Editorial

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Open AccessEditorial

Zeolite Catalysis

by Andreas Martin

Catalysts 2016, 6(8), 118; https://doi.org/10.3390/catal6080118 - 02 Aug 2016

Cited by 4 | Viewed by 3763

The Special Issue “Zeolite Catalysis” published in the online journal Catalysts was recently successfully completed.[...] Full article

(This article belongs to the Special Issue Zeolite Catalysis)

Research

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2292 KiB

Open AccessArticle

Photocatalytic Oxidation of NO over Composites of Titanium Dioxide and Zeolite ZSM-5

by Akram Tawari, Wolf-Dietrich Einicke and Roger Gläser

Catalysts 2016, 6(2), 31; https://doi.org/10.3390/catal6020031 - 19 Feb 2016

Cited by 19 | Viewed by 6004

Abstract

Composites of TiO₂ (Hombikat, P25, sol-gel synthesis) and zeolite ZSM-5 (n_Si/n_Al = 55) with mass fractions from 25/75 to 75/25 were prepared by mechanical mixing, solid-state dispersion and sol-gel synthesis. Characterization of the composites by X-ray diffraction (XRD), N [...] Read more.

Composites of TiO₂ (Hombikat, P25, sol-gel synthesis) and zeolite ZSM-5 (n_Si/n_Al = 55) with mass fractions from 25/75 to 75/25 were prepared by mechanical mixing, solid-state dispersion and sol-gel synthesis. Characterization of the composites by X-ray diffraction (XRD), N₂-sorption, scanning electron microscopy (SEM), and UV-Vis spectroscopy show that mechanical mixing and solid-state dispersion lead to comparable textural properties of the composites. A homogeneous distribution and intimate contact of small TiO₂ particles on the crystal surface of zeolite ZSM-5 were achieved by sol-gel synthesis. The composites were studied in the photocatalytic oxidation (PCO) of NO in a flatbed reactor under continuous flow according to ISO 22197-1. The highest NO conversion of 41% at an NO₂ selectivity as low as 19% stable for 24 h on-stream was reached over the TiO₂/ZSM-5 composite from sol-gel synthesis with equal amounts of the two components after calcination at 523 K. The higher activity and stability for complete NO oxidation than for pure TiO₂ from sol-gel synthesis, Hombikat, or P25 is attributed to the adsorptive properties of the zeolite ZSM-5 in the composite catalyst. Increasing the calcination temperature up to 823 K leads to larger TiO₂ particles and a lower photocatalytic activity. Full article

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1701 KiB

Open AccessArticle

Insights to Achieve a Better Control of Silicon-Aluminum Ratio and ZSM-5 Zeolite Crystal Morphology through the Assistance of Biomass

by Alessandra V. Silva, Leandro S. M. Miranda, Márcio Nele, Benoit Louis and Marcelo M. Pereira

Catalysts 2016, 6(2), 30; https://doi.org/10.3390/catal6020030 - 18 Feb 2016

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Abstract

The present study attempts to provide insights for both the chemical composition (Si/Al) and the crystal morphology of ZSM-5 zeolites while using biomass template compounds in the synthesis. The solution containing biomass-derivative compounds was obtained after treating biomass in a sodium hydroxide aqueous [...] Read more.

The present study attempts to provide insights for both the chemical composition (Si/Al) and the crystal morphology of ZSM-5 zeolites while using biomass template compounds in the synthesis. The solution containing biomass-derivative compounds was obtained after treating biomass in a sodium hydroxide aqueous solution under reflux. The latter alkaline solution was used as a solvent for zeolite nuclei ingredients to form the gel phase under hydrothermal conditions (170 °C during 24, 48 or 72 h). This approach allowed for preparing MFI zeolites having a broad range of Si/Al ratio, i.e., from 25 to 150. Likewise, MFI crystals with different morphologies could be obtained, being different from the pristine zeolite formed in the absence of biomass. Full article

