Low-temperature Reaction Research Articles

Promotion effect of nitrogen doping on the low-temperature NH3-SCR of NO over activated carbon: Characterization and mechanism analysis

Heteroatom nitrogen doping in carbon catalysts is recognized an effective strategy for tailoring the properties of carbon catalysts for various flue gas de-NOx applications. However, accurately discerning the active structures after nitrogen doping and elucidating the promotion effect on low-temperature selective catalytic reduction activity remains a formidable challenge under different nitrogen doping preparation conditions. In this study, a series of nitrogen-doped activated carbon catalysts was synthesized through the L16(45) orthogonal array design method, and the degree of influence of various preparation conditions on de-NOx catalytic activities was also assessed. The optimal preparation conditions determined by range analysis were employed to synthesize NOAC-17, achieving the NO conversion of 95% and N2 selectivity of 99% at 300 °C, respectively. Subsequently, various characterization results proved that nitrogen doping induced the formation of abundant basic groups. The imine, amide, amine, and N-6 groups altered the acid-base of the activated carbon surface and increased the adsorption of acidic NOx. The N-5 and N-Q groups enhanced electronic interaction in the carbon matrix and accelerated electron mobility in the catalytic reaction process. Moreover, the N-6 group played multiple roles beyond the aforementioned effect due to its special structure. It also enhanced the accumulation of oxygen vacancies, which were closely associated with further oxidation of adsorbed NO. The lone electron pair in the N-6 group within the activated carbon framework can alter the polarity of the catalyst, thereby exerting a positive influence on the adsorption and activation of NH3. The nitrogen-doped catalyst identified through range analysis of the orthogonal experiment primarily facilitated the NH3-SCR reaction via the E-R mechanism with supplementary contribution from L-H mechanism at low temperatures. The nitrogen doping conditions obtained for the activated carbon catalyst provide valuable insights for the strategic enhancement of its catalytic performance in low-temperature NH3-SCR reactions.

Role of Metal-Oxide Interfaces in Methanol Decomposition: Reaction of Methanol on CeO2/Ag(111) Inverse Model Catalysts.

Metal-oxide interfaces play a critical role in catalytic processes, such as methanol adsorption and decomposition reactions. In this work, we investigated methanol reactions on the inverse model CeO2/Ag(111) catalyst surfaces, i.e., submonolayer CeO2 films on Ag(111), under ultrahigh vacuum (UHV) conditions to specially address the role of CeO2-Ag interface in the catalytic methanol decomposition reactions. Using scanning tunneling microscopy (STM), low-energy electron diffraction (LEED), and synchrotron radiation photoemission spectroscopy (SRPES), we found that, at the submonolayer ceria coverages, the CeO2 nanoislands exhibit a hexagonal CeO2(111) lattice with fully oxidized Ce4+ on Ag(111). At higher ceria coverages, multilayer ceria nanoislands form on the Ag(111) surface instead of a well-ordered film. A combination of temperature-programmed desorption (TPD) and SRPES reveals that methanol adsorbs dissociatively on the CeO2/Ag(111) surfaces at 110 K, resulting in the formation of methoxy groups. These methoxy groups subsequently decompose via two pathways: (i) interaction with lattice oxygen to produce formate species at 230 K, which then decompose to CO, and (ii) direct dehydrogenation of methoxy to formaldehyde. Notably, the surface with submonolayer CeO2 film on Ag(111) demonstrates low-temperature reactivity (440 K) for methoxy dehydrogenation to formaldehyde, which occurs at a much lower temperature, compared to the surface of multilayer CeO2 on Ag(111) surface (530 K). This finding emphasizes that the CeO2-Ag(111) interfaces provide unique active sites for methoxy dehydrogenation reactions.

