Solid-state Ion-exchange Method Research Articles

Effect of Fe precursors on the catalytic activity of Fe/SAPO-34 catalysts for N2O decomposition

Different Fe/SAPO-34 catalysts were prepared by a solid-state ion exchange method and used to catalyze N2O decomposition. The catalytic performance of these catalysts was strongly related to their Fe precursors. Relevant characterization was carried out using X-ray diffraction, N2 adsorption-desorption, UV–vis spectroscopy, electron paramagnetic resonance, and H2 temperature-programmed reduction. The data indicated that the nature and distribution of Fe species in the catalysts changed with different Fe precursors used. Furthermore, monomeric Fe3+ ions and small oligomeric FexOy were the active Fe species for the Fe/SAPO-34 catalysts. Finally, it is reasonable to speculate that such a Fe source effect could be explored for other reactions.

Selective Catalytic Reduction of Nitric Oxide with Propylene over Fe/Beta Catalysts Under Lean-Burn Conditions

Fe/Beta catalysts were used for the selective catalytic reduction of nitric oxide with propylene (C3H6-SCR) under lean-burn conditions, which were prepared by liquid ion-exchange (LIE), solid-state ion-exchange (SIE), and incipient wet-impregnation (IWI) methods. The iron species on Fe/Beta were characterized and identified by a combination of several characterization techniques. The results showed preparation methods had a significant influence on the composition and distribution of iron species, LIE method inclined to produce more isolated Fe3+ ions at ion-exchanged sites than IWI and SIE method. C3H6-SCR activity tests demonstrated Fe/Beta(LIE) possessed remarkable catalytic activity and N2 selectivity at temperature 300–450 °C. Kinetic studies of C3H6-SCR reaction suggested that isolated Fe3+ species were more active for NO reduction, whereas Fe2O3 nanoparticles enhanced the hydrocarbon combustion in excess of oxygen. According to the results of in situ DRIFTS, more isolated Fe3+ sites on Fe/Beta(LIE) would promote the formation of the key intermediates, i.e., NO2 adspecies and formate species, then led to the superior C3H6-SCR activity. The slight decrease of SCR activity after hydrothermal aging of Fe/Beta(LIE) catalyst might be due to the migration of isolated Fe3+ ions into oligomeric clusters and/or Fe2O3 nanoparticles.

Characterization of soda-lime glass with aluminum doping as a planar wave guide using electric-field-assisted solid-state ion exchange method

Characterization of soda-lime has been done with aluminum doping on soda-lime glass using an electric-field-assisted solid-state ion exchange method (EFASSiE) to produce an aluminum coating on the glass. EFASSIE is an ion-exchange method that enables the doping of glass surfaces with aluminum ions. The variations used in ion exchange are temperature and electric fields. Variations of temperature start from 400°C until 500°C, increased temperature will cause the ions inside the glass to vibrate and forming a gap, allowed aluminum ions to penetrate into the glass structure. Variations of electric field start from 300-500 V/mm. Electric field that been exposed to the soda lime glass will accelerate the penetration process of the aluminum ion and pushes the smallest ion out of the glass. The results of the soda-lime glass characterization test shows that the greater the value of temperature and electric field used, refractive index of the soda lime after the ion exchange will increase. Otherwise, glass transmittance after ion exchange process has a relatively small compared to the glass before the process. Soda-lime glass Microstructure after the ion exchange process are known from SEM-EDX test, the result proved that alumunium ion penetrate into the soda-lime glass.

Cu/SAPO-34 prepared by a facile ball milling method for enhanced catalytic performance in the selective catalytic reduction of NOx with NH3.

