ZSM-5/ZSM-57复合分子筛催化剂上混合C4烃的催化转化反应

以ZSM-5/ZSM-57复合分子筛为催化剂, 考察了其对混合C4烃催化转化的反应性能. 采用氨程序升温脱附(NH3-TPD)和吡啶吸附傅立叶变换红外(FT-IR)光谱技术表征复合分子筛的酸性质. 结果表明, 当复合分子筛中ZSM-5的含量较低时, 比ZSM-5具有更高的催化活性及乙烯和丙烯选择性, 这是因为此时复合分子筛酸强度较高、酸量较多, 且小孔ZSM-57有利于乙烯和丙烯的择形反应. 而当复合分子筛中ZSM-5的含量较高时, 具有较高的苯和甲苯选择性, 其原因可能是其孔结构及共晶生长时的结构匹配性对芳构化反应有利.     

Ru/ZSM-5催化葡萄糖选择性加氢制备山梨醇(英)

采用无有机模板剂一步法制备了Ru/ZSM-5催化剂,利用X射线衍射、N₂吸附-脱附、NH₃-程序升温脱附和CO₂-程序升温脱附、扫描电镜和透射电镜等方法对催化剂进行了表征.考察了反应温度、钌负载量和催化剂重复利用等因素对Ru/ZSM-5上葡萄糖加氢反应性能的影响,并与浸渍法制备的Ru/ZSM-5催化剂进行了对比.结果表明,与传统浸渍法相比,一步法制备的Ru/ZSM-5催化剂钌粒子具有更高的分散性和稳定性.在120℃和4 MPa的温和反应条件下,葡萄糖接近完全转化,山梨醇选择性高达99.2%,催化剂可重复利用5次,仍保持较高活性.     

ZSM-5／MOR复合分子筛催化剂对混合C4烃转化反应的催化性能

以ZSM-5/丝光沸石(MOR)复合分子筛为催化剂,对混合C4烃的催化转化反应进行了评价,并采用程序升温脱附和原位红外光谱技术对ZSM-5/MOR的酸性进行了表征. 结果表明,与ZSM-5相比, MOR具有很低的催化活性,但ZSM-5/MOR复合分子筛具有较高的催化活性,随着ZSM-5/MOR复合分子筛中ZSM-5含量的增加, C4烃转化率稍有升高;在C4烃转化率大致相同的情况下,乙烯和丙烯的总选择性比较接近,但苯和甲苯的总收率却快速升高. 随着ZSM-5/MOR复合分子筛中ZSM-5含量的增加,弱酸和中强酸的酸量逐渐减少,强酸的酸量有所增加. 由于ZSM-5/MOR复合分子筛中MOR对ZSM-5起到分散作用而产生更多的L酸中心,且此L酸中心处于分子筛的外表面而具有较高的能量,导致苯和甲苯的总收率升高.     

C−C Bond Formation in Syngas Conversion over Zinc Sites Grafted on ZSM-5 Zeolite

Despite significant progress achieved in Fischer–Tropsch synthesis (FTS) technology, control of product selectivity remains a challenge in syngas conversion. Herein, we demonstrate that Zn²⁺-ion exchanged ZSM-5 zeolite steers syngas conversion selectively to ethane with its selectivity reaching as high as 86 % among hydrocarbons (excluding CO₂) at 20 % CO conversion. NMR spectroscopy, X-ray absorption spectroscopy, and X-ray fluorescence indicate that this is likely attributed to the highly dispersed Zn sites grafted on ZSM-5. Quasi-in-situ solid-state NMR, obtained by quenching the reaction in liquid N₂, detects C₂ species such as acetyl (-COCH₃) bonding with an oxygen, ethyl (-CH₂CH₃) bonding with a Zn site, and epoxyethane molecules adsorbing on a Zn site and a Brønsted acid site of the catalyst, respectively. These species could provide insight into C−C bond formation during ethane formation. Interestingly, this selective reaction pathway toward ethane appears to be general because a series of other Zn²⁺-ion exchanged aluminosilicate zeolites with different topologies (for example, SSZ-13, MCM-22, and ZSM-12) all give ethane predominantly. By contrast, a physical mixture of ZnO-ZSM-5 favors formation of hydrocarbons beyond C₃₊. These results provide an important guide for tuning the product selectivity in syngas conversion.     

