Alkaline-treated Samples Research Articles

Effect of alkali treatment and fungal degradation on the nanostructure and cellulose arrangement in Scots pine cell walls – A neutron and X-ray scattering study

Research on new conservation treatments for historical wood requires considerable amounts of appropriate wood material, which is hard to acquire. Thus, we produced biologically and chemically degraded model wood that could be used as a representative material in future research on consolidating agents. Using chemical composition determinations, we found that fungal decay targeted mainly polysaccharides, while alkaline treatment mostly reduced hemicelluloses and lignin content. X-ray and neutron scattering showed that all decayed samples had increased disorder in microfibril alignment and larger elementary fibril cross-sections, and alkaline-treated samples had much larger elementary fibril spacing compared to those decayed by fungi. These nanoscale and chemical differences correlate with physical property changes. For example, decreased cellulose crystallinity and increased disorder of the microfibrils in degraded cell walls likely contribute to the lower elastic moduli measured for these cell walls. The obtained data improves understanding of how degradation alters wood structures and properties across length scales and will be valuable for future studies focusing on archeological wood. Moreover, it leads to the conclusion that it is more appropriate to develop treatments that consider not only spatial variability and degree of wood degradation but also the corresponding molecular and nanoscale changes in the cell walls.

Enhancing nutritional quality and bioactivity of wheat bran through acid and alkaline pretreatments

The effect of chemical processing, such as acid and alkaline pretreatments, on the phenolic profile, lipid components, and hydrosoluble protein content (HPC) in wheat bran (WB) was investigated. After acid pretreatment, the results provided an increase of over twofold in total reducing sugar (TRS). The sugars that have been identified are maltose, glucose, and fructose. After acid pretreatment, the total phenolic content increased by 41.95% compared with the untreated sample. Antioxidant potential, as assessed by the DPPH assay, significantly increased from 95.08 ± 1.13 μM TE/g DW in the untreated sample to 575.83 ± 2.41 μM TE/g DW following acid pretreatment. In the alkaline-treated sample, the total HPC increased to 16.58 ± 0.38 mg/100 g DW from 4.01 ± 0.17 mg/100 g DW. The fatty acid profile confirmed the presence of oleic acid (C18:1, n-9), linoleic acid (C18:2, n-6), and palmitic acid (16:0) as major components in analyzed samples. Chemical pretreatments significantly influenced all 13 identified phenolic compounds in WB, including avenanthramides, cinnamic acids (e.g., p-coumaric acid, ferulic acid, synaptic acid), and benzoic acids (e.g., vanillic acid). The study provides valuable insights into the development of sustainable approaches for using cereal bran to produce bioactive compounds with potential health benefits.

Improved Catalytic Performances of the NaOH-Treated ZSM-22 Zeolite in the 1-Butene Skeletal Isomerization Reaction: Effect of External Acid Sites.

In this paper, a series of alkaline-treated ZSM-22 zeolite samples were prepared by treating the parent ZSM-22 zeolite using NaOH aqueous solution with different concentrations. By investigating the effects of alkaline treatment on the parent ZSM-22 zeolite, we discovered that the alkaline treatment contributed to the reduction of Brønsted acid sites due to the coverage of extra-framework Al on its external surface. In addition, it was found that the alkaline-treated samples were favorable to the improvement of the isobutene yield and selectivity, while these features appeared to be low for the subsequent acid-washed counterparts in the skeletal isomerization reaction of 1-butene. These results indicate that the catalytic performance of ZSM-22 zeolite is related to reduced amounts of Brønsted acid sites in it. To further reveal the reasons for the promoted catalytic performances of the alkaline-treated ZSM-22 series zeolites, we studied the properties of coke deposited on the two series of samples using Raman spectroscopy and thermogravimetric analysis and mass spectrometry (TG/MS-TPO). It was shown that the carbon deposited on the alkaline-treated series samples was mainly distributed at the outer surface, while the coke was distributed to a relatively lesser extent at the exterior surface for the acid-washed series samples. Moreover, by partially passivating outer acid sites of the parent zeolite, the selected alkaline-treated zeolite, and acid-washed zeolite, their isobutene selectivities were all improved with the decrease in outer acid sites. These phenomena confirmed that the improved catalytic performances of the alkaline-treated samples are related to their decreased external Brønsted acid site density, which further demonstrated that the high isobutene yield and selectivity in the skeletal isomerization reaction of 1-butene is realized via the monomolecular reaction pathway of 1-butene.