Cu/SAPO-34 catalysts were prepared by different solid-state ion exchange methods, i.e., mechanical mixing (Cu/SAPO-34-M) and ball milling (Cu/SAPO-34-B), and were used for selective catalytic reduction of NOx with NH3 (NH3-SCR) reaction. Compared with Cu/SAPO-34-M, Cu/SAPO-34-B exhibited more excellent NH3-SCR catalytic activity. Various characterization methods, including XRD, SEM, N2 adsorption-desorption, UV-vis, H2-TPR, EPR, NO + O2-TPD, NH3-TPD, and in situ DRIFTS, were used to elucidate their different catalytic performances. The characterization results suggested that ball milling could be beneficial for increasing the amount of isolated Cu2+ ions in the Cu/SAPO-34 catalyst. In comparison with Cu/SAPO-34-M, Cu/SAPO-34-B had more isolated Cu2+ ions, which mainly contributed to the NOx adsorption and Lewis acid sites. Furthermore, ball milling could improve the redox property of the Cu/SAPO-34 catalyst. The in situ DRIFTS results verified that NH3 adsorbed on Lewis acid sites were more active than those adsorbed on Brønsted acid sites. Therefore, it was believed that ball milling was a suitable method to prepare more efficient Cu/SAPO-34 catalysts for NOx removal from diesel exhaust.

Selective catalytic reduction of nitric oxide with ammonia over Fe-Cu modified highly silicated zeolites

In the present study, the solid-state ion exchange method (SSIE) was applied to introduce iron and copper into highly silicate zeolites: beta (BEA, Si/Al = 12.5), ferrierite (FER, Si/Al = 10) and mordenite (MOR, Si/Al = 10). The activity of the prepared samples in the selective catalytic reduction of NO with ammonia (NH3-SCR) was measured. The highest performance was recorded for Cu-Fe-BEA followed by Cu-Fe-MOR while Cu-Fe-FER showed a low catalytic activity over the entire reaction temperature range. It is shown in this study that the zeolite framework is one of the parameters controlling the amount, environment and distribution of metal species formed during the ion exchange process in Cu-Fe-zeolite catalysts.

CH4 oxidation to oxygenates with N2O over iron-containing Y zeolites: Effect of preparation

Abstract Developing effective iron-incorporated zeolites and determining their active centers for the direct oxidation of CH4 to oxygenates have remained challenging topics so far. In this paper, we successfully prepare the highly-dispersed iron supported Y zeolites by a facile solid-state ion-exchange method with ferrocene, which was conducted under water-free conditions followed by a series of calcination. Moreover, extra-framework dinuclear Fe2 + complexes are identified as so-called active α-iron sites on zeolites. ICP-OES, N2 adsorption–desorption test, X-ray diffraction, solid-state 27Al NMR, N2O titration, TEM, EPR and 57Fe Mossbauer spectra were carried out to characterize properties of sample structure, acid sites, as well as the supported iron species. Characterization results indicate that high-temperature treatments have no effect on the typical structure feature of zeolites. Compared with catalysts synthesized by conventional impregnation, the samples prepared by the facile approach possess abundant dinuclear Fe2 + complexes but no Fe2O3 bulks and show weak acidity. These lead to a higher oxygenate selectivity in CH4 oxidation to oxygenates. Remarkably, the oxygenate (HCHO and CH3OH) selectivity of 6.5% at 375°C can be eventually obtained.

A Strategy for the Simultaneous Synthesis of Methallyl Alcohol and Diethyl Acetal with Sn-β.

A new strategy was developed to simultaneously produce two important chemicals, namely, methallyl alcohol (Mol) and diethyl acetal (Dal) from methacrolein in ethanol solvent at low temperature with the use of Beta zeolites modified by tin (Sn-β catalysts). All the Sn-β catalysts were prepared by the solid-state ion-exchange method, wherein the calcination step was conducted under different gas atmospheres. The catalyst precalcined in Ar (Sn-β-Ar) had a reduced number of extra-framework Sn species and enabled more Sn species to be exchanged into the framework as isolated tetrahedral SnIV , enhancing the catalytic activity of the Meerwein-Ponndorf-Verley (MPV) reaction. The sodium-exchanged Sn-β-Ar, with a reduced number of weak Brønsted acid sites, led to an even better selectivity for Mol, owing to the restriction of the side reactions such as acetalization, addition, and etherification. Under optimized catalyst and reaction conditions, the yield of Mol and Dal reached approximately 90 % and 96 %, respectively. The possible reaction pathways, along with a complex network of side products, was proposed after a detailed investigation through the use of different substrates as reactants. The fine-tuning of Sn-β catalysts through different treatments discussed in this work is of great significance toward the understanding and manipulation of complex reactions between α,β-unsaturated aldehydes and primary alcohols.

