Effect of metal/acid balance in Pt-loaded large pore zeolites on the hydroisomerization ofn-Hexane andn-heptane

Large-pore zeolites H-Beta, H-Mordenite and H-Omega were loaded with platinum and applied for the hydroisomerization of n-hexane andn-heptane. The catalytic activity of Pt-loaded zeolite showed good correlation with the effective acidity probed by pyridine rather than with the total acidity probed by ammonia when equal amounts of metal sites are present. The selectivity to multibranched isomers over three different catalysts was found dependent upon the conversion ofn-paraffin. At low conversion, the selectivity to multibranched isomers was higher over Pt-load-ed zeolites with high acid strength. At high conversion level, however, the selectivity was mainly governed by the metal/acid balance. On H-Mordenite and H-Omega, large amount of strong acid sites are located in the small pore or cage. In Pt/H-MOR, the metal/acid balance was poor because there was detrimental loss of metal sites caused by isolation of Pt in the side pockets of 8-MR and/or pore blockage of the linear 12-MR channel. Even though the acidity of H-Beta was very low compared to H-MOR and H-Omega, Pt/H-Beta yielded the best performance for the hydroisomerization ofn-paraffin because of better metal/acid balance in Pt/H-Beta.     

正十二烷在Pt/ZSM-22和Pt/ZSM-23上的加氢异构反应性能

采用常规水热合成法合成了ZSM-22和ZSM-23分子筛,进而制备了分别含有上述分子筛的催化剂,并借助XRD、SEM、NH3-TPD和Py-IR表征了这两种分子筛和催化剂的结构和酸性,同时以正十二烷为模型化合物,采用固定床反应器研究了Pt/ZSM-22和Pt/ZSM-23催化剂上正十二烷加氢异构反应性能。结果表明,在这种模型反应基础上,催化剂的反应活性和选择性主要取决于催化剂的酸量和酸强度以及酸分布,相对而言,ZSM-22分子筛催化剂由于其弱酸和中等强度酸的含量较高,具有更佳的异构化选择性。     

Hydroisomerization of long-chain paraffins: Mechanism and catalysts. Part I

A review of the literature on the catalysts of hydroisomerization of long-chain paraffins is presented. Part I describes the mechanisms of paraffin hydroisomerizations and presents an analysis of data on the catalysts of hydroisomerization based on zeolites of various types. Part II is devoted to catalysts based on structured mesoporous materials, partially reduced molybdenum oxides and oxycarbides, and mixtures of tungsten and zirconium oxides. Industrial catalysts that have found use in isodewaxing of diesel fuels and oils are described.     

Mn-Containing AlPO-11 and SAPO-11 Catalysts for Simultaneous Isomerization and Dehydrogenation of n-Butane

Ferrierite-based catalysts have been evaluated in 1-butene isomerization using a continuous flow reactor operating under microwave and conventional heating conditions. The key feature of this study is the application of a single-mode microwave cavity, which can considerably enhance the heating efficiency compared to traditional microwave ovens. Our results demonstrate that the transformations of low polarity organic compounds over siliceous zeolites can be induced by microwave radiation. Despite the high power density in the utilized single-mode system, no structural degradation of the catalysts has been detected using FTIR and XRD. Our catalytic data confirm that medium-pore ferrierite is an effective isomerization catalyst providing high selectivity towards isobutene, particularly under conditions favoring the monomolecular reaction mechanism. The catalytic performance of ferrierite in the reactions carried out under microwave and conventional heating is very similar, although under the microwave irradiation this zeolite demonstrates a slightly higher yield and selectivity towards isobutene.     

Effect of pillared clays on the hydroisomerization of n-heptane

Different montmorillonites and saponites were pillared with Al polyoxocations to obtain catalytic supports for the hydroisomerization of n-heptane. The catalysts were characterized by different techniques such as X-ray diffraction, elemental analysis and N₂ adsoprtion. The temperature-programmed desorption of ammonia indicated that pillared clays exhibited moderate and strong acid sites. The concentration of the acid sites depended on the starting clays as well as the type of the clays. The pillared saponites are more effective for the hydroisomerization of n-heptane at 300 °C, however, it decreased over the Al-pillared montmorillonites, and mainly cracking products were obtained.     

