HBEA Zeolite Research Articles

Growth mechanism of coke on HBEA zeolite during ethanol transformation

HBEA (11) zeolite was deactivated rapidly by coking during the ethanol transformation into hydrocarbons, at 623K and 30bar. The nature of carbonaceous deposit was studied, after zeolite dissolution by hydrofluoric acid both by gas chromatography coupled with mass spectrometry and by matrix-assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF MS). The coke on the external zeolite surface was characterized directly on the spent catalyst by laser desorption/ionization time of flight mass spectrometry (LDI-TOF MS). The coke species were identified and classified into 17 families following their unsaturation number (4–23). The coke was polyaromatic, and it was very alkylated (methyl, ethyl, and propyl groups). It is compounded of alkylbenzenes, mainly hexamethylbenzene (HMB), and alkyl-pyrenes, located within the zeolite pore, which could migrate to the external zeolite surface and grow into polyaromatic compounds constituted up to eight aromatic rings and up to 40 carbon atoms. Pulsed electron paramagnetic resonance spectroscopy measurements and molecular simulation by using Cerius2 software have shown that HMBs are distant of 0.6nm inside the zeolite pores.

Aqueous Phase Hydroalkylation and Hydrodeoxygenation of Phenol by Dual Functional Catalysts Comprised of Pd/C and H/La-BEA

Aqueous phase catalytic phenol hydroalkylation and hydrodeoxygenation have been explored using Pd/C combined with zeolite H-BEA and La-BEA catalysts in the presence of H2. The individual steps of phenol hydrogenation, cyclohexanol dehydration, or alkylation with phenol were individually investigated to gain insight into the relative rates in the cascade reactions of phenol hydroalkylation. The hydroalkylation rate, determined by the concentrations of phenol and cyclohexanol in phenol hydroalkylation, required the hydrogenation rate to be relatively slow. The optimized H+/Pd ratio was 21, which allowed achieving comparable cyclohexanol formation rates via phenol hydrogenation and consumption rates from alkylation with phenol in phenol hydroalkylation. La-BEA was shown to be more selective for hydroalkylation than H-BEA in combination with Pd/C, because cyclohexanol dehydration was retarded selectively compared to alkylation of phenol. This indicates that dehydration is solely catalyzed by Bronsted acid sit...

Selective gas phase hydrogenation of maleic anhydride over Ni-supported catalysts: Effect of support on the catalytic performance

The gas phase hydrogenation of maleic anhydride to obtain γ-butyrolactone was studied using Ni supported on SiO2, SiO2–Al2O3 and zeolite H-BEA as catalysts. The samples were prepared by incipient wetness impregnation and characterized by N2 adsorption at −196°C (Sg), X-ray diffraction (XRD), temperature programmed reduction (TPR), temperature programmed desorption of NH3 (TPD-NH3) and chemisorption of H2. The reaction was carried out at 170°C and 220°C in a fixed bed reactor operating at atmospheric pressure. From the characterization results, it was determined that the degree of Ni2+–support interaction varies according to the following pattern: Ni/HBEA>Ni/SiO2–Al2O3>Ni/SiO2. All catalysts were very active in the hydrogenation of maleic anhydride to succinic anhydride. However, hydrogenolytic activity and stability of nickel-based catalyst varies with the degree of interaction Ni2+–support. Ni/H-BEA, in which Ni2+–support interaction is the highest, was active in the hydrogenolysis of succinic anhydride to γ-butyrolactone but it was not stable. By contrast, Ni/SiO2–Al2O3 and Ni/SiO2, with medium or low degree of Ni2+–support interaction, were more stable than Ni/H-BEA. In addition, Ni/SiO2–Al2O3, with a medium degree of Ni2+–support interaction, was the most stable and selective to γ-butyrolactone, especially when the reaction was carried out at 220°C.

