One-Pot Three-Dimensional Printing Robust Self-Supporting MnO _x /Cu-SSZ-13 Zeolite Monolithic Catalysts for NH ₃ -SCR

Abstract

Open AccessCCS ChemistryRESEARCH ARTICLE1 May 2022One-Pot Three-Dimensional Printing Robust Self-Supporting MnOx/Cu-SSZ-13 Zeolite Monolithic Catalysts for NH3-SCR Yingzhen Wei, Mengyang Chen, Xiaoyu Ren, Qifei Wang, Jinfeng Han, Wenzheng Wu, Xiangguang Yang, Shuang Wang and Jihong Yu Yingzhen Wei State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, College of Chemistry, Jilin University, Changchun 130012 , Mengyang Chen State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, College of Chemistry, Jilin University, Changchun 130012 International Center of Future Science, Jilin University, Changchun 130012 , Xiaoyu Ren State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, College of Chemistry, Jilin University, Changchun 130012 , Qifei Wang State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, College of Chemistry, Jilin University, Changchun 130012 , Jinfeng Han State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, College of Chemistry, Jilin University, Changchun 130012 , Wenzheng Wu School of Mechanical and Aerospace Engineering, Jilin University, Changchun 130025 , Xiangguang Yang State Key Laboratory of Rare Earth Resource Utilization, Jilin Province Key Laboratory of Green Chemistry and Process, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022 , Shuang Wang *Corresponding authors: E-mail Address: [email protected] E-mail Address: [email protected] Henan Province Function-Oriented Porous Materials Key Laboratory, College of Chemistry and Chemical Engineering, Luoyang Normal University, Luoyang 471934 and Jihong Yu *Corresponding authors: E-mail Address: [email protected] E-mail Address: [email protected] State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, College of Chemistry, Jilin University, Changchun 130012 International Center of Future Science, Jilin University, Changchun 130012 https://doi.org/10.31635/ccschem.021.202100942 SectionsSupplemental MaterialAboutAbstractPDF ToolsAdd to favoritesDownload CitationsTrack Citations ShareFacebookTwitterLinked InEmail Honeycomb cordierite coated with Cu-SSZ-13 zeolite is widely used for the selective catalytic reduction of NOx with NH3 (NH3-SCR) to reduce pollutants from vehicle emissions. However, conventional honeycomb catalysts fabricated via coating techniques are limited by low zeolite loadings, loss of the deposited zeolites, and complicated preparation processes. Herein, a facile, one-step three-dimensional (3D) printing strategy is developed to construct MnOx/Cu-SSZ-13 monolithic catalysts with excellent catalytic performance for NH3-SCR. Iron-containing halloysite nanotubes (Fe-HNTs) are introduced as printing ink additives to ensure mechanical stability and modulate the NH3-SCR performance of monolithic catalysts in high temperature conditions. In situ incorporation of Mn into the Cu-SSZ-13 zeolite monoliths during the 3D printing process boosts the mechanical strength of the monolithic structures from 2.54 MPa to 4.33 MPa as well as broadens the temperature window (165–550 °C) of the catalysts for NH3-SCR with NOx conversion of above 80%. Such robust multicomponent-integrated 3D-printed self-supporting catalysts not only possess high zeolite loading and excellent catalytic activity, but also avoid complicated manufacturing processes, which contrasts with conventional honeycomb catalysts fabricated by extrusion coupled with coating. Download figure Download PowerPoint Introduction Nitrogen oxides (NOx) are some of the most prominent air pollutants and cause serious environmental problems and harm human health.1–3 The selective catalytic reduction of NOx with NH3 (NH3-SCR) is an efficient method to remove NOx from vehicles and industrial emissions.4–6 The Cu-SSZ-13 zeolite with Chabazite ( CHA) structure has been extensively used in NH3-SCR reactions in recent years due to its high catalytic activity, excellent selectivity, and hydrothermal stability.7–10 However, the limited activity window of the Cu-SSZ-13 zeolite still cannot satisfy the practically applied requirements for cold starts and high temperatures.11,12 In recent years, various metals have been incorporated into Cu-SSZ-13 zeolites