Catalysts For Aromatization Research Articles

Improved performance of hierarchical porous Mo/H-IM-5 catalyst in methane non-oxidative aromatization

Two novel hierarchical porous IM-5-S and IM-5-M materials were synthesized using mesoporous silica SBA-15 and MCM-48 as the silica sources, and for comparison conventional IM-5-C zeolite was also synthesized with the same synthesis composition. IM-5-S and IM-5-M samples exhibited larger crystal sizes and different textural properties than the conventional IM-5-C zeolite. Moreover, Mo-modified catalysts, Mo-IM-5-S, Mo-IM-5-M, and Mo-IM-5-C, were prepared for the non-oxidative aromatization of methane. The physical properties and acidities of the samples were characterized by XRD, SEM, TEM, BET, and NH3-TPD. Compared with Mo-IM-5-C, the Mo-IM-5-S and Mo-IM-5-M catalysts showed higher yields of aromatics and better stabilities. The preferable catalytic behaviors of Mo-modified mesoporous IM-5 catalysts may be attributed to the generation of secondary mesoporous systems within the zeolite crystals, which may influence the location and state of the active Mo species, simultaneously lead to easier access to the active sites for reactants and be favorable for the diffusion of products formed in the microporous channels during the methane aromatization reaction.

Synergy effect between hierarchical structured and Sn-modified H[Sn, Al]ZSM-5 zeolites on the catalysts for glycerol aromatization

Hierarchical H[Sn, Al]ZSM-5 zeolites were successfully prepared by hydrothermal method with directly incorporating Sn species into framework of HZSM-5 zeolites followed by alkali treatment. The prepared samples were characterized by XRD, BET, SEM-EDX, TEM, NH3-TPD, FT-IR and Py-IR. The results indicate that Sn species were successfully incorporated into HZSM-5 zeolites. The catalytic performances of all prepared zeolites were evaluated by glycerol aromatization. The highest catalytic performance of GTA synthesis was observed with H[Sn, Al]ZSM-5 treated with 0.3 M NaOH (32.1% carbon yield of BTX aromatics and 13 h catalyst lifetime), which was prior to the pure HZSM-5 (17.8% carbon yield of BTX aromatics and 3 h catalyst lifetime). The remarkably improved performance in catalytic activity and stability of H[Sn, Al]ZSM-5/0.3AT zeolitize could be attributed to synergy effect between Sn species doped into HZSM-5 zeolite and the generated micro-mesoporous structure by alkali treatment.

Upgrading of stranded gas via non-oxidative conversion processes

Ethane aromatization was carried out using metal promoted ZSM-5 catalysts. Desired products including ethylene and aromatics were obtained over Pt and Mo promoted ZSM-5 zeolite under reaction conditions of 600°C, 0.1MPa and GHSV=1000h−1. Results indicated that aromatics were formed via ethylene intermediate. Although ethane conversion and selectivity to aromatics were influenced by metal promoters, the distribution of benzene, toluene, xylenes and C9 aromatics depends mainly on the shape selective property of the ZSM-5. Ethane aromatization catalyst deactivated over time due to carbon deposition and metal leaching. Although oxidative regeneration could recovered 90% activity, the catalyst deactivated even faster after regeneration. For the purpose of economic comparison between direct and indirect natural gas conversion, the performance of edge coated Co-Re/γ-Al2O3 Fischer-Tropsch synthesis catalyst was presented. Even with capital savings on downstream refining, indirect natural gas conversion shows lower internal rate of return (IRR), largely because of higher capital and operating costs in syngas production.

Physicochemical and catalytic properties of Ga and In pentasils in the reaction of propane aromatization

Ga and In ZSM-5 zeolites are obtained via hydrothermal crystallization from alkali aluminosilicate gels. Their physicochemical and catalytic properties during conversion of propane into aromatic hydrocarbons are studied. These catalysts exhibit different activity and selectivity in propane aromatization process due to their specific physicochemical properties and the localization of promoter atoms in different sites of the zeolite structure. A zeolite containing 1.85 wt % of gallium oxide is the most effective catalyst for propane aromatization.