A New <Emphasis Type="Italic">n</Emphasis>-Alkane Hydroisomerization Catalyst Modified with Nanosized Molybdenum Carbides and Its Catalytic Properties in Diesel Fraction Hydroisomerization. Part III: Comparison of the Catalytic Properties of Bifunctional SAPO-31 and SAPO-11 Based Catalysts

Part III of this work continues the study of the catalytic properties of new molybdenum carbide based hydroisomerization catalysts, which are resistant to sulfur compounds and allow the synthesis of waxy diesel fuels with the same quality characteristics as those of platinum-containing catalysts. The catalytic properties of such bifunctional catalysts as 7%Mo₂C/SAPO-31 (LCCH-2) and 7%Mo₂C/SAPO-11 (LCCH-2-2) in diesel fraction hydroisomerization in the temperature range of 320–400°C are compared. It is shown that LCCH-2 ensures a higher yield of the hydroisomerized diesel fraction with a lower freezing point as compared to LCCH-2-2 at temperatures above 320°C. The ratio between mono- and di-isomers in reaction products is analyzed. It is concluded that SAPO-31 based catalyst is more selective to the formation of terminal monosubstituted alkanes than SAPO-11 based catalyst. The resistance of both catalysts to deactivation with coke deposits (tests over 100 h at 320 and 360°C in hydroisomerization) is studied. It is established that LCCH-2-2 is less resistant to deactivation than LCCH-2. These findings are due to differences in acidity, the degree of uniformity in the distribution of acidic hydrogenating/dehydrogenating sites in the catalysts, and the structural type of their acidic supports.     

Theoretical and experimental study on the selectivity of dehydrogenation of α-limonene in ZSM-5 and zeolite-Y

Dehydrogenation of the natural terpene α-limonene to the industrially important p-cymene was studied over two zeolite-supported Pd catalysts, ZSM-5 and zeolite-Y. Reactor tests indicate that transalkylation of the p-cymene product can be avoided by employing the shape-selective properties of a medium-pore ZSM-5 catalyst. The diffusion properties of the three isomers of cymene were then calculated in the two zeolites using molecular mechanics. In case of ZSM-5, p-cymene was found to have the lowest barrier of the three isomers for diffusion through the straight, spherical channel of the zeolite. For zeolite-Y, differences in diffusivity for the three isomers were very small. Theory and experiments showed, in excellent agreement, that only ZSM-5 selectively produces p-cymene. This work shows that molecular mechanics is a powerful and reliable method for the screening of zeolites for performing shape-selective catalysis. This revised version was published online in July 2006 with corrections to the Cover Date.     

含双金属的超稳Y沸石负载SO2-4/ZrO2强酸性催化剂上正庚烷临氢异构化

用超稳Y沸石（USY）负载SO2-4/ZrO2固体超强酸，并以此为载体制备含Pt双金属催化剂，用XRD和H2-TPR表征了催化剂的物化性质，并在常压固定床反应器上考察催化剂的正庚烷临氢异构化反应性能。结果表明， USY负载了SO2-4/ZrO2和双金属以后仍能保持沸石原有结构；贵金属Pt、金属助剂以及ZrO2等在USY载体上能够高度分散。在含Pt的催化剂中掺杂了Cr或Al金属助剂以后，正庚烷异构化产物选择性有了明显的提高，且具有更好的稳定性和低温活性；在USY负载SO2-4/ZrO2和0.4%Pt的催化剂上，正庚烷的转化率为42.1%时，异构化产物的选择性只有69.6%，而在掺杂了与Pt摩尔比为5∶1的Cr或Al后，正庚烷的转化率分别为44.3%和42.1%时，异构化产物的选择性分别可提高到88.9%和89.5%。     