to optimize the catalytic activity for NH3-SCR.13,14 For instance, compared with Cu-SSZ-13, Fe/Cu-SSZ-13 catalysts show enhanced high-temperature activity, owing to abundant active sites and increased redox capacity.15 Manganese compounds with many valence states enhance acid sites on the catalyst surface as well as inhibit aggregation of Cu species; therefore, Mn-modified Cu-SSZ-13 zeolites show outstanding low-temperature activity and excellent hydrothermal stability.16–18 However, these multiple metal-doped zeolite catalysts are conventionally prepared through time-consuming and relatively complex processes, such as ion-exchange and impregnation, which are unfavorable for industrial commercialization.19 In addition, all these metal-optimized catalysts are based on zeolite powder and must be shaped into macro-sized bodies for use in the industrial reactor, which is a key step for the implementation of laboratory-designed catalysts into scale-up forms.20 In practical NH3-SCR catalytic applications, active zeolites are usually deposited onto the surface of cordierite supports with honeycomb structures, which have been fabricated via extrusion.21–23 The honeycomb monoliths can promote high flow transfer while reducing the pressure drop in catalytic reactions.24 However, such catalysts fabricated via these complicated techniques have drawbacks of low zeolite loading and easy loss of the active coating. In addition, the parallel channels of the honeycomb-structure support constructed by the extrusion method restrict the uniform mixing of the flow, which in turn leads to the performance degradation of the catalyst.25 In recent years, research on monolithic catalysts has mainly focused on the construction technology of catalysts, without further modification and optimization, which is far behind powder development.2 Therefore, it is highly desirable to develop an effective strategy to prepare a catalyst that can overcome configuration issues while possessing optimized catalytic performance. Recently, as an innovative technology, additive manufacturing/three-dimensional (3D) printing has demonstrated significant advantages in precisely constructing geometries with adaptability, flexibility, and complexity.26–28 The unique capability of 3D printing in customizing geometries makes it a promising approach to efficiently design and manufacture catalysts and adsorbents with optimized properties, which is readily available for industrial scale-up.29–32 Recently, a variety of self-supporting zeolite monoliths have been constructed via 3D printing.33,34 These catalysts hold high zeolite loading capacities of 65–90% and interconnected channels, which increase the volume efficiency of the reactor and mass transfer of the fluid. Furthermore, different from the complex and time-consuming metal doping methods, such as impregnation, 3D printing can directly integrate multifunctional materials into the zeolites during the printing procedure, enabling modification and optimization of the zeolite monoliths.35 Consequently, self-supporting zeolite monoliths manufactured by 3D printing technology can fuse the superior features of high loadings of active species and tunable structures as well as functional components, which can fulfill multiple requirements in various applications. Nonetheless, the deficient mechanical strength severely limits the actual service lifetime of these 3D-printed catalysts, in particular they must withstand an excessive and long-term impact from temperature, pressure, and stress changes. It has been found that the types and characteristics of the composition of printing ink additives play a crucial role in the printability of the printing inks and the physicochemical properties of the final structures.33,36 Recently, our group developed a "3D printing and zeolite soldering" strategy, in which halloysite nanotubes (HNTs) served as both reinforcement and precursor due to the unique ingredients and features of high strength, high aspect ratio, and nanotubular structure. Subjected to hydrothermal treatment, the HNTs were converted into zeolites, leading to a further enhanced mechanical stability of the zeolite monoliths.37 In addition, Rownaghi's group reported a series of metal-doped Zeolite Socony Mobil #5 (ZSM-5) monolithic