Additional Reaction Steps Research Articles

Methane pyrolysis in molten salt slurry systems: Evaluation of activity and mechanism in binary salt mixtures with molybdenum disulfide suspensions

In this study we evaluated three binary salt mixtures of 50 wt% potassium bromide and 50 wt% sodium chloride, manganese chloride, or magnesium chloride for methane pyrolysis in a bubble column reactor configuration. Initial results confirm preferential mixtures of reciprocal salts that tune salt ionicity. This study focusses on the interactions of these binary salt mixtures with 5 wt% suspensions of 2-μm 2H-MoS2 with a 100 mm bubble path at 800 and 850 oC. Magnesium chloride and potassium bromide show a favourable enhancement with MoS2, with an apparent activation energy of 251 kJ mol−1 (salt mixture) decreasing to 96 kJ mol−1 (slurry mixture). Assessing the results indicates that MgCl2-KBr melts promote increased contact with MoS2 relative to NaCl-KBr and MnCl2-KBr, and this in turn improves hydrogen yield. Further investigation of slurry system through deuterium-methane exchange confirms molybdenum disulfide promotes methane decomposition to protium, hydrogen, methyl radical, and methylene, preferentially intensified by magnesium mixtures. Additional reaction steps vary depending on salt selection. At 850 oC, the salt effect is significant, leading to an inverse relationship between net increase of side products in the slurries and salt activity. In contrast, at 800 oC, the salt effect is small, and activity is dictated by the MoS2 suspension.

Bimetal (CuNi and CuCo) substituted CeO2: An approach for low temperature dry reforming of methane

The solution combustion synthesis method was used to make CuNi substituted CeO2 (7.5 at.% of Cu+7.5 at.% of Ni), and CuCo substituted CeO2 (7.5 at.% of Cu+7.5 at.% of Co) catalysts. The catalysts were characterized by x-ray diffraction (XRD),XPS, BET surface area measurements, scanning electron microscopy (SEM), and H2-temperature-programmed reduction(H2-TPR). Further, these catalysts were tested for endothermic dry reforming of methane (DRM) reaction. The CuNi substituted CeO2 catalyst started dry reforming of methane (DRM) at around 350 °C, while the CuCo substituted CeO2 catalyst started DRM at around 450 °C. This indicates that the CuNi catalyst has a lower activation temperature for the DRM reaction compared to the CuCo catalyst. The CuNi substituted CeO2 catalyst converted CH4 better than the CuCo substituted CeO2 at all temperatures reaching 98 % conversion at 800 °C The CuNi substituted CeO2 showed higher H2/CO ratio in comparison to the CuCo substituted CeO2 but the long-term stability followed the opposite order. Thermal gravimetric analysis (TGA), SEM and O2-TPO were used to quantify as well as to understand the nature of carbon that had built up on spent catalysts and it is mostly amorphous. Transient studies have shown that along with the lattice oxygen participation, controlled methane decomposition step is necessary for stability of catalysts. Transient studies also recommended additional reaction steps during DRM where an exothermic methane partial oxidation step reduces the endothermicity of DRM. Also, CO2 activation also goes via the defect dissociation route, an additional step to the conventional carbon oxidation (CO2+C→CO) step. So, novelty of this work is in elucidating the exact role of lattice oxygen in imparting the activity and stability to the DRM catalyst.

A step-economical divergent approach to isoflavenes based on Suzuki-Miyaura cross coupling of a 3-boryl-2H-chromene with aryl bromides: application to total synthesis of isoflavonoid natural products.

We present a step-economical divergent synthetic approach for isoflavene derivatives using the Suzuki-Miyaura cross coupling of a 3-boryl-2H-chromene and three aryl bromides. 3-Boryl-2H-chromene, which is not a well-explored species, was prepared via Miyaura-Ishiyama borylation of a 3-chloro-2H-chromene obtained through a Claisen rearrangement cyclization cascade reaction. Further conversion of the cross-coupling products, three isoflavene derivatives, afforded three isoflavonoid natural products with one or two additional reaction steps.

