Solid-state Ion-exchange Method Research Articles

Harnessing solid-state ion exchange for the environmentally benign synthesis of high-efficiency Mn4+-doped phosphors.

In this study, a solid-state ion exchange (SSIE) method is proposed to synthesize a series of Mn4+-doped fluoride phosphors, which avoids the use of HF solution during the Mn4+-doping process. The obtained Mn4+-doped fluoride phosphors exhibit strong red emission with a quantum yield of 46%.

Post-synthesis metal (Sn, Zr, Hf) modification of BEA zeolite: Combined Lewis and Br⊘nsted acidity for cascade catalysis

Zeolites modified by Lewis acidic metal centers such as Sn, Zr, and Hf are promising catalysts for numerous reactions relevant to biorefining, such as isomerization of carbohydrates and Meerwein-Ponndorf-Verley (MPV) reduction of furans. Preferred catalysts contain these metal ions in the framework of large-pore BEA zeolite, requiring often complex multistep preparation procedures based on expensive organometallic precursors. Herein, we developed a facile approach for obtaining highly dispersed isolated Sn, Zr, and Hf incorporated in dealuminated BEA zeolite with high metal content (Si/M ratio of 50–75) via a solid-state grinding approach using simple inorganic metal precursors. The efficient incorporation of isolated metal sites in the BEA framework with high content was achieved by methanol treatment before calcination, which removes excess metal. The Lewis acid sites derive from isolated metal ions in open sites for Sn, Zr, and Hf, while Sn-modified BEA also contains closed Sn sites. The open Sn sites display the highest Lewis acidity. The Br⊘nsted acidity stems from silanols perturbed by Lewis acidic metal ions of open metal sites and the OH group connected to the open metal sites. The metal-modified zeolites are active in the cascade reductive etherification of cinnamaldehyde, involving the MPV reduction to cinnamyl alcohol and the subsequent etherification to cinnamyl propyl ether with the isopropanol solvent over Lewis and Br⊘nsted acid sites, respectively. Sn-modified BEA was the most active sample, which stems from its strongest Lewis acidity, which is crucial for the first MPV step. Sn modification of the optimized solid-state ion-exchange method was applied to various BEA zeolites with different morphologies (nanocrystalline, hierarchical, and conventional BEA), showing that pore hierarchization can further benefit cascade reductive etherification reaction.

Pore-engineering-dependence and hydrophobicity-dependence on stannosilicate zeolite catalyst for efficient Baeyer-Villiger oxidation

As robust heterogeneous catalysts, stannosilicate zeolites (in particular Sn-Beta) exhibit excellent catalytic performance in aqueous Baeyer-Villiger oxidation due to their unique activation ability of carbonyl group. For a specific Sn-containing zeolite, pore-engineering and hydrophobicity are generally two coupled factors to impact catalytic behavior. How to distinguish the function of each factor in this selective oxidation is still a pending question. Bearing this in mind, five stannosilicate zeolites (Sn-MFI, Sn-MWW, Sn-Beta, Sn-MCM-41, and Sn-Y) were prepared to establish the relationship between the structure (Lewis acidity, pore-engineering, and hydrophobicity) and catalytic performance. Particularly, hierarchical Sn-Y zeolite was post-synthesized by a simple solid-state ion-exchange method, where Sn4+ ions were incorporated into zeolite framework via reacting with silanol nests derived from dealumination process. In comparison with other stannosilicate zeolites, the obtained Sn-Y possessed excellent catalytic activity in Baeyer-Villiger oxidation irrespective of using aqueous hydrogen peroxide or bulky tert-butyl hydroperoxide as the oxidant. Structure-performance relationship revealed that Lewis acid site was the catalytically active center and the catalytic activity was depended on zeolite pore-engineering and hydrophobicity in aqueous B-V oxidation system. The relatively high catalytic activity of Sn-Y zeolite was ascribed to its excellent hydrophobicity and opened channel system. The former can be further enhanced by silanization treatment. Finally, the recyclability and deactivation mechanism were given insight. This work is aimed to provide some guidance for elaborately designing efficient stannosilicate zeolite catalyst for Baeyer-Villiger oxidation by precisely modulating pore-engineering and hydrophobicity.