The chlorination and separation of aluminum using low-temperature sulfur chloride reagents

ABSTRACT There is currently no strategy for the permanent waste disposal or recycling for used nuclear fuels from research reactors. For this reason, low-temperature reactions have been developed for the chlorination of the Al alloys and subsequent separation from used nuclear fuels to reduce the volume of high-level waste in storage. Three sulfur chloride reagents – S2Cl2, SOCl2, and SO2Cl2—were tested, and two were found to quantitatively chlorinate Al metal and Al alloys under mild conditions. These low-temperature reactions proceed between 298 and 411 K, and up to 5 g of metal is chlorinated in 1–3 h. Preliminary results indicate that the reactivity and exothermicity of the reaction between the Al and sulfur chloride reagents is highly dependent on the surface area-to-volume ratio of the metal and the volume of solvent. Elemental S is produced as a by-product during the chlorination with S2Cl2 but can be quantitatively rechlorinated under mild conditions to regenerate the initial chlorination reagent. Therefore, in this case, chlorine is the only element consumed in the reaction, thus minimizing the waste generated during the chlorination process. The AlCl3 may then be separated from other materials present in Al 6061 or Al 8001 because of its high solubility in the sulfur chloride reagents. This process may also be extended to chlorinate Al from research reactor fuels.

Research Progress in the Composition and Performance of Mn-Based Low-Temperature Selective Catalytic Reduction Catalysts

NH3 selective catalytic reduction (NH3-SCR) is the most prevalent and effective method for removing nitrogen oxides. Over the past few decades, manganese (Mn)-based catalysts have demonstrated strong catalytic activity and have been extensively studied for low-temperature NH3-SCR reactions. This paper provides an in-depth introduction to four forms of Mn-based catalysts: single manganese oxide-based catalysts, binary Mn-based metal oxide catalysts, ternary and multivariate Mn-based metal oxide catalysts, and nano-Mn-based catalysts. Advances have been made in enhancing Mn-based catalysts’ redox performance and acidity, increasing the active component’s dispersion, lowering binding energy, enlarging specific surface area, raising the Mn4+/Mn3+ ratio, and enriching surface adsorbed oxygen by optimizing preparation methods, altering the oxidation state of active components, modifying crystal phases, and adjusting morphology and dispersion, along with various metal modifications. The mechanism of low-temperature NH3-SCR reactions has been elucidated using various characterization techniques. Finally, the research directions and future prospects of Mn-based catalysts for low-temperature NH3-SCR reactions are discussed, aiming to accelerate the commercial application of new Mn-based catalysts.

Boosting light olefin production from pyrolysis of low-density polyethylene: A two-stage catalytic process

The increasing production of waste plastics poses significant environmental and health risks. Low-density polyethylene (LDPE), a major component of plastic waste, is a high-quality feedstock for pyrolysis due to its high carbon and hydrogen content. Traditional pyrolysis methods, such as thermal cracking and one-step catalytic pyrolysis, have limitations in yield and selectivity of valuable products like light olefins. This study introduces a two-stage catalytic pyrolysis (TSCP) process aimed at enhancing the production of light olefins from LDPE. In the first stage, LDPE undergoes pyrolysis with MCM-41 catalyst, yielding a substantial number of liquid products and a minor portion of light olefins. The second stage utilizes Mg-ZSM-5 catalyst to further crack the high-temperature volatile matter into light olefins. The optimal conditions identified were 450 °C in the first stage and 500 °C in the second stage, achieving a maximum light olefin yield of 45.80 wt% and a low reaction temperature, decreasing the energy consumption. Additionally, the MCM-41 catalyst demonstrates excellent regeneration performance, with only a slight decrease in liquid yield after nine cycles. The Mg-ZSM-5 catalyst maintains high stability, with light olefin yield remaining at 83.60 % of the initial yield after 48 h of operation.

Effects of the surface properties and particle size of hydrated lime on desulfurization

In the gas treatment center in smelters, hydrogen fluoride (HF) is separated from the outlet gases of electrolysis cells, which are used to produce aluminum from alumina. However, SO2 largely remains in the effluent gas. Another method has to be developed to separate this gas which is harmful to the environment. In this study, semi-dry desulfurization of a SO2 containing gas was performed at low SO2 concentrations using hydrated lime [Ca(OH)2] as a catalytic desulfurizer under specific humidity conditions. The low reaction temperature of 100 °C and minimal use of the Ca-based desulfurizer under 17 % relative humidity achieved more than 95 % removal of SO2. The morphological changes and presence of sulfur in different lime samples were analyzed by scanning electron microscopy and energy-dispersive X-ray spectroscopy. Brunauer–Emmett–Teller (BET) analysis showed changes in the surface properties of hydrated lime after desulfurization. X-ray photoelectron spectroscopy (XPS) analysis provided the phase and composition identification of the sulfur species on hydrated lime and the CaSO3/CaSO4 product ratio. Based on the experimental results, the optimum catalyst surface area with a specific particle size is critical to the effective conversion of Ca(OH)2 into CaSO3 and CaSO4. The practicality of a Ca-based desulfurizer and its ability to convert into the required product may be the key to reducing the overall cost of desulfurization in aluminum industry.