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1364 KiB

Open AccessArticle

High Selectively Catalytic Conversion of Lignin-Based Phenols into para-/m-Xylene over Pt/HZSM-5

by Guozhu Liu, Yunxia Zhao and Jinhua Guo

Catalysts 2016, 6(2), 19; https://doi.org/10.3390/catal6020019 - 22 Jan 2016

Cited by 20 | Viewed by 6642

Abstract

High selectively catalytic conversion of lignin-based phenols (m-cresol, p-cresol, and guaiacol) into para-/m-xylene was performed over Pt/HZSM-5 through hydrodeoxygenation and in situ methylation with methanol. It is found that the p-/m-xylene selectivity is uniformly [...] Read more.

High selectively catalytic conversion of lignin-based phenols (m-cresol, p-cresol, and guaiacol) into para-/m-xylene was performed over Pt/HZSM-5 through hydrodeoxygenation and in situ methylation with methanol. It is found that the p-/m-xylene selectivity is uniformly higher than 21%, and even increase up to 33.5% for m-cresol (with phenols/methanol molar ratio of 1/8). The improved p-/m-xylene selectivity in presence of methanol is attributed to the combined reaction pathways: methylation of m-cresol into xylenols followed by HDO into p-/m-xylene, and HDO of m-cresol into toluene followed by methylation into p-/m-xylene. Comparison of the product distribution over a series of catalysts indicates that both metals and supporters have distinct effect on the p-/m-xylene selectivity. Full article

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3244 KiB

Open AccessCommunication

The Fabrication of Ga₂O₃/ZSM-5 Hollow Fibers for Efficient Catalytic Conversion of n-Butane into Light Olefins and Aromatics

by Jing Han, Guiyuan Jiang, Shanlei Han, Jia Liu, Yaoyuan Zhang, Yeming Liu, Ruipu Wang, Zhen Zhao, Chunming Xu, Yajun Wang, Aijun Duan, Jian Liu and Yuechang Wei

Catalysts 2016, 6(1), 13; https://doi.org/10.3390/catal6010013 - 15 Jan 2016

Cited by 35 | Viewed by 7023

Abstract

In this study, the dehydrogenation component of Ga₂O₃ was introduced into ZSM-5 nanocrystals to prepare Ga₂O₃/ZSM-5 hollow fiber-based bifunctional catalysts. The physicochemical features of as-prepared catalysts were characterized by means of XRD, BET, SEM, STEM, NH [...] Read more.

In this study, the dehydrogenation component of Ga₂O₃ was introduced into ZSM-5 nanocrystals to prepare Ga₂O₃/ZSM-5 hollow fiber-based bifunctional catalysts. The physicochemical features of as-prepared catalysts were characterized by means of XRD, BET, SEM, STEM, NH₃-TPD, etc., and their performances for the catalytic conversion of n-butane to produce light olefins and aromatics were investigated. The results indicated that a very small amount of gallium can cause a marked enhancement in the catalytic activity of ZSM-5 because of the synergistic effect of the dehydrogenation and aromatization properties of Ga₂O₃ and the cracking function of ZSM-5. Compared with Ga₂O₃/ZSM-5 nanoparticles, the unique hierarchical macro-meso-microporosity of the as-prepared hollow fibers can effectively enlarge the bifunctionality by enhancing the accessibility of active sites and the diffusion. Consequently, Ga₂O₃/ZSM-5 hollow fibers show excellent catalytic conversion of n-butane, with the highest yield of light olefins plus aromatics at 600 °C by 87.6%, which is 56.3%, 24.6%, and 13.3% higher than that of ZSM-5, ZSM-5 zeolite fibers, and Ga₂O₃/ZSM-5, respectively. Full article

(This article belongs to the Special Issue Zeolite Catalysis)

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4561 KiB

Open AccessArticle

Effects of Dealumination and Desilication of Beta Zeolite on Catalytic Performance in n-Hexane Cracking

by Yong Wang, Toshiyuki Yokoi, Seitaro Namba and Takashi Tatsumi

Catalysts 2016, 6(1), 8; https://doi.org/10.3390/catal6010008 - 05 Jan 2016

Cited by 100 | Viewed by 8340

Abstract

Catalytic cracking of n-hexane to selectively produce propylene on Beta zeolite was carried out. The H-Beta (HB) (Si/Al = 77) zeolite showed higher catalytic stability and propylene selectivity than the Al-rich HB (Si/Al = 12), due to its smaller number of acid [...] Read more.