Diisopropyl ether one-step generation from acetone-rich feedstocks

A one-step integrated process for the generation of the high-octane fuel ether, diisopropyl ether (DIPE), from acetone-rich feedstocks has been demonstrated. Three continuous, downflow, reactor configurations have been considered, including a two-bed catalyst design separated by inerts, gradient multicatalyst combinations, and an integrated two-zone layout with differing catalyst compositions. The bifunctional catalysts have both hydrogenation and etherification/dehydration capabilities and may comprise groups IB, VIB, and VIII metals incorporated into acidic, large and medium-pore zeolites, groups III or IV metal oxides, as well as heteropoly acid structures. DIPE syntheses are typically conducted at 100–165°C, under hydrogen pressure. The gradient reactor design, with careful choice of hydrogenation and etherification catalysts, allows DIPE to be generated in high selectivity and productivity. This revised version was published online in July 2006 with corrections to the Cover Date.     

正构烷烃临氢异构化催化剂研究进展

随环保法规和燃料质量要求逐步严格,作为生产高辛烷值汽油、低凝点柴油和高黏度指数润滑油的重要工艺技术,正构烷烃临氢异构化反应至关重要。本文综述了临氢异构化反应中的双功能催化剂是由提供加氢/脱氢活性的金属中心和用于骨架异构化的酸性载体组成。介绍了双功能催化剂中不同金属中心和酸性载体的贡献,相对于负载贵金属双功能催化剂,双金属、过渡金属磷化物及稀土掺杂催化剂活性相当,抗硫性高,成本低。此外,介微孔分子筛不仅具有易于反应物和产物扩散的较大孔径,还具有适宜酸性,能够促进骨架异构化,用于临氢异构化催化剂的载体而受到广泛关注。最后探讨了影响双功能催化剂异构化性能主要因素取决于金属和酸性载体之间的平衡,即金属中心和酸中心比例及距离。当催化剂存在适宜金属中心/酸中心比例,且金属-酸中心距离处于纳米级范围时,催化活性和异构化产物选择性会更高。     

Simultaneous isomerization of n-heptane and saturation of benzene over Pt/Beta catalysts: The influence of zeolite crystal size on product selectivity and sulfur resistance

In this work we show that decreasing the zeolite crystal size has a clear benefit on product selectivity and sulfur resistance of Pt/Beta catalysts during the simultaneous hydroisomerization of n-heptane and hydrogenation of benzene. The higher isomerization selectivity of the catalyst prepared from a nanocrystalline Beta zeolite can be ascribed to a faster diffusion of the iso-C₇ products through the small crystallites preventing cracking reactions to occur, while the improved sulfur resistance can be related to a better dispersion of Pt owing to its higher surface area and mesoporosity.     

Catalytic cracking of vacuum gas oil on alumina/zeolites mixtures — Effects of precipitation pH of alumina and zeolite type on product distribution

Catalytic cracking of vacuum gas oil on aluminas mixed with steam-treated zeolites (SY and SM) was investigated at 500 °C using a micro-activity tester. The catalysts containing SY and alumina prepared at pH 9. 5 showed a higher conversion and more fraction of gasoline and K+D (kerosene+diesel) in products than those containing SM and alumina prepared at pH 7.8. This could be explained by acidic properties and pore structure of catalyst. The distribution of produced benzene, toluene and xylene on the catalyst containing SY or SM was different due to the pore size of zeolites. The difference in hydrogen transfer rate over the catalysts containing SY or SM leads to a different composition of unsaturated and saturated products.     

Performance of Pt/Al-SBA-15 catalysts in hydroisomerization of n-dodecane

A series of Al-SBA-15 materials with different Si/Al ratios have been prepared via a post-alumination procedure. The results show that Al species can be introduced into the SBA-15 framework. Only the medium acid sites can be observed on the Al-SBA-15 samples, and the number of acid sites decreases with the increase of the Si/Al ratio. The hydroisomerization activities of n-dodecane over 1% Pt/Al-SBA-15-n catalysts increase with the number of acid sites, and the largest isomers yield reaches to 51%. It suggests that the Al-SBA-15 material is a suitable acid component for bifunctional catalysts for hydroisomerization of long chain n-paraffins.     