PH and ultrasound driven structure-function relationships of soy protein hydrolysate

The structural, thermodynamic and functional properties of soy protein hydrolysate (SPH) modified by treatment at different pH values (3, 5, and 9 and pH 7 as control) followed by ultrasound treatment (240 W, 30 min) were investigated. The treatment of SPH at alkaline pH combined with ultrasound treatment resulted in a reduction in the particle size and turbidity, enhancement in the surface negative charge and disulfide bond (SS) content, and exposure of more surface sulfhydryl (SH) groups, resulting in increased surface hydrophobicity and fluorescence intensity compared to those of the samples treated at pH 3–7. In addition, the alkaline-treated samples were more structurally stable than those treated at other pH values, having higher denaturation temperatures and enthalpies; moreover, these samples had higher solubility and emulsifying and foaming capacities. In addition, ultrasound-assisted pH treatment altered the secondary and tertiary structures of SPH by altering the covalent and non-covalent interactions, although there was no effect on the molecular weight distribution of proteins. In conclusion, ultrasound-assisted pH treatment is an effective method to improve physicochemical properties of SPH for applications in the food industry.

Extraction and Characterization of Cellulose from Agricultural By-Products of Chiang Rai Province, Thailand.

Cellulose is an abundant component of the plant biomass in agricultural waste valorization that may be exploited to mitigate the excessive use of synthetic non-biodegradable materials. This work aimed to investigate the cellulose utilized by alkaline extraction with a prior bleaching process from rice straw, corncob, Phulae pineapple leaves, and Phulae pineapple peels. The bleaching and alkaline extraction process was performed using 1.4% acidified sodium chlorite (NaClO2) and 5% potassium hydroxide (KOH) in all the samples. All the samples, without and with the alkaline process, were characterized for their physico-chemical, microstructure, thermal properties and compared to commercial cellulose (COM-C). The extraction yield was the highest in alkaline-extracted cellulose from the corncob (AE-CCC) sample (p < 0.05), compared to the other alkaline-treated samples. The undesired components, including mineral, lignin, and hemicellulose, were lowest in the AE-CCC sample (p < 0.05), compared to raw and alkaline-treated samples. The microstructure displayed the flaky AE-CCC structure that showed a similar visibility in terms of morphology with that of the alkaline-treated pineapple peel cellulose (AE-PPC) and COM-C samples compared to other alkaline-treated samples with a fibrous structure. Fourier Transform Infrared (FTIR) and X-ray Diffraction (XRD) of AE-CCC samples showed the lowest amorphous regions, possibly due to the elimination of hemicellulose and lignin during bleaching and alkaline treatment. The highest crystallinity index obtained in the AE-CCC sample showed a close resemblance with the COM-C sample. Additionally, the AE-CCC sample showed the highest thermal stability, as evidenced by its higher Tonset (334.64 °C), and Tmax (364.67 °C) compared to the COM-C and alkaline-treated samples. Therefore, agricultural wastes after harvesting in the Chiang Rai province of Thailand may be subjected to an alkaline process with a prior bleaching process to yield a higher cellulose content that is free of impurities. Thus, the extracted cellulose could be used as an efficient, eco-friendly, and biodegradable material for packaging applications.

Use of Chènevotte, a Valuable Co-Product of Industrial Hemp Fiber, as Adsorbent for Pollutant Removal. Part I: Chemical, Microscopic, Spectroscopic and Thermogravimetric Characterization of Raw and Modified Samples.

FINEAU (2021–2024) is a trans-disciplinary research project involving French, Serbian, Italian, Portuguese and Romanian colleagues, a French agricultural cooperative and two surface-treatment industries, intending to propose chènevotte, a co-product of the hemp industry, as an adsorbent for the removal of pollutants from polycontaminated wastewater. The first objective of FINEAU was to prepare and characterize chènevotte-based materials. In this study, the impact of water washing and treatments (KOH, Na2CO3 and H3PO4) on the composition and structure of chènevotte (also called hemp shives) was evaluated using chemical analysis, X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) spectroscopy, X-ray computed nanotomography (nano-CT), attenuated total reflectance–Fourier transform infrared (ATR-FTIR) spectroscopy, solid state NMR spectroscopy and thermogravimetric analysis. The results showed that all these techniques are complementary and useful to characterize the structure and morphology of the samples. Before any chemical treatment, the presence of impurities with a compact unfibrillated structure on the surfaces of chènevotte samples was found. Data indicated an increase in the crystallinity index and significant changes in the chemical composition of each sample after treatment as well as in surface morphology and roughness. The most significant changes were observed in alkaline-treated samples, especially those treated with KOH.