Catalytic cracking of n-hexane to selectively produce propylene on Beta zeolite was carried out. The H-Beta (HB) (Si/Al = 77) zeolite showed higher catalytic stability and propylene selectivity than the Al-rich HB (Si/Al = 12), due to its smaller number of acid sites, especially Lewis acid sites (LAS). However, catalytic stability and propylene selectivity in high n-hexane conversions were still not satisfactory. After dealumination with HNO₃ treatment, catalytic stability was improved and propylene selectivity during high n-hexane conversions was increased. On the other hand, catalytic stability was not improved after desilication with NaOH treatment, although mesopores were formed. This may be related to the partially destroyed structure. However, propylene selectivity in high n-hexane conversions was increased after alkali treatment. We successfully found that the catalytic stability was improved and the propylene selectivity in high n-hexane conversions was further increased after the NaOH treatment followed by HNO₃ treatment. This is due to the decrease in the number of acid sites and the increase in mesopores which are beneficial to the diffusion of coke precursor. Full article

(This article belongs to the Special Issue Zeolite Catalysis)

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464 KiB

Open AccessArticle

Switching off H₂O₂ Decomposition during TS-1 Catalysed Epoxidation via Post-Synthetic Active Site Modification

by Ceri Hammond and Giulia Tarantino

Catalysts 2015, 5(4), 2309-2323; https://doi.org/10.3390/catal5042309 - 21 Dec 2015

Cited by 19 | Viewed by 7122

Abstract

Despite its widespread use, the Lewis acidic zeolite, TS-1, still exhibits several unfavourable properties, such as excessive H₂O₂ decomposition, which decrease its overall performance. In this manuscript, we demonstrate that post-synthetic modification of TS-1 with aqueous NH₄HF₂ [...] Read more.

Despite its widespread use, the Lewis acidic zeolite, TS-1, still exhibits several unfavourable properties, such as excessive H₂O₂ decomposition, which decrease its overall performance. In this manuscript, we demonstrate that post-synthetic modification of TS-1 with aqueous NH₄HF₂ leads to modifications in epoxidation catalysis, which both improves the levels of epoxide selectivity obtained, and drastically minimises undesirable H₂O₂ decomposition. Through in situ spectroscopic study with UV-resonance enhanced Raman spectroscopy, we also observe a change in Ti site speciation, which occurs via the extraction of mononuclear [Ti(OSi)₄] atoms, and which may be responsible for the changes in observed activity. Full article

(This article belongs to the Special Issue Zeolite Catalysis)

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807 KiB

Open AccessArticle

Zeolite Catalysts for Phenol Benzoylation with Benzoic Acid: Exploring the Synthesis of Hydroxybenzophenones

by Gherardo Gliozzi, Sauro Passeri, Francesca Bortolani, Mattia Ardizzi, Patrizia Mangifesta and Fabrizio Cavani

Catalysts 2015, 5(4), 2223-2243; https://doi.org/10.3390/catal5042223 - 16 Dec 2015

Cited by 9 | Viewed by 8913

Abstract

In this paper, we report on the reaction of phenol benzoylation with benzoic acid, which was carried out in the absence of solvent. The aim of this reaction is the synthesis of hydroxybenzophenones, which are important intermediates for the chemical industry. H-beta zeolites [...] Read more.

