Cr Precursor Research Articles

Development of porous MIL-101 derived catalyst application for green diesel production

A novel three-dimensional MIL-101 derived porous carbon-based Ni-doped catalyst was synthesised via slow pyrolysis of Ni/MIL-101(Cr) precursor at 600 °C for 4 h. The catalytic activities were evaluated via one-pot hydrodeoxygenation (HDO) reactions by using palmitic acid (PA) as a model compound to produce green diesel within the range of a paraffinic hydrocarbon. The results show that Ni/P-MIL-101 exhibited excellent catalytic activity and recyclability in the HDO reaction of PA at a reaction temperature of 400 °C for 3 h under 3 MPa purified H2 pressure with 5 wt% catalyst loading. The conversion of PA and hydrocarbon selectivity were found to be 100 % with Ni loading > 8 wt% on P-MIL-101. In addition, both 25 and 14 wt% Ni/P-MIL-101 catalysts were able to recycle up to 7 and 15 times, respectively, and nearly 100 % alkane yield was achieved. The unique properties of Ni/P-MIL-101 catalyst such as finely dispersed added Ni, abundant acid and basic sites, and the presence of Cr2O3 active sites from pyrolysed MIL-101 with its mesoporous structures play a synergetic role in obtaining a very efficient catalyst for hydrodeoxygenation reaction. It is worth mentioning that the catalyst has an excellent catalytic effect on different kinds of fatty acid (ester) raw materials. Therefore, this Ni/P-MIL-101 catalyst has good prospects and potential for industrial application in green diesel production.

Sulfosuccinic acid-based metal-center catalysts for the synthesis of HMF from carbohydrates

5-Hydroxymethylfurfural (HMF) has been highlighted as a promising platform chemical and a keystone for the implementation of carbohydrate-based biorefineries. However, substrate cost remains a hurdle for the industrialization of HMF. Using Cr, Zr, and Ti precursors, three novel bifunctional catalysts with sulfosuccinic acid as ligand were developed, and their catalytic properties tested on the synthesis of HMF. Cr-SSA was the most effective in producing HMF, reaching 60% yield after 3 h. Similar results were obtained from sucrose, reaching 60% molar yield. Kinetic models were developed to provide a better understanding of the reactions’ pathway, suggesting that glucose-to-fructose isomerization was the preferred pathway for HMF formation when using Cr-SSA.

Cr-Zn/Ni-Containing Nanocomposites as Effective Magnetically Recoverable Catalysts for CO2 Hydrogenation to Methanol: The Role of Metal Doping and Polymer Co-Support

CO2 hydrogenation to methanol is an important process that could solve the problem of emitted CO2 that contributes to environmental concern. Here we developed Cr-, Cr-Zn-, and Cr-Ni-containing nanocomposites based on a solid support (SiO2 or Al2O3) with embedded magnetic nanoparticles (NPs) and covered by a cross-linked pyridylphenylene polymer layer. The decomposition of Cr, Zn, and Ni precursors in the presence of supports containing magnetic oxide led to formation of amorphous metal oxides evenly distributed over the support-polymer space, together with the partial diffusion of metal species into magnetic NPs. We demonstrated the catalytic activity of Cr2O3 in the hydrogenation reaction of CO2 to methanol, which was further increased by 50% and 204% by incorporation of Ni and Zn species, respectively. The fine intermixing of metal species ensures an enhanced methanol productivity. Careful adjustment of constituent elements, e.g., catalytic metal, type of support, presence of magnetic NPs, and deposition of hydrophobic polymer layer contributes to the synergetic promotional effect required for activation of CO2 molecules as well. The results of catalytic recycle experiments revealed excellent stability of the catalysts due to protective role of hydrophobic polymer.