In-situ observation and evaluation of silver precipitation behavior in borosilicate glass

Applying voltage to alkali-containing glass, doped with silver ions by the solid-state ion-exchange method, yields silver precipitates inside the glass. We attempted in-situ observation of the precipitation phenomena to elucidate the silver precipitation mechanisms, where the direction of the voltage application was rotated 90 deg. to increase the precipitation area compared to that of our previous method. The results show that the shape of the precipitate changed from clumpy to dendritic as the applied voltage increased. The shape of the precipitate, predicted by the dielectric breakdown model, implied that the higher the precipitation probability (i.e., the higher the frequency of a silver ion to encounter with the precipitate), the more branches the precipitate formed. In addition, the un-doped, silver-doped, and silver-precipitated areas inside the glass were modeled as electrical resistances to predict the growth behavior of the precipitated areas.

Mechanistic insight into the effect of active site motif structures on direct oxidation of methane to methanol over Cu-ZSM-5.

Direct oxidation of methane to methanol (DMTM), a highly challenging reaction in C1 chemistry, has attracted lots of attention. Herein, we investigate the continuous H2O-mediated N2O-DMTM over a series of Cu-ZSM-5-n zeolites prepared by a solid-state ion-exchange method. Excellent CH3OH productivity (194.8 μmol gcat-1 h-1) and selectivity (67.1%) can be achieved over Cu-ZSM-5-0.3%, which surpasses most recently reported zeolite catalysts. The effect of the active site motif structure on the reaction was systematically investigated by the combined experimental and theoretical studies. It has been revealed that both the monomeric [Cu]+ and binuclear [Cu]+-[Cu]+ sites function to produce CH3OH, following the radical rebound mechanism, wherein the latter one plays a dominant role due to the synergistic effect of neighboring [Cu]+ that can efficiently reduce the N2O dissociation barrier to generate active oxygen for CH4 oxidation. Microkinetic modeling results further show that the dicopper site possesses a much higher net reaction rate (1.23 × 105 s-1) than the monomeric Cu site (0.962 s-1); moreover, H2O can shift the rate determining step from the CH3OH desorption step to the N2O dissociation step over the dicopper site, thereby efficiently favoring CH3OH production and resisting carbon deposition. Generally, the study in the present work would substantially favor other highly efficient catalyst designs.

Copper-zeolites Prepared by Solid-state Ion Exchange - Characterization and Evaluation for the Direct Conversion of Methane to Methanol

AbstractDirect conversion of methane to methanol (MTM) over Cu-zeolites is a so-called “dream reaction” for the chemical industry. There is still a lot that can be done in order to optimize the reaction by e.g. achieving a deeper understanding of the reaction mechanism and the nature of the Cu-sites. In this study, we investigated a solid-state ion exchange method to incorporate CuI ions into zeolites (MOR, BEA, ZSM-5 and FAU), as a more scalable technique. The solid-state ion exchange led to a Cu/Al ration of about 0.8, however with a heterogeneous distribution of Cu. Regardless, Fourier transform-infrared spectroscopy still revealed that most Brønsted acid sites were exchanged in all four samples. Further, CH4-temperature programmed reaction experiments showed that some Cu-sites formed were reactive towards CH4, with CuI-MOR and CuI-FAU having the largest CH4 consumption. Ultimately, the CuI-zeolites were tested in the MTM reaction and proved capable of producing methanol, even without the presence of Brønsted sites. A MOR with lower Cu/Al ratio (0.30) was also tested for comparison, and as this sample obtained a much higher productivity than the CuI-MOR with high Cu-loading (0.10 vs. 0.03 molMeOH/molCu), it was demonstrated that some fine-tuning is necessary to obtain the active Cu sites for methane activation.

Understanding the Catalytic Deactivation upon Hydrothermal Aging at 850 °C of WO3/Fe-Cu-ZSM-5 Catalyst for Selective Catalytic Reduction of NO by NH3

A WO3/Fe-Cu-ZSM-5 catalyst was prepared using the solid state ion exchange method (SSIE) and its performance for the Selective Catalytic Reduction of NO with NH3 (NH3-SCR of NO) was investigated. The study shows that the tungsten addition can slightly improve the high temperature catalytic activity of Fe-Cu-ZSM-5. The influence of hydrothermal aging at 850 °C for 5 h on the structural and textural properties of WO3/Fe-Cu-ZSM-5 was also studied in this paper. The XRD and FE-SEM measurements did not indicate a breakdown of the zeolite structure upon steam treatment for both aged catalysts. The aged W-base catalyst demonstrates a lower deactivation and better catalytic activity for NO reduction than the bimetallic catalyst after hydrothermal aging despite the lower acidic properties as shown by FTIR-Pyr spectroscopy owing to the presence of tungsten oxide crystallites. The “severe” stage of aging occurring in the absence of W led to the formation of copper oxide agglomerates detected using STEM and H2-TPR techniques being responsible for the deterioration of SCR activity of the aged Fe-Cu-ZSM-5.