Green Synthesis and Characterization of Bi2O3 Nanorods as Catalyst for Aromatization of 1,4-Dihydropyridines

Bismuth oxide (Bi2O3) nanorods was prepared via one pot sol-gel method using Bi(NO3)3.5H2O and starch (as template) in water under hydrothermal condition followed by calcination at 320˚C within 3 h. The resultant solid product was characterized by scanning electron microscope (SEM), X-ray diffraction (XRD), thermogravimetry (TGA), and FTIR techniques. Based on the obtained results, the formation of Bi2O3 nanoparticles and nanorods at lower and higher percentage of starch is promising. It was found that Bi2O3 nanorods catalyse the aromatization of 1,4-dihydropyridines (DHPs) with 100% conversion and 100% selectivity.

Studying Newly Synthesized and Developed 4-Hydroxy-3-Methoxybenzaldehyde Schiff Bases by UV Spectrophotometry and High Performance Liquid Chromatography

Green synthesis is the design of chemical products and processes that reduces or eliminates the use and generation of hazardous substances. Schiff bases of 4-hydroxy-3- methoxybenzaldehyde (vanillin) were prepared using various aromatic amines and base catalyst in the presence of aqueous media. High performance liquid chromatography (HPLC) and ultraviolet (UV) spectrophotometry methods were developed for qualitative study of the synthesized 4-hydroxy-3- methoxybenzaldehyde Schiff bases. HPLC was carried out by reversed phase on a C18 column with a mobile phase composed of acetonitrile and 0.5% triethyl amine (pH 4.5 adjusted with orthophosphoric acid (60:40, v/v)). UV measurements were performed at λmax 286 nm for compound V1 ((E)-4-(4-hydroxy-3-methoxybenzylideneamino)benzoic acid), λmax 336 nm for compound V2 ((E)-4-(4-hydroxy-3-methoxybenzylideneamino)phenol), and λmax 320 nm for compound V3 ((2-methoxy-4-(E)-(phenylimino)methyl)phenol). Both the HPLC and UV methods showed good reproducibility and precision and were successfully applied to study 4-hydroxy-3- methoxybenzaldehyde derivatives. The standard de-viations of relative peak area and retention times for 4-hydroxy-3-methoxybenzaldehyde derivatives were within 2% indicating the suitability of the system. The proposed economical methods can be applied for rou-tine analysis of 4-hydroxy-3-methoxybenzaldehyde derivatives of any type.

A Ni-Mg-Al layered triple hydroxide-supported Pd catalyst for heterogeneous acceptorless dehydrogenative aromatization.

In the presence of a Ni-Mg-Al layered triple hydroxide-supported Pd catalyst, the acceptorless dehydrogenative aromatization of a wide range of cyclohexanols/cyclohexanones and cyclohexylamines efficiently proceeded to give the corresponding phenols and anilines, respectively, in moderate to high yields with the liberation of molecular hydrogen.

Heterogeneous mesoporous manganese oxide catalyst for aerobic and additive-free oxidative aromatization of N-heterocycles.

Herein, we report a heterogeneous, aerobic, additive-free and environmentally benign catalytic protocol for oxidative aromatization of saturated nitrogen-heterocycles using a mesoporous manganese oxide material. The aromatized products can be separated by easy filtration and the catalyst is reusable for at least four cycles. Mechanistic investigation provides evidence for radical intermediates, a multi-electron redox cycle between Mn centers, and an oxygen exchange mechanism.

Promoted effect of zinc–nickel bimetallic oxides supported on HZSM-5 catalysts in aromatization of methanol

