Influence of binder on catalytic performance of Ni/HZSM-5 for hydrodeoxygenation of cyclohexanone

A Comparative Review of Binder-Containing Extrusion and Alternative Shaping Techniques for Structuring of Zeolites into Different Geometrical Bodies

Zeolites are crystalline metallosilicates displaying unique physicochemical properties with widespread applications in catalysis, adsorption, and separation. They are generally obtained by a multi-step process that starts with primary mixture aging, followed by hydrothermal crystallization, washing, drying, and, finally, a calcination step. However, the zeolites obtained are in the powder form and because of generating a pressure drop in industrial fixed bed reactors, not applicable for industrial purposes. To overcome such drawbacks, zeolites are shaped into appropriate geometries and the desired size (a few centimeters) using extrusion, where zeolite powders are mixed with binders (e.g., mineral clays or inorganic oxides). The presence of binders provides good mechanical strength against crushing in shaped zeolites, but binders may have adverse impacts on zeolite catalytic and sorption properties, such as active site dilution and pore blockage. The latter is more pronounced when the binder has a smaller particle size, which makes the zeolite internal active sites mainly inaccessible. In addition to the shaping requirements, a hierarchical structure with different levels of porosity (micro-, meso-, and macropores) and an interconnected network are essential to decrease the diffusion limitation inside the zeolite micropores as well as to increase the mass transfer through the presence of larger auxiliary pores. Thus, the generation of hierarchical structure and its preservation during the shaping step is of great importance. The aim of this review is to provide a comprehensive survey and detailed overview on the binder-containing extrusion technique compared to alternative shaping technologies with improved mass transfer properties. An emphasis is allocated to those techniques that have been less discussed in detail in the literature.

Preparation and Performance of the Lipid Hydrodeoxygenation of a Nickel-Induced Graphene/HZSM-5 Catalyst

Graphene-encapsulated nickel nanoclusters are a feasible strategy to inhibit the nickel deactivation of nickel-based catalysts. In this work, graphene-encapsulated catalysts (Ni@C/HZSM-5) were prepared by a compression forming process, using pseudo-boehmite, Al2O3, and ZrO2 as binders. The pseudo-boehmite was gradually transformed from amorphous to crystalline alumina at high temperatures, which destroyed the nucleation of Ni@C. In contrast, the crystal-stabilized zirconia was more favorable for the nucleation of Ni@C. The extensive dispersion of alumina on the surface of HZSM-5 covers the acid sites of HZSM-5. In contrast, when zirconia was used as the binder, the binder existed in the form of the direct aggregation of ~100 nm zirconia spheres; this distribution form reduced better the damage of the binder to the acid site of the catalyst. Furthermore, the particle size of Ni crystals in the graphene-encapsulated catalysts decreased significantly (mostly <11 nm), and no evident agglomeration of nickel particles appeared. It was found that the stabilization of the metal interface delayed, to an extent, the accumulation rate of carbon deposits and, thus, postponed the deactivation of the acid sites. After 8 h of continuous reaction, the conversion of the traditional catalyst Ni/Z5+Zr dropped significantly to 60%. In contrast, the conversion of Ni@C catalysts prepared with ZrO2 remained above 90%. The regeneration test shows that air roasting could effectively remove carbon deposits and restore the catalyst activity.

Effect of Preparation Method on the Catalytic Performance of HZSM-5 Zeolite Catalysts in the MTH Reaction

A kind of nano-ZSM-5 zeolite crystal was synthesized by the hydrothermal method, and HZSM-5 zeolite powder was obtained via acid exchange. By using pseudoboehmite as a binder, a series of HZSM-5 zeolite catalysts for methanol-to-hydrocarbons (MTH) were prepared through adjusting the binder content between 20 and 50% in addition to the molding method of wet extrusion and mechanical mixing. XRD, 27Al NMR, SEM-EDS, ICP, low-temperature N2 adsorption and desorption, NH3-TPD, Py-FTIR, FT-IR, TG and elemental analyses were used to characterize the properties of fresh catalysts and coke-deposited catalysts. Then, MTH catalytic performance was evaluated in a continuous-flow fixed-bed reactor. The characterization and evaluation results showed that the addition of dilute nitric acid during the molding process increased the amount of moderate-strength acid and formed a hierarchical pore distribution, which helped to reduce the reaction ability of cracking, aromatization and hydrogen transfer, improve the diffusion properties of the catalyst and slow down the coke deposition rate. The catalyst with a binder content of 30% made by wet extrusion with dilute nitric acid had the best performance, whose activity stability of MTH increased by 96 h, higher than other catalysts, and the coke deposition rate was slower, which was due to the most suitable distribution of acid strength and B/L ratio as well as the most obvious hierarchical pore structure.

A facile way to improve zeolite Y-based catalysts' properties and performance in the isobutane-butene alkylation reaction

Different amounts of SiO₂ were added to the Al₂O₃ binders to investigate the binder effect on zeolite Y-based catalysts. The added SiO₂ improved the mesopore volume and acidity of the catalysts. Characterization results showed that the catalysts' acid amount increased with increasing the SiO₂ amount in the binder, which achieved maximum value when 12% SiO₂ was added to the binder. The doped SiO₂ in Al₂O₃ binders improved the Al₂O₃ phase transformation temperature, which is crucial for Al species to break out of the phase energy and migrate into the zeolite. The lifetime of catalyst Y-Al₂O₃-12SiO₂ is 3.7 times higher than that of Y-Al₂O₃-0SiO₂, and the selectivity of the target products simultaneously improved by 7 percentage point. This work should bring some inspiration to the design and application of zeolite-based catalysts.

An Overview on Zeolite Shaping Technology and Solutions to Overcome Diffusion Limitations

Synthetic zeolites are widely used as catalysts/carriers for many petrochemical reactions and in refining processes. These materials are usually synthesized in a powder form and must be shaped prior to use in industrial reactors. This review presents the state-of-the-art of the zeolite shaping technology describing the main modifications induced by the interactions between the zeolite and the binder. Additionally, a strategy is presented to overcome the diffusion limitations associated to the microporous structure of zeolites, consisting in the introduction of hierarchical porosity in the binder. Several developments in the field of hierarchical aluminas are summarized in this article, highlighting the possibility to design different ordered/disordered mesoporous and macroporous structures.