Effect of postsynthesis preparation methods on catalytic performance of Ti-Beta zeolite in ketonization of propionic acid

Heteroatom metal-zeolite, with heteroatom metal (oxide) dispersed in the zeolite framework, enables the reactions typically catalyzed by bulk metal oxide counterpart but with maximized the atomic utilization. However, the distribution of heteroatoms in the framework is strongly influenced by the preparation method. In this work, Ti-Beta zeolites were postsynthesized using the recrystallization (Ti-Beta-Re) and solid-state ion-exchange (Ti-Beta-SSIE) methods. Characterizations showed that more Ti species were incorporated in the tetrahedral framework site of Ti-Beta-Re to form Lewis acid sites than in that of Ti-Beta-SSIE. In addition, intra-crystallite mesopores were developed in Ti-Beta-Re due to partial dissolution of BEA framework during alkaline etching and subsequent recrystallization of the etched framework. These zeolites were then tested for ketonization of biomass derived propionic acid at 350 °C and atmospheric pressure. The turnover frequency of ketonization was found to be 25% higher on Ti-Beta-Re (0.25 min−1) than on Ti-Beta-SSIE (0.20 min−1), whereas the apparent activation energy of 80 kJ/mol on Ti-Beta-Re is lower than 95 kJ/mol on Ti-Beta-SSIE. Moreover, the selectivity of 3-pentanone kept > 95% on Ti-Beta-Re while it dropped to ∼63% on Ti-Beta-SSIE with increase of reaction time at a space time of 2 h. This work demonstrated that the tetrahedrally coordinated Ti species are the active sites and the presence of intra-crystallite mesopores facilitates selective ketonization of carboxylic acids.

Low-cost Mn–Fe/SAPO-34 catalyst from natural ferromanganese ore and lithium-silicon-powder waste for efficient low-temperature NH3-SCR removal of NOx

The development of low-temperature selective catalytic reduction of NOx with NH3 (NH3-SCR) catalysts is desirable but still challenging. Herein, a low-cost Mn–Fe/SAPO-34 catalyst was successfully synthesized using natural ferromanganese ore (FO) and industrial waste lithium-silicon-powder (LSP) by solid-state ion exchange (SSIE) method, and showed high NH3-SCR activity at low temperature range (150–200 °C) with high N2 selectivity. After loading FO, Mn–O and Fe–O bonds on Mn–Fe/SAPO-34 were weakened, which were beneficial to electron transfer and the oxidation-reduction cycle of SCR. The coexisting of Mn and Fe promoted the dispersion of Fe, resulted in high amounts of Oa, Mn4+ and Fe3+ which facilitated the adsorption and activization of NH3 over Mn–Fe/SAPO-34 catalyst. The Brønsted and Lewis acid sites participate in NH3-SCR, and the adsorbed nitrate species could quickly react with the adsorbed NH3 species via the Langmuir–Hinshelwood (L-H) mechanism. The Mn–Fe/SAPO-34 integrated the advantages of low-cost, resource saving and environment friendly, giving a low-carbon and sustainable choice for the industrial application of NOx abatement.

Bilayer Silver Precipitation in Glass Formed by Alternate Doping of Silver and Sodium Ions and Additive Voltage Application

The solid-state ion exchange method enables to dope metal ions to alkali-containing glass surfaces. When silver is used as a dopant material, a silver precipitation layer is formed in the silver-doped area by additive voltage application. Because of the high electrical conductivity, the precipitation layer can be used as an internal wiring in a glass substrate. In this study, we tried to form bilayer wiring in a glass substrate. For the bilayer precipitation, two silver-doped areas are necessary to be separated by a silver-undoped area. Therefore, silver, sodium and silver ions were sequentially doped to a borosilicate glass surface. To prevent silver ions being mixed into the sodium-doped area, the diffusion behaviors of two ionic species were numerically analyzed. The temperature dependences of their diffusion coefficients were also determined by comparing experimental and numerical results carried out under various temperature conditions. Calculated results showed that low temperature doping of sodium ions to silver-doped area is preferable. By adopting suggested conditions, the formation of electrically-insulated two silver precipitation layer was achieved.