Effect of Alkaline Treatment on Characteristics of Bio-Calcium and Hydroxyapatite Powders Derived from Salmon Bone

Alkaline treatment has been extensively implemented in the extraction process of hydroxyapatite (HAp) extraction from various kinds of bio-materials, such as animal bone and scales. The main purpose of such treatment is to remove proteinaceous substances from raw materials. The influence of the alkaline treatment that could alter not only the organic contents but also chemical composition—specifically the Ca/P mole ratios of bio-calcium, HAp, and the biphasic apatite powders derived from salmon bone, a by-product from the salmon industry—was investigated. Both HAp and biphasic apatite powders were obtained from the calcination of bio-calcium powders with and without alkaline treatment, respectively. An X-ray diffraction analysis confirmed the presence of hydroxyapatite and β-tricalcium phosphate (β-TCP) in the calcined bone powder without alkaline treatment while only a single phase of hydroxyapatite was observed in the alkaline-treated sample. Calcium and phosphorus contents were measured by an inductively coupled plasma optical emission spectrometer (ICP-OES). A variation of Ca/P ratios was observed among all samples, depending on the chemical and heat treatment conditions. Organic molecules, such as protein, fat, hydroxyproline, and TBARS, were significantly lowered in bio-calcium powders with the alkaline treatment. This work represents important research on chemical treatment prior to the raw material conversion process, which significantly influences chemical and phase compositions of the bio-calcium and hydroxyapatite powder derived from salmon bone waste.

Effect of surface treatment on moisture absorption, thermal, and mechanical properties of sisal fiber

Natural fibers are increasingly being used as composite reinforcement for both thermoplastic and thermoset resin, mainly for automotive application. Due to their hydrophilic nature, natural fibers have certain limitations during composite manufacture especially owing to their poor resin wettability, weak fiber–polymer interface, high moisture absorption, and being affected by high temperature in case of thermoplastic resin. This work investigates the impact of sisal fiber modification techniques on moisture absorption, thermal, and mechanical properties of the fiber. Four sisal fiber samples were prepared; untreated, alkaline treated, acetylated, and a combined alkaline-treated/acetylation samples. The samples were evaluated for their hygroscopic nature, thermal stability, and tensile properties. It is found that acetylation resulted in a reduction of moisture absorption of sisal fiber as the acetylated and alkaline-treated/acetylated samples recorded a decrease of 42% and 28%, respectively. Alkaline treatment increased the absorbency owing to the removal of hemicellulose and lignin. The thermogravimetric result revealed that alkaline treatment improved the thermal stability as the alkali-treated and alkali-treated/acetylated samples showed improvement in thermal properties. The acetylated sample resulted in a significant reduction in tensile strength. But, the results from tensile tests of the alkaline-treated samples showed an insignificant decrease in tensile strength and improvement in the modulus for all treated samples. Fourier-transform infrared and scanning electron microscopic analysis were included in the study to supplement the results with structural and microstructural changes. The effect of those treatments on the sisal–PET composite properties was studied and will be submitted in part 2 of the study.

Morphological Optimization of Chemical-Conversion Sodium Titanate and Chitosan/Glass Nanocomposite Dip Coatings Deposited on a Titanium Alloy

In this paper, the effect of some parameters of a two-step surface-modification process, consisting of alkaline treatment followed by chitosan/bioactive glass nanocomposite coating, on the surface morphology of Ti–6Al–4V alloy is investigated. According to the results, the heat treatment of the alkaline-treated sample is critical to obtain a crack-free structure. It was also found that the deposition of three composite layers with the immersion time of 3 min for each layer is optimal to develop a desirable distribution of the composite nanoparticles on the surface. In other words, a coordinated optimization approach of composite-coating variables is required to control the morphology of the deposits.