Multifunctional interfaces for multiple uses: Tin(II)-hydroxyapatite for reductive adsorption of Cr(VI) and its upcycling into catalyst for air protection reactions

Evidence collected to date by our group has demonstrated that tin(II)-functionalized hydroxyapatites (Sn/HAP) are a newly discovered class of ecofriendly reductive adsorbents for Cr(VI) removal from wastewaters.In this work an upgraded series of Sn/HAP materials assured a maximum removal capacity of ≈ 20 mgCr/g, doubling the previously reported value for Sn/HAP materials, thanks to higher Sn-dispersion as proved by X-ray photoelectron spectroscopy and electron microscopy.Insights on kinetics and thermodynamics of the reductive adsorption process are provided and the influence of pH, dosage, and nature of Cr(VI) precursors on chromium removal performances have been investigated. Pseudo-second-order kinetics described the interfacial reductive adsorption process on Sn/HAP, characterized by low activation energy (21 kJ mol−1), when measured in the 278–318 K range.Tests performed in the 2–6 pH interval showed similar efficiency in terms of Cr(VI) removal.Conventional procedures of recycling and regeneration resulted ineffective in restoring the pristine performances of the samples due to surface presence of both Sn(IV) and Cr(III). To overcome these weaknesses, the used samples (Sn + Cr/HAP) were upcycled into catalysts in a circular economy perspective.Used samples were tested as catalysts in gas-phase catalytic processes for air pollution remediation: selective catalytic reduction of NOx (NH3-SCR), NH3 selective catalytic Oxidation (NH3-SCO), and selective catalytic oxidation of methane to CO2. Catalytic tests enlightened the interesting activity of the upcycled Sn + Cr/HAP samples in catalytic oxidation processes, being able to selectively oxidize methane to CO2 at relatively low temperature.

The S solubility of Cr and Al containing simulated low-activity waste glass

The presence of sulfur-containing molten salt phases during vitrification is a particular problem which can be detrimental to the melter. Borosilicate compositions were designed to explore both the effects of a fixed amount of Cr, as Cr2O3 or Na2CrO4, and the impact of Al2O3, on sulfur solubility as determined by progressively adding elemental S. The NABS series (with Al2O3) has a higher SO3 solubility of ∼3.5 mol% while the NBS series (without Al2O3) has a SO3 solubility of ∼2 mol%. Crystalline Cr2O3 formed in the NABS series upon the addition of S but is not present in the NBS series. At the highest S addition, a separate salt phase always forms, and was identified as Na2(S,Cr)O4 via electron dispersive spectroscopy, ultraviolet-visible spectroscopy, x-ray diffraction, and thermal analysis. Magic angle spinning nuclear magnetic resonance identified no change in the B coordination in either series as S is added, suggesting that the Na is scavenged from other locations, such as the Si sites, to charge compensate sulfate, whether in the glass or in the salt. The Cr precursor identity did not affect the observed overall behavior regarding sulfur, but did impact Cr redox as identified with Raman spectroscopy.

Ultrafine PdRu Nanoparticles Immobilized in Metal–Organic Frameworks for Efficient Fluorophenol Hydrodefluorination under Mild Aqueous Conditions

Ultrafine PdRu Nanoparticles Immobilized in Metal–Organic Frameworks for Efficient Fluorophenol Hydrodefluorination under Mild Aqueous Conditions

Selective laser sintering in reactive atmospheres: Towards in-situ synthesis of net-shaped carbide and nitride ceramics

Selective laser reaction sintering techniques (SLRS) were investigated to produce near net-shape non-oxide ceramic materials that were previously incompatible with powder-bed fusion additive manufacturing (AM) methodologies. Specifically, reaction-bonded layers of carbide and nitride materials (Cr3C2 and CrN) were fabricated using SLRS from a model system of Cr and Cr2O3 precursor materials. Varied particle sizes (<5–45 µm) were simultaneously chemically-converted and reaction bonded into layers during selective laser processing in 100 vol% CH4 or NH3 gas. For each precursor material, factors such as particle size, chemistry, optical properties, and microstructure were investigated using quantitative phase characterization and microstructural imaging to understand important aspects of carbide and nitride phase formation within an AM context. SLRS processing of metal or metal oxide precursor systems produced yields up to 100 wt% total for carbide formation and 100 wt% total for nitrides during reactive processing. However, when either metal or metal oxide precursor was processed by itself, the simultaneous synthesis and reaction bonding approach resulted in volumetric changes during in-situ gas-solid conversion that adversely affected layer microstructure. To circumvent the internal stresses that accompanied volumetric changes induced from conversion of the metal (which expands during conversion) and the metal oxide (which contracts), we demonstrate an alternative method for the production of near-net shape carbide and nitride materials for AM. By combining optimized ratios of metal/metal oxide precursors for processing in CH4 or NH3 reactant gas, the novel precursor formulations produced undistorted, crack-free refractory ceramic layers with sub-millimeter spatial resolution and viable layer thickness for powder bed fusion-AM. The results not only demonstrate the formation of near net-shape carbides and nitrides using AM-compatible techniques but suggest that transition metal carbide and nitrides may be compatible with AM processing even though they cannot be processed using more traditional laser-assisted AM approaches.