Functionalization of SSZ-13 and Fe-Beta with Copper by NH3 and NO Facilitated Solid-State Ion-Exchange

We show that functionalization of SSZ-13 (CHA) and Fe-beta (*BEA) with copper using a recently reported solid-state ion-exchange method, facilitated by NH 3 and nitrogen oxides (NO), is a viable route to prepare Cu-SSZ-13 and (Cu + Fe)-beta catalysts, starting from H-SSZ-13 and Fe-beta, respectively. The physicochemical properties of the prepared catalysts are characterized by XRD, UV-Vis-spectroscopy and STEM-EDS, confirming that copper originally present in the physical mixture of CuO and H-SSZ-13, and CuO and Fe-beta, is inserted into the micropores of SSZ-13 and Fe-beta, respectively. Activity measurements in gas-flow reactor show that the samples are active for NO reduction by NH 3 -SCR over a broad temperature range, i.e., 150–500 ∘ C. For the Cu-SSZ-13 catalysts, which have a copper loading range of 0.5–4 wt. %, the sample prepared from the physical mixture with a CuO/SSZ-13 ratio corresponding to 2 wt. % Cu is the most active catalyst for NH 3 -SCR under the present reaction conditions. Furthermore, the (Cu + Fe)-beta catalyst shows higher NH 3 -SCR activity over a broader temperature range and especially at low temperature as compared to the Fe-beta and Cu-beta counterparts. The results encourage further elaboration on sequential ion-exchange procedures for bimetallic functionalization of zeolites.

CuO/ZnO/Al2O3 Catalyst Prepared by Mechanical-Force-Driven Solid-State Ion Exchange and Its Excellent Catalytic Activity under Internal Cooling Condition

CuO/ZnO/Al2O3 catalysts were prepared by a mechanical-force-driven solid-state ion-exchange method, and their catalytic performance for methanol synthesis was investigated in a manufactured reactor with an internal cooling system. With the increasing of milling speed during ball-milling, the ion exchange between Cu2+ and Zn2+ in catalyst precursors is enhanced. After calcination, CuO nanoparticles are neighboring to ZnO nanoparticles and ZnO nanoparticles serve as spacers to prevent the agglomeration of CuO nanoparticles, leading to a cross-distribution of CuO and ZnO in catalysts. The as-prepared catalysts exhibit excellent catalytic activities, and the highest CO2 conversion and CH3OH yield at 240 °C and 4 MPa can reach 59.5% and 43.7%, respectively. The extraordinary catalytic performance can be attributed to both the cross-distribution of CuO and ZnO nanoparticles caused by solid-state ion exchange and the promotion of reversible CO2 hydrogenation reaction toward methanol synthesis by the internal cooling system.

Ag/Ag2SO3 plasmonic catalysts with high activity and stability for CO2 reduction with water vapor under visible light.

The conversion of CO2 into useful raw materials for fuels and chemicals by solar energy is described using a plasmonic photocatalyst comprised of Ag supported on Ag2SO3 (Ag/Ag2SO3) fabricated by a facile solid-state ion-exchange method and subsequent reduction with hydrazine hydrate. The optimum molar ratio of Ag(0)/Ag(+) was 5%. Visible light irradiation (>400nm) of the Ag/Ag2SO3 powder in the presence of CO2 and water vapor led to the formation of CH4 and CO with a quantum yield of 0.126%, and an energy returned on energy invested of 0.156%. The Ag/Ag2SO3 retained high catalytic activity after ten successive experimental cycles. The catalysts were characterized using X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy with energy-dispersive X-ray analysis, UV/Vis absorption spectroscopy, and Brunauer-Emmett-Teller analyses, as well as photocurrent action spectroscopy. It is proposed that the photocatalytic activity of the catalysts is initiated by energy conversion from incident photons to localized surface plasmon resonance oscillations of silver nanoparticles. This plasmonic energy is transferred to the Ag2SO3 by direct electron transfer and/or resonant energy transfer, causing the separation of photogenerated electron/hole pairs.