catalysts for methanol conversion and n-hexane cracking reactions.38–40 Notably, the incorporation of certain metals has a positive effect on the compressive strength of the zeolite monoliths. Encouraged by these works, we believe that a self-supporting catalyst with promising properties for NH3-SCR can be fabricated by merging the multiple components (such as metal oxides and printing ink additives) into a 3D-printed structure during the 3D printing process. In this work, for the first, 3D-printed MnOx/Cu-SSZ-13 monoliths with interconnected channels were successfully used in NH3-SCR. The monolithic catalysts were constructed via 3D printing multifunctional composite materials, which integrate manufacturing support, coating active species, and doping metal within the 3D printing fabrication. The introduction of natural iron-containing HNTs as inorganic binders promoted the mechanical stability and catalytic activity of the monolithic catalysts. Strikingly, the catalyst incorporating MnOx displayed an enhanced NH3-SCR performance at low temperature compared with a bare Cu-SSZ-13 monolith. Furthermore, the introduction of a small amount of Mn greatly improved the mechanical stability of the monolithic structures. This work introduces a reliable, controllable, and versatile strategy for efficiently designing and manufacturing zeolite monolithic catalysts with interconnected channels for NH3-SCR. Experimental Methods Preparation of Cu-SSZ-13 powder Cu ions were introduced into SSZ-13 zeolite powder (SiO2/Al2O3 = 18.6) by an aqueous solution ion-exchange method.12 First, Cu(NO3)2·3H2O (99.5%; Tianjin Fuchen Chemical Reagent Factory, Tianjin, China) was dissolved in deionized water to obtain a Cu(NO3)2 solution (0.10 M). Commercial H-SSZ-13 powder (ZR Catalyst Co., Ltd., Dalian, Liaoning Province, China; Supporting Information Figures S1a and S1b) was added into the Cu(NO3)2 solution, and the pH of the solution was adjusted to 3.5 by 1.0 M HNO3. Ion-exchange was carried out in an 80 °C water bath for 2 h. Then the slurry was filtered, washed, dried, and the resulting powder was calcined at 550 °C for 6 h to obtain a Cu-SSZ-13 powder (Cu/Al = 0.30). Fabrication of 3D-printed zeolite monoliths Mn-doped Cu-SSZ-13 zeolite monoliths (3D-0.8MnOx/Cu-SSZ-13) were prepared via 3D printing technology. Specifically, 84.2 wt % Cu-SSZ-13 powder, 15 wt % iron-containing halloysite nanotubes (Fe-HNTs; Shanxi Province, China), 0.8 wt % manganese (added in the form of manganese nitrate tetrahydrate, Mn(NO3)2·4H2O, 99%; Beijing Innochem Science & Technology Co., Ltd., Beijing, China), moderate hydroxypropyl methylcellulose (HPMC; plasticizer, Shanghai Aladdin Reagent Co., Ltd., Shanghai, China), and deionized water were mixed and vigorously stirred at 20–25 °C for 2 h at 1500 rpm by a mechanical mixer (Eumix R30, Fluko Shanghai, China) to generate a printing ink with favorable viscosity and homogeneity. Then the monolithic catalysts with tailor-made structures were printed via a pneumatic-injection 3D printing system (EFD EV-3; Nordson Corp., Westlake, OH). The pristine 3D-printed monoliths were dried overnight and subsequently calcined under air at 600 °C for 6 h to improve the mechanical strength and remove HPMC. The method of fabricating bare Cu-SSZ-13 zeolite monoliths (3D-Cu-SSZ-13) was the same as that of 3D-0.8MnOx/Cu-SSZ-13. Specifically, the Cu-free MnOx/SSZ-13 monolith (3D-0.8MnOx/SSZ-13) was prepared using SSZ-13 powder to exclude the influence of Cu. For comparation, sepiolite nanofiber (Osthoff Omega Group, Norderstedt, Germany) and natural halloysite nanotubes (HNTs; Shanxi Province, China) with less contents of iron were also selected as printing ink additives to fabricate Cu-SSZ-13 zeolite monoliths. All printed parameters were the same as those of 3D-0.8MnOx/Cu-SSZ-13. The resultant catalysts were named as 3D-Cu-SSZ-13-Sepi and 3D-Cu-SSZ-13-HNTs, respectively. Characteristics of monolithic catalysts Transmission electron microscopy (TEM; Tecnai G2 S-Twin F20, FEI Company, Hillsboro, OR) and scanning electron microscopy (SEM; JSM-7800F, JEOL Ltd., Tokyo, Japan) were used to observe and record the morphologies and elemental distributions of the samples. Powder X-ray diffraction (PXRD) analysis was performed using a Rigaku