Direct Ink Writing of Metal Oxide/H-ZSM-5 Catalysts for n-Hexane Cracking: A New Method of Additive Manufacturing with High Metal Oxide Loading

Abstract

Previously, 3D printing of porous materials and metal oxides was limited to low loading metal loadings, as increasing the nitrate salt concentrations, which are used to generate the oxide component, gave rise to poor rheological properties beyond 10 wt %. In this study, we addressed this problem by directly printing insoluble oxides alongside H-ZSM-5 zeolite, which allowed for increased oxide loadings. Various metal oxides such as V2O5, ZrO2, Cr2O3, and Ga2O3 were doped onto H-ZSM-5 through the additive manufacturing method. Characterization and correlation between the X-ray diffraction, NH3-temperature-programmed desorption, O2-temperature programmed oxidation, temperature-programmed reduction, scanning electron microscopy–energy dispersive spectroscopy, and in situ CO2 DRIFTS experiments revealed that directly 3D printing metal oxides/H-ZSM-5 inks leads to significant modification in the surface properties and oxide bulk dispersion, thereby enhancing the composites’ reducibility and giving rise to widely differing product distributions in n-hexane cracking reaction. The obtained metal oxide/zeolite structured materials were used as bifunctional structured catalysts for the selective formation of light olefins from hexane at 550–600 °C and GHSV = 9000 mL/gcatalst·h in a packed-bed reactor. Among the various compositions of metal oxides/H-ZSM-5 examined (i.e., 15 wt % Ga2O3, 15 wt % ZrO2, 15 wt % V2O5, 15 wt % Cr2O3, or 5 wt % Cr/10 wt % ZrO2/10 wt % V2O5/10 wt % Ga2O3 balanced with H-ZSM-5), the 15 wt % Cr/ZSM-5 monolith displayed the best n-hexane cracking performance, as it achieved 80–85% conversion of hexane with a 40% selectivity toward propylene, 30% selectivity toward ethylene, and 10% selectivity toward butene at 550 °C. The sample also showed zero benzene/toluene/xylene selectivity and no deactivation after 6 h. This study represents a proof-of-concept for tailoring customizable heterogeneous structured catalysts by directly 3D printing high loading of metal oxides/porous zeolite and is a breakthrough in material science.

Structured Bifunctional Catalysts for CO2 Activation and Oxidative Dehydrogenation of Propane

“…The paste ratios in Table were 3D printed to form structured monolithic catalysts using the techniques described in our recent publications. − As before, ∼10 mL of distilled water was the only solvent required to formulate a printable rheology, where a printable rheology was considered to be one with self-standing behavior, good retention of solvent, and separation of printed layers. The pastes were rolled for 48 h prior to printing to achieve homogeneity and were densified at 400 rpm at 60 °C for ∼3 h to reach a printable rheology.…”

“…Specifically, we reported a third route of catalyst printing where insoluble metal oxides can be dispersed alongside ZSM-5 within a single printing paste to form a stable rheology, thereby allowing for loadings beyond the 10 wt % threshold and generating desirable contact between the various active species. Not only did this new method allow for oxide loadings up to 85 wt %, but it also gave rise to catalysts with exceptional stability, olefin selectivity, and reactant conversion across multiple reactions, including ODHP and n -hexane cracking. − Specifically looking at ODHP, one of our recent studies reported that printing a catalyst containing a mixture of 5 wt % Cr, 10 wt % Ga, 10 wt % V, and 10 wt % Zr oxides balanced against 65 wt % ZSM-5 could achieve 40% propane conversion, 95% propylene selectivity, zero BTX production, and no deactivation at 550 °C over 6 h . In this regard, the catalysts produced by this new printing method can be considered exceptionally promising materials for industrial reactionary processes.…”

Hierarchically Structured Components: Design, Additive Manufacture, and Their Energy Applications

“…[198][199][200] The shear-thinning rheological properties of the inks are critical to print ideal architecture without collapse. [46,156,201] Highly concentrated GO, [46] cellulose nanofiber, [154] and methylcellulose [202] lead to suitable viscosity for extrusion-type 3D printing. [156] The prominent advantage of the powder bed fusion method is the use of the powder bed which not only provides the raw material but serves as an in-process support allowing complex shapes with high geometrical accuracy.…”

“…The methylcellulose, halloysite nanotubes, and carbon nanotubes can be used to adjust the rheological properties. [74,202,215] In order to increase the amount of nanopores, Shuang et al employed a hydrothermal processing after the sintering to transfer the inorganic binder to zeolite. [215] Joseph et al [216] and Clara et al [217] reported modified DIW methods to prepare the ceramic HSCs, respectively, where the air bubbles and additives (PVA) were introduced into the alumina slurries to form stable foam inks.…”

“…[3,9,10] Moreover, adsorption is the first step for chemical and electrochemical reactions. [2,202,232] The 3D printed HSCs act as the monolithic adsorbents, structured catalysts, and electrodes in the adsorption, [6,7,73,74] chemical reaction, [47,48,157,181,199,233] and electrochemical cells, [13,81,234] respectively. On the other hand, the recent development of the batteries [2,3,[11][12][13] and microreactors [8,[14][15][16][17][18] requires the novel electrodes, catalysts, and adsorbents for the high energy efficiency and power density, high conversion efficiency, rapid reaction rate, and great capacity.…”