&lt;i&gt;Eichhornia Crassipes&lt;/i&gt; Plant Extract Templated Green Synthesis of Cr &lt;sub&gt;2&lt;/sub&gt;O &lt;sub&gt;3&lt;/sub&gt;/ZnO Composite Catalyst for the Degradation of Organic Dye

Water hyacinth (Eichhornia Crassipes) plant extract mediated ZnO, Cr2O3, and Cr2O3/ZnO composite catalysts with the addition of different amount of Cr precursor abbreviated as 0.1CrZn, 0.08CrZn, 0.06CrZn, 0.04CrZn and 0.02CrZn at fixed Zn content (0.1 molar) were synthesized by green co-precipitation routes. The resulting samples were characterized and tested for MB dye degradation under visible light irradiation. The catalytic degradation of MB dye by 0.08CrZn catalyst was achieved 85% within 90 min irradiation time. However, in the presence of 0.1CrZ, 0.062CrZ, 0.04CrZ, 0.02Cr, ZnO, and CrO3 catalysts, degrades only 80, 74, 79, 76, 52, and 74% of MB dye, respectively. The results indicated that the addition of optimum amount of Cr in the preparation of Cr2O3/ZnO composite catalysts with the aid of Eichhornia crassipes plant extract enhances the catalytic activities. This could be due to lowering the electron and hole separation and the porosity resulted from the plant extract in the catalyst system.

Influence of Film Coverage on CrOx Protective Layers for Pt-Based Water-Splitting Catalysts

The generation of hydrogen from renewable sources is of great interest in sustainable fuel production and storage. Emerging technologies such as photocatalytic water splitting are being considered as cost effective solutions for the production of hydrogen. In these applications Pt is commonly employed as it is highly effective for the hydrogen evolution reaction (HER), however loss of efficiency can be a problem due to back-reactions (for example the oxygen reduction reaction (ORR)) and to a lesser extent poisoning from contaminants (e.g. CO). CrOx-based protective layers have been shown to improve selectivity towards hydrogen for Pt catalysts, for which lower concentrations of the chromate precursor are preferred due to toxicity issues. Still, there is a lack of fundamental understanding of coating procedures and the levels required. In this study cyclic voltammetry and eQCM have been used to systematically investigate the dependence of concentration and deposition time on the extent of film growth and activity in the relevant reactions for photocatalytic water splitting. Specifically we highlight trends in the HER and ORR activity on the buried Pt surface and evaluate stability as a function of CrOx coverage. It has been shown by the experimental results that an optimum can be found between minimising the overpotential required for HER whilst fully protecting against the oxygen reduction back-reaction. Thus, these results reveal the lowest Cr precursor concentrations that can be effectively applied in photocatalysis.

Stainless steel-like FeCrNi nanostructures via electrodeposition into AAO templates using a mixed-solvent Cr(III)-based electrolyte

Electrodeposition of stainless steel-like materials such as FeCrNi alloy into micro- and nanotemplates provides a sustainable framework for creating biomedical-oriented micro- and nanocomponents with outstanding characteristics. While Cr(III)-based electrodeposition represents a ‘green’ alternative to toxic Cr(VI), its use is limited by Cr(III) aqueous chemistry which leads to the incorporation of impurities and the hydrogen evolution reaction (HER). These factors are responsible for low deposition efficiencies, brittleness and porosity. The current work sought to investigate the use of ‘green’ Cr(III)-glycine electrolyte to improve FeCrNi electrodeposition from Cr(III) precursors. Mixed-solvent electrolyte containing ethylene glycol (EG) was employed to reduce HER aftereffects. FeCrNi mixed EG electrolytes were compared to their aqueous counterparts to observe differences in Cr(III)-glycine complexation, coatings' composition and current efficiency. The feasibility of this method for creating nanostructures was verified by template-assisted electrodeposition using anodic aluminium oxide (AAO) templates. This study established that mixed-solvent electrolytes are an effective strategy to improve Cr(III)-based plating of alloys into miniaturised moulds. For the first time, electrodeposited FeCrNi nanowires (NWs) and nanotubes (NTs) were achieved via the framework developed in this work. The possible mechanisms controlling the morphological variations in FeCrNi nanostructures were discussed in relation to the kinetic and growth models in single metal electroplating into nanotemplates.