Phosphorylation in liquid sulfur dioxide under prebiotically plausible conditions

In nature, organophosphates provide key functions such as information storage and transport, structural tasks, and energy transfer. Since condensations are unfavourable in water and nucleophilic attack at phosphate is kinetically inhibited, various abiogenesis hypotheses for the formation of organophosphate are discussed. Recently, the application of phosphites as phosphorylation agent showed promising results. However, elevated temperatures and additional reaction steps are required to obtain organophosphates. Here we show that in liquid sulfur dioxide, which acts as solvent and oxidant, efficient organophosphate formation is enabled. Phosphorous acid yields up to 32.6% 5′ nucleoside monophosphate, 3.6% 5′ nucleoside diphosphate, and the formation of nucleoside triphosphates and dinucleotides in a single reaction step at room temperature. In addition to the phosphorylation of organic compounds, we observed diserine formation. Thus, we suggest volcanic environments as reaction sites for biopolymer formation on Early Earth. Because of the simple recyclability of sulfur dioxide, the reaction is also interesting for synthesis chemistry.

Convenient in situ synthesis of injectable lysine-contained peptide functionalized hydrogels for spinal cord regeneration

Injectable hydrogels provide a promising strategy to fill the irregular cystic cavity in spinal cord injury. However, a simple and convenient functionalization approach of injectable hydrogels is still a huge challenge. Herein, we report a facile in situ synthetic strategy of injectable lysine-contained peptide functionalized hydrogels for the treatment of spinal cord injury. The ibuprofen-KYIGSRK conjugated hydrogels are in situ synthesized via in situ Michael addition without catalysts and additional reaction-steps. Ibuprofen-KYIGSRK conjugated soft hydrogels promote the adhesion and neurite extension of DRG neurons by upregulating of Sall3, Pou3f3, Lhx5, Shank1 and Sall1. The long-term implanted ibuprofen-KYIGSRK hydrogel is injected into the spinal cord injured site for promoting motor functional recovery. Increased neurites and decreased glial scars are detected with effective functional improvements in footprint. This injectable hydrogel can not only fill the irregular cavities for inhibiting the glial scar formation, but also significantly suppress inflammatory responses and promote nerve regeneration. This study supplies a convenient in situ synthetic route of injectable peptide functionalized hydrogels for the treatment of spinal cord injury or other biomedical applications.

Coaxial Multiphase Flame for Continuous‐Flow Assembly of Ternary Nanocomposite Photocatalysts

AbstractFor the low‐cost production of graphene (G)‐included composites, the growth of graphene on a transition metal in hydrocarbon flames is introduced, where the hydrocarbons are adsorbed on the metal surface, followed by catalytic decomposition, leading to continuous G formation. On the other hand, the flame synthesis of G is still a batch process, limiting the practical applications of such materials. Moreover, the hybridization of G for enhanced catalytic activities requires additional reaction and separation steps. Here, a coaxial multiphase flame is generated and combined with a rotating Cu–Ni foil and ultrasonic bath for the continuous‐flow assembly of ternary G composites with low‐cost and rapid implementation. The continuous flows to generate a multicomponent flame consist of MoS2 particle‐laden N2 gas (inner), titanium isopropoxide vapor‐laden CH4‐air (middle), and ethanol liquid (outer), while Cu–Ni foil plies between the flame and ultrasonic bath for the assembly and dispersion of MoS2–TiO2@G composites. The configuration of the composite can be modulated by replacing the MoS2 flow with a CdS flow to construct CdS–TiO2@G. From photocatalytic H2 production and CO2 reduction tests, the developed coaxial flame provides comparable performance with analogous architectures from the usual multistep methods despite the high‐throughput production.

The role of negative hydroxyl ions in the electron generation and breakdown during plasma formation in liquid water

The role of negative hydroxyl ions in liquid-phase plasma discharge formation is investigated using an inhouse modeling framework. Two tunneling sources for electrons are considered—tunneling ionization of water molecules and tunneling detachment of negative hydroxyl ions together with additional reaction steps. The simulations are conducted for a needle-like powered electrode with two different nanosecond rise time voltage profiles—a linear and an exponential rise. Both the profiles have a maximum voltage of 15 kV. The predictions show that the electron detachment, which has a much lower threshold energy requirement, provides a stream of electrons at low applied voltage during the initial rise time. The electrical forces from the electron detachment process generate stronger compression but a weaker expansion regime in the liquid resulting in ∼40% increase in the density and only ∼1% decrease. The electron detachment tunneling process is found to be not limited by the electric field, but rather by the availability of negative hydroxyl ions in the system and ceases when these ions are depleted. The tunnel ionization of water molecules forms the electron wave at a higher applied voltage, but the resulting peak electron number density is typically six orders of magnitude larger than the detachment tunneling. The higher electron number density allows the recycling of depleted negative hydroxyl ions in the system and can reestablish tunneling detachment. In addition, the system experiences a larger variation in density; specifically, a decrease in density due to tunnel ionization. The prediction also shows that irrespective of the initial electron sources (i.e. tunnel ionization or tunnel detachment) the reduced electric field is not sufficient enough to allow electron impact ionization to be active and make a significant contribution. Path flux analysis is conducted to determine the kinetics responsible for the recycling of the negative hydroxyl ions.