Desulfurization of model FCC feedstocks by alkylation: Transformation of thiophenic compounds in presence of 2-methyl-1-pentene over acidic zeolites

The transformation of benzothiophene (BT) with 2-methyl-1-pentene was investigated over HBEA, HMCM-22 and HY zeolites having similar Brønsted acidities, at 85°C under atmospheric pressure in a fixed bed reactor. Over these zeolites, BT underwent only alkylation, whereas 2-methyl-1-pentene underwent alkylation, isomerization and oligomerization. HY was shown to be the most active and stable in BT conversion. HMCM-22 had a low initial activity and a poor stability, due to both diffusional limitations and fast deactivation of its acid sites, even those located in the external pockets. HBEA presented an intermediate behavior. The presence of toluene led to a decrease of BT conversion, which was attributed to competitive adsorptions of the aromatic and the olefin.Whatever the zeolite and the conversion, BT was predominantly transformed into monoalkylated products whereas 3-methylthiophene led essentially to dialkylated products. These results are in agreement with those obtained from theoretical calculations. HMCM-22 zeolite was shown to be the most selective toward alkylation versus olefin oligomerization.

Interaction of Zn2+ with extraframework aluminum in HBEA zeolite and its role in enhancing n-pentane isomerization

The electrodeposition method was used to produce Zn2+ cation precursors, followed by the introduction of Zn2+ cation precursors to HBEA by the ion exchange technique. The introduction of Zn2+ cations slightly changed the specific surface area and crystallinity of HBEA. IR, XPS and solid state MAS NMR results showed that Zn2+ cations interacted with (AlO)+ extraframework aluminum to form Zn(OAl)2 and simultaneously induced the formation of bridging hydroxyl groups, Si(OH)Al. The pyridine adsorbed IR study revealed that the presence of Zn2+ cations fully eliminated weak and partially eliminated strong Brønsted acid sites. As a result, strong and relatively weak Lewis acid sites were formed in which the pyridine probe molecule desorbed at 623K and below. The presence of Zn2+ cations enhanced the catalytic activity of HBEA in n-pentane isomerization due to the presence of strong Lewis acid sites; the sites may facilitate the formation and maintenance of active protonic acid sites through a hydrogen spillover mechanism. At 598K, the yield of isopentane for Zn-HBEA was 25.7% higher than that of HBEA. Within a reaction temperature range of 373–648K, the apparent activation energy for isomerization of n-pentane over HBEA and Zn-HBEA was 118.76 and 90.79kJ/mol, respectively.

Selective catalytic hydroalkylation and deoxygenation of substituted phenols to bicycloalkanes

Phenol and substituted phenols are hydroalkylated and hydrodeoxygenated to bi-cycloalkanes in a tandem reaction over Pd nanoclusters supported on a large-pore molecular sieve HBEA at 473–523K using water as solvent. The HBEA-supported Pd catalyst (metal–acid ratio: 1:22mol/mol) optimally balances the competing rates of metal catalyzed hydrogenation as well as of solid acid-catalyzed dehydration and carbon–carbon coupling to combine hydrodeoxygenation and dimerization of phenol derivatives to C12–C18 bicycloalkanes in a single reaction sequence. A detailed kinetic study of the elementary reactions of (substituted) phenol and their potential products (cyclohexanol, cyclohexanone, and cyclohexene) demonstrates that phenol selectively reacts with the in situ generated cyclohexanol or cyclohexene on Brønsted acid sites. The acid-catalyzed alkylation of phenol with alcohol intermediates and alcohol dehydration are parallel reactions, which are subtly influenced by the competing hydrogenation reactions as well as by the presence of water as solvent. IR spectroscopy of adsorbed species and preliminary molecular modeling indicate that phenol and cyclohexanol enrichment in the large pores of zeolite HBEA is critical for the high activity and hydroalkylation selectivity.

Catalyst of Palladium Supported on H-Beta Zeolite with Nanosized Al<sub>2</sub>O<sub>3</sub> for Isomerization of <i>n</i>-Hexane

Synthesis isoparaffins from light naphtha was studied using n-hexane conversion. The main target products were multi-branched isoparaffins. Which are harder to form than mono-branched isoparaffins in the zeolitic pores. Nano-technology was applied to form composites of zeolites and nano-sized (defined as 5-50 nm, and here called ns) oxides, to improve the state of metal species for isomerization into multi-branched isoparaffins. Skeletal isomerization of n-hexane was advanced, based on catalyst optimization with 0.1-2 wt% Pt or Pd on 35 wt% ns Al2O3 or ns SiO2 and 65 wt% H-BEA zeolite (SiO2/Al2O3 = 16-39). The presence of ns Al2O3 in the catalyst increased the mechanical strength of the shaped zeolite catalyst and reformed the surface acidity of the zeolite to milder acid suitable for skeletal isomerization without cracking. X-ray photoelectron spectroscopy showed that the nano-alumina dispersed and combined to the anisotropic surface of BEA zeolite to form an ionic and highly developed surface for palladium dispersion to improve the catalyst activity and selectivity.