Age-Dependent Decline in Cardiac Function in Guanidinoacetate-N-Methyltransferase Knockout Mice.

AimGuanidinoacetate N-methyltransferase (GAMT) is the second essential enzyme in creatine (Cr) biosynthesis. Short-term Cr deficiency is metabolically well tolerated as GAMT–/– mice exhibit normal exercise capacity and response to ischemic heart failure. However, we hypothesized long-term consequences of Cr deficiency and/or accumulation of the Cr precursor guanidinoacetate (GA).MethodsCardiac function and metabolic profile were studied in GAMT–/– mice >1 year.ResultsIn vivo LV catheterization revealed lower heart rate and developed pressure in aging GAMT–/– but normal lung weight and survival versus age-matched controls. Electron microscopy indicated reduced mitochondrial volume density in GAMT–/– hearts (P < 0.001), corroborated by lower mtDNA copy number (P < 0.004), and citrate synthase activity (P < 0.05), however, without impaired mitochondrial respiration. Furthermore, myocardial energy stores and key ATP homeostatic enzymes were barely altered, while pathology was unrelated to oxidative stress since superoxide production and protein carbonylation were unaffected. Gene expression of PGC-1α was 2.5-fold higher in GAMT–/– hearts while downstream genes were not activated, implicating a dysfunction in mitochondrial biogenesis signaling. This was normalized by 10 days of dietary Cr supplementation, as were all in vivo functional parameters, however, it was not possible to differentiate whether relief from Cr deficiency or GA toxicity was causative.ConclusionLong-term Cr deficiency in GAMT–/– mice reduces mitochondrial volume without affecting respiratory function, most likely due to impaired biogenesis. This is associated with hemodynamic changes without evidence of heart failure, which may represent an acceptable functional compromise in return for reduced energy demand in aging mice.

Controlled Growth and Thickness-Dependent Conduction-Type Transition of 2D Ferrimagnetic Cr2 S3 Semiconductors.

2D magnetic materials have attracted intense attention as ideal platforms for constructing multifunctional electronic and spintronic devices. However, most of the reported 2D magnetic materials are mainly achieved by the mechanical exfoliation route. The direct synthesis of such materials is still rarely reported, especially toward thickness-controlled synthesis down to the 2D limit. Herein, the thickness-tunable synthesis of nanothick rhombohedral Cr2 S3 flakes (from ≈1.9 nm to tens of nanometers) on a chemically inert mica substrate via a facile chemical vapor deposition route is demonstrated. This is accomplished by an accurate control of the feeding rate of the Cr precursor and the growth temperature. Furthermore, it is revealed that the conduction behavior of the nanothick Cr2 S3 is variable with increasing thickness (from 2.6 to 4.8 nm and >7 nm) from p-type to ambipolar and then to n-type. Hereby, this work can shed light on the scalable synthesis, transport, and magnetic properties explorations of 2D magnetic materials.

Cr doped mesoporous silica spheres for propane dehydrogenation in the presence of CO2: Effect of Cr adding time in sol-gel process

Abstract CrOX-doped mesoporous silica spheres (Cr/MSS-X) were prepared by adding Cr precursors at different preparation stages using sol-gel method (X = 1, 2, 3) and incipient-wetness impregnation method (X = 4), and their catalytic performances of propane oxidative dehydrogenation were evaluated in the presence of CO2. The results indicate that for the Cr/MSS-X catalysts prepared by sol-gel method, Cr adding time significantly influences the Cr dispersion, surface physic-chemical properties and their catalytic performance. Cr/MSS-2 catalysts obtained by adding Cr precursor after the tetraethyl-orthosilicate (TEOS) show the optimal catalytic activity. Although Cr/MSS-1 also shows good CrOX dispersion, part CrOX wrapped in the center of mesoporous silica spheres presents weaker catalytic activity. In this work, the catalyst preparation method is quite facile and has the potential to be utilized for industrial production.

