Zeolite ZSM-5 is one of the most widely used zeolites, in particular in heterogeneous catalysis. This work investigates the incorporation of Al in the silica framework of monoclinic ZSM-5 and the Al speciation during steam treatment for four ZSM-5 samples with different Si/Al ratios, using ultrahigh field 27Al NMR (22.3 T), 29Si NMR, X-ray diffraction, and IR spectroscopy. 27Al MQMAS NMR at 22.3 T allows identification and quantification of 10 distinct tetrahedral framework resonances which are assigned to the crystallographic sites by their average T–O–T angles, determined from powder XRD patterns for the same samples. A clear Al site preference is observed and found to be dependent on the Si/Al ratio of the parent zeolite. The framework sites facing the intersections in ZSM-5 are found to be most prone to dealumination, whereas Al in the straight and sinusoidal-shaped channels are more stable toward steam treatment at high temperatures. Extra-framework Al species with 5- and 6-fold coordination and two ...

Distribution of Aluminum over the Tetrahedral Sites in ZSM-5 Zeolites and Their Evolution after Steam Treatment

Industrial olefin metathesis catalysts generally suffer from low reaction rates and require harsh reaction conditions for moderate activities. This is due to their inability to prevent metathesis active sites (MASs) from aggregation and their intrinsic poor adsorption and activation of olefin molecules. Here, isolated tungstate species as single molecular MASs are immobilized inside zeolite pores by Bronsted acid sites (BASs) on the inner surface. It is demonstrated that unoccupied BASs in atomic proximity to MASs enhance olefin adsorption and facilitate the formation of metallocycle intermediates in a stereospecific manner. Thus, effective cooperative catalysis takes place over the BAS-MAS pair inside the zeolite cavity. In consequence, for the cross-metathesis of ethene and trans-2-butene to propene, under mild reaction conditions, the propene production rate over WO x/USY is ca. 7300 times that over the industrial WO3/SiO2-based catalyst. A propene yield up to 79% (80% selectivity) without observable deactivation was obtained over WO x/USY for a wide range of reaction conditions.

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Entrapped Single Tungstate Site in Zeolite for Cooperative Catalysis of Olefin Metathesis with Brønsted Acid Site

This review covers the research and industrial activities on mainly Ga- and Zn-promoted ZSM-5 catalysts for the production of bio-aromatics in the thermochemical conversion of biomass and waste. The promoted ZSM-5 catalysts currently favoured in biomass aromatization have not initially been designed for biomass processing, but for the conversion of petrochemical feeds. In biomass pyrolysis, however, aromatization catalysts have to perform additional tasks to aromatization, such as cracking, reforming, decarboxylation, decarbonylation and the water-gas shift reaction. In addition, catalysts in biomass processing may have to operate with feeds containing acids, sulphur, nitrogen and minerals. Nevertheless, there is great similarity between the optimum catalysts for both petrochemical and biomass aromatization. The preferred aromatization catalysts for both gasification and pyrolysis are Ga- and Zn-promoted ZSM-5 catalysts that synergistically combine a dehydrogenation and an acidic function. Reduced extra-framework Ga cations residing at ZSM-5 exchange positions in close proximity to Bronsted acid sites are the likely active sites for aromatization. For Ga a reduction/oxidation activation procedure to form these sites is beneficial. For Zn/ZSM-5 catalysts ZnOH+ species appear to be the active sites. For these catalysts no reduction/oxidation activation is required. The key process parameters for aromatization are a temperature of 400–550 °C and a low space velocity of 0.5–1.0 h−1. In agreement with the bifunctional nature of Ga/ZSM-5 there exists an optimal Ga loading for each SAR. Best results were obtained with a molar ratio Ga/H+ or Zn/H+ close to 1.0. These catalysts also show the best stability

Promoted ZSM-5 catalysts for the production of bio-aromatics, a review

The efficient production of light olefins from renewable biomass is a vital and challenging target to achieve future sustainable chemical processes. Here we report a hetero-atomic MFI-type zeolite (NbAlS-1), over which aqueous solutions of γ-valerolactone (GVL), obtained from biomass-derived carbohydrates, can be quantitatively converted into butenes with a yield of >99% at ambient pressure under continuous flow conditions. NbAlS-1 incorporates simultaneously niobium(v) and aluminium(iii) centres into the framework and thus has a desirable distribution of Lewis and Bronsted acid sites with optimal strength. Synchrotron X-ray diffraction and absorption spectroscopy show that there is cooperativity between Nb(v) and the Bronsted acid sites on the confined adsorption of GVL, whereas the catalytic mechanism for the conversion of the confined GVL into butenes is revealed by in situ inelastic neutron scattering, coupled with modelling. This study offers a prospect for the sustainable production of butene as a platform chemical for the manufacture of renewable materials. Production of olefins from biomass-derived γ-valerolactone could lead to sustainable chemical processes, but catalysts suffer from deactivation due to water. Here, a MFI-type zeolite doped with Nb(v) and Al(iii) shows >99% yield at 320 °C and catalyst stability over 180 hours.