Catalyst of Palladium Supported on H-Beta Zeolite with Nanosized Al<sub>2</sub>O<sub>3</sub> for Isomerization of <i>n</i>-Heptane

Synthesis isoparaffins from light naphtha was studied using n-hexane conversion. The main target products were multi-branched isoparaffins. Which are harder to form than mono-branched isoparaffins in the zeolitic pores. Nano-technology was applied to form composites of zeolites and nano-sized (defined as 5-50 nm, and here called ns) oxides, to improve the state of metal species for isomerization into multi-branched isoparaffins. Skeletal isomerization of n-hexane was advanced, based on catalyst optimization with 0.1-2 wt% Pt or Pd on 35 wt% ns Al2O3 or ns SiO2 and 65 wt% H-BEA zeolite (SiO2/Al2O3 = 16-39). The presence of ns Al2O3 in the catalyst increased the mechanical strength of the shaped zeolite catalyst and reformed the surface acidity of the zeolite to milder acid suitable for skeletal isomerization without cracking. X-ray photoelectron spectroscopy showed that the nano-alumina dispersed and combined to the anisotropic surface of BEA zeolite to form an ionic and highly developed surface for palladium dispersion to improve the catalyst activity and selectivity.

Adsorptive removal of α-endosulfan from water by hydrophobic zeolites. An isothermal study

This paper deals with the removal of α-endosulfan from water over HY and steamed HBEA zeolites. Experiments were performed to understand the adsorption mechanisms of α-endosulfan on zeolites and to determine the most efficient adsorbent for the purification of water contaminated by this pesticide. The experiments exhibit that α-endosulfan was adsorbed in the micropores. In the case of HY zeolites an adsorption of α-endosulfan molecules on BrØnsted sites was pointed out, due to a preferential water adsorption in mesopores. Moreover a physisorption of α-endosulfan occurred in micropores. For steamed HBEA zeolites physisorption in micropores was pointed out as the adsorption mode. For both types of zeolites a decrease of the adsorption capacities was noticed when the acidity of zeolites increased. There was also a linear relation between the adsorption capacities of α-endosulfan and the hydrophobicity (HI) of the samples and by determining the values of HI for a type of zeolite it was possible to deduce the uptake of α-endosulfan. The HY(40) sample was the most efficient for the removal of α-endosulfan from water because of preferential adsorption of water molecules in mesopores and lower acidity. For this sample the adsorption capacity for α-endosulfan was about 833.33 mg/g where for the most effective HBEA sample (St700(3)) the adsorption capacity was about 793.65 mg/g.

Tert-Butylation of diphenylamine over zeolite catalysts comparison of different alkylation agents and catalysts

Abstract tert -Butylation of diphenylamine (DPA) with different tert -butylation agents isobutylene (IB), tert -butanol (TBA), and C 4 -fraction (C4-IB) in the liquid phase was studied over zeolite catalyst H-BEA (H-BEA CP 814E). This zeolite and acidic clay catalysts Nobelin and Fulcat 22B were compared in tert -butylation of diphenylamine with isobutylene and tert -butanol. The study of the influence of tert -butylation agents in alkylation of DPA over H-BEA showed that isobutylene is the most suitable in tert -butylation of diphenylamine over the particular H-BEA zeolite catalyst in terms of conversion and selectivity to desired products. Comparative study of catalyst type influence on tert -butylation of DPA with TBA and IB employed zeolite catalyst H-BEA and two clay ones Nobelin and Fulcat 22B. The study showed that all catalysts perform well in alkylation of DPA but H-BEA with the highest total acidity is the most active. tert -Butylation of diphenylamine over H-BEA zeolite catalyst and acidic clays appears to be an environmental alternative to other catalysts (e.g. Friedel-Crafts) in industrial preparation of tert -butylated diphenylamines.

