Comparison of H + and NH 4 + forms of zeolites as acid catalysts for HMF etherification

Pyrolysis of waste expanded polystyrene and reduction of styrene via in-situ multiphase pyrolysis of product oil for the production of fuel range hydrocarbons

Upgraded fuel oil was produced from the waste expanded polystyrene (WEPS) using pyrolysis and in-situ selective aromatization in a specially designed reactor. The catalytic pyrolysis of WEPS was performed keeping the catalyst in three different types of catalyst arrangements inside the reactor i.e., A-type/catalyst in liquid phase, B-type/catalyst in vapour phase, and AB-type or Multiphase/catalyst in both liquid and vapour phases, respectively. The ZSM-5 ammonium powder was used as a catalyst with varying feed to catalyst ratio and 20:1 was found to be optimum. Aromatics of fuel range like benzene, toluene, and ethylbenzene (BTE) were significantly increased and styrene got reduced by many folds when AB-type/multiphase catalytic pyrolysis was performed. The thermal pyrolysis produced maximum liquid yield of 94.37 wt% at a temperature of 650 °C and a heating rate of 15 °C/min. The maximum liquid yield of 88.05 wt%, 78.85 wt%, and 75.11 wt% were obtained for the A-type, B-type, and AB-type catalytic pyrolysis at the temperature of 600 °C, 550 °C and 550 °C, respectively using the same heating rate. The liquid oil of thermal pyrolysis contains very low amount of fuel range aromatics i.e., BTE of 11.38 wt% and the highest amount of styrene (84.74 wt%). In contrarily, BTE content for the catalytic process increased progressively in the order of 18.98 wt% (A-type) < 24.27 wt% (B-type) < 28.12 wt% (AB-type). The styrene content significantly decreased to a very low value of 46.30 wt% for AB-type/multiphase pyrolysis at the temperature of 550 °C.

Co-hydrolysis and Seed-Induced Synthesis of Basic Mesoporous ZSM-5 Zeolites with Enhanced Catalytic Performance

For zeolite catalysts, the regulation of active site and pore structure plays an important role in the enhancement of their catalytic performance. In this work, a one-pot and organic template-free co-regulation route is proposed to straightforwardly synthesize basic mesoporous ZSM-5 zeolites with adjustable alkaline-earth metal species. The synthesis pathway combines two decisive strategies: 1) the seed-induced interface assembly growth method and 2) the acidic co-hydrolysis/condensation of aluminosilicate species and alkaline-earth metal (e.g., Mg, Ca, Sr, or Ba) sources. It is interesting that the mesoporous structure was self-evolved through particle-attached seed-interfacial crystallization without the assistance of any template. Meanwhile, the incorporation of alkaline-earth metals species is homogeneous and highly dispersed in the solid products during the whole crystallization process, and finally generate the superior basicity. Catalysis tests of the as-synthesized samples displayed their novel performance in the typical base reaction of Knoevenagel condensation, even for bulky substrates owing to the enhanced diffusion arising from the meso/microporous network. This finding opens new possibilities for facile, cost-effective, and environmentally friendly synthesis of mesoporous high-silica zeolites with tunable acid/base properties, and deepens our understanding of the particle-attached crystallization.

Magnetic Fe3O4@SiO2-Pt and Fe3O4@SiO2-Pt@SiO2 Structures for HDN of Indole

The effect of a second porous SiO₂ shell in the activity and selectivity of the Fe₃O₄@SiO₂–Pt catalyst in the hydrodenitrogenation of indole is reported. The double Fe₃O₄@SiO₂–Pt@SiO₂ structure was prepared by coating Fe₃O₄ nanoparticles with tetraethyl orthosilicate (TEOS) with a further impregnation of 1.0 wt.% of Pt on the (3-aminopropyl)triethoxysilane functionalized Fe₃O₄@SiO₂ structures. The second porous SiO₂ shell, obtained by using a hexadecyltrimethylammonium bromide (CTAB) template, covered the Fe₃O₄@SiO₂–Pt catalyst with a well-defined and narrow pore-sized distribution. The full characterization by TEM, inductively coupled plasma-optical emission spectroscopy (ICP-OES), XRD, and N₂ adsorption isotherm at 77 K and vibrating sample magnetometry (VSM) of the catalysts indicates homogeneous core@shell structures with a controlled nano-size of metallic Pt. A significant effect of the double SiO₂ shell in the catalytic performance was demonstrated by both a higher activity to eliminate the nitrogen atom of the indole molecule present in model liquid fuel and the improvement of the catalytic stability reaching four consecutive reaction cycles with only a slight conversion level decrease.