Effects of the ultrasound-assisted pretreatments using borax and sodium hydroxide on the physicochemical properties of Chinese fir

This work investigated the physicochemical properties of Chinese fir after ultrasound-assisted pretreatments with borax and sodium hydroxide additives in an aqueous solution. TGA, FTIR, and XRD were used to analyze the thermal degradation processes, changes in chemical structures, and crystallinity of the treated samples, respectively. Additionally, the release of volatiles from wood pyrolysis was measured on-line by the TG-FTIR apparatus. In thermal analysis, all samples showed main degradation stages at 220–500 °C, and alkaline compounds could efficiently shift the process to lower temperatures with lower maximum weight loss rate (MWLR) and more residues. From TG-FTIR, it was observed that CO2 was the primary gas product from pyrolysis in the alkaline-treated samples, while there were more carbonyl compounds released in the control and deionized water groups. Due to the destruction and removal of hemicellulose and lignin after alkaline treatments, the related peaks changed greatly. Changes in the ester groups caused by saponification also accounted for one of the most significant differences between samples. Moreover, except for the deionized water group without sonication, the crystallinity of the samples increased from 6.34% to 11.29%. Overall, comparing the samples treated with or without ultrasound, the results showed that the ultrasound treatment did influence the samples’ physicochemical properties, and its’ effects varied by the basicity of the solution. This in-depth investigation offers a better understanding of ultrasound-assisted and alkaline pretreatments of wood materials.

Evidence for the Formation of Benzacridine Derivatives in Alkaline-Treated Sunflower Meal and Model Solutions.

Sunflower extraction meal (SEM) is an economically interesting protein source. During alkaline extraction of proteins, the presence of chlorogenic acid (CQA) in the meal gives rise to the formation of o-quinones. Reactions with nucleophiles present in proteins can lead to green discoloration. Although such reactions have been known for a long time, there is a lack of information on the chemical nature of the reaction products. SEM and model systems consisting of amino acids and CQA were subjected to alkaline treatment and, for comparison, to oxidation of CQA by polyphenoloxidase (PPO). Several green trihydroxy benzacridine (TBA) derivatives were tentatively identified in all samples by UHPLC-DAD-MS/MS. Surprisingly, in alkaline-treated samples of particular amino acids as well as in SEM, the same six TBA isomers were detected. In contrast, the enzymatically oxidized samples resulted in only three TBA derivatives. Contrary to previous findings, neither peptide nor amino acid residues were attached to the resultant benzacridine core. The results indicate that the formation of TBA derivatives is caused by the reaction between CQA quinones and free NH2 groups. Further research is necessary to elucidate the structure of the addition products for a comprehensive evaluation of food and feed safety aspects.

Comparison of in vitro behavior of as-sprayed, alkaline-treated and collagen-treated bioceramic coatings obtained by high velocity oxy-fuel spray

Abstract Hydroxyapatite (HAp)–TiO2 samples obtained using high velocity oxy-fuel spray (HVOF), that had previously shown excellent mechanical behaviour, were innovatively surface treated in order to improve their biological performance. The chosen treatments were an alkaline treatment to increase –OH radicals density on the surface (especially on TiO2 zones), and a collagen treatment to bond collagen fibrils to the –OH radicals present in hydroxyapatite. These coatings were analysed using scanning electron microscopy, energy-dispersive X-ray spectroscopy and infrared spectroscopy, and tested for human osteoblast biocompatibility and functionality. In the case of the alkaline treatment, although the –OH radicals density did not increase compared to the as-sprayed coatings, a nanostructured layer of sodium hydroxycarbonate precipitated on the surface, thus improving biological behaviour due to the nanoroughness effect. For the collagen-treated samples, collagen fibrils appeared well-adhered to the surface, and in vitro cell culture tests showed that these surfaces were much more conducive to cell adhesion and differentiation than the as-sprayed and alkaline-treated samples. These results pointed to collagen treatment as a very promising method to improve bioactivity of HAp–TiO2 thermal-sprayed coatings.

The structural changes of lignin and lignin–carbohydrate complexes in corn stover induced by mild sodium hydroxide treatment

Non-woody biomass such as corn stover is a very abundant and sustainable biofuel feedstock in the US whose technical hurdles for enzymatic hydrolysis have not been adequately addressed. There is very little useful data on the lignin and the lignin–carbohydrate complexes of corn stover and the impacts of them on bioconversion to fermentable sugars. The following principal tasks were addressed, which will help to develop the roadmap of effective saccharification of corn stover: (1) corn stover was separated into stem, cob, and leaf; (2) lignin (cellulolytic enzyme lignin, CEL) and lignin–carbohydrate complexes (milled wood lignin, MWLc) were isolated from the extractive-free and the alkaline-treated samples, respectively; and (3) the structural changes of lignin and lignin–carbohydrate complexes (LCCs) were characterized by alkaline nitrobenzene oxidation, 13C, and 1H–13C HSQC NMR. The results indicated: (1) a significant amount of p-coumarate and ferulate esters was identified and quantified; (2) lignin of the alkaline-treated sample was more condensed; (3) an unanticipated amount of LCCs was quantified in the extractive-free sample, however, the amount of LCCs decreased significantly with the alkaline treatment. Therefore, lignin and LCCs of the treated sample should be characterized to elucidate their effects on the enzymatic saccharification.