Simplified synthesis of Pt-MnOx supported on three dimensional Co3O4 for catalytic removal of toluene

In this study, a simplified method was developed for synthesizing Pt-(MnOx)/three-dimensional (3D)-Co3O4 catalysts. This approach represents a convenient alternative to the typical procedure of initially synthesizing nanoparticles (NPs) and subsequently depositing them onto supports. The Pt1-(MnOx)1/3D Co3O4 catalyst, with a molar ratio of Pt:Mn=1:1, demonstrated excellent catalytic efficacy at a comparatively low reaction temperature and displayed commendable thermal stability during prolonged operation in the deep oxidation of toluene. The T90 (temperature required for 90% conversion) of Pt1-(MnOx)1/3D Co3O4 was merely 163 °C. Characterization analysis revealed that the catalyst's remarkable catalytic efficiency is attributed to the elevated concentration of oxygen vacancy defects on Pt1-(MnOx)1/3D Co3O4 and its low-temperature reducibility. In situ DRIFTS analysis was conducted to investigate the possible reaction pathway of Pt1-(MnOx)1/3D Co3O4. The results indicated that the rapid dehydrogenation of methyl and the demethylation of toluene facilitate the cleavage of the benzene ring on the Pt1-(MnOx)1/3D Co3O4 catalyst, due to the abundant absorption of oxygen species. This process enhances the catalytic combustion of toluene

Insight into the Pyrolysis Behaviors of Petroleum-Driven Mesophase Pitch via ReaxFF Molecular Dynamics and In Situ TG-FTIR/MS.

Mesophase pitch is regarded as a profoundly promising candidate for the production of advanced carbon-based multifunctional materials such as carbon fibers, carbon microspheres, and carbon foams owing to its excellent intrinsic properties. Consequently, a deeper understanding of pyrolytic chemistry is indispensable for the efficient and environmentally friendly utilization of mesophase pitch. In this study, details about the structure compositions and microscopic morphologies of petroleum-driven mesophase pitch (pMP) were investigated through ultimate, FTIR, XPS, and 13C-NMR analyses. Furthermore, a large-scale molecular model of typical pMP with 11,835 atoms was constructed to unveil the comprehensive pyrolysis behaviors and the underlying reactions. Significantly, the evolution of specific chemical bonds and the decomposition of crucial molecular fragments were elucidated within an amalgamation of experimental TG-FTIR/MS and ReaxFF MD simulation. Accordingly, three fundamental reaction stages were artificially divided, including the low-temperature reaction, rapid thermal decomposition, and the molecular condensation reaction. During the rapid thermal decomposition stage, the cleavages of C-C and C-O bonds cooperatively contributed to the formation of C2H4 and H2O gaseous products. As the temperature escalated to the molecular condensation stage, the pyrolysis process was governed by the dehydrogenation condensation, accompanied by an augmentation of C-C and H-H bonds and a diminution of C-O and C-H bonds. Additionally, the rare graphitization phenomenon was observed, suggesting a remarkable degree of structural organization in pMP. Overall, the results of ReaxFF MD simulations complement experimental observations, successfully reproducing the microstructure of pMP and atomic-scale pyrolysis behavior, thereby providing invaluable insights for the rational guidance of efficient utilization of pMP and other related carbonaceous precursors.

Spatial distribution and temporal evolution of wall-stabilized DME/O2 premixed cool flames