Study of Catalytic Combustion of Chlorobenzene and Temperature Programmed Reactions over CrCeOx/AlFe Pillared Clay Catalysts.

In this study, both AlFe composite pillaring agents and AlFe pillared clays (AlFe-PILC) were synthesized via a facile process developed by our group, after which mixed Cr and Ce precursors were impregnated on AlFe-PILC. Catalytic combustion of organic pollutant chlorobenzene (CB) on CrCe/AlFe-PILC catalysts were systematically studied. AlFe-PILC displayed very high thermal stability and large BET surface area (SBET). After 4 h of calcination at 550 °C, the basal spacing (d001) and SBET of AlFe-PILC was still maintained at 1.91 nm and 318 m2/g, respectively. Large SBET and d001-value, along with the strong interaction between the carrier and active components, improved the adsorption/desorption of CB and O2. When the desorption temperatures of CB and O2 got closer to the CB combustion temperature, the CB conversion could be increased to a higher level. CB combustion on CrCe/AlFe-PILC catalyst was determined using a Langmuir–Hinshelwood mechanism. Adsorption/desorption/oxidation properties were critical to design highly efficient catalysts for CB degradation. Besides, CrCe/AlFe-PILC also displayed good durability for CB combustion, whether in a humid environment or in the presence of volatile organic compound (VOC), making the catalyst an excellent material for eliminating chlorinated VOCs.

Structural and Diffuse Reflectance Study of Cr-Doped ZnO Nanorod-Pigments Prepared via Facile Thermal Decomposition Technique

Ceramic coloured nanopigments are promising for commercial cool paint applications. This study was carried out to examine the near infrared (NIR) reflectivity of Cr-doped ZnO nanopigments prepared by simple thermal decomposition of zinc acetate dihydrate and chromium(III) acetate hydroxide as precursors of Zn and Cr, respectively. XRD, FTIR and SEM have been used to characterize the microstructure and morphological properties of the synthesized nanopigments. The obtained results referred to ZnO wurtzite hexagonal structure in absence of other ZnO phases or any phases based on chromium. The obtained particles of the investigated samples are uniform rod-like shape with average diameter about 50 nm. The diffuse reflectance measurements exhibited the decrease in NIR reflectance with increasing Cr content. The sample with lower content of Cr, 0.5 wt% of Cr precursor to Zn precursor, exhibited a maximum value of NIR solar reflectance (R*) of 53.1% with respect to the other doped samples. The optical energy gap (Eg) of the investigated nanopigments were calculated using diffuse reflectance spectrum in view of Kubelka–Munk assumptions and the obtained average value of Eg is 3.219 eV with small standard deviation ± 0.015 eV.

High-temperature oxidation resistance of chromium-based coatings deposited by DLI-MOCVD for enhanced protection of the inner surface of long tubes

For nuclear safety issues, there is an international effort to develop innovative “Enhanced Accident Tolerant Fuels” (EATF) materials. EATF cladding tubes are of particular interest because they constitute the first barrier against radioactive fission species dispersal in case of accidental scenario such as LOCA (LOss of Coolant Accident). Actual nuclear fuel claddings are made from Zr-based alloys and to increase safety margins, both mechanical strength and resistance to high-temperature oxidation have to be improved. Several alternatives using high-temperature oxidation resistant coatings for outer-wall protection have been proposed worldwide but there is currently no solution for the inner-wall protection. In order to resist to high temperature steam environment upon LOCA transients, internal Cr-based coatings deposited by DLI-MOCVD (Direct Liquid Injection of MetalOrganic precursors) were investigated. These hard metallurgical coatings could also be used in high-temperature corrosive environments as those encountered in aeronautics and other industries to protect 3D complex components. Thanks to a suitable chemistry of the liquid Cr precursor, bis(ethylbenzene)chromium, different coatings were deposited including: metal Cr, chromium carbides CrxCy and mixed carbides CrxSizCy. The high-temperature behavior of these Cr-based coatings under oxidizing atmospheres has been studied using several techniques and various oxidation tests including pure steam environment followed by water quenching down to room temperature to be representative of LOCA situations. Amorphous CrxCy coatings showed the most promising properties. For instance compared to uncoated substrate, they shift the catastrophic oxidation towards higher temperatures and delay the complete oxidation of the substrate at 1473K of >2h. The results are discussed in terms of oxidation mechanisms and protection of the fuel claddings inner surface deduced from fine characterizations of the samples before and after oxidation tests.