Thermal decomposition of ammonium nitrate

SummaryThe thermal decomposition reactions of ammonium nitrate (AN) are reviewed. Both neat AN and AN containing various contaminants are examined, however quantitative kinetics results are not encompassed. Also not included is the performance of AN as the oxidizer in rocket propellants or in explosives such as ANFO. The review is intended to be the most comprehensive review of decomposition reactions of AN since Berthelot's treatise of 1892. Despite hundreds of papers on the topic that have appeared in the intervening years, understanding of decomposition mechanisms remains only modestly more complete than it was in Berthelot's day. However, some additional reaction steps and mechanisms have been identified and these are discussed. Explosions of AN most commonly involve fire as the proximate cause, yet chemical‐mechanism research on the topic is nil. A modest number of studies have explored the potentiation of AN decomposition by organic contaminants. These have, thus far, not produced guidance useful for promoting of safety from fire‐related causes. Contamination from inorganic sources, notably chlorides is better understood and some mechanisms have been studied. The UN classification of AN as an oxidizer, instead of as an explosive, should not be interpreted literally, since AN has been associated with numerous detonation disasters.

Construction of a synthetic pathway for the production of 1,3-propanediol from glucose

In this work, we describe the construction of a synthetic metabolic pathway enabling direct biosynthesis of 1,3-propanediol (PDO) from glucose via the Krebs cycle intermediate malate. This non-natural pathway extends a previously published synthetic pathway for the synthesis of (L)-2,4-dihydroxybutyrate (L-DHB) from malate by three additional reaction steps catalyzed respectively, by a DHB dehydrogenase, a 2-keto-4-hydroxybutyrate (OHB) dehydrogenase and a PDO oxidoreductase. Screening and structure-guided protein engineering provided a (L)-DHB dehydrogenase from the membrane-associated (L)-lactate dehydrogenase of E. coli and OHB decarboxylase variants derived from the branched-chain keto-acid decarboxylase encoded by kdcA from Lactococcus lactis or pyruvate decarboxylase from Zymomonas mobilis. The simultaneous overexpression of the genes encoding these enzymes together with the endogenous ydhD-encoded aldehyde reductase enabled PDO biosynthesis from (L)-DHB. While the simultaneous expression of the six enzymatic activities in a single engineered E. coli strain resulted in a low production of 0.1 mM PDO from 110 mM glucose, a 40-fold increased PDO titer was obtained by co-cultivation of an E. coli strain expressing the malate-DHB pathway with another strain harboring the DHB-to-PDO pathway.

Rolling circle extension-actuated loop-mediated isothermal amplification (RCA-LAMP) for ultrasensitive detection of microRNAs

Rolling circle amplification (RCA) is an elegant and well-recognized isothermal nucleic acid amplification mechanism that has been widely used for the detection of various kinds of genetic biomarkers. However, traditional RCA is a linear signal amplifying mechanism so that the amplification efficiency is generally not satisfactory. Herein, we rationally combine RCA with efficient loop-mediated isothermal amplification (LAMP) to establish a rapid and ultrasensitive RCA-LAMP method for the detection of microRNAs (miRNAs). In the RCA-LAMP, the target let-7a miRNA can directly template the ligation of a padlock probe to trigger RCA reaction, producing long and tandem amplification products. Only such RCA-produced long DNA repeats can act as the template to generate a lot of double stem-loop DNAs with functional sequences, which are the essential starting materials to initiate subsequent LAMP. Finally, the products of LAMP reaction, the amount of which is dependent on the initial miRNA dosage, can be fluorescently monitored in a real-time manner. Through the combination of ligation-mediated RCA with LAMP, the amplification efficiency and the detection sensitivity has been significantly improved. As a result, even 10 aM miRNA target can be clearly and accurately detectable. Despite the excellent analytical performance for miRNA analysis, compared with conventional RCA-based miRNA assays, the combination of RCA with LAMP does not introduce any additional reaction steps or sample transfer operations. Both the RCA and LAMP are fulfilled in a single step. Therefore, this facile and ultrasensitive RCA-LAMP assay provides a new promising tool for miRNA analysis and can be extended to the detection of various kinds of genetic biomarkers.