Methane to Liquid Hydrocarbons over Tungsten-ZSM-5 and Tungsten Loaded Cu/ZSM-5 Catalysts

Metal containing ZSM-5 can produce higher hydrocarbons in methane oxidation. Many researchers have studied the applicability of HZSM-5 and modify ZSM-5 for methane conversion to liquid hydrocarbons, but their research results still lead to low conversion, low selectivity and low heat resistance. The modified HZSM-5, by loading with tungsten (W), could enhance its heat resistant performance, and the high reaction temperature (800℃) did not lead to a loss of the W component by sublimation. The loading of HZSM-5 with tungsten and copper (Cu) resulted in an increment in the methane conversion as well as CO2 and C5 selectivities. In contrast, CO, C2-3 and H2O selectivities were reduced. The process of converting methane to liquid hydrocarbons (C5 ) was dependent on the metal surface area and the acidity of the zeolite. High methane conversion and C5 selectivity, and low H2O selectivity are obtained over W/3.0Cu/HZSM.     

A Doping Technique that Suppresses Undesirable H2 Evolution Derived from Overall Water Splitting in the Highly Selective Photocatalytic Conversion of CO2 in and by Water

Photocatalytic conversion of CO₂ to reduction products, such as CO, HCOOH, HCHO, CH₃OH, and CH₄, is one of the most attractive propositions for producing green energy by artificial photosynthesis. Herein, we found that Ga₂O₃ photocatalysts exhibit high conversion of CO₂. Doping of Zn species into Ga₂O₃ suppresses the H₂ evolution derived from overall water splitting and, consequently, Zn‐doped, Ag‐modified Ga₂O₃ exhibits higher selectivity toward CO evolution than bare, Ag‐modified Ga₂O₃. We observed stoichiometric amounts of evolved O₂ together with CO. Mass spectrometry clarified that the carbon source of the evolved CO is not the residual carbon species on the photocatalyst surface, but the CO₂ introduced in the gas phase. Doping of the photocatalyst with Zn is expected to ease the adsorption of CO₂ on the catalyst surface.     

Oxidative conversion of methane over MgO/ZSM-5 catalysts with different Si/Al ratios

It is found that the lower the Si/Al ratio of ZSM-5 in the catalytic system MgO/ZSM-5, the higher is the activity and selectivity in the reaction of oxidative conversion of methane. The catalytic properties reflect quite closely the basic properties of the samples, studied by means of temperature-programmed desorption of CO₂.     

Oxidative Hydroxylation of Benzene and Toluene by Nitrous Oxide Over Fe-Containing ZSM-5 Zeolites

The gas-phase partial oxidation of benzene and toluene to phenol and to cresols over Fe-containing ZSM-5 zeolites prepared by various methods was studied using N₂O as oxidant. Over FeZSM-5 synthesized by either isomorphous substitution or ion exchange the phenol selectivity reached nearly 100% at 573 K, however, only 25-30% cresol (mainly p-cresol) selectivity was observed in the oxidation of toluene because of the formation of benzaldehyde and benzoic acid in the fast oxidation of the methyl group.     