Impact of pretreatment on solid state anaerobic digestion of yard waste for biogas production

Solid state anaerobic digestion, as a safe and environment-friendly technology to dispose municipal solid wastes, can produce methane and reduce the volume of wastes. In order to raise the digestion efficiency, this study investigated the pretreatment of yard waste by thermal or chemical method to break down the complex lignocellulosic structure. The composition and structure of pretreated yard waste were analyzed and characterized. The results showed that the pretreatment decreased the content of cellulose and hemicelluloses in yard waste and in turn improved the hydrolysis and methanogenic processes. The thermal pretreatment sample (P1) had the highest methane yield, by increasing 88% in comparison with digesting the raw material. The maximum biogas production reached 253 mL/g volatile solids (VS). The largest substrate mass reduction was obtained by the alkaline pretreatment (P5). The VS of the alkaline-treated sample decreased about 60% in comparison with the raw material.

Enzymatic hydrolysis of wood with alkaline treatment

Pulverized samples of wood, cedar and eucalyptus were treated with 5 N NaOH solutions at 25–150 °C. Hemicellulose and lignin content in the samples decreased with increasing treatment temperatures, while the recovery of glucose was maintained at nearly 90 %. X-ray diffraction analysis showed that the content of the original cellulose I structure in the samples decreased with increasing temperature, and most of the cellulose in the sample treated at 150 °C was converted to cellulose II by mercerization. Enzymatic hydrolysis of the alkaline-treated samples was carried out at 37 °C using solutions comprising a mixture of cellulase and β-glucosidase. The samples treated at higher temperatures showed better enzymatic degradability. Treatment with an alkaline solution of lower concentration (1 N NaOH) at 150 °C was also used. Despite significant quantities of hemicellulose and lignin being removed, mercerization was not induced. The enzymatic degradability was much lower than that of the sample treated with a 5 N NaOH solution at 150 °C. Thus, treatment with concentrated alkaline solution at high temperature led to not only the removal of hemicellulose and lignin, but also to modification of the cellulose structure, which resulted in high efficiency of enzymatic saccharification of the wood samples.

Mesoporous ZSM-22 zeolite obtained by desilication: peculiarities associated with crystal morphology and aluminium distribution

Mesoporous ZSM-22 zeolite (TON structure) is prepared by controlled silicon extraction in aqueous NaOH under different conditions of concentration, temperature, and time. The first challenge is to synthesize a pure ZSM-22 sample, since ZSM-5 and cristobalite impurities are hard to avoid. For this purpose, hydrothermal syntheses in autoclaves of 30–1000 cm3 using tumbling or magnetic mixing were conducted. The parent (calcined) and alkaline-treated samples are characterised by XRD, AAS, N2 and Ar adsorption, TEM, 27Al MAS NMR, and FTIR. The introduction of mesoporosity in ZSM-22 crystals is not straightforward due to their peculiar characteristics: the rod-like morphology of their small crystallites, the one-dimensionality of the ellipsoidal micropore system, and an uneven Al distribution. Compared to other zeolite frameworks such as MFI, the generation of up to 95 m2 g−1 of (both inter- and intracrystalline) mesopore surface area by NaOH treatment leads to a sizeable drop of the micropore volume (down to 0.006 cm3 g−1), attributed to blocking by re-deposited Al species. A subsequent mild acid treatment in aqueous HCl restores ca. 90% of the original micropore volume and increases the mesopore surface area to 114 m2 g−1. However, due to the particular Al distribution in the parent ZSM-22 crystals, only 37% of the original Brønsted acidity is recovered. A new descriptor ‘desilication efficiency’ is introduced to relate the mesopore area generated to the mass of zeolite dissolved. In the case of ZSM-22 nanorods and ferrierite platelets, the desilication efficiency is relatively low compared to ZSM-5, most likely due to the crystal morphology of the former two zeolites. The auxiliary mesoporosity developed in ZSM-22 brings new prospects to catalytic applications of the zeolite due to the extensive creation of pore mouths in the hierarchical sample.