Zn/ZSM-5 (NZ2) and Zn/Ni/ZSM-5 (NZ3) as the catalysts for methanol to aromatics (MTA) were synthesized by a simple ultrasonic impregnation. The textural and acid properties of all catalysts were characterized using XRD, HRTEM, NH3-TPD, Py-IR, XPS, XRF and TG techniques. The XRD and HRTEM results showed that the basic zeolite structures were not affected much with the incorporation of Zn and Ni species. However, great changes have taken place in acid properties. The Py-IR and XPS results indicated that the Zn-Lewis acid sites (ZnOH+ species), which have stronger interaction with the zeolite framework compared with ZnO species, were generated at the expense of B acid sites with the incorporation of zinc species. Moreover, the product analysis results showed that the incorporation of zinc species promoted the primary aromatization by enhancing the dehydroaromatization and suppressing the cracking and subsequent H-transfer reaction. Furthermore, the addition of Ni species well inhibited the loss of zinc species by converting partial ZnO species to ZnOH+ species, and thus improved the aromatization activity and catalyst stability. The catalytic performance results showed that the NZ3 possess higher conversion of methanol in a longer time and lower average rate of coke formation compared with NZ2. In addition, the NZ3 also exhibited the highest yield of BTX as the reaction proceeds.

Catalytic conversion of propane to BTX over Ga, Zn, Mo, and Re impregnated ZSM-5 catalysts

A systematic study of the comparative performances of 1wt.% and 3wt.% Ga, 1wt.% and 3wt.% Zn, 3wt.% Mo, and 3wt.% Re impregnated ZSM-5 catalysts for propane aromatization is presented. It was found that methane, ethene, ethane, benzene, toluene, and xylene are the major products on all of these catalysts at typical propane aromatization temperature (∼550°C). 3% Zn/ZSM-5 catalyst shows the highest propane conversion among all the tested catalysts with approximately 56% total selectivity toward benzene, toluene, and xylene (i.e., BTX) but lower selectivity to methane, ethene, and ethane (i.e., light hydrocarbons). In sharp contrast, 3% Mo/ZSM-5 catalyst shows the lowest activity with lower BTX selectivity but as high as 52% total selectivity toward methane, ethene, and ethane. Further, calculations indicate that 1% Zn/ZSM-5 catalyst displays the highest H2 and BTX formation rates (mmol/s/mol–metal), followed by 1% Ga, 3% Re, 3% Zn, and 3% Ga impregnated ZSM-5 catalysts, while 3% Mo/ZSM-5 catalyst shows remarkably lower H2 and BTX formation rates. This suggests that the addition of 1% Zn into ZSM-5 via impregnation significantly improves the dehydrogenation and subsequent chain growth reaction as well as cyclization, thereby favoring propane aromatization. However, compared to other promoters (i.e., Zn, Ga, and Re), the promotional effect of Mo over ZSM-5 is insignificant for propane aromatization, thus resulting in substantial formation of methane, ethene, and ethane.

Hierarchically micro-/mesoporous Pt/KL for alkane aromatization: Synergistic combination of high catalytic activity and suppressed hydrogenolysis

Pt/KL is a highly active and selective monofunctional catalyst for aromatization of n-alkanes due to its 1-dimensionally connected cage-like micropores. The unique micropore structure of the KL zeolite, however, can also inhibit the diffusion of bulky aromatic products out of the catalyst, which can cause unwanted side reactions that can decrease the aromatic yields. In this work, we investigated the effect of secondary mesoporosity, which can substantially facilitate molecular diffusion in Pt/KL during C6–C8 alkane aromatizations. The results showed that the hierarchically micro-/mesoporous Pt/KL synthesized with a subsequent dealumination/desilication method exhibited enhanced aromatic yields, compared with a conventional Pt/KL. In particular, in C7 and C8 aromatizations, the hierarchical Pt/KL showed substantially less formation of dealkylated aromatic products than the Pt/KL due to suppressed secondary hydrogenolysis. Pt supported on a solely mesoporous γ-Al2O3 also showed significantly suppressed secondary hydrogenolysis (dealkylation), which indicates that fast diffusion of alkylated aromatics out of the catalyst structure is important for suppressing the secondary hydrogenolysis. However, the solely mesoporous Pt/γ-Al2O3 showed markedly lower aromatization activities than the KL-supported catalysts, which indicates that Pt located inside the zeolite micropores is crucial for obtaining high catalytic activity due to the preorganization of n-alkanes in the micropores. The present results showed that the hierarchical Pt/KL provides the synergistically combined benefits of the Pt/KL and the mesoporous Pt catalyst, namely high aromatization activity and suppressed secondary hydrogenolysis, respectively.