Ce-promoted Fe–Cu–ZSM-5 catalyst: SCR-NO activity and hydrothermal stability

Fe–Cu–ZSM-5 and Ce–Fe–Cu–ZSM-5 solids prepared using solid-state ion exchange method (SSIE) were tested in the NH3–SCR of NO reaction and were characterized using N2 physisorption at 77 K, MAS 27Al magnetic resonance, X-ray diffraction, scanning electron microscopy, EPR spectroscopy and transmission electron microscopy coupled to energy-dispersive X-ray spectroscopy in order to follow the effect of Ce addition on the textural and structural properties of Fe–Cu–MFI system as well as the detection of the changes in local environment and state of iron and copper species, and the degradation of the zeolite texture and structure after a severe aging treatment at 850 °C for 5 h. Fresh Ce-promoted sample showed better NO conversion up to 450 °C than unpromoted Fe–Cu–ZSM-5 catalyst. An activity loss was observed on aged catalysts, but remaining less pronounced for the catalyst containing Ce. The changes in catalyst structure and texture did not occur during aging, while a probable migration of metal active species and change in their coordination has occurred.

Recent Understanding of Low-Temperature Copper Dynamics in Cu-Chabazite NH3-SCR Catalysts

Dynamic motion of NH3-solvated Cu sites in Cu-chabazite (Cu-CHA) zeolites, which are the most promising and state-of-the-art catalysts for ammonia-assisted selective reduction of NOx (NH3-SCR) in the aftertreatment of diesel exhausts, represents a unique phenomenon linking heterogeneous and homogeneous catalysis. This review first summarizes recent advances in the theoretical understanding of such low-temperature Cu dynamics. Specifically, evidence of both intra-cage and inter-cage Cu motions, given by ab initio molecular dynamics (AIMD) or metadynamics simulations, will be highlighted. Then, we will show how, among others, synchrotron-based X-ray spectroscopy, vibrational and optical spectroscopy (diffuse reflection infrared Fourier transform spectroscopy (DRIFTS) and diffuse reflection ultraviolet-visible spectroscopy (DRUVS)), electron paramagnetic spectroscopy (EPR), and impedance spectroscopy (IS) can be combined and complement each other to follow the evolution of coordinative environment and the local structure of Cu centers during low-temperature NH3-SCR reactions. Furthermore, the essential role of Cu dynamics in the tuning of low-temperature Cu redox, in the preparation of highly dispersed Cu-CHA catalysts by solid-state ion exchange method, and in the direct monitoring of NH3 storage and conversion will be presented. Based on the achieved mechanistic insights, we will discuss briefly the new perspectives in manipulating Cu dynamics to improve low-temperature NH3-SCR efficiency as well as in the understanding of other important reactions, such as selective methane-to-methanol oxidation and ethene dimerization, catalyzed by metal ion-exchanged zeolites.

Preparation of CuHY catalyst via solid-state ion exchange method and its catalytic performance in isobutane/2-butene alkylation.

CuHY samples prepared by solid-state ion exchange of HY zeolite with CuCl were used as catalysts in isobutane/2-butene alkylation. The results show that both the addition amount of CuCl and the calcination temperature affect the ion exchange degree. Cu+ can be introduced into Y zeolite by replacing H+ in the HY zeolite after the solid-state ion exchange, causing a decrease of the amount of Brønsted acid sites and an increase of that of Lewis acid sites. When taking CuHY as the catalyst in isobutane/2-butene alkylation, the 3d104s0 valence electron configuration of Cu+ makes it favorable for inhibiting the oligomerization of 2-butene and accelerating the hydride transfer reaction rate by indirectly increasing the local isobutane/olefin ratio around the acid sites of the catalyst. As a result, the selectivity of C8 and trimethylpentanes over CuHY in alkylate are improved compared with those of HY.

Nature of active Fe species and reaction mechanism over high-efficiency Fe/CHA catalysts in catalytic decomposition of N2O

Fe/CHA catalysts for N2O decomposition with various Fe loadings (Fe/SAPO-34 and Fe/SSZ-13) were synthesized by a solid-state ion exchange method. Under the same reaction conditions, obviously superior activities of Fe/CHA catalysts were observed in comparison with the current state-of-the-art Fe/zeolite, i.e., Fe/FER. Meanwhile, Fe/CHA catalysts exhibited a robust high-temperature hydrothermal stability. The characterization results and density functional theory (DFT) calculations indicated that the dispersion of Fe species over Fe/CHA catalysts was strongly influenced by the nature of the support, although SAPO-34 and SSZ-13 have similar morphology. Combined with the catalytic performance, dinuclear [HO–Fe–O–Fe–OH]2+ species were identified as the most active Fe species for Fe/CHA catalysts in the N2O decomposition reaction. Furthermore, the dimeric Fe species in SSZ-13 were more active than those in SAPO-34, due to lower Fe–O binding energies. Finally, DFT calculations provided a comprehensive understanding of the N2O decomposition mechanism over Fe/CHA catalysts.