The low-temperature oxidation of dimethyl ether (DME) was investigated in premixed wall-stabilized cool flames at two equivalence ratios (ϕ) of 0.2 and 0.5. Using a time-of-flight mass spectrometry (TOF-MS) coupled with gas chromatography (GC), the spatial distributions of major intermediate species, including DME, CH2O (formaldehyde), CO, CO2, and CH3OCHO (methyl formate), were quantified under well-controlled boundary conditions. Moreover, the temporal evolutions of multiple intermediate species in the wall-stabilized cool flame ignition process were measured via TOF-MS, while the wall temperature was gradually ramped up from 550 K to 730 K. Several kinetic models were examined herein to assess the estimated low-temperature reactivity of DME by comparing the one-dimensional axisymmetric simulation results with the experimental data. Wall-stabilized cool flame structures at equivalence ratios ϕ of 0.2 and 0.5 were quantitatively examined with the major intermediate species. It is found that the kinetic models reasonably predict the onset of the reaction zone near the wall. Among these models, Kurimoto et al.’s model gives better predictions for the distributions of CH2O and CO, which are characteristic species of cool flames. In addition, time-resolved measurements of the unsteady cool flames identified the negative temperature coefficient (NTC) turnover points for different species across various temperature regions. It is also found that the Kurimoto et al. model still indicates a slightly higher reactivity of DME in the low-temperature range, resulting in earlier DME consumption and a shift of NTC window to lower temperatures at ϕ = 0.2.

Insight into Synergistic Brønsted and Lewis Acidic Deep Eutectic Solvent for Beckmann Rearrangement of Cyclohexanone Oxime

ε‐Caprolactam (CPL) is industrially produced by Beckmann rearrangement of cyclohexanone oxime (CHO) under fuming sulfuric acid, resulting in corrosive and environmental issues. Herein, we prepared triethylamine hydrochloride (TEAHC) and ZnCl2 formed deep eutectic solvent (DES) [TEAHC:2ZnCl2] with Brønsted and Lewis acid sites for efficient liquid rearrangement, achieving 100% conversion of CHO and 95.5% yield of CPL at 80 oC for only 1 h. The results show that ZnCl2 in [TEAHC:2ZnCl2] can promote the detachment of proton, which acts as Brønsted acid site combined with another ZnCl2 molecule to synergistically catalyze the reaction. In the Brønsted acid catalyzed process, the nitrogen atom in CHO as reactive site can be readily attacked by the proton to form protonated CHO, which subsequently undergoes rearrangement. By adding ZnCl2 into TEAHC to obtain [TEAHC:2ZnCl2], the formation of ZnCl2‐CHO complex results in a significant reduction in reaction energy barrier through synergistic effect of Brønsted and Lewis acids. Particularly, the fitted reaction kinetics and low activation energy also confirm the rearrangement can occur under low reaction temperature. Thus, the DESs with efficient catalytic performances for ketoxime rearrangements provide a potential method to design active sites for Beckmann rearrangements of oximes under mild reaction conditions.

Selective Hydrogenolysis Conversion of Polyethylene into Alkyl Oil Over Iridium-based Catalyst.

Plastic not only brings convenience but also places a great burden on the environment. Utilizing plastic as a low-cost feed-stock for producing valuable chemicals and fuels is one of the most attractive directions. Among the huge types of plastics, polyolefins (PO), especially polyethylene (PE), were the most abundant type and the most difficult to upgrade. Hydrocracking and hydrogenolysis operate at relatively low reaction temperatures which show promising applications. Herein, Iridium-based catalysts were developed and proved to be effective in PE hydrogenolysis under relatively mild conditions. Catalysts were characterized by TEM, HRTEM, SEM, HAADF-STEM, XPS, CO chemisorption and H2 chemisorption etc. The Ir catalysts showed similar reactivity but better selectivity for liquid products than Ru under similar conditions. A highest 92.7 % percent of liquid products could be obtained under 250 °C, 3 MPa of H2 in 8 hours with Ir/γ-Al2O3 catalyst. The support could also affect the performance, including Lewis acid amount, surface areas, and morphology. And we suppose Iridium catalysts could serve as another choice for plastic hydrogenolysis under mild conditions.

Research on Catalytic Pyrolysis Process of Coconut Coat of Tropical Agricultural and Forestry Wastes

The effects of reaction temperature, reaction time, heating rate, nitrogen flow rate, and catalyst quality on the oil yield and oxygen content in oil were investigated by using the single-factor principle. Too high and too low reaction temperature, nitrogen flow rate, heating rate, and reaction time improved the yield of bio-oil, but the oxygen content in bio-oil was higher. The reduction in catalytic dose is beneficial to the increase in oil yield but not conducive to the increase in aromatic compound content. The optimal reaction conditions were observed as a reaction temperature of 500 °C, a nitrogen flow rate of 110 mL/min, a heating rate of 20 °C/min, a reaction time of 15 min, a mass ratio of catalyst to coconut coat powder of 1, an oil yield of 4.97%, a water yield of 35.80%, and a solid yield of 30.78%. The gas yield was 28.45%, the oxygen content was 10.3%, and the aromatic compound content was 89.7%. The analysis of the catalytic cracking mechanism shows that most of the oxygen-containing compounds in bio-oil are generated into water and aromatic compounds by a catalytic cracking reaction at high temperature, thus removing oxygen.