In this paper, we report on the reaction of phenol benzoylation with benzoic acid, which was carried out in the absence of solvent. The aim of this reaction is the synthesis of hydroxybenzophenones, which are important intermediates for the chemical industry. H-beta zeolites offered superior performance compared to H-Y, with a remarkably high conversion of phenol and high yields to the desired compounds, when using a stoichiometric amount of benzoic acid. It was found that the reaction mechanism did not include the intramolecular Fries rearrangement of the primary product phenyl benzoate, but indeed, the bimolecular reaction between phenyl benzoate and phenol mainly contributed to the formation of hydroxybenzophenones. The product distribution was greatly affected by the presence of Lewis-type acid sites in H-beta; it was suggested that the interaction between the aromatic ring and the electrophilic Al3+ species led to the preferred formation of o-hydroxybenzophenone, because of the decreased charge density on the C atom at the para position of the phenolic ring. H-Y zeolites were efficient than H-beta in phenyl benzoate transformation into hydroxybenzophenones. Full article

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719 KiB

Open AccessArticle

Facile Synthesis of Yolk/Core-Shell Structured TS-1@Mesosilica Composites for Enhanced Hydroxylation of Phenol

by Houbing Zou, Qingli Sun, Dongyu Fan, Weiwei Fu, Lijia Liu and Runwei Wang

Catalysts 2015, 5(4), 2134-2146; https://doi.org/10.3390/catal5042134 - 14 Dec 2015

Cited by 14 | Viewed by 5579

Abstract

In the current work, we developed a facile synthesis of yolk/core-shell structured TS-1@mesosilica composites and studied their catalytic performances in the hydroxylation of phenol with H₂O₂ as the oxidant. The core-shell TS-1@mesosilica composites were prepared via a uniform coating process, [...] Read more.

In the current work, we developed a facile synthesis of yolk/core-shell structured TS-1@mesosilica composites and studied their catalytic performances in the hydroxylation of phenol with H₂O₂ as the oxidant. The core-shell TS-1@mesosilica composites were prepared via a uniform coating process, while the yolk-shell TS-1@mesosilica composite was prepared using a resorcinol-formaldehyde resin (RF) middle-layer as the sacrificial template. The obtained materials were characterized by X-ray diffraction (XRD), N₂ sorption, Fourier transform infrared spectoscopy (FT-IR) UV-Visible spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The characterization results showed that these samples possessed highly uniform yolk/core-shell structures, high surface area (560–700 m² g⁻¹) and hierarchical pore structures from oriented mesochannels to zeolite micropores. Importantly, owing to their unique structural properties, these composites exhibited enhanced activity, and also selectivity in the phenol hydroxylation reaction. Full article

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396 KiB

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Adsorption and Diffusion of Xylene Isomers on Mesoporous Beta Zeolite

by Aixia Song, Jinghong Ma, Duo Xu and Ruifeng Li

Catalysts 2015, 5(4), 2098-2114; https://doi.org/10.3390/catal5042098 - 08 Dec 2015

Cited by 21 | Viewed by 5696

Abstract

A systematic and detailed analysis of adsorption and diffusion properties of xylene isomers over Beta zeolites with different mesoporosity was conducted. Adsorption isotherms of xylene isomers over microporous and mesoporous Beta zeolites through gravimetric methods were applied to investigate the impact of mesopores [...] Read more.

A systematic and detailed analysis of adsorption and diffusion properties of xylene isomers over Beta zeolites with different mesoporosity was conducted. Adsorption isotherms of xylene isomers over microporous and mesoporous Beta zeolites through gravimetric methods were applied to investigate the impact of mesopores inside Beta zeolites on the adsorption properties of xylene isomers in the pressure range of lower 20 mbar. It is seen that the adsorption isotherms of three xylene isomers over microporous and mesoporous Beta zeolites could be successfully described by the single-site Toth model and the dual-site Toth model, respectively. The enhanced adsorption capacities and decreased Henry’s constants (K_H) and the initial heats of adsorption (Q_st) for the all xylene isomers are observed after the introduction of mesopores in the zeolites. For three xylene isomers, the order of Henry’s constant is o-xylene > m-xylene > p-xylene, whereas the adsorption capacities of Beta zeolite samples for xylene isomers execute the following order of o-xylene > p-xylene > m-xylene, due to the comprehensive effects from the molecular configuration and electrostatic interaction. At the same time, the diffusion properties of xylene isomers in the mesoporous Beta zeolites were also studied through the desorption curves measured by the zero length column (ZLC) method at 333–373 K. It turned out that the effective diffusion time constant (D_eff/R²) is a growing trend with the increasing mesoporosity, whereas the tendency of the activation energy is just the reverse, indicating the contribution of mesopores to facilitate molecule diffusion by shortening diffusion paths and reducing diffusion resistances. Moreover, the diffusivities of three xylene isomers in all Beta zeolites follow an order of p-xylene > m-xylene > o-xylene as opposed to K_H, conforming the significant effects of adsorbate-adsorbent interaction on the diffusion. Full article

