H-beta Zeolite Catalyst Research Articles

One-pot three-component Kabachnik–Fields synthesis of α-aminophosphonates using H-beta zeolite catalyst

One-pot three-component Kabachnik–Fields synthesis of α-aminophosphonates with high yields from the reaction between carbonyl compound, primary amine, and substituted phosphite can be carried out in a short period, using H-beta zeolite as a reusable catalyst.

Efecto del uso de Catalizadores Ácidos Sobre la Distribución de Productos en la Pirólisis de Neumáticos

The thermal and catalytic pyrolysis of tyres in a high heating rate commercial microreactor has been studied by following two reaction strategies: in situ catalytic and thermal pyrolysis followed by on-line catalytic pyrolysis. The catalysts have been prepared based on HZSM-5, HY and HBeta zeolites and they have been used in situ in the pyrolysis reactor and on-line, in a fixed bed reactor. The use of the catalyst in situ decreases the pyrolysis temperature by 50 K (from 773K to 723 K) and significantly increases the yield of gas and C10- light aromatics. The shape selectivity of HZSM-5 zeolite and the higher micropore size and hydrogen transfer capacity of HY zeolite significantly affect product distribution. The HBeta zeolite catalyst has an intermediate behaviour. The yields of gases, C10aromatics and tar increase in the catalytic reforming of thermal pyrolysis.

The formation mechanism of Mo-methylidene species over Mo/HBeta catalysts for heterogeneous olefin metathesis: A density functional theory study

Density Functional Theory (DFT) calculations were performed to optimize the Mo active sites in HBeta zeolite catalysts as well as to locate the reaction pathways to form the Mo-methylidene species. Two different Mo active sites, i.e., the oxidized Mo VIO 2 and its reduced form Mo VO(OH), were developed and incorporated into HBeta zeolites by replacing a pair of Brønsted acidic sites. The Mo-methylidene species were found to be produced through two elementary reaction steps, and the Mo-oxametallacyclobutanes were identified as the intermediates. The activation barriers of the decompositions of the oxametallacyclobutane intermediates (Step 2) were estimated to be higher than those of the ethene addition on the Mo active sites (Step 1). The oxidation states of the Mo centers exerted marked influences on the stabilities of the intermediates as well as on the activation barriers and reaction heats of Steps 1 and 2, which were elucidated by the electronic properties of the O b-ligands directly bonded to the Mo centers. Both free energy barriers and reaction heats have indicated that the whole processes of generating the Mo-methylidene species were preferred over the Mo(VI) rather than Mo(V) active site. Accordingly, the Mo(VI) active site was more efficient in catalyzing the formation of Mo-methylidene species in the heterogeneous Mo/HBeta catalytic systems.

Olefins alkylation thiophenic sulfur of the real gasoline over the fluorinated Hbeta zeolite catalyst

The efficiency of the catalytic alkylation, the first step of the olefins alkylation thiophenic sulfur (OATS) process was investigated in three typical gasoline samples with different olefins contents over a fluorinated Hβ zeolite catalyst. Under the reaction conditions of 120 °C, 1.5 MPa and WHSV 0.5 h − 1 , over 95% light sulfur compounds in the feeds could be transformed to be heavier than the heptyl-thiophenes within a period of time-on-stream. The lifetime of the catalyst could prolong from 10 h to 26 h when the olefins content in the gasoline feed decreased from 40.87 wt.% to 9.20 wt.%. It was also found that the olefins content decrease was favorable for keeping and promoting the octane number by redistributing the components of the treated gasoline. In addition, the influence of the reaction conditions such as the temperature and WHSV on the efficiency of the catalytic alkylation was investigated.