Alkylation of 3-methylthiophene by 2-methyl-1-pentene over HY, HBEA and HMCM-22 acidic zeolites

The alkylation of 3-methylthiophene with 2-methyl-1-pentene was investigated over acidic zeolites at 85 °C under atmospheric pressure in a fixed bed reactor. Three zeolites were tested, HY, HBEA and HMCM-22, which presented different pore systems but the same Brønsted acidity. Over these zeolites, 3-methylthiophene was only transformed by alkylation whereas 2-methyl-1-pentene underwent isomerization, alkylation and dimerization. No effect of the zeolite pore architecture on the initial activity was noted, but differences in stability and selectivity were observed. Indeed, HBEA was the most stable whereas HMCM-22 was the most selective in alkylation compared to olefin dimerization. The addition of toluene led to a decrease of the initial activity and the stability for all zeolites, due to competitive adsorption and coke formation. An Eley–Rideal mechanism was proposed for the alkylation reaction, where the thiophenic molecule reacts with the protonated olefin. The product distribution obtained experimentally was explained on the basis of the calculated B3LYP/cc-pVDZ stabilities of the intermediate carbocations involved in the steps proposed as rate determining.

Zeolite H-BEA catalysed multicomponent reaction: One-pot synthesis of amidoalkyl naphthols – Biologically active drug-like molecules

Zeolite has been used as an efficient and a novel heterogeneous catalyst for one-pot synthesis of biologically active drug-like molecules, amidoalkyl naphthols. This green route involves multicomponent reaction of 2-naphthol, aromatic aldehydes and amide in the presence of a catalytic amount of zeolite H-Beta (H-BEA) under solvent reflux as well as solvent-free conditions.

Synthesis of 1-Tetralones by Intramolecular Friedel-Crafts Reaction of 4-Phenylbutyric Acids Using Modified Zeolite H-BEA

以乙二胺四乙酸二钠（EDTA）、柠檬酸、草酸、酒石酸改性制备了H-BEA,并根据XRD和NH3-TPD对沸石H-BEA进行表征。采用上述改性沸石催化4-苯基丁酸分子内付克反应合成1-萘满酮进行催化剂反应活性评价。实验结果表明,以柠檬酸改性沸石H-BEA具有较高的催化活性。进一步对催化剂用量、反应温度、反应时间等工艺条件优化得到最佳工艺条件,在最佳工艺条件下,产物1-萘满酮产率达到94.3%。

Catalytic consequences of acid strength in the conversion of methanol to dimethyl ether

The effects of acid identity on CH 3OH dehydration are examined here using density functional theory (DFT) estimates of acid strength (as deprotonation energies, DPE) and reaction energies, combined with rate data on Keggin polyoxometalate (POM) clusters and zeolite H-BEA. Measured first-order ( k mono) and zero-order ( k dimer) CH 3OH dehydration rate constants depend exponentially on DPE for POM clusters; the value of k mono depends more strongly on DPE than k dimer does. The chemical significance of these rate parameters and the basis for their dependences on acid strength were established by using DFT to estimate the energies of intermediates and transition states involved in elementary steps that are consistent with measured rate equations. We conclude from this treatment that CH 3OH dehydration proceeds via direct reactions of co-adsorbed CH 3OH molecules for relevant solid acids and reaction conditions. Methyl cations formed at ion-pair transition states in these direct routes are solvated by H 2O and CH 3OH more effectively than those in alternate sequential routes involving methoxide formation and subsequent reaction with CH 3OH. The stability of ion-pairs, prevalent as intermediates and transition states on solid acids, depends sensitively on DPE because of concomitant correlations between the stability of the conjugate anionic cluster and DPE. The chemical interpretation of k mono and k dimer from mechanism-based rate equations, together with thermochemical cycles of their respective transition state formations, show that similar charge distributions in the intermediate and transition state involved in k dimer cause its weaker dependence on DPE. Values of k mono involve uncharged reactants and the same ion-pair transition state as k dimer; these species sense acid strength differently and cause the larger effects of DPE on k mono. Confinement effects in H-BEA affect the value of k mono because the different sizes and number of molecules in reactants and transition states selectively stabilize the latter; however, they do not influence k dimer, for which reactants and transition states of similar size sense spatial constraints to the same extent. This combination of theory and experiment for solid acids of known structure sheds considerable light on the relative contributions from solvation, electrostatic and van der Waals interactions in stabilizing cationic transition states and provides predictive insights into the relative contributions of parallel routes based on the size and charge distributions of their relevant intermediates and transition states. These findings also demonstrate how the consequences of acid strength on measured turnover rates depend on reaction conditions and their concomitant changes in the chemical significance of the rate parameters measured. Moreover, the complementary use of experiment and theory in resolving mechanistic controversies has given predictive guidance about how rate and equilibrium constants, often inextricably combined as measured rate parameters, individually depend on acid strength based on the magnitude and spatial distributions of charges in reactants, products and transition states involved in relevant elementary steps. The unique relations between k mono, k dimer and DPE developed here for CH 3OH dehydration can be applied in practice to assess the acid strength of any solid acid, many of which have unknown structures, preventing reliable calculations of their DPE by theory.