Chemical Synthesis of Conjugation-Ready Trisaccharides Corresponding to Biological Repeating Units of Pseudomonas aeruginosa Serotype 10 and 19 O-Antigens.

Here we report the chemical synthesis of conjugation-ready trisaccharides, representing biological repeating units of Pseudomonas aeruginosa serotype 10 and 19 O-antigens. The α-d-QuiN3 glycosidic bond was stereoselectively synthesized through TMSI─Ph3P═O mediated 1,2-cis glycosylation. Selective oxidation of the C6-OH group at the disaccharide stage allowed for benzylidene-promoted construction of the α-l-GalN3 glycosidic bond and simplification of the postglycosylation process at the trisaccharide stage. The low reaction temperature and neighboring electron-donating effect facilitated the efficient synthesis of the trisaccharide.

Poly-(aminoethyl piperazine) membranes with ultra-thin selective layers prepared via a rate-retarded interfacial polymerization method

New monomers have been exploring to fabricate interfacial polymerized thin film composite membranes for decades. N-aminoethyl piperazine (AEP), an aliphatic amine with a heterocyclic structure, was used in this work as an amine monomer to synthesize nanofiltration membranes. Due to the high reactivity nature of AEP, a rate-retarded interfacial polymerization method was applied, which was realized by applying ultra-low AEP concentration (0.07 wt%), low reaction temperature (4 °C monomer solutions), and ice-water quench. The resulting AEP membrane had much better performance (3–4 times permeance and closed rejections) compared with the membranes prepared by the hot water post-treatment and the oven heat treatment. At lower monomer concentrations, an NF membrane with a selective layer thickness of only around 20 nm was prepared by the rate-retarded interfacial polymerization method. The membranes had a negatively charged surface with "willow leaf" like morphology. The MWCO was around 200 g mol−1, and the water permeance was up to 22.8 L m−2 h−1 bar−1, which is comparable with the commercial polyamide membrane NF270. Therefore, AEP is a very competitive alternative monomer for NF membrane synthesis.

Optimization of the full-load combustion schemes of n-butanol/biodiesel reactivity-controlled compression ignition (RCCI) toward high-efficiency and low-emission engines

Biodiesel and n-butanol, as popular alternative fuels, can be used in advanced reactivity-controlled compression ignition (RCCI) engines for efficient and clean combustion. However, the complex interactions between n-butanol and biodiesel, as well as the best combustion schemes at different loads, remain poorly understood. Given this, the objective of this paper is to identify optimal fuel organizations for n-butanol/biodiesel RCCI engines across different load scenarios by combining engine simulation with a global optimization algorithm, explore the potential synergies of control parameters, and analyze microscopic dual-fuel interactions based on the integrated average reaction path analysis. Results show that the optimal scheme at low load employs almost homogeneous fuel-air mixtures at elevated temperature atmosphere above 390 K, with n-butanol energy share exceeding 96% and optimal biodiesel injection timing between −70 and −50 °CA. Higher n-butanol ratio coupled with increased intake temperature improves engine performance. For mid load, biodiesel injection timing is retarded to −55 to −30 °CA, and biodiesel proportion is increased to introduce reactivity stratification, while maintaining its energy share below 20% to mitigate NOx emissions. Notably, biodiesel density is identified as the primary physical property influencing NOx formation. At high load, a split combustion scheme involving premixing and subsequent diffusion combustion is optimal. The physical effects of n-butanol addition minimally impact the low-temperature ignition of biodiesel, while its chemical effects significantly defer the low-temperature reactivity. The reaction path analysis reveals that n-butanol competes with biodiesel for OH radical consumption, with a large proportion of OH and HO2 consumed in the cyclic reactions of nC4H9OH and nC4H8OH. Adjusting the reactivity stratification affects the reaction state of n-butanol entrained by the biodiesel jets. Higher reactivity gradient intensifies biodiesel reactions to induce the pyrolysis of the involved n-butanol through nC4H8OH => 2C2H4 + OH, therefore resulting in more staged heat release.