Cu functionalized nano crystalline ZSM-5 as efficient catalyst for selective oxidation of toluene

Nano crystalline ZSM-5 (NZ) functionalized with Cu has been explored for the selective oxidation of toluene to benzoic acid for the first time, where a comparison is made with the traditional microcrystalline ZSM-5 (MZ) based catalyst having similar framework Si/Al ratios at organic solvent-less reaction conditions in presence of H₂O₂ as a green oxidant. The ZSM-5 catalysts exhibited oxidation property even in the absence of any Cu species, but with low toluene conversions and benzoic acid yields. Functionalization with Cu greatly enhanced the benzoic acid formation, especially on NZ loaded with 0.4 wt% of Cu (Cu-NZ) to produce 92 wt% of benzoic acid, by virtue of the presence of highly dispersed nano particles of CuO along with Cu⁺² ions on the high surface area, mesopore possessing NZ support, revealed from XRD, N₂ adsorption-desorption, XPS, SEM, TEM, FITR, TPR and TPD analysis.     

Toluene Alkylation to Selective Formation of p-Xylene over Co-Crystalline ZSM-12/ZSM-5 Catalyst

The alkylation of toluene with methanol to selective formation of p-xylene has been systematically studied. ZSM-12 (MTW)/ZSM-5 co-crystalline zeolite in 40:60 proportions have been synthesized by the same molar gel composition, but at different temperatures and periods than that of ZSM-12 and ZSM-5, separately. All the prepared samples are characterized by XRD, SEM, BET, and XRF. The activity of toluene alkylation was investigated with a mixture of toluene and methanol as a feed over the ZSM-12, ZSM-12/ZSM-5 co-crystalline, ZSM-5, and physical mixture of ZSM-12/ZSM-5. Prom characterization, it is observed that the ZSM-12/ZSM-5 co-crystalline material is different from that of ZSM-12, ZSM-5, and their physical mixture. Further, the ZSM-12/ZSM-5 co-crystalline zeolite produces the highest content of xylene and has better selectivity for p-xylene than ZSM-12, ZSM-5, and their physical mixture.     

ZSM-5沸石结晶度对乙苯叔丁基化对位选择性的影响(英文)

Highly crystalline ZSM-5 zeolites are important for para-selective alkylation of alkyl aromatics, because they carry few external acid sites for isomerization of p-dialkyl products. Such zeolites (Si/Al = 25, 50, and 75) were synthesized in a fluoride medium between pH 4 and 6. Their crystallinities, crystal sizes, and surface areas were higher than those of a commercial ZSM-5 zeolite. Their para selectivities in alkylation were tested for vapor-phase tert-butylation of ethylbenzene between 200 and 400 °C. As expected, all the catalysts showed more than 90% para selectivity. At 300 °C, ethylbenzene conversion decreased in the order ZSM-5(25, commercial) > ZSM-5(25) > ZSM-5(50) > ZSM-5(75). The catalysts had weak, medium, and strong acid sites, but all the acid sites of ZSM-5(75) were weaker than those of ZSM-5(25) and ZSM-5(50). The high activity of commercial ZSM-5 was caused by its strong acid sites being stronger than those of the synthesized zeolites. Although the activity of the commercial catalyst was higher than those of the present catalysts, the selectivity for 4-t-butylethylbenzene (4-t-BEB) was low. The optimum feed ratio (ethylbenzene:t-butyl alcohol) was 2:1 and the feed rate was 1.65 h?1 for high ethylbenzene conversion and 4-t-BEB selectivity. Time-on-stream studies showed slow catalyst deactivation. Highly crystalline ZSM-5 zeolites are therefore better than a commercial zeolite for para-selective alkylation of alkyl aromatics. They do not require much post-modification for high para selectivity. A fluoride medium is therefore better than an alkaline medium for obtaining highly crystalline para-selective ZSM-5 zeolites.     