Structures and Energetics of the Methylation of 2-Methylnaphthalene with Methanol over H-BEA Zeolite

The methylation of 2-methylnaphthalene (2-MN) with methanol to the 2,6 (2,6-DMN) and 2,7 (2,7-DMN) dimethylnaphthalenes catalyzed over nanoporous BEA zeolite has been investigated quantum chemically using the M06-2X density functional. The catalytic cycle consists of three elementary steps: (1) formation of a methoxy species from methanol that is bound to a zeolite oxygen atom, (2) methylation of 2-MN to DMN with methoxy leading to naphthalynic carbocations, and (3) formation of DMN by proton back-donation from naphthalynic carbocations. The reaction profiles are similar for both the 2,6 and the 2,7 isomer and are in agreement with the experimental observation that they are produced in equal amounts on acidic BEA zeolite. A possible side reaction, the formation of dimethyl ether via the self-activation of methanol, is also discussed. The stability of the intermediates inside the pores is, to a large extent, governed by the steric constraints and the van der Waals dispersion interactions induced by the pore structure of BEA zeolite. These are the key parameters for understanding the relationship between zeolite topology and catalytic activity.

Selective production of isobutylene from acetone over alkali metal ion-exchanged BEA zeolites

Selective production of isobutylene from acetone was examined over BEA zeolites. Isobutylene production from acetone proceeds over solid-acid catalysts via a series of consecutive reactions, which include propylene and ethylene formation by cracking and coke formation. Because the isobutylene is an intermediate chemical in this process, low diffusion resistance of the isobutylene within the pore of the catalyst is needed to prevent its further conversion. To achieve this goal, we selected a BEA-type zeolite with 12-membered rings and a 3-dimensional pore structure. To obtain high yields of isobutylene, it is also important to inhibit undesired reactions of isobutylene and other intermediates that produce aromatics and coke. In this study, the acidity of the BEA zeolites was controlled using an ion-exchange method with alkali metals. The order of catalytic activity of the ion-exchanged BEA zeolites is as follows: H-BEA, Na-BEA, K-BEA, Rb-BEA, Cs-BEA, and is the same as the order of acidity of the zeolites. Though H-BEA zeolite showed a high acetone conversion at an initial reaction time, the activity of the catalyst drastically decreased due to coke formation. In contrast, the alkali metal ion-exchanged BEA zeolites exhibited high isobutylene selectivity at high acetone conversion conditions. Moreover, the amount of coke deposited on the catalyst decreased as compared to H-BEA zeolite. In K-BEA zeolite, the isobutylene yield reached 55%.