Synergy between vanadium and molybdenum in bimetallic ZSM-5 supported catalysts for ethylene ammoxidation

Ammoxidation of ethylene to acetonitrile was studied on V/ZSM-5, Mo/ZSM-5 and V–Mo/ZSM-5 catalysts prepared by a solid-state ion exchange method.

Catalytic oxidation of trichloroethylene over Fe-ZSM-5: Influence of the preparation method on the iron species and the catalytic behavior

Fe-ZSM-5 zeolite was synthesized by following different routes namely ion exchange from solution, impregnation and solid state ion exchange. All the catalysts were tested in the oxidation of trichloroethylene (TCE) in vapor phase. The catalysts were characterized using different physico-chemical technique which included BET surface area analysis, NH3-TPD analysis, H2-TPR analysis, XRD analysis, TEM analysis, DRS UV–vis, EPR, and XPS. The characterization results gave significant insight on the active sites responsible for the oxidation. It was found that Fe nanoparticles present in the extra framework of the zeolite were largely responsible for oxidation rather than the acidic sites. The catalysts prepared by impregnation or solid state ion exchange method were found to be active in the oxidation of TCE; however, comprehensively less active than the catalyst synthesized by ion exchange method. The activity of Fe-ZSM-5 was also compared with H-ZSM-5, and it was found that the activity and stability of Fe-ZSM-5 catalyst was much higher than the protonic form. Studies on the deactivation mechanism of the catalysts showed that the major reason for loss in activity was due to formation of FeCl3 rather than coke deposition.

The performance of pelletized Ce-Y and Ni-Y zeolites for removal of thiophene from model gasoline solutions

H-Y zeolite was prepared with Na-Y zeolite via ion-exchange method. Ni-Y and Ce-Y zeolites were then prepared with H-Y zeolite via solid-state ion-exchange (SSIE) method. The pellet form of the zeolites was employed for removal of thiophene from samples containing 194, 116 and 72 ppmw sulfur in a batch system at ambient condition. The removal of sulfur over the three types of the adsorbents decreased according to the following order: Ce-Y (81.7%) >Ni-Y (75.2%)>Na-Y (51.7%), indicating that the Ce-Y zeolite was the most effective adsorbent for removing of sulfur compounds from gasoline. Adsorption isotherms of thiophene on Ni-Y and Ce-Y zeolites were obtained and correlated with six well-known isotherms. The equilibrium data of thiophene adsorption were well fitted to the isotherms and the corresponding parameters and fitting error criteria of the isotherm equations were obtained.

Economical way to synthesize SSZ-13 with abundant ion-exchanged Cu+ for an extraordinary performance in selective catalytic reduction (SCR) of NOx by ammonia.

In this study, an economical way for SSZ-13 preparation with the essentially cheap choline chloride as template has been attempted. The as-synthesized SSZ-13 zeolite after ion exchange by copper nitrate solution exhibited a superior SCR performance (over 95% NOx conversion across a broad range from 150 to 400 °C) to the traditional zeolite-based catalysts of Cu-Beta and Cu-ZSM-5. Furthermore, the opportune size of pore opening (∼3.8 Å) made Cu-SSZ-13 exhibiting the best selectivity to N2 as well as satisfactory tolerance toward SO2 and C3H6 poisonings. The characterization (XRD, XPS, XRF, and H2-TPR) of samples confirmed that Cu-SSZ-13 possessed the most abundant Cu cations among three investigated Cu-zeolites; furthermore, either on the surface or in the bulk the ratio of Cu(+)/Cu(2+) ions for Cu-SSZ-13 is also the highest. New finding was announced that CHA-type topology is in favor of the formation of copper cations, especially generating much more Cu(+) ions than the others, rather than CuO. The activity test of Cu(CuCl)-ZSM-5 (prepared by a solid-state ion-exchange method) clearly indicated that Cu(+) ions could make a major contribution to the low-temperature deNOx activity. The activity of protonic zeolites (H-SSZ-13, H-Beta, H-ZSM-5) revealed the topology effect on SCR performances.