D-Max 2550 diffractometer (Rigaku Corp., Tokyo, Japan) with Cu Kα radiation (λ = 1.5418 Å, 50 kV). The relative crystallinity was evaluated by comparing the total area of the peaks (at 2θ = 9.7°, 13.1°, 14.2°, 16.3°, 18.1°, 20.9°, 25.3°, 26.4°, 31.1°, and 31.6°) of the 3D-printed samples with that of Cu-SSZ-13 powder sample. The chemical compositions of the catalysts were measured using inductively coupled plasma optical emission spectroscopy (ICP-OES) analysis on a Perkin-Elmer Optima 3300 DV ICP-OES instrument (PerkinElmer, Inc., Waltham, MA). N2 adsorption–desorption measurements were performed at 77 K with a Micromeritics ASAP 2020 instrument (Micromeritics Instrument Corp., Norcross, GA) after the samples had been degassed under vacuum at 350 °C. A Thermo ESCALAB 250 spectrometer (Thermo Scientific, New York, NY) with monochromatic Al Kα excitation was used to measure the X-ray photoelectron spectroscopy (XPS) spectra of the catalysts. UV–vis spectra were collected on a Shimadzu UV-2450 spectrometer (Shimadzu Co., Kyoto, Japan). The temperature-programmed desorption of ammonia (NH3-TPD) was carried out on a Micromeritics AutoChem II 2920 automated chemisorption analysis unit with a thermal conductivity detector (TCD) under helium flow. The compressive strength experiments were captured on a universal testing machine (UTM6104; Shenzhen Sun Co., Ltd., Shenzhen, Guangdong Province, China), in which all catalysts were printed into cuboid structures with dimensions of 2, 2, and 0.85 cm in length, width, and height, respectively. A Discovery HR-2 hybrid rheometer (TA Instrument, New Castle, DE) was used to determine the viscosity of the printing ink. According to test requirements, the monolithic catalysts were ground into powders for PXRD, N2 adsorption-desorption, XPS, and NH3-TPD analysis. Catalytic testing The NH3-SCR activity tests were performed in a fixed-bed quartz flow reactor. To explore the influence of inorganic binders and manganese loading on the catalytic performance, the monolithic catalysts were ground into particles with a 40–60 mesh size. The reaction conditions of these granule samples were 500 ppm NO, 500 ppm NH3, 5% O2, Ar balance, with a total gas hourly space velocity (GHSV) of 200,000 mL/(g·h), and the reaction gas was continuously monitored by an online quadrupole mass spectrometer (QIC-20; Hiden Analytical Ltd., Warrington, UK). To further investigate the catalytic performance of 3D-printed catalysts, a 3D model was designed to match the size of the quartz tube (6 mm internal diam) used for the catalytic testing and the catalysts (3D-Cu-SSZ-13 and 3D-0.8MnOx/Cu-SSZ-13) were printed according to the 3D model. The balance gas of the test for the monolithic catalysts was nitrogen, GHSV = 30,000 h−1 with 2% H2O, and the other conditions remained the same as that of the granule samples. The gas concentrations were measured by a Fourier transform infrared (FTIR) spectrometer (MultiGas 2030HS; MKS Instruments, Inc., Andover, MA). The NOx conversion and N2 selectivity were calculated per eqs 1 and 2, respectively. NO x conversion = ( 1 − [ NO ] out + [ NO 2 ] out [ NO ] in + [ NO 2 ] in ) × 100 % (1) N 2 selectivity = ( 1 − [ NO 2 ] out + 2 [ N 2 O ] out [ NO ] in + [ NO 2 ] in + [ NH 3 ] in ) × 100 % (2) Results and Discussion Fabrication of self-supporting 3D-printed catalysts Self-supporting Mn-doped Cu-SSZ-13 zeolite monoliths with interconnected channels were constructed via 3D printing multifunctional composite materials. As illustrated in Figure 1, all powdery precursors including Cu-SSZ-13 zeolites ( Supporting Information Figures S1c and S1d), Mn(NO3)2·4H2O, and Fe-HNTs (inorganic binders, Supporting Information Figures S1e and S1f) were vigorously mixed and ground for 30 min, leading to a metal-containing homogeneous mixture with a formulation of 84.2 wt % Cu-SSZ-13 zeolite, 0.8 wt % Mn, and 15 wt % Fe-HNTs. Then a hydrosol of HPMC (plasticizer) was added to the mixture to generate an aqueous paste under stirring. The rheological properties of the printing inks before and after the introduction of Mn were carried out by a rheometer, and the results indicate that the inks achieve shear thinning effects desired for 3D printing ( Supporting Information Figure S2). Then the printing ink was loaded