Iron–Chromium Precursors for Hard-Magnetic Fe–Cr–Co Alloys

The effect of the chromium concentration on the magnetic properties of Fe–Cr precursors for hard-magnetic Fe–Cr–Co materials is studied. Nitrogen used as a sintering atmosphere and a long annealing time enhance are found to increase the coercive force Hc of the materials. The phase formation in Fe–30% Cr alloys is traced during heat treatment in nitrogen and argon atmosphere using thermal analysis.

Cr–Containing Magnetic Oxides in a Methanol Synthesis: Does Cr Ion Distribution Matter?

AbstractHere, we report on the development of novel Cr‐containing magnetic oxide nanoparticles (NPs) as catalysts for a syngas‐to‐methanol reaction which constitutes a sustainable route to obtain value‐added chemicals. These NPs have been synthesized in a one‐pot reaction by thermal decomposition of Cr acetylacetonate and doping metal acetylacetonates (if used) in the reaction solution of preformed magnetite NPs stabilized by polyphenylquinoxaline. For all the samples, the NP surface is enriched with Cr. At the same time, the Cr species are finely dispersed in the magnetite phase. This exposes Cr catalytic species to reacting molecules and creates an intimate contact between Cr3+ and Fe3O4. As a result, the methanol productivity rate for the Cr‐containing magnetic oxide prepared with 0.5 mmol of the Cr precursor is approximately three orders of magnitude higher than that for the conventional Cu/ZnO/Al2O3 catalyst. Additional doping of this Cr‐containing magnetic oxide with small amounts of Ni or La leads to even higher catalytic activity (by 40–49%).

Inverse Compton emission from a cosmic-ray precursor in RX J1713.7−3946

Recently, the High Energy Stereoscopic System (H.E.S.S.) reported two new interesting results for a γ-ray emitting supernova remnant, RX J1713.7−3946 (G347.3−0.5). The first result is the establishment of a broken power-law spectrum of GeV–TeV γ-rays. The other is a more extended γ-ray spatial profile than the one in the X-ray band. In this paper, we show both of these results can be explained by inverse Compton emission from accelerated electrons. If the maximum energy of electrons being accelerated decreases with time, the broken power-law spectrum can be generated by accumulation. Furthermore, the extended component of γ-ray profile can be interpreted as a CR precursor of currently accelerated electrons.

Solution combustion synthesis of nano-chromia as catalyst for the dehydrofluorination of 1,1-difluoroethane

Nano-Cr2O3 was prepared via solution combustion synthesis (SCS) with Cr(NO3)3·9H2O as the Cr precursor and glycine as the fuel. The effect of molar ratio of glycine to Cr in the feed during solution combustion was investigated. Cr2O3 samples were characterized by XRD, SEM, TEM, H2-TPR, and XPS. In addition, these catalysts were evaluated for the dehydrofluorination of 1,1-difluoroethane producing vinyl fluoride (VF, CH2=CHF). The results confirm that Cr2O3 is in relatively uniform flakes or flat particles via solution combustion synthesis with the particle size of 50–200 nm and composed by the aggregation of 58–77 nm nanoparticles. The specific surface area of higher than 30 m2 g−1 is achieved, which is comparable to the values obtained by solvothermal route. For the dehydrofluorination of 1,1-difluoroethane, high conversion levels (83 % for commercial catalyst and 93 % for SCS catalyst) are achieved at 350 °C, and the activity of SCS catalyst is at least 2× higher than that of commercial Cr2O3 at reaction temperatures below 300 °C. Compared with commercial Cr2O3, XPS, and H2-TPR reveal the higher CrO3 contents on the surface of Cr2O3 derived from SCS. It is suggested that CrO3 plays a major role in the catalytic performance as high-valent Cr species such as Cr(VI) are vital for the reaction because they could be transformed to the active species such as CrO x F y . In addition to the high activity, compared with commercial Cr2O3, SCS catalyst also show higher stability. Following the reaction of 120 h at 300 °C, no noticeable deactivation is observed while the activity of commercial Cr2O3 declines with TOS. High surface area and much smaller size of Cr2O3 crystalline favors the formation of CrO x F y during reaction over Cr2O3-3.33 catalyst probably contribute to the high activity and stability.