A Mathematical Modeling and Experimental Study on Adsorptive Desulfurization of Model Gasoline Using Synthesized Ni–Y and Ce–Y Zeolites

Abstract In this study, Ni–Y and Ce–Y zeolites are prepared using synthesized Na–Y zeolite through solid-state ion-exchange method. The adsorptive desulfurization of a model gasoline containing 194, 116 and 72 ppmw sulfur is evaluated in a batch system under ambient conditions. A dynamic model is established in order to investigate the performance of the adsorption process. The model predictions are compared with the obtained experimental results for thiophene adsorption on Ni–Y and Ce–Y zeolites from model solution containing different concentrations of thiophene, and a good agreement is observed. The model parameters: diffusivity and mass transfer coefficient are estimated by comparing the model predictions and experimental data.

NH3-SCR over Cu/SAPO-34 – Zeolite acidity and Cu structure changes as a function of Cu loading

A series of SAPO-34 catalysts with various Cu loadings (ranging 0.7–3.0wt%) were prepared by the solid state ion exchange method (SSIE) and the acid properties of the catalysts were characterized by NH3-TPD and in situ DRIFTS. During synthesis, more Cu migrates and exchanges at the Brønsted acid sites with increasing amounts of Cu precursor during the SSIE, resulting in a monotonic reduction in the total number of Brønsted acid sites. Interestingly, the Lewis acid sites created by Cu ions linearly increased with increasing Cu loading up to 2.0wt% and then only slightly increased with a further increase of Cu loading up to 3.0wt%. XRD, H2-TPR, UV–vis and DRIFTS were used to probe Cu structures. From the DRIFTS, two different perturbed TOT vibrations were observed for both the zeolite skeleton and NH3 adsorption spectra, indicating two different types of exchanged Cu species exist. This is also consistent with the results of NO adsorption DRIFTS spectra, in which two different Cu2+ sites were observed to adsorb NO molecules. One of the sites was considered to be the isolated Cu2+ species and the other could be another type of exchanged Cu site, possibly CuxOy clusters (dimeric or oligomeric Cu species). The isolated Cu2+ on each sample was further identified by UV–vis and quantified by H2-TPR experiments. Based on these results, isolated Cu2+ species were found to be the active sites of NH3-SCR at low temperature. Furthermore, CuO phases were detected on the samples with high Cu loadings via XRD. The presence of CuxOy may promote NH3 oxidation by O2, leading to the observed decrease in standard SCR performance at high temperature.

Preparation of caesium-substituted phosphomolybdic acid via solid-state ion exchange method

Abstract In this paper, we report the preparation of caesium-exchanged phosphomolybdic acid, Cs3PMo12O40, via the solid-state reaction between caesium chloride and ammonium phosphomolybdate. The calcination of this mixture was performed at 400 °C–600 °C. The thermal genesis of Cs3PMo12O40 from its precursors was explored using thermo-gravimetric (TGA), differential thermal (DTA), Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM) and energy dispersive X-ray analyses. The results obtained indicated that pure ammonium phosphomolybdate hydrate first lost its crystal water and later decomposed at temperatures higher than 450 °C. In the CsCl and (NH4)3PMo12O40 mixture, it was demonstrated that Cs+ moves into exchange positions at such temperature without destroying the Keggin structure of the heteropoly compound.