Oxidation of methane to methanol and formaldehyde over Co–ZSM-5 molecular sieves: Tuning the reactivity and selectivity by alkaline and acid treatments of the zeolite ZSM-5 agglomerates

Alkaline treatment of templated Na–ZSM-5 zeolites with NaOH solutions resulted in the creation of intercrystalline mesopores within the zeolite agglomerates, while preserving the micropore volume and crystallinity. It was found that the zeolite external surface area increased with increasing NaOH concentration and pretreatment time. These alkaline-treated samples were loaded with cobalt and a linear relationship between the number of cobalt oxidic species and the external surface area of the zeolite could be established. This in turn leads to a linear relationship between the ZSM-5 surface area and the amount of methanol produced over Co–ZSM-5 from methane and oxygen at 423 K. Attempts to remove extra framework alumina species by an acid treatment were successful. However, this acid treatment increased, after Co-deposition, the amount of highly dispersed Co 2+ inside the ZSM-5 channels, which resulted in a higher selectivity towards formaldehyde. The nature of the charge-compensating cation also determined the cobalt speciation. Co–H–ZSM-5 samples contained more cobalt inside the channels and were more selective towards formaldehyde formation than Co–Na–ZSM-5 samples.

Preparation and Characterization of Activated Carbon from the Pyrolysis of Physic Nut (Jatropha curcas L.) Waste

Use of waste as raw material for producing porous carbon was investigated in this work. Physic nut (Jatropha curcas L.) residue from oil extraction for biodiesel production was pyrolyzed at 400–800 °C with hold times of 15, 120, and 240 min to obtain char precursors. Activated carbon, with favorable Brunauer–Emmett–Teller surface area in a narrow range, was prepared by soaking these chars in concentrated KOH, H3PO4, as well as a pure CO2 gas flash activator. The maximum specific surface area of 532.30 m2 g−1 was developed for the alkaline-treated sample. The carbon fraction of activated materials was as much as 90 wt %, significantly higher than the char precursor. Mesopore of 2–50 nm and total pore volumes of the materials were also significantly enhanced by these activations. Nitrogen adsorption isotherms of physic-nut-waste-activated carbons indicated that they were mainly mesopores. Pores of char activated by KOH and H3PO4 are irregular, of different shapes and sizes, and the macropores seemed to be connected to mesopores, especially for the KOH-activated case. Surface analysis of pyrolyzed and activated char using Fourier transform infrared spectroscopy indicated main functional groups that are considerably different to those of activated materials, which may lead to greater adsorption potential of activated samples. However, functional groups on each activated carbon are quite similar even with different activation processes. According to the data obtained, physic nut residue pyrolyzed at 800 °C and followed by KOH activation could be used as a low-cost adsorbent with favorable surface properties.

New application of hierarchical zeolite in life science: Fast trapping nitrosamines in artificial gastric juice by alkaline-tailored HZSM-5

To open a new application of zeolite in life science, hierarchical zeolites were prepared for the struggle of anti-cancer. Adsorption of N-nitrosopyrrolidine (NPYR), one of the volatile nitrosamines, by alkaline-treated MFI zeolite in artificial gastric juice with pH of 1.2 was investigated. Through the creation of mesopores in zeolite to fasten mass transport, all alkaline-treated samples exhibited higher adsorptive capability than HZSM-5 zeolite, and the equilibrium adsorption data could be fitted to the Freundlich equation.

Iron site modification upon alkaline treatment of Fe-ZSM-5 zeolites—Opportunities for improved N 2O decomposition activity

Alkaline treatment of Fe-ZSM-5 zeolite induces substantial intracrystalline mesoporosity and enhances the population of isolated Fe 3+ at the expense of oligonuclear clusters. In situ UV/vis showed that this redispersion affects the redox properties of the alkaline-treated zeolite and leads to lower activity in direct N 2O decomposition compared with the parent sample. Subsequent ion exchange of the alkaline-treated sample in ammonium nitrate solutions induced a renewed alteration in iron speciation, resulting in a similar constitution as in the parent zeolite but with a higher concentration of Fe 2+ sites able to activate N 2O. Mechanistic investigations in the TAP reactor furthermore affirmed that these newly obtained species had improved oxygen desorption, which correlates with the superior activity in direct N 2O decomposition.