催化裂化汽油在多元沸石基催化剂上加氢改质研究

采用浸渍法分别制备了以丝光沸石（HM）、Hβ和HZSM-5及其组合为载体的沸石基Ni-Mo-P催化剂,考察了载体组成对催化裂化汽油加氢改质反应性能的影响。结果表明,由适宜比例的三者组合得到的沸石基Ni-Mo-P催化剂具有良好的加氢异构化、脱硫、芳构化活性及稳定性,可在催化裂化汽油脱硫降烯烃的同时保证产品的辛烷值不降低。考察了工艺条件对三元沸石基Ni-Mo-P催化剂反应性能的影响。在温度300 ℃、氢油体积比350、液相体积空速2.5 h-1和反应压力1.5 MPa反应条件下,催化裂化汽油异构烷烃收率、芳烃收率、脱硫率及液相收率分别达41.9%、31.7%、51.0%和98.3% 。     

Mesoporous zeolite single crystal catalysts: Diffusion and catalysis in hierarchical zeolites

During the last years, several new routes to produce zeolites with controlled mesoporosity have appeared. Moreover, an improved catalytic performance of the resulting mesoporous zeolites over conventional zeolites has been demonstrated in several reactions. In most cases, the mesoporous zeolites exhibit higher catalytic activity, but in some cases also improved selectivity and longer catalyst lifetime has been reported. The beneficial effects of introducing mesopores into the zeolites has in most instances been attributed to improved mass transport to and from the active sites located in the zeolite micropores. Here, we briefly discuss the most important ways of introducing mesopores into zeolites and, for the first time, we show experimentally that the presence of mesopores dramatically increases the rate of diffusion in zeolite catalysts. This is done by studying the elution of iso-butane from packed beds of conventional and mesoporous zeolite catalysts. Moreover, we discuss in detail the recent observation of improved activity and selectivity in the alkylation of benzene with ethene using mesoporous zeolite single crystal catalysts. For this reaction, we show by calculation of the Thiele modulus that this improved performance can be mainly attributed to a diffusional limitation of ethylbenzene in the zeolite pores. This is verified in new ethylbenzene dealkylation experiments where mesoporous zeolite catalysts show significantly improved activity over conventional zeolite catalysts.     

Disproportionation and Methylation of Toluene with Methanol Over Zeolite Catalysts

Zeolites TNU-9, SSZ-33, mordenite (MOR) and ZSM-5 were evaluated for their activities in toluene disproportionation and methylation reaction of toluene with methanol. The medium-pore zeolite TNU-9 was found to possess the highest conversion in toluene disproportionation as compared with SSZ-33, mordenite and ZSM-5 based catalyst. Zeolite mordenite with the highest Si/Al ratio of 135.9 (the lowest concentration of active sites) exhibited the highest toluene conversion and maximum xylene yield in toluene methylation. On mordenite, the presence of channel intersections allows more reaction space for the formation of bulky intermediates and/or products and the 12-ring channels on the other hand, allow diffusion without trapping, since the channel diameter is large enough. In toluene methylation, xylene selectivity at the same conversion level follows the order: ZSM-5 > TNU-9 > MOR > SSZ-33, which implies that xylene selectivity is directly related to the size of channels from medium to large pore zeolites. The medium-pore zeolite ZSM-5, with 10-ring channels, shows the lowest reactivity for further alkylation of xylene, while mordenite with 12-ring channel shows the highest reactivity for further alkylation of xylene.     

n-Heptane Hydroisomerization over Mesoporous Zeolites made by Utilizing Carbon Particles as the Template for Mesoporosity