Catalytic Oxidation of Methane by Nitrous Oxide on H[Al]ZSM-5 Zeolite, Silicalite, and Amorphous SiO2 Modified by Iron, Silver, and Gadolinium Ions

Methane oxidation by an excess of N₂O on the catalytic sites formed in HZSM-5 zeolite, silicalite, and SiO₂ after modification with iron, silver, and gadolinium cations in different combinations is studied. Introduction of iron and silver ions into H[Al]ZSM-5 zeolite is shown to result in the formation of the sites that are active in methane oxidation, while the systems obtained on the basis of crystalline silicalite or amorphous SiO₂ demonstrate poor or no catalytic activity, respectively. Complete oxidation of methane with 100% conversion is observed on the Fe/HZSM-5 and Ag/HZSM-5 catalysts at temperatures higher than 350 and 450°C, respectively. A decrease in the reaction temperature and in the methane conversion is accompanied by coking of the catalysts and, in the case of Fe/HZSM-5, by the appearance of trace amounts of methanol and formic acid in the gas phase. The temperature dependence of the activity and selectivity for the Ag/HZSM-5 and (Ag + Gd)/HZSM-5 catalysts exhibits a pronounced hysteresis at 330–480°C, and the formation of coke proceeds much faster than in the case of iron-containing samples. Catalytic properties of (Fe + Ag)/HZSM-5 are similar to those of Fe/HZSM-5. The introduction of Gd does not influence significantly the activity and selectivity of the catalysts. ESR and TG–DTA were used to determine the state and distribution of Fe, Ag, and Gd in the samples and to examine the processes of coke formation.     

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     

Hydrocarbon Formation in the Catalytic Conversion of Methanol Over Zeolite ZSM-5

The reaction mechanism of methanol conversion to hydrocarbons on HZSM-5 zeolite was studied. From the selectivity plots of products in an integral fixed-bed flow reactor, paraffins were classified as primary and secondary stable products, light olefins as primary unstable products, aromatics as primary and secondary unstable or stable products. The results of the ¹⁴C-labelled methanol reaction indicated that the C₁–C₅ surface intermediates generated by dimethyl ether / methanol equilibrium gave paraffins and olefins at 300°C. The concentration of intermediates and adsorbed methanol on ZSM-5 decreased with increasing temperature. The distribution of radioactivity showed that propylene played an important role in the autocatalysis of the reaction.     

CO\begin{document}$ _{2} $\end{document} Reduction on Metal-Doped SnO\begin{document}$ _{2} $\end{document}(110) Surface Catalysts: Manipulating the Product by Changing the Ratio of Sn:O

The electrocatalytic carbon dioxide reduction reaction (CO₂RR) producing HCOOH and CO is one of the most promising approaches for storing renewable electricity as chemical energy in fuels. SnO₂ is a good catalyst for CO₂-to-HCOOH or CO₂-to-CO conversion, with different crystal planes participating the catalytic process. Among them, (110) surface SnO₂ is very stable and easy to synthesisze. By changing the ratio of Sn: O for SnO₂(110), we have two typical SnO₂ thin films: fully oxidized (stoichiometric) and partially reduced. In this work, we are concerned with different metals (Fe, Co, Ni, Cu, Ru, Rh, Pd, Ag, Os, Ir, Pt, and Au)-doped SnO₂(110) with different activity and selectivity for CO₂RR. All these changes are manipulated by adjusting the ratio of Sn: O in (110) surface. The results show that stochiometric and reduced Cu/Ag doped SnO₂(110) have different selectivity for CO₂RR. More specifically, stochiometric Cu/Ag-doped SnO₂(110) tends to generate CO(g). Meanwhile, the reduced surface tends to generate HCOOH(g). Moreover, we also considered the competitive hydrogen evolution reaction (HER). The catalysts SnO₂(110) doped by Ru, Rh, Pd, Os, Ir, and Pt have high activity for HER, and others are good catalysts for CO₂RR.     