Zinc containing methane aromatization catalyst, method of making a method of using the catalyst

Zinc containing methane aromatization catalyst, method of making a method of using the catalyst

Selective aromatization of biomass derived diisobutylene to p-xylene over supported non-noble metal catalysts

To obtain the valuable p-xylene from biomass with a high selectivity, several transition non-noble metals as main components of catalysts for aromatization of diisobutylene were explored. A volcano curve with the top marked by Cr(3d54s1) could be found between the activity and the atomic outer-shell electrons number of transition metals. The further addition of alkaline earth metal showed that the modification of surface properties by Mg doping could improve the catalytic performance. With Cr–Mg–Al–O as catalysts, the enhanced selectivity and single pass yield for the p-xylene formation could be obtained. Meanwhile, the side reaction of cracking could be suppressed, which might be attributed to the increment of the weak/strong acid ratio by Mg addition. Moreover, the catalysts kept a stable catalytic performance in the regeneration and reuse cycles.

Mitigation of Methane Selectivity on Pt/KL-Zeolite Aromatization Catalysts by Ag Promotion

Silver addition, in low amounts (0.0054 or 0.013 %), to a 1 %Pt/KL catalysts prepared by a sequential CVD procedure using acetylacetonates resulted in improved benzene selectivity at similar conversion levels compared to the undoped 1 %Pt/KL CVD catalyst. Both hydrogenolysis and aromatization require an ensemble of atoms to constitute the active site, but hydrogenolysis is more structure sensitive. Silver, which is a relatively inert metal catalyst, blocks a fraction of Pt surface sites, lowering the overall n-hexane rate. When added in low levels, silver disrupts to a greater degree the Pt ensembles responsible for hydrogenolysis relative to those required for aromatization. This was confirmed by DRIFTS of adsorbed CO measurements, which showed that higher wavenumber bands attributed to larger Pt ensembles were suppressed to a greater extent relative to lower wavenumber bands (i.e., arising from smaller ensembles).

Vanadium(iv and v) complexes of pyrazolone based ligands: Synthesis, structural characterization and catalytic applications.

The ONO donor ligands obtained from the condensation of 4-benzoyl-3-methyl-1-phenyl-2-pyrazoline-5-one (Hbp) with benzoylhydrazide (H2bp-bhz I), furoylhydrazide (H2bp-fah II), nicotinoylhydrazide (H2bp-nah III) and isonicotinoylhydrazide (H2bp-inh IV), upon treatment with [VIVO(acac)2], lead to the formation of [VIVO(bp-bhz)(H2O)] 1, [VIVO(bp-fah)(H2O)] 2, [VIVO(bp-nah)(H2O)] 3 and [VIVO(bp-inh)(H2O)] 4, respectively. At neutral pH the in situ generated aqueous K[H2VVO4] reacts with ligands I and II, forming potassium salts, K(H2O)2[VVO2(bp-bhz)] 5 and K(H2O)2[VVO2(bp-fah)] 6, while ligands III and IV give neutral complexes, [VVO2(Hbp-nah)] 9 and [VVO2(Hbp-inh)] 10, respectively. Acidification of aqueous solutions of 5 and 6 with HCl also gives neutral complexes [VVO2(Hbp-bhz)] 7 and [VVO2(Hbp-fah)] 8, respectively. Complexes 1-4, upon slow aerial oxidation in methanol, convert into monooxidovanadium(v) complexes, [VVO(bp-bhz)(OMe)] 11, [VVO(bp-fah)(OMe)] 12, [VVO(bp-nah)(OMe)] 13 and [VVO(bp-inh)(OMe)] 14, respectively. All complexes were characterized by various spectroscopic techniques like FT-IR, UV-visible, EPR (for complexes 1-4) and NMR (1H, 13C and 51V), elemental analysis, thermogravimetry and single crystal X-ray diffraction (for complexes 5-10 and 12). In the solid state, all complexes characterized by X-ray diffraction show the metal ion 5-coordinated in a distorted square pyramidal geometry. Complexes 11-14 were tested as catalysts for the one-pot three-component (ethylacetoacetate, benzaldehyde and ammonium acetate) dynamic covalent assembly, via Hantzsch reaction, using hydrogen peroxide as oxidant in solution and under solvent-free conditions. The complexes are also active catalysts for the oxidation of tetralin to tetralone with H2O2 as oxidant. The influence of the amounts of catalyst and oxidant, and solvent, temperature and time on the catalyzed reactions was investigated.