Investigating the oxidation characteristic of a hydro-processed bio-jet fuel: Experimental and modeling study

A rapid transition from conventional jet fuels to sustainable aviation fuels (SAFs) is imperative in order to reduce carbon emissions. Hydro-processed esters and fatty acids synthetic paraffinic kerosene (HEFA-SPK), as a type of SAF, exhibits broad applications. In this study, a new HEFA-SPK named ZH-HEFA was investigated. The fuel comprises 14% n-alkanes, 85% iso-alkanes and only 1% cycloalkanes by weight, with the majority of alkanes ranging from C9 to C17. Oxidation experiments of the fuel were conducted using an atmospheric pressure flow reactor at temperatures ranging from 550 K to 1075 K under three equivalence ratios (0.5, 1.0 and 1.5). Species mole fraction profiles were measured by an on-line gas chromatographic (GC). For comparison purposes, an experiment was also performed on RP-3, a conventional jet fuel commonly used in China, under the equivalence of 0.5. Compared to RP-3, ZH-HEFA exhibited significantly stronger low temperature reactivity and higher combustion conversion rates while demonstrating considerably lower yields of aromatics at high temperatures. The kinetic simulation of ZH-HEFA was achieved by proposing two surrogates and their corresponding kinetic models. Surrogate S-1 consisted solely of n-dodecane, while S-2 comprised 35% n-dodecane and 65% 2,6,10-trimethyl dodecane by weight. Both surrogate models were validated by the experimental data. S-1 exhibited a closer resemblance to the global oxidation characteristics of ZH-HEFA, whereas S-2 demonstrated improved accuracy in predicting the formation of small hydrocarbon intermediates during the fuel oxidation. Rate of production analysis revealed that the branched alkane component in S-2 possessed more pathways and greater capability than S-1 in generating C3 intermediates, which are important for the generation of aromatics. Furthermore, both models displayed good predictive performance for the auto-ignition properties of HEFA-SPK fuels.-

Synthesis and investigation of the optical characteristics of RE3+ activated Ca2Li2Si2O7 (Rare earth = Eu, Tb) phosphor for W-LED application

Novel Eu3+ and Tb3+ ions-doped Ca2Li2Si2O7 luminescent materials were prepared by a low-temperature solid-state reaction technique for LED application. The electronic transitions of 5D0 → 7F2 (Eu3+) and 5D4 → 7F5 (Tb3+) have caused the luminescent material to exhibit strong luminosity in 613 nm (red) and 545 nm (green), respectively. Fourier transform infrared (FT-IR) spectra were applied for the identification of functional groups, and powder X-ray diffraction (XRD) was used for structural analysis. Morphological data was gathered using scanning electron microscopy (SEM). Its color was also determined by calculating the CIE coordinates. The excitation, PL properties, and luminescence decay time of the emission transitions of Eu3+ (5D0 → 7F2) and Tb3+ (5D4 → 7F5) were measured in order to analyze luminosity spectra.

An ultra-durable ZIT glass-ceramic composite for immobilization of radioactive mixed lanthanide oxides

Zinc Titanate (ZIT) glass-ceramic composite is a potential candidate waste form for immobilizing radioactive lanthanide oxides due to its relatively high lanthanide embedding capacity and low reaction temperature. However, the composition of lanthanide oxides after electrolytic refining is very complex and the immobilization mechanism of lanthanide oxides by ZIT composite is not clear. Herein, we prepared ZIT-PrEu glass-ceramic waste forms by a solid-phase sintering method at 1200 °C for 4 h using mixed lanthanide oxides of Pr6O11 and Eu2O3 simulated as radioactive waste. The XRD and SEM results show that different mixed lanthanide oxide ratios have very little effect on the composition and microstructure of ZIT-PrEu waste forms with different waste embedding rates. With the increase of waste embedding rate, the density of the ZIT-PrEu glass-ceramic waste forms with different mixed lanthanide oxide ratios first increases and then decreases. When the embedding rate increases to 25 wt.%, the density of ZIT-PrEu waste forms with different mixed lanthanide oxide ratios reaches a maximum. The ZIT-PrEu glass-ceramic waste forms embedded with 25 wt.% waste exhibit excellent chemical durability, and the leaching rates of Pr ion and Eu ion are only 10-6 - 10-7 g·m-2·d-1 after 28 days at 90 °C. Moreover, the phase evolution of the ZIT composites immobilizing lanthanide oxides at different temperatures is revealed by XRD and FT-IR measurements. The lanthanides (Ln) are mainly present in the form of LnPO4 monazite phases.