Design and synthesis of the honeycomb PtSnNa/ZSM-5 monolithic catalyst for propane dehydrogenation

A novel PtSnNa/ZSM-5 monolithic catalyst was designed and synthesized for the propane dehydrogenation reaction, which was a significant transformation in industry. Experimental results showed that although the propane conversion and the propylene selectivity gradually fell down along with the reaction time, the descent speed of the PtSnNa/ZSM-5 monolithic catalyst was slower than that of the granule catalyst and the propane conversion and propylene selectivity of the reaction with monolithic catalyst still remained at a high level after 12 hr. The monolithic catalyst had regular pore structure that facilitated the separation of the product from the catalyst and reduced the limitation on internal and external diffusion and mass transfer, and led to the high catalytic activity and stability. The catalyst could be easily fabricated and was of highly industrial application potential.     

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.     

Gas Phase Selective Catalytic Oxidation of Toluene to Benzaldehyde on V2O5-Ag2O／η-Al2O3 Catalyst

Gas phase selective catalytic oxidation of toluene to benzaldehyde was studied on V2O5-Ag2O/η-Al2O3 catalyst prepared by impregnation. The catalyst was characterized by XRD, XPS, TEM,and FT-IR. The catalytic results showed that toluene conversion and selectivity for benzaldehyde on catalyst sample No.4 (V/(V Ag)=0.68) was higher than other catalysts with different V/Ag ratios. This was attributed to the higher surface area, larger pore volume and pore diameter of the catalyst sample No.4 than the other catalysts. The XRD patterns recorded from the catalyst before and after the oxidation reaction revealed that the new phases were developed, and this suggested that silver had entered the vanadium lattice. XPS results showed that the vanadium on the surface of No.4 and No.5 sample was more than that in the bulk, thus forming a vanadium rich layer on the surface. It was noted that when the catalyst was doped by potassium promoter, the toluene conversion and selectivity for benzalde hydewere higher than those on the undoped catalyst. This was attributed to the disordered structure of V2O5 lattice of the K-doped catalyst and a better interfacial contact between the particles.     

Ethanol electrooxidation on Pt/ZSM-5 zeolite-C catalyst

The electrooxidation of ethanol on Pt/ZSM-5 zeolite-C catalyst was investigated in sulfuric acid aqueous solution. Because of high stability in general acidic solution, ZSM-5 zeolite particles were selected as the support and the second catalyst. The micrograph and elemental composition of Pt/ZSM-5 zeolite particles were characterized by scanning electron microscopy and energy disperse X-ray spectroscopy. The electrocatalytic properties of Pt/ZSM-5 zeolite-C catalyst for ethanol oxidation have been investigated by cyclic voltammetry. Under the same Pt-loading mass and experimental conditions for ethanol oxidation, Pt/ZSM-5 zeolite-C catalyst shows higher activity than Pt/C catalyst. Additionally, Pt/ZSM-5 zeolite-C catalyst possesses good long-term cycle stability. The results indicate that Pt/ZSM-5 zeolite-C catalyst may have good potential application in direct ethanol fuel cell.     

Sustainable Synthesis of Core-Shell Structured ZSM-5@Silicalite-1 Zeolite

Core-shell structured ZSM-5@Silicalite-1 zeolite could effectively hinder the deactivation of catalyst surface. Currently, organic structure directing agents(OSDAs) are necessary in the conventional route for the synthesis of this core-shell zeolite under hydrothermal conditions, which is costly and environmental-unfriendly. In this research, a synthesis of the core-shell structured ZSM-5@Silicalite-1 zeolite with a strategy of alcohol filling and zeolite seeding without any organic template or solvent is exhibited. The obtained products are well characterized by X-ray powder diffractometer(XRD), scanning electron microscopy(SEM), transmission electron microscopy(TEM), N₂ sorption isotherms, solid magic angle spinning(MAS) NMR, temperature-programmed-desorption of ammonia(NH₃-TPD), and X-ray photoelectron spectroscopy(XPS) techniques, in order to confirm the core-shell structure. More importantly, the core-shell structured ZSM-5@Silicalite-1 zeolite exhibits a long lifetime and a high p-xylene selectivity in the alkylation of toluene with methanol, compared with the conventional ZSM-5 catalyst.