obtained for vapour phase reactions have shown a higher catalytic activity at 350 and 400 °C. The catalysts, however, exhibited a faster deactivation rate. The results obtained for liquid phase reaction have shown a higher selectivity for para-diethylbenzene (84.4%) than the vapour phase reaction (41.5%). MnAPO-5 was found to be active up to 240 h for the liquid phase reaction. para-Diethylbenzene, meta-diethylbenzene and polyalkylbenzene were the major products obtained for ethylation of ethylbenzene. When ethylbenzene passed over MnAPO-5 yielded products, such as benzaldehyde, acetophenone, styrene and 2,3-diphenylbutane. This showed a preference for oxidation rather than disproportionation followed by alkylation. Notwithstanding the better acid characteristics of ZSM-5, MnAPO-5 could be a better choice for this class of reaction essentially due to its higher para selectivity.     

表面富硅型ZSM-5分子筛的甲醇制对二甲苯联产低碳烯烃催化性能

通过表面化学改性制备表面富硅型ZSM-5分子筛,采用XRD、N2等温吸附-脱附、TEM、NH3-TPD和Py-FTIR等手段对其孔结构和酸性质进行了表征,考察其甲醇制对二甲苯联产低碳烯烃反应的催化性能。结果表明,引入Zn使催化剂中一部分强酸转变为中强酸,并增加了具有脱氢作用的Zn-L酸中心,提高乙烯和丙烯的选择性;Mg改性不仅可以调节孔道的择形性,而且增加了L酸中心的数量,有利于PX的生成;不同硅源的多次硅沉积使得SiO₂可以更均匀地沉积在外表面,调变催化剂的酸性质和孔结构,从而进一步提高对二甲苯及乙烯和丙烯的选择性。最终,二甲苯中对位选择性可达到87.1%,二甲苯及乙烯和丙烯的选择性达到61%,乙烯在C₂烃类的选择性高达97.8%,丙烯在C₃烃类中选择性高达90.6%。