Catalytic performance of different types of iron zeolites in N2O decomposition

A series of Fe/zeolites (ZSM-35, ZSM-5, beta, and mordenite) samples with Fe/Al molar ratios of 0.33 were prepared using a solid-state ion-exchange method. A combination of ultraviolet-visible diffuse reflectance, in-situ Fourier-transform infrared, and in-situ visible Raman spectroscopic techniques, with a transient response method, was used to investigate the influence of the zeolite framework on the catalytic properties of the Fe/zeolites in N2O decomposition. The results show that the catalytic activity of the Fe/zeolites-HT (HT denotes high-temperature treatment) samples is in the order Fe/ZSM-35-HT > Fe/beta-HT > Fe/ZSM-5-HT > Fe/mordenite-HT. There is a linear relationship between the rate of N2O decomposition and the concentration of binuclear iron sites. This indicates that binuclear iron sites are the active sites for N2O decomposition. A correlation between the formation of binuclear iron sites and Fe ion distribution among the cationic sites is proposed. Two Fe(II) cations located in two adjacent six-membered rings in a 10-membered ring channel (α sites) or in two neighboring six-membered rings in an eight-membered ring channel (β sites) of Fe/ZSM-35 are favorable for the formation of active binuclear iron sites. Similar structure can also be formed in two adjacent six-membered rings in polymorphs A and B of beta zeolite or in the six-membered rings at the intersection of the straight and sinusoidal channels of the ZSM-5 framework. For the Fe/mordenite-HT sample, most of the iron species are present as isolated iron cations, so it has the lowest activity in N2O decomposition.

NH3-SCR Performance of Fresh and Hydrothermally Aged Fe-ZSM-5 in Standard and Fast Selective Catalytic Reduction Reactions

Hydrothermal stability is one of the challenges for the practical application of Fe-ZSM-5 catalysts in the selective catalytic reduction (SCR) of NO with NH3 (NH(3)-SCR) for diesel engines. The presence of NO(3) in the exhaust gases can enhance the deNOx activity because of the fast SCR reaction. In this work, a Fe-ZSM-5 catalyst was prepared by a solid-state ion-exchange method and was hydrothermally deactivated at 800 °C in the presence of 10% H(2)O. The activity of fresh and hydrothermal aged Fe-ZSM-5 catalysts was investigated in standard SCR (NO(2)/NOx = 0) and in fast SCR with NO(2)/NOx = 0.3 and 0.5. In standard SCR, hydrothermal aging of Fe-ZSM-5 resulted in a significant decrease of low-temperature activity and a slight increase in high-temperature activity. In fast SCR, NOx conversion over aged Fe-ZSM-5 was significantly increased but was still lower than that over fresh catalyst. Additionally, production of N(2)O in fast SCR was much more apparent over aged Fe-ZSM-5 than over fresh catalyst. We propose that, in fast SCR, the rate of key reactions related to NO is slower over aged Fe-ZSM-5 than over fresh catalyst, thus increasing the probabilities of side reactions involving the formation of N(2)O.

Hexane activation over vanadium modified zeolite ZSM-5

The influence on the form of ZSM-5, vanadium content and the elimination of the exterior surface, on the activity and selectivity of n-hexane oxidation was studied using a fixed bed reactor. Blank reactor studies (carborundum packed reactor) showed no conversion below 450 °C with the highest conversion (8 %) at 500 °C. The dominant products were found to be carbon oxides (Sel./% = 90) with minor selectivities to the hexene isomers (7 %) with the remainder being cracked products, THF and benzene. H-ZSM-5 with different SiO2/Al2O3 ratios (100 and 320) and Na-ZSM-5 (SiO2/Al2O3 ratio of 100) were tested under non-oxidative conditions. As the ratio of the SiO2/Al2O3 increased the aluminium content decreases and so too does the cracking ability of the zeolite (i.e. yield of cracked products dropped from 36 to 8 %). However, the use of the Na- form of the ZSM-5 zeolite completely eliminated acid cracking and therefore this system was further investigated. Na-V-ZSM-5 (~1 % loading) was synthesized using the solid state ion-exchange method. Time on stream experiments (fresh batch of catalyst for each experiment with sampling at the same time for a period of 24 h) were conducted and temperature (350, 400 and 450 °C), contact time (0.5, 0.8, 1.1 and 1.5 s) and fuel/air ratios (0.7, 1.3 and 2) were varied. The optimum conditions (Conv./% = 39) for terminal functionalised products were found to be at 400 °C at a contact time of 1.1 s and a fuel air ratio of 1.3. With the lower fuel air ratio of 0.7 (oxygen rich conditions), hexanal formation was favoured.