Zeolites Promoting Quinoline Synthesis via Friedländer Reaction

Catalytic performance of zeolites H-BEA, H-MFI, H-FAU and H-MOR, exhibiting textural differences and with different Bronsted and Lewis acid sites concentration, have been studied in the synthesis of quinolines via Friedlander reaction. H-BEA and H-FAU efficiently promoted the condensation of 2-aminoaryl ketones 3 with ethyl acetoacetate (4a) or acetylacetone (4b) under mild reaction conditions, those being the first examples of zeolites as catalysts for this transformation. While H-FAU showed similar catalytic behaviour than that reported for (Al)SBA-15 affording mixtures of quinolines 5 and quinolones 6, H-BEA mainly led to quinolines 5 in almost total selectivity and good yields. However, H-MFI and H-MOR zeolites afforded quinolones 6 as the major reaction product. Methodology reported here was found to be useful for the synthesis of biologically active compounds with excellent yields avoiding unnecessary purifications protocols and tedious work-up procedures.

Zeolites Efficiently Promote the Cyclization of Nonactivated Unsaturated Alcohols

Excellent cyclization: Zeolites H-BEA, H-MFI, H-FAU, and H-STF were found to be efficient, selective, and reusable catalysts in the cyclization of cis-4-decenol, affording the corresponding tetrahydrofuran with excellent yields to provide a new synthetic route to alkylfurans. Brønsted and Lewis acid sites in the zeolites under study are probably the active sites, because both of them catalyze this reaction.

Comparative Evaluation of Catalysts Containing 0.35% Pt Supported on H-BEA Zeolite Dealuminated via EDTA, HCl Leaching, or Hydrothermally With Steam

H-BEA was steamed at 500°C for 2 hr and then loaded with Pt to produce 0.35% Pt/St-H-BEA catalyst. Also, H-BEA was dealuminated with ethylenediamine tetraacetic acid (EDTA) and then loaded with Pt to produce 0.35% Pt/EDTA-H-BEA catalyst. Finally, H-BEA was dealuminated via HCl leaching followed by Pt loading to produce 0.35%Pt/HCl-H-BEA catalyst. These catalysts were reduced under H2 flow at 500°C to give Pt metal. All catalysts were tested at 250°C–450°C for n-hexane hydroconversion. Maximum hydroisomerization of n-hexane was attained (75.1%) on 0.35% Pt/EDTA-H-BEA and 0.35% Pt/HCl-H-BEA catalysts but at 275°C on the former catalyst and at 300°C on the latter. At this temperature, n-hexane hydrocracking is only 1.2%. The hexane isomers selectivity on both catalysts was >99%. For the 0.35% Pt/St H-BEA catalyst, isohexanes yield and selectivity were lower than the above-mentioned catalysts. The catalyst of choice is 0.35% Pt/EDTA-H-BEA for its economic application at 275°C.

Study of the phenol methylation mechanism on zeolites HBEA, HZSM5 and HMCM22

The mechanism of gas-phase alkylation of phenol with methanol was studied on zeolites HBEA, HZSM5 and HMCM22. The nature, density and strength of the acid sites were determined by temperature-programmed desorption of NH 3 and FTIR spectroscopy of adsorbed pyridine. In all the cases, anisole, o-cresol and p-cresol were the primary products, but the initial product distribution greatly depended on the zeolite pore structure and surface acid properties. The complete reaction network was established by investigating the formation of secondary products (xylenols, methylanisoles, m-cresol) via the reactions of primary products with phenol and methanol. On HBEA, phenol was alkylated to primary and secondary products without significant diffusional restraints and the yield to dialkylated products increased when phenol conversion was increased. o-Cresol was consecutively alkylated to 2,4- and 2,6-xylenols ( C-alkylation), and 2-methylanisole ( O-alkylation). Anisole reacted with phenol to yield o- and p-cresol isomers, and with methanol to form methylanisoles. Selectivities to primary products on HZSM5 were similar to those determined on HBEA, but the formation of bulky intermediates leading to dialkylated compounds was hampered because of diffusional constraints. The alkylation of phenol with anisole to yield cresol isomers was completely suppressed on HZSM5. The particular pore structure of zeolite HMCM22 promoted the selective formation of p-cresol among the primary products of phenol methylation and drastically suppressed the consecutive reactions forming secondary products. In contrast, isomerization reactions between monoalkylated products were promoted on zeolite HMCM22 because of its high concentration of strong Brønsted acid sites. The activity decay on stream was significant on the three zeolites, probably because of the formation of coke intermediates via both anisole dealkylation and methanol dehydration reactions.