Bio-based nylon intermediates from γ-valerolactone: Catalyst modifications for an enhanced selectivity to methyl 4-pentenoate

Ring-opening transesterification of bio-based γ-valerolactone (GVL) to produce a mixture of methyl pentenoate isomers (MPs) such as methyl 4-pentenoate (M4P), methyl 3-pentenoate (M3P) and methyl 2-pentenoate (M2P) has been carried out using modified Zr-containing catalysts in a gas phase continuous process. As the three MP isomers are potential nylon intermediates, this approach is sustainable from a green chemistry point of view to synthesize bio-based polymers. The reaction was carried out in a fixed bed catalytic reactor at ambient pressure and in the temperature range from 255 to 335°C. In the present study, SiO2 supported zirconia catalysts were prepared by wet impregnation with varying Zr loadings in the range from 5 to 30wt%. The catalysts were characterized by various techniques. The surface areas were determined by N2 adsorption, acid-base properties by NH3-TPD and CO2-TPD techniques. In addition, the distinction of Lewis and Brønsted sites were also estimated by Py-FTIR. Among all catalysts, 25% Zr/SiO2 exhibited the best performance. The influence of various key reaction parameters on the activity/selectivity was explored and suitable reaction conditions were optimized. The conversion of GVL and product distribution was found to be strongly dependent on the reaction temperature and Zr content of the catalysts. The sum selectivity of all the three MP isomers varied in the range from 97 to 99%, of which M4P was always the dominant product. At low reaction temperature (255°C), M4P was the major product while M2P was a minor product. However, with increase in temperature, the selectivity of M2P and M3P increased at the expense of M4P due to isomerisation of the C=C double bond. In addition, the effect of support on the best Zr loading was also explored and it was found that the SiO2 support exhibited superior performance compared to others. In the direction of enhancing the selectivity of M4P, Cr-doping was also done onto 25Zr/SiO2, the best catalyst of this study. Such incorporation of chromium significantly enhanced the selectivity of M4P above 80% at acceptably high conversion of GVL.

Al(Si)/Al2O3 and NiAl(Si)/Al2O3 co-continuous composites obtained by low temperature Reactive Metal Penetration of dense silica preforms.

Interpenetrating network Al(Si)/Al2O3 composites, obtained by a reactive metal penetration process, where pure aluminum metal reacts with a dense amorphous silica preform, are an interesting class of metal/ceramic composites, with two continuous networks of metal (Al-Si alloy) and ceramic (Al2O3). These composites have high stiffness and hardness, while retaining acceptable toughness and good thermal and electrical conductivity, and can be used in wear or thermal management applications. A second infiltration step with nickel allows to substitute the Al(Si) alloy with an intermetallic, obtaining an interpenetrating network NiAl(Si)/Al2O3 composite, with very high hardness and melting point. While in the standard process the temperature for obtaining the Al(Si)/Al2O3 composites is in the 1100-1200 °C range, in this paper we studied instead the 700-1000 °C temperature range and its effect on the microstructure of the final NiAl(Si)/Al2O3 composite. After the first infiltration step, the microstructure of Al(Si)/Al2O3 composites depends on both temperature and time of the treatment. At 700-800 °C and for reaction time of 1-2 hours, the grain size is completely sub-micrometric. When temperature and time of reaction increase, islands with a coarser microstructure, of micrometric size, form, reaching a fully micrometric coarser microstructure at 1100-1200 °C. The islands formation is due to the transformation from transition aluminas, formed at low temperature and low reaction time, to α-alumina, while at high temperature α-alumina forms directly. In a second step, the Al(Si) metal network was replaced with an intermetallic one, by contacting the composite with liquid nickel, that reacted with the Al(Si) alloy forming an Al-Ni-Si intermetallic. The temperature and duration of the first infiltration step strongly influences not only the microstructure of the Al(Si)/Al2O3 composite but also of the final NiAl(Si)/Al2O3 one, that is finer when the first step (reaction of aluminum with silica) occurs at lower temperature.