Solvent-Free Synthesis of Core–Shell Zn/ZSM-5@Silicalite-1 Catalyst for Selective Conversion of Methanol to BTX Aromatics

Study of Catalytic Properties of the HoxMg1-xAl2O4 Modified HZSM-5 Zeolite in Conversion of Methanol to C2-C4 Alkenes and p-Xylene

Selective conversion of methanol to C2-C4 alkenes and p-xylene is one of the appealing chemical routes. Currently, there are no effective catalysts for the co-production of C2-C4 alkenes and p-xylene from methanol. To date, modified medium-pore ZSM-5 zeolites are considered one of the excellent candidates for the development of selective catalysts for the conversion of methanol to lower alkenes and aromatic hydrocarbons. In this paper, nanosized (30-33nm) powders of HoхMg1-хAl2O4 spinel structure were obtained by the method of combustion of nitrate solutions of aluminium, magnesium, holmium, diethylmalonate and hydrazine monohydrate with the further calcination of nanopowders at 1000 °C. Obtained nanopowders used in the preparation of a solid-phase catalytic composition of HoхMg1-хAl2O4-HZSM-5. Various physico-chemical properties of the catalytic composition were investigated using X-ray diffraction (XRD), pyridine adsorption (BİO-RAD FTS 3000 MX) and low-temperature nitrogen adsorption (BET) techniques. The textural properties and acidity of the catalysts were altered by adjusting the nanopowder concentration (1.0-5.0 wt.%) in the catalytic composition. The conversion of methanol in the presence of the catalytic compositions was carried out in flow-type fixed-bed catalytic reactor at 400 °C, in the presence of nitrogen carrier gas with 1.0 h-1 flow rate. A correlation between the selectivity to C2-C4 alkenes and p-xylene with a ratio of Lewis (L) and Brønsted (B) acid sites and the volume of the catalyst pore, the amount of the modifier in the catalytic system has been established. As the amount of HoхMg1-хAl2O4 nanopowder increases, the ratio of B/L acid sites and the volume of the catalyst pore decrease, which play a significant role in the increase of the selectivity to C2-C4 alkenes and p-xylene. Maximum yield of C2-C4 alkenes (31.6%) and selectivity to p-xylene (80.5%) is achieved on a catalytic composition containing 5.0 wt.% HoxMg1-xAl2O4. Copyright © 2022 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0). 

Improvement of adsorption and catalytic properties of zeolites by precisely controlling their particle morphology

An aluminosilicate zeolite has a porous structure with openings comparable to the molecular size, which endows it with unique adsorptive and catalytic properties that are highly dependent on its chemical composition and crystal morphology. Thus, the precise control or rational design of zeolite's particle morphology has attracted much attention as it can greatly improve the adsorptive separation and catalytic properties by effectively adjusting the diffusion path of adsorbates, reactants and products. This paper reviews the recent progress made in the synthesis and application of zeolites with a specific crystal/particle morphology with emphasis on the control of the crystal size and facet exposure degree, oriented assembly of crystals, creation of hierarchical porous structures and synthesis of core-shell structures. It is shown that an appropriate decrease of the crystal size and/or an increase of the exposure degree of certain facets by adding seeds and optimizing the synthesis conditions enhances the catalytic stability and product selectivity in some reactions. This can also be achieved by introducing plenty of mesopores and/or macropores in zeolites as a result of significant alleviation of diffusion limitation. Assembly of zeolite crystals into membranes on porous substrates improves the adsorptive separation performance of zeolites, for e.g. alcohol/water mixture and xylene and butane isomers. Core-shell-structured composites with metal nanoparticles or subnanoparticles as the core and the zeolite, including its modified counterpart, as the shell show excellent catalytic performance in some hydrogenation, dehydrogenation and oxidation reactions. In addition, attempts to illustrate the relationship between zeolite's particle morphology and its catalytic performance are discussed and strategies for the rational design of zeolite's particle size and behavior are envisioned.

Towards the development of the emerging process of CO2 heterogenous hydrogenation into high-value unsaturated heavy hydrocarbons

The emerging process of CO₂ hydrogenation through heterogenous catalysis into important bulk chemicals provides an alternative strategy for sustainable and low-cost production of valuable chemicals, and brings an important chance for mitigating CO₂ emissions. Direct synthesis of the family of unsaturated heavy hydrocarbons such as α-olefins and aromatics via CO₂ hydrogenation is more attractive and challenging than the production of short-chain products to modern society, suffering from the difficult control between C-O activation and C-C coupling towards long-chain hydrocarbons. In the past several years, rapid progress has been achieved in the development of efficient catalysts for the process and understanding of their catalytic mechanisms. In this review, we provide a comprehensive, authoritative and critical overview of the substantial progress in the synthesis of α-olefins and aromatics from CO₂ hydrogenation via direct and indirect routes. The rational fabrication and design of catalysts, proximity effects of multi-active sites, stability and deactivation of catalysts, reaction mechanisms and reactor design are systematically discussed. Finally, current challenges and potential applications in the development of advanced catalysts, as well as opportunities of next-generation CO₂ hydrogenation techniques for carbon neutrality in future are proposed.

Sustainable one-pot preparation of fully crystalline shaped zeolite catalysts

Fully crystalline shaped zeolite catalysts with MFI, MTT, and TON structures have been successfully prepared via a sustainable one-pot route.

Tandem catalysts for the conversion of methanol to aromatics with excellent selectivity and stability

A schematic diagram of the construction methods and reaction paths of different catalysts.

Selective Conversion of CO2 into para-Xylene over a ZnCr2 O4 -ZSM-5 Catalyst

An oxide-zeolite (ZnCr₂ O₄ -ZSM-5) catalyst for directly converting CO₂ to aromatics was designed and developed. It showed high PX/X (the C-mol ratio of p-xylene to all xylene) and PX/aromatics (the C-mol ratio of p-xylene to aromatics) ratios, which reached 97.3 and 63.9 %, respectively.

Enhancing the matching of acid/metal balance by engineering an extra Si–Al framework outside the Pd/HBeta catalyst towards benzene hydroalkylation

We have designed and constructed an extra Si–Al framework coating outside the Pd/HBeta catalyst, which exhibits excellent catalytic performance for benzene hydroalkylation reaction, due to the better matching relationship between metal and acid sites.