Zeolite-Based Catalysts: A Valuable Approach toward Ester Bond Formation

Zeolite-based catalysts are versatile catalytic systems for a wide range of laboratory studies and industrial scale processes. The chemical composition, ion exchange, and pore size structure attributes of zeolites are responsible for their extensive catalytic applications. Esterification is one of the most important and routinely processes in diverse fields of organic synthesis. It has a long history in both industrial processes and laboratory work due to its versatility. This review intends to give a detailed insight into the significance of zeolite-based catalysts for ester bond formation

C-O Bond Hydrogenolysis of Aqueous Mixtures of Sugar Polyols and Sugars over ReOx-Rh/ZrO2 Catalyst: Application to an Hemicelluloses Extracted Liquor

The recovery and upgrade of hemicelluloses, a family of heteropolysaccharides in wood, is a key step to making lignocellulosic biomass conversion a cost-effective sustainable process in biorefinery. The comparative selective catalytic C-O bond hydrogenolysis of C5-C6 polyols, sugars, and their mixtures for the production of valuable C6 and C5 deoxygenated products was studied at 200 °C under 80 bar H2 over ReOx-Rh/ZrO2 catalysts. The sugars were rapidly converted to the polyols or converted into their hydrogenolysis products. Regardless of the reactants, C-O bond cleavage occurred significantly via multiple consecutive deoxygenation steps and led to the formation of linear deoxygenated C6 or C5 polyols. The distribution of products depended on the nature of the substrate and C-C bond scission was more important from monosaccharides. In addition, we demonstrated effective hydrogenolysis of a hemicellulose-extracted liquor from delignified maritime pine containing monosaccharides and low MW oligomers. Compared with the sugar-derived polyols, the mono- and oligosaccharides in the liquor were more rapidly converted to hexanediols or pentanediols. C-O bond scission was significant, giving a yield of desired deoxygenated products as high as 65%, higher than in the reaction of the synthetic mixture of glucose/xylose of the same C6/C5 sugar ratio (yield of 30%).

Incorporating Hierarchy into Conventional Zeolites for Catalytic Biomass Conversions: A Review

Zeolites are promising catalysts that are widely used in petrochemical, oil, and gas industries due to their unique characteristics, such as ordered microporous networks, good hydrothermal stability, large surface area, tunable acidity, and shape-selectivity. Nevertheless, the sole presence of microporous channels in zeolites inevitably restricts the diffusion of bulky reactants and products into and out of the microporous networks, leading to retarded reaction rates or catalyst deactivation. This problem can be overcome by developing hierarchical zeolites which involve mesoporous and macroporous networks. The meso- and macro-porosities can enhance the mass transport of molecules and simultaneously maintain the intrinsic shape selectivity of zeolite microporosity. Hierarchical zeolites are mainly developed through post-synthesis and pre-synthesis or in situ modification of zeolites. In this review, we evaluated both pre-synthesis and post-synthesis modification strategies with more focus on post-synthesis modification strategies. The role of various synthesis strategies on the intrinsic properties of hierarchical zeolites is discussed. The catalytic performance of hierarchical zeolites in important biomass reactions, such as catalytic pyrolysis of biomass feedstock and upgradation of bio-oil, has been summarized. The utilization of hierarchical zeolites tends to give a higher aromatic yield than conventional zeolites with microporosity solely.

Hierarchical Low Si/Al Ratio Ferrierite Zeolite by Sequential Postsynthesis Treatment: Catalytic Assessment in Dehydration Reaction of Methanol

In contrast to high silica zeolites, it is difficult to obtain mesoporosity in zeolites with low Si/Al ratio (e.g., <20) via conventional NaOH-based treatment, making the obtainment of hierarchical zeolites with high acidity a challenging target. In this paper, we report the preparation of hierarchical FER-type zeolite at low Si/Al molar ratio (about 10) by postsynthesis etching involving a sequence of three treatments with NaAlO2, HCl, and NaOH solutions and investigate the effect of both NaAlO2 solution concentration and time of treatment on the textural properties. The obtained materials exhibit a mesoporous volume higher than the parent ferrierite with no significant effect on the sample acidity. The catalytic activity of some samples was investigated in vapour-phase methanol dehydration to dimethyl ether, revealing the superiority of hierarchical zeolites in terms of methanol conversion, although the presence of mesopores causes formation of light hydrocarbons at high temperatures.

Direct versus acetalization routes in the reaction network of catalytic HMF etherification

The etherification of HMF (5-hydroxymethylfurfural) to EMF (5-(ethoxymethyl)furan-2-carbaldehyde) is studied over a series of MFI-type zeolite catalysts containing different heteroatoms (B, Fe, Al), aiming to understand the effect of different isomorph substitutions in the MFI framework on the reaction pathways of HMF conversion.