Mesoporous zeolites were successfully synthesized by utilizing carbon black particles during the sol–gel synthesis as a template for the network of mesopores. Mesoporous samples of ZSM-12, and Zeolite Beta were synthesized with this method with an average pore size about 400 Å. The size and the percentage of mesopores increases with the C/Si ratio. Our TEM investigations validate the formation of mesoporous networks and voids. This study proves that this method can be generalized for both high and low aluminum zeolites. Selected samples were tested for the hydroisomerization of n-heptane, a probe reaction of great importance for the upgrading of light naphthas. It was found that under identical operating conditions the mesoporous samples exhibited higher, almost fourfold, activity. The selectivity for C7 isomers was higher over the mesoporous samples in comparison with the regular ones. More specifically, the selectivities towards mono- and dibranched isomers increases monotonically with the degree of mesoporosity. The increase of branching over the mesoporous zeolite samples we observed is due to the combined effect of reduced residence times in the zeolite crystal for the reaction products, and the larger “average” pores of the mesoporous samples that allow the formation of bulkier reaction state intermediates. Moreover, the mesoporous samples resulted in generation of less light hydrocarbons (C3, C4). The above behavior is a testimony of the tremendous potential that mesoporous zeolite crystals offer and could be very beneficial for numerous refining processes.     

Synthesis and structural characteristics of highly graphitized carbon nanofibers produced from the catalytic decomposition of ethylene: Influence of the active metal (Co, Ni, Fe) and the zeolite type support

In order to study the influence of the metal phase in the carbon yield and structural characteristics of carbon nanofibers (CNFs) synthesized by CVD over supported catalysts, different catalysts were prepared using iron, cobalt and nickel as active metal and zeolites Y and mordenite as support. The results showed that the metal precursor produced a great influence on the catalytic activity, fact that could be explained in according to the different solubility of carbon in the metals or in the differences in the diffusion and segregation of carbon through the metal particles. Characterization data of the solid carbon products revealed unique structures and textural properties as well as crystalline conditions on function of metal used. Additionally, support-metal interaction was evaluated, where experiments with similar nickel load over Y and mordenite zeolites were carried out, finding higher carbon yields and more ordered structures when Y zeolite was used.     

Hydroisomerization of n-dodecane over Pt/MeAPO-11 (Me = Mg,Mn, Co or Zn) catalysts

Mg-, Mn-, Co- and Zn-substituted AlPO-11 molecular sieves were synthesized, characterized and used as acidic supports of the bifunctional Pt/MeAPO-11 catalysts in the hydroisomerization of n-dodecane. As compared to AlPO-11, the acidity of MeAPO-11 increased considerably, while the metallic properties of Pt over MeAPO-11 was weakened, especially for Mn- and Co-containing catalysts. In the hydroisomerization of n-dodecane, the activity of Pt/MeAPO-11 was primarily determined by the acidic strength of MeAPO-11, whereas the isomerization selectivity was controlled by the combined effect of the acidity of MeAPO-11 and the (de)hydrogenation function of Pt.     

Pt/ZSM-35催化长链正构生物烷烃加氢裂化/异构化制航空煤油

以生物质油加氢脱氧得到的长链正构生物烷烃为原料，考察了H-MCM-49、H-ZSM-5、H-ZSM-22和 H-ZSM-35这4种不同分子筛催化剂的物化性质及其加氢裂化/异构化制生物航空煤油的性能。在此基础上，以H-ZSM-35分子筛为载体，制备并表征了一系列低负载量（0.1%、0.2%和0.3%）的Pt/ZSM-35双功能催化剂，以长链正构生物烷烃转化率、C₉~C₁₆产物选择性、生物航空煤油收率和异正比为指标，对其加氢裂化/异构化制生物航空煤油反应性能进行了评价，并对反应工艺条件进行优化。结果表明：H-ZSM-35的强酸中心强度高、酸量大，其结构中较小的孔口和较大的球型笼使其具有一定的容烃量和较好的择形性能，0.1%~0.3% Pt负载后， Pt/ZSM-35双功能催化剂表现出很好的加氢裂化/异构化活性和选择性。采用0.1% Pt/ZSM-35双功能催化剂在反应条件为320℃、1MPa、0.7h^-1、氢油比840∶1时，长链正构生物烷烃的转化率为84.3%，生物航空煤油收率达41.1%，产物异正比为1.34。81h长运转测试结果表明，该催化剂具有很好的稳定性。