Mesoporous ZnZSM-5 zeolites synthesized by one-step desilication and reassembly: a durable catalyst for methanol aromatization

A mesoporous ZnZSM-5 zeolite synthesized by simple alkaline desilication and CTAB-mediated reassembly shows obviously improved catalytic stability for methanol aromatization.

Alkaline modification of ZSM-5 catalysts for methanol aromatization: The effect of the alkaline concentration

The effects of alkaline treatment on the physical properties of ZSM-5 catalysts and on their activities for methanol to aromatics conversion have been investigated. A mild alkaline treatment (0.2 and 0.3 mol/L NaOH) created mesopores in the parent zeolite with no obvious effect on acidity. The presence of mesopores gives the catalyst a longer lifetime and higher selectivity for aromatics. Treatment with 0.4 mol/L NaOH decreased the number of Bronsted acid sites due to dealumination and desilication, which resulted in a lower deactivation rate. In addition, more mesopores were produced than with the mild alkaline treatment. As a result, the lifetime of the sample treated with 0.4 mol/L NaOH was almost five times that of the parent ZSM-5. Treatment with a higher alkaline concentration (0.5 mol/L) greatly reduced the number of Bronsted acid sites and the number of micropores resulting in incomplete methanol conversion. When the alkaline-treated catalysts were washed with acid, some of the porosity was restored and a slight increase in selectivity for aromatics was obtained.

The Improvement of FCC Gasoline Aromatization for Olefins Reduction With Modified Nano-scale HZSM-5

The aromatization and olefin-reduction catalyst M has been applied in commercial unit for HDS desulfurization and olefin-reduction process with the heavy fraction of Fluid Catalytic Cracking gasoline. To solve the problems at higher reaction temperature, a series of modification procedures are taken on catalyst M. The characterization of four types of nano-scale HZMS-5 is conducted by XRD, Py-FT-IR, TEM, and BET analysis for the catalyst M modification. A modified catalyst M-II is successfully developed. Compared with catalyst M, the aromatics increases more than 1.3% and RON is 0.7 higher at the equivalent level of olefin reduction.

Aromatization of Propane over Element-Alumosilicate Catalysts with ZSM-5 Structure

A method of hydrothermal crystallization of alkaline alumosilicagels is used to manufacture element-alumosilicates with ZSM-5 structure. Their physicochemical and acid properties are investigated and their catalytic activity in the course of propane conversion to aromatic hydrocarbons is determined. The Ga-alumosilicate is found to be the most efficient zeolite catalyst for propane aromatization.

Interaction between Ni and HZSM-5 in aromatization-enhanced reactive adsorption desulfurization catalysts for FCC gasoline upgrading

A compound catalyst (RA) consisted of Ni, ZnO and HZSM-5 with functions of reactive adsorption desulfurization (RADS) and olefin aromatization for fluid catalytic cracking (FCC) gasoline upgrading was prepared. X-ray powder diffraction (XRD), temperature-programmed reduction and low-temperature N2 adsorption were used to characterize the properties of the catalysts. Performance evaluation by FCC gasoline was carried out, and the result showed that the catalyst RA performed well in desulfurization and aromatization. For comparison, RADS catalyst (represented by DS) consisted of Ni and ZnO and aromatization catalyst (represented by Ar) consisted of HZSM-5 were prepared, respectively. They were combined in different ways to help investigating interaction between Ni and HZSM-5. Performance evaluated by FCC gasoline showed that catalyst RA performed best in desulfurization with a slight octane number loss. Interaction between Ni and HZSM-5 is a significant factor which influences the performance of the catalyst.