Effect of acid catalysts on scrap tyre pyrolysis under fast heating conditions

A study has been carried out on the effect of acid catalysts prepared based on HZSM-5, HY and HBeta zeolites on the distribution of volatile products (gas, non-aromatic C 5–C 10 fraction, aromatic C 10 − and tar), in the pyrolysis of tyre material carried out in a fast heating microreactor. The results have been compared with those of thermal pyrolysis. The strategies of using the catalyst in situ and reforming the volatiles generated in thermal pyrolysis have also been compared. The use of a catalyst in situ lowers the pyrolysis temperature by 50 K (to 723 K) and produces a significant increase in the yield of gases and light aromatic C 10 − , at the expense of a decrease in the yield of non-aromatic C 10 − . The yield of tar increases only slightly. The shape selectivity of each zeolite has a significant effect and, consequently, HY zeolite leads to the formation of heavier structures that make up the tar and to aromatic C 10 − , which is favoured by hydrogen transfer capacity. HZSM-5 is more efficient for the formation of gases, although it contributes only to decreasing the molecular weight of aromatic C 10 − fraction. HBeta zeolite catalyst has an intermediate behaviour. Reforming pyrolysis volatiles at 723 K using a HZSM-5 zeolite catalyst efficiently increases (from 2 to 20 wt%) the yield of gases, with a high yield of ethene and propene. The yields of BTX fraction are also very high (around 11.5 wt%).

A Novel Radioisotope Method for Studying Catalytic Transformations over Alumina, H-ZSM-5 and H-Beta Zeolite Catalysts: Investigation of Conversion of11C-Labeled Methanol to11C-Labeled Dimethyl Ether and Hydrocarbons

A novel radiochemical method for investigating the catalytic transformations of the 11C-radioisotope labeled methanol over H-ZSM-5 and H-Beta zeolite catalysts has been introduced. The catalysis process was monitored by gamma detectors and the 11C-labeled products were analyzed by radio-gas chromatography. The medium pore H-ZSM-5 and H-Beta zeolite catalysts were synthesized and characterized using X-ray powder diffraction, scanning electron microscope, nitrogen adsorption, X-ray fluorescency and FTIR spectroscopy. The investigations of 11C-labeled product distributions and reaction mechanism of the conversion of [11C]methanol over H-ZSM-5 and H-Beta zeolite catalysts have been elaborated in terms of structure and acidity of the catalysts. In microreactors the effect of natural carbon compounds from environment can be a disturbing effect for the detection of inactive carbon products. Applied radio detection method eliminates these disturbing effects and detects only 11C-labeled compounds during the whole catalytic process. In the study of the transformations of carbon compounds, besides the well known 14C tracer technique and 13C MAS NMR spectroscopy investigation, the 11C-method is a new, more sensitive and simple one to monitor the transformation of the starting 11C-labeled compound by radio detectors (gamma detector) and for analyzing the 11C-labeled products by radio-gas chromatography.

Acetylation of 2-methoxynaphthalene in the presence of beta zeolites: influence of reaction conditions and textural properties of the catalysts

The Friedel-Crafts acetylation of 2-methoxynaphthalene (2-MN) in the liquid phase has been studied over three H-beta zeolite catalysts, featuring the same composition and acidity, but exhibiting different textural characteristics. The various catalysts led to significantly different yields of acetylated products, 1-acetyl-2-methoxynaphthalene (1-Ac-2-MN) and 2-acetyl-6-methoxynaphthalene (2-Ac-6-MN). On the basis of the relationship between the product yields and the textural characteristics of the samples, the formation of the two acetylated products has been assumed to occur at different locations: inside the micropores in the case of 2-Ac-6-MN and on the outer surface of the crystals in the case of 1-Ac-2-MN.

Tert-Butylation of biphenyl over H-Y and H-beta zeolites; formation and identification of main and by-products

tert-Butylation of biphenyl with tert-butanol has been studied over large-pore H-Y (15) and H-beta (25) zeolites under liquid phase conditions using cyclohexane as a solvent. The identification of main and by-products has been performed by GC-MS analysis. The main products of the alkylation reaction were mono- tert-butylbiphenyls and di-( tert-butyl)biphenyls with preferential formation of para- and para, para′-isomers. Higher alkylbiphenyls with alkyl group from C 4 to C 10′ were identified as by-products. These compounds can be formed by alkylation of biphenyl and/or mono- tert-butylbiphenyls with different alkenes, generated by dehydration of tert-butanol, followed by oligomerisation and disproportionation of the formed isobutylene. A peculiar effect of the small change in dimensions of micropores of H-beta (elliptic pores 0.76 nm×0.64 nm) in comparison with H-Y zeolite (circular pores 0.74 nm) has been reflected by the transalkylation of mono- tert-butylbiphenyls to cyclohexylbiphenyls and methylcyclopentylbiphenyls over the more acid H-beta zeolite catalyst, whereas this transalkylation has been not monitored in the experiments with H-Y zeolite. The occurrence of transalkylation reactions has been supported by thermodynamic analysis and calculations.