An Enhanced Li3AlH6 Anode Prepared by a Solid-State Ion Exchange Method for Use in a Solid-State Lithium-Ion Battery

An Enhanced Li3AlH6 Anode Prepared by a Solid-State Ion Exchange Method for Use in a Solid-State Lithium-Ion Battery

Smart Modification of HZSM-5 with Manganese Species for the Removal of Mercury.

In this study, a series of Mn-modified HZSM-5 samples were synthesized using the solid-state ion-exchange method, and the effects of the manganese loading amount, calcination temperature, reaction temperature, and gas components on mercury removal efficiency were systematically explored. Given that the mass ratio of HZSM-5 to KMnO4 and the calcination and reaction temperatures were set to 10:2.6 and 400 and 150 °C, Hg0 removal efficiency could reach a peak value of 96.4% when exposed to the flue gas containing 5% O2 and N2 as the balance. Among the various gas components, O2 and NO showed a positive impact on Hg0 removal; Hg0 removal efficiency could even reach ca. 100% when O2 and NO were simultaneously introduced. In contrast, the introduction of SO2 led to a decline of Hg0 removal efficiency by ca. 16%. In addition, Hg0 removal efficiency could still retain ca. 92% of that for the fresh sample after six regeneration and reuse cycles, which is indicative of a satisfactory stability and renewability. Finally, Mars–Maessen mechanisms dominated in the mercury chemical adsorption process.

Influence of extra-framework Al in Fe-MOR catalysts for the direct conversion of methane to oxygenates by nitrous oxide

Iron-containing zeolites play an important role in the selective oxidation of methane to oxygenates by nitrous oxide. A solid-state ion exchange method is adopted to prepare Fe-MOR zeolite catalysts with different amounts of extra-framework Al. EPR spectra and UV–vis spectra show that the percentage of iron ions in tetrahedral or octahedral coordination increases while those of clustered Fe species decrease by the addition of extra-framework Al species. Nitrous oxide titration reveals that more active Fe centers are formed, which promote the nitrous oxide consumption. The number of active centers in the catalyst with the introduction of extra-framework Al is about four times that of the catalyst without the addition of extra-framework Al. Due to this, there is an increase in the methane conversion, total selectivity and yield of oxygenates.

Catalytic behaviour of molybdenum-based zeolitic materials prepared by organic-medium impregnation and sublimation methods

Molybdenum-exchanged ZSM-5 catalysts were tested in ethane ammoxidation into acetonitrile at 500 °C and at a very low contact time (0.08 s). The solids were prepared by sublimation, impregnation in CCl4 and solid-state ion exchange methods. The hydration state of the zeolite strongly affected the nature of MoCl5 and Mo(CO)6 decomposition products and, therefore, the concentration of stabilized Mo species in the final catalysts. In effect, using dehydrated ZSM-5 zeolite, the sublimation of MoCl5 led to the most active catalyst (TOF = 8.78 s−1) due to the presence, essentially, of [MoO4]2− (77%) and [Mo2O7]2− (10%) besides less-active crystalline MoO3 (12%) and traces of heptamers. However, the impregnation and the solid-state ion exchange of MoCl5 as well as the sublimation of Mo(CO)6 led to less-active catalysts owing to the presence of inefficient MoO3 oxide phase. In fact, moderate concentrations of crystalline MoO3 should coexist with [MoO4]2− species in order to activate C2H6 into C2H4 instead of enhancing the deep hydrocarbons’ oxidation.

Formation of Surface Oxygen Species and the Conversion of Methane to Value-Added Products with N2O as Oxidant over Fe-Ferrierite Catalysts

Formation of active oxygen species from N2O over Fe-ferrierite (Fe-FER) catalyst prepared by solid-state ion-exchange method at moderate temperatures was studied using spectroscopic and solid chara...

Low-Temperature Solid-State Ion-Exchange Method for Preparing Cu-SSZ-13 Selective Catalytic Reduction Catalyst

Solid-state ion-exchange (SSIE) is an effictive method to prepare Cu-SSZ-13, but usually requires high temperatures or assistance of NH3 for catalyst activation. Herein, an environmentally friendly...