into a syringe with nozzle, and the predesigned structures were printed layer-by-layer via a pneumatic-injection 3D printing system at ambient temperature, resulting in zeolite monoliths with different structures. After drying and high-temperature calcination, the HPMC was removed and the monoliths showed increased mechanical strength. Figure 1 | Schematic illustration of the fabrication procedure of 3D-printed Mn-doped monolithic catalysts. Download figure Download PowerPoint By this facile construction strategy, self-supporting Mn-doped Cu-SSZ-13 zeolite monoliths (3D-0.8MnOx/Cu-SSZ-13) with different geometric structures and sizes were successfully manufactured (Figure 2a). The structural diversity proves that 3D printing is capable of direct fabrication of monolithic catalysts, which can meet the structure and size requirements in different application systems. The SEM images of a representative monolith show that the 3D-printed catalysts with interconnected channels reserve their internal structural integrity, and the crossing rods possess uniform dimensions and smooth outer surfaces (Figures 2b–2d). Figure 2e shows a high-magnification SEM image of the cross section of the monolithic catalyst. The zeolite particles are bonded together by inorganic binders, demonstrating the prominent structural integrity of the self-supporting 3D-printed monolith. Furthermore, some intercrystalline pores are formed due to the removal of HPMC matrix via drying and calcination. These highly interconnected channels and intercrystalline pores provide a clear path for mass transfer in the catalytic process. Figure 2 | (a) Digital photograph of self-supporting 3D-printed monoliths with different structures. SEM images of a representative monolith (S3): top view (b), side view (c), and cross-sectional view (d and e). (f) Elemental mapping images of a typical 3D-0.8MnOx/Cu-SSZ-13 monolith (S1, red: Si, blue: Al, yellow: Cu, orange: Mn, purple: Fe). Download figure Download PowerPoint The distribution of metals in the 3D-0.8MnOx/Cu-SSZ-13 was investigated by SEM elemental mapping (Figure 2f). It showed that the metal oxides were successfully introduced into zeolite monoliths, and the metal oxide nanoparticles were uniformly distributed throughout the 3D-0.8MnOx/Cu-SSZ-13 monoliths. The elemental compositional analyses of the catalysts were further measured by ICP-OES. As shown in Supporting Information Table S1, the metal loadings in 3D-0.8MnOx/Cu-SSZ-13 monoliths were Cu 2.1 wt %, Mn 0.75 wt %, and Fe 0.47 wt %, generally in line with the metal content of the original powder mixture used for printing monoliths (84.2 wt % Cu-SSZ-13, 0.8 wt % Mn, and 15 wt % Fe-HNTs). Physicochemical properties of 3D-printed monolithic catalysts The PXRD patterns of the 3D-printed monolithic catalysts with and without doping Mn, along with Cu-SSZ-13 powder are presented in Figure 3a. All samples show a typical CHA zeolite structure with good crystallinity, indicating that the process of 3D printing and the addition of Mn have no effect on the structure of the zeolite framework. There are no additional peaks attributed to copper or manganese compounds, which means the introduced metals are all uniformly dispersed into the catalysts. Nevertheless, the relative crystallinity of 3D-Cu-SSZ-13 (69.6%) and 3D-0.8MnOx/Cu-SSZ-13 (68.7%) slightly decreased compared to Cu-SSZ-13 powders, which could be attributed to the presence of Fe-HNTs and the sintering during the calcination process. Figure 3 | PXRD patterns (a) and N2 adsorption–desorption isotherms (b) of Cu-SSZ-13 powder, 3D-Cu-SSZ-13, and 3D-0.8MnOx/Cu-SSZ-13. Representative stress–strain curves and compressive strength of 3D-Cu-SSZ-13 and 3D-0.8MnOx/Cu-SSZ-13. Download figure Download PowerPoint The properties of Cu-SSZ-13 zeolite powder, 3D-Cu-SSZ-13, and 3D-0.8MnOx/Cu-SSZ-13 were by N2 adsorption–desorption As shown in Figure all isotherms at indicating typical characteristics of materials. The in 3D-Cu-SSZ-13 and 3D-0.8MnOx/Cu-SSZ-13 at the of are with in structures. The size distributions calculated by functional further the of in the 3D-printed monoliths ( Supporting Information Figure which is to the of Fe-HNTs ( Supporting Information Figure and the intercrystalline the of materials and the interconnected