(This article belongs to the Special Issue Zeolite Catalysis)

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143 KiB

Open AccessFeature PaperArticle

Catalytic Cracking of Triglyceride-Rich Biomass toward Lower Olefins over a Nano-ZSM-5/SBA-15 Analog Composite

by Xuan Hoan Vu, Sura Nguyen, Tung Thanh Dang, Binh Minh Quoc Phan, Duc Anh Nguyen, Udo Armbruster and Andreas Martin

Catalysts 2015, 5(4), 1692-1703; https://doi.org/10.3390/catal5041692 - 10 Oct 2015

Cited by 22 | Viewed by 7192

Abstract

The catalytic cracking of triglyceride-rich biomass toward C₂–C₄ olefins was evaluated over a hierarchically textured nano-ZSM-5/SBA-15 analog composite (ZSC-24) under fluid catalytic cracking (FCC) conditions. The experiments were performed on a fully automated Single-Receiver Short-Contact-Time Microactivity Test unit (SR-SCT-MAT, Grace [...] Read more.

The catalytic cracking of triglyceride-rich biomass toward C₂–C₄ olefins was evaluated over a hierarchically textured nano-ZSM-5/SBA-15 analog composite (ZSC-24) under fluid catalytic cracking (FCC) conditions. The experiments were performed on a fully automated Single-Receiver Short-Contact-Time Microactivity Test unit (SR-SCT-MAT, Grace Davison) at 550 °C and different catalyst-to-oil mass ratios (0–1.2 g∙g⁻¹). The ZSC-24 catalyst is very effective for transformation of triglycerides to valuable hydrocarbons, particularly lower olefins. The selectivity to C₂–C₄ olefins is remarkably high (>90%) throughout the investigated catalyst-to-oil ratio range. The superior catalytic performance of the ZSC-24 catalyst can be attributed to the combination of its medium acid site amount and improved molecular transport provided by the bimodal pore system, which effectively suppresses the secondary reactions of primarily formed lower olefins. Full article

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Review

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Open AccessReview

Zeolite Membranes in Catalysis—From Separate Units to Particle Coatings

by Radostina Dragomirova and Sebastian Wohlrab

Catalysts 2015, 5(4), 2161-2222; https://doi.org/10.3390/catal5042161 - 16 Dec 2015

Cited by 34 | Viewed by 10865

Abstract

Literature on zeolite membranes in catalytic reactions is reviewed and categorized according to membrane location. From this perspective, the classification is as follows: (i) membranes spatially decoupled from the reaction zone; (ii) packed bed membrane reactors; (iii) catalytic membrane reactors and (iv) zeolite [...] Read more.

Literature on zeolite membranes in catalytic reactions is reviewed and categorized according to membrane location. From this perspective, the classification is as follows: (i) membranes spatially decoupled from the reaction zone; (ii) packed bed membrane reactors; (iii) catalytic membrane reactors and (iv) zeolite capsuled catalyst particles. Each of the resulting four chapters is subdivided by the kind of reactions performed. Over the whole sum of references, the advantage of zeolite membranes in catalytic reactions in terms of conversion, selectivity or yield is evident. Furthermore, zeolite membrane preparation, separation principles as well as basic considerations on membrane reactors are discussed. Full article

(This article belongs to the Special Issue Zeolite Catalysis)

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