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Quantitative production of butenes from biomass-derived γ-valerolactone catalysed by hetero-atomic MFI zeolite

The development of efficient catalysts to break down and convert woody biomass will be a paradigm shift in delivering the global target of sustainable economy and environment via the use of cheap, highly abundant, and renewable carbon resources. However, such development is extremely challenging due to the complexity of lignocellulose, and today most biomass is treated simply as waste. The solution lies in the design of multifunctional catalysts that can place effective control on substrate activation and product selectivity. This is, however, severely hindered by the lack of fundamental understanding of (i) the precise role of active sites, and (ii) the catalyst–substrate chemistry that underpins the catalytic activity. Moreover, active sites alone often cannot deliver the desired selectivity of products, and full understanding of the microenvironment of the active sites is urgently needed. Here, we review key recent advances in the study of reaction mechanisms of biomass conversion over emerging heterogeneous catalysts. These insights will inform the design of future catalytic systems showing improved activity and selectivity.

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Emerging heterogeneous catalysts for biomass conversion: studies of the reaction mechanism.

Herein, we report the catalytic decarboxylation of γ-valerolactone (GVL) over Zn/ZSM-5 to butene, followed by aromatization at high yield with co-feeding of water. An evaluation of the catalytic performance after prolonged periods of time showed that a water molecule is essential to maintain the decarboxylation and aromatization activities and avoid rapid catalyst deactivation. Synchrotron X-ray powder diffraction and Rietveld refinement were then used to elucidate the structures of adsorbed GVL and immobilized Zn species in combination with EXAFS and NMR spectroscopy. A new route for the cooperative hydrolysis of GVL by framework Zn-OH and Bronsted acidic sites to butene and then to aromatic compounds has thus been demonstrated. The structures and fundamental pathways for the nucleophilic attack of terminal Zn-OH sites are comparable to those of Zn-containing enzymes in biological systems.

Decarboxylation of Lactones over Zn/ZSM-5: Elucidation of the Structure of the Active Site and Molecular Interactions.

Here, we report a catalytic process of decarboxylating gamma-valerolactone, GVL (the biomass derived lactone as an example) over Zn/ZSM-5 to butene, followed by aromatization at high yield with co-feed water. Evaluation of catalytic performance at prolonged time shows that water molecule is essential in maintaining the decarboxylation/ aromatization activity without rapid deactivation. Synchrotron X-ray diffraction and Rietveld refinement are then used to elucidate the adsorbed structures of GVL and immobilized Zn-species with the support of EXAFS and NMR. A new route of cooperative hydrolysis of GVL by framework Zn-OH and Bronsted acid sites to butene and then to aromatics is for the first time demonstrated. The structures and fundamental pathways for nucleophilic attack of terminal Zn-OH site are comparable to that of reported Zn-containing enzymes in biological systems.

A New Route for De-carboxylation of Lactones over Zn/ZSM-5: Elucidation of Structure and Molecular Interactions

The present invention relates to a process for preparing an aromatic hydrocarbon, and processes for producing p-xylene and terephthalic acid. The process for producing said aromatic hydrocarbon comprises a step of contacting an olefin with a diene in the presence of a catalyst to produce an aromatic hydrocarbon, which is characterized in that, at least a part of said olefin is substituted with dienophile. The reaction pressure can be reduced and the xylene selectivity can be increased with the improvement of the present invention.

Processes for producing aromatic hydrocarbon, p-xylene and terephthalic acid

Diese Erfindung betrifft ein Verfahren zur Herstellung eines aromatischen Kohlenwasserstoffes und Verfahren zur Erzeugung von p-Xylol und Terephthalsaure. Das Verfahren zur Erzeugung des aromatische Kohlenwasserstoffes enthalt einen Schritt zum Kontaktieren eines Olefins mit einem Dien in der Gegenwart eines Katalysators, zur Erzeugung eines aromatischen Kohlenwasserstoffes, dadurch gekennzeichnet, dass zumindest ein Teil des Olefins mit einem Dienophil substituiert ist. Der Reaktionsdruck kann reduziert und die Xylolselektivitat kann durch die Verbesserung dieser Erfindung erhoht werden.

Verfahren zur Erzeugung von aromatischem Kohlenwasserstoff, p-Xylol und Terephthalsäure

The invention relates to a method for producing aromatic hydrocarbon by cycloaddition. The method comprises the following step: enabling raw materials to be in contact with a catalyst to produce aromatic hydrocarbon flow containing benzene, methylbenzene or dimethylbenzene. The raw materials comprise diene and dienophile. The diene has a structural formula (I) as shown in the specification, in the formula (I), R1 and R2 are hydrogen, optional substituted C1-20 straight chain or branched chain alkyls, optional substituted C2-20 straight chain or branched chain alkenyls, optional substituted C2-20 straight chain or branched chain alkynyls, optional substituted C3-20 cycloalkyls or optional substituted C6-20 aryls, and the dienophile is C2-C4 alcohol. The method can be used for industrial production of preparation of aromatic hydrocarbons by non-fossil resources.

Song Qi

Papers

Decarboxylation of Lactones over Zn/ZSM-5: Elucidation of the Structure of the Active Site and Molecular Interactions.

A New Route for De-carboxylation of Lactones over Zn/ZSM-5: Elucidation of Structure and Molecular Interactions

Processes for producing aromatic hydrocarbon, p-xylene and terephthalic acid

Verfahren zur Erzeugung von aromatischem Kohlenwasserstoff, p-Xylol und Terephthalsäure

Method for producing aromatic hydrocarbon by cycloaddition