channels, the monolithic catalysts a highly which mass transfer and an increased chemical reaction The N2 and the of monolithic catalysts by the method ( Supporting Information are in Supporting Information Table After 3D the surface area of 3D-Cu-SSZ-13 from to and the volume from to owing to the of the 3D-printed monoliths. The introduction of Mn results in a in and of the monolithic catalysts, which is with the increase in from to ( Supporting Information Table S2). For practical applications, the mechanical stability of 3D-printed monolithic catalysts is a key The compressive strength tests of 3D-Cu-SSZ-13 and 3D-0.8MnOx/Cu-SSZ-13 were carried and the representative curves are in Figure All catalysts show a a stress is which is by a The compressive of the 3D-printed zeolite monoliths calculated from at tests are in Figure As the 3D-0.8MnOx/Cu-SSZ-13 with Mn doping could stress 3D-Cu-SSZ-13 The enhanced mechanical strength of 3D-0.8MnOx/Cu-SSZ-13 is that of the most reported self-supporting zeolites fabricated via 3D printing ( Supporting Information Table This is the introduction of Mn the ( Supporting Information Table to of the zeolite particles in the greatly the mechanical strength ( Supporting Information These results are with on metal-doped The properties of all samples were investigated by NH3-TPD and the results are shown in Figure The Cu-free MnOx/SSZ-13 monolith was further prepared and named as in which the sites introduced by Mn could be investigated the influence of Cu. for all samples desorption peaks at and respectively. The low-temperature desorption is attributed to NH3 or NH3 at the acid while the high-temperature at °C is with the NH3 on acid Specifically, the desorption at °C for Cu-SSZ-13 zeolite powder, 3D-Cu-SSZ-13, and 3D-0.8MnOx/Cu-SSZ-13 is to the acid sites introduced by copper The total amount of of the monoliths after 3D due to the addition of inorganic In acid sites can promote the low-temperature NH3-SCR while the acid sites play an role in catalytic activity at Notably, the of acid sites for 3D-0.8MnOx/Cu-SSZ-13 is increased due to the introduction of manganese oxide as acid sites in the which can NH3 and to improved catalytic Figure | NH3-TPD curves of Cu-SSZ-13 zeolite, 3D-printed monolithic catalysts, and Fe-HNTs UV–vis spectra of Cu-SSZ-13 and 3D-printed catalysts spectra of Cu on Cu-SSZ-13 zeolite powder, 3D-Cu-SSZ-13, and and Mn on 3D-0.8MnOx/Cu-SSZ-13. For test requirements, all monolithic catalysts were ground into Download figure Download PowerPoint The of active species on different samples was collected through UV–vis spectroscopy (Figure The of Cu-SSZ-13 zeolite powder and The can be attributed to while the at and the of with Cu-SSZ-13 zeolite powder, is a at in the 3D-printed catalysts owing to the introduction of Fe-HNTs ( Supporting Information Figure After the introduction of Mn, the based on the electron transfer from to The at is which be to the of manganese species with multiple valence states and redox To further the chemical states of active metal species on the surfaces of the Cu-SSZ-13 zeolite and the monolithic catalysts, spectra of Cu and Mn were collected and the results are shown in Figures and As all materials Cu and Cu peaks at and The Cu at is to the species, while a of is to the The peaks at indicate that are of species on the catalyst In the of Mn (Figure the Mn at and Mn at both to which the of the species on the catalyst The peaks at and are to indicating the presence of species on the Therefore, Mn mainly in the form of and at the surface of monolithic catalysts. high N2 selectivity and is active in the low-temperature NH3-SCR reaction of its enhanced electron transfer Catalytic Inorganic binders play a key role in the printability of zeolite printing inks and the physicochemical properties of the structures. To the influence of inorganic binders on the catalytic performance, materials nanofiber and natural HNTs with less contents of Supporting Information Figure were selected as printing ink additives for the fabrication of Cu-SSZ-13 zeolite monoliths, and the resultant catalysts were named as 3D-Cu-SSZ-13-Sepi and 3D-Cu-SSZ-13-HNTs, respectively. The 3D-printed monolithic catalysts were ground a

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