The conversion of methanol to hydrocarbons over zeolite H-beta

The conversion of methanol to hydrocarbons over an H-beta zeolite catalyst at 400°C has been investigated. The experiments were carried out at a methanol pressure of about 150 mbar, using a WHSV of 0.8 or 7.2 h −1. With WHSV=0.8 h −1 the methanol conversion was still 30% after 16 h on stream. There was a preponderance of saturated and aromatic hydrocarbons in the product. Ethene, propene, propane, isobutane, hexamethylbenzene and some pentamethylbenzene were the dominant products. Methane was initially a rather minor product, but with progressive catalyst deactivation it became a major product. Methanol was also converted over dealuminated H-mordenite and H-ZSM-5 under identical conditions. The aromatic products over these zeolites are quite different. Zeolite beta is selective for hexamethylbenzene and mordenite is selective for pentamethylbenzene, while ZSM-5 gives mostly di- and trimethylbenzenes and some small amounts of the slimmest tetramethylbenzene, i.e. durene. The product compositions are compared and discussed.

Liquid Phase Synthesis of MTBE from Methanol and Isobutene over Acid Zeolites and Amberlyst-15

The liquid phase synthesis of methyl tert-butyl ether (MTBE) from methanol and isobutene over H-Beta and US-Y zeolite catalysts was studied in the temperature range 30–120°C. Up to 100°C, commercial H-Beta zeolite samples with small crystal size were more active than acid Amberlyst-15 (reference catalyst) and noticeably more active than US-Y, confirming results obtained under vapour phase conditions. The influence of methanol/isobutene (MeOH/IB) molar ratio, pressure, and space time on the conversion and MTBE selectivity was investigated. At optimized reaction conditions, MTBE yields of 85–90% can be reached with zeolite H-Beta as well as Amberlyst-15. On zeolites, side reactions of isobutene are more important than on Amberlyst-15, necessitating operation at MeOH/IB ratios higher than 1 : 1. For the same reason, at high conversion on H-Beta, the MTBE yields are more sensitive to contact time compared to Amberlyst-15. On H-Beta zeolite, no deactivation was observed during a period of more than 50 h on stream at 65°C, 1.4 MPa pressure, and a WHSV of 14 h−1. The catalytic activity of the zeolites is related to the external specific surface area, and to the concentration of bridging hydroxyls and silanol groups in the mesopores. A zeolite H-Beta sample with a Si/Al ratio of 36 has an optimum silanol and bridging hydroxyl content leading to stoichiometric methanol and isobutene adsorption, highest activity and MTBE yields.

A novel catalytic method for the acylation of aromatics to the corresponding ketones over zeolite catalysts

A novel and convenient procedure for the catalytic acylation of a series of aromatic compounds such as benzene, toluene, xylenes (o-, m-, p-), mesitylene, isopropylbenzene and N,N-dimethylaniline to the corresponding ketones using medium- and large-pore zeolites as catalyst and acetic acid or acetyl chloride as acylating agent at different reaction temperatures in a tubular reactor is demonstrated for the first time. The H-ZSM5 and H-beta zeolite catalysts exhibited the higher turnover rates (TOF× 10-3 s-1 mol-1 Al) for the acetic acid or acetyl chloride conversion to the products. In some cases, nearly total conversion of acylating agent with very high selectivity to the para product is achieved. It is found that the reactivity of the aromatic compounds increases with the increase of -CH3 groups in the benzene ring. Mechanistically, it is assumed that an active species (CH3CO+) is generated catalytically from the acylating agent by an acidic zeolite which attacks the aromatic ring and produces corresponding aromatic ketones.