A mixing heteroduplex mobility assay (mHMA) to genotype homozygous mutants with small indels generated by CRISPR-Cas9 nucleases

The development of gene editing technologies, especially the CRISPR-Cas9 system, has been pivotal for understanding the functional role of proteins. Rapid and efficient genotyping methods are necessary to screen for generated mutations and streamline the isolation of homozygotes. CRISPR-Cas9 system targeting a single site in the gene typically results in small indels. Many genotyping methods utilize the heteroduplex that is formed when wild-type and mutant amplicons with small indels anneal during PCR creating a bubble due to mismatched strands. These methods include T7 endonuclease/Cel-I assay, high resolution melting (HRM) analysis, and heteroduplex mobility assay (HMA). Our protocol explains a simple, two step method of a mixing HMA (mHMA) to identify homozygous mutants, a modification of the previously published HMA. We have utilized the mHMA for screening and genotyping numerous CRISPR generated models. The mHMA method to differentiate homozygous wild type from homozygous mutant animals eliminates - •DNA sequencing, even with small indels that can be difficult to discern on a gel.•additional enzymatic reaction steps, such as with the T7EI/Cel-I assay.•specialized equipment and analysis tools, such as with HRM analysis.

A One-Step Chemoenzymatic Labeling Strategy for Probing Sialylated Thomsen-Friedenreich Antigen.

Abnormal expression of sialylated Thomsen–Friedenreich antigen (Neu5Acα2-3Galβ1-3GalNAcα-O-Ser/Thr, sialyl-T) has a strong relationship with various types of human cancers and many other diseases. However, the size and structural complexity, and relatively lower abundance of sialyl-T have posed a significant challenge to its detection. Therefore, details about the role of sialyl-T in a variety of physiological and pathological processes are still poorly understood. Here, a one-step chemoenzymatic labeling strategy to probe sialyl-T is described. This approach enables the sensitive, selective, and rapid detection of sialyl-T, and global profiling and identification of unknown sialyl-T-attached glycoproteins, which are potential therapeutic targets or biomarkers. The use of one-step labeling strategy not only has a higher sensitivity than a typical two-step reporter strategy but also avoids undergoing an additional chemical reaction step to introduce a reporter group after the labeling reaction, making it particularly useful for detecting low-abundance glycan epitopes on living cells.

Selective Liquid‐Phase Extraction of Carboxylate‐Rich Graphene Quantum Dots from Graphene Oxide Dispersions

AbstractAn advanced simple synthetic route for graphene quantum dots (GQDs) is great importance to progress from laboratory research to industrial applications. Unfortunately, the existing state of synthesis methods of carboxylic acid‐rich GQDs needs additional reaction steps including oxidation, hydro‐ or solvo‐thermal reaction with bulk carbon sources. Besides, its yield is too low compared to starting amount of carbon sources due to complicated purification processes. Hence, production expense is inevitably increased to obstacle actual industrial applications. Here, we report a new synthetic method based on the liquid‐phase extraction technique to separate carboxylate‐rich GQDs (CGQDs) with high yield (> 30%) from graphene oxide (GO) dispersions without additional oxidation and purification processes.

Microemulsion and Sol-Gel Synthesized ZrO₂-MgO Catalysts for the Liquid-Phase Dehydration of Xylose to Furfural.

Two series of catalysts were prepared by sol-gel and microemulsion synthetic procedure (SG and ME, respectively). Each series includes both pure Mg and Zr solids as well as Mg-Zr mixed solids with 25%, 50% and 75% nominal Zr content. The whole set of catalysts was characterized from thermal, structural and surface chemical points of view and subsequently applied to the liquid-phase xylose dehydration to furfural. Reactions were carried out in either a high-pressure autoclave or in an atmospheric pressure multi-reactor under a biphasic (organic/water) reaction mixture. Butan-2-ol and toluene were essayed as organic solvents. Catalysts prepared by microemulsion retained part of the surfactant used in the synthetic procedure, mainly associated with the Zr part of the solid. The MgZr-SG solid presented the highest surface acidity while the Mg3Zr-SG one exhibited the highest surface basicity among mixed systems. Xylose dehydration in the high-pressure system and with toluene/water solvent mixture led to the highest furfural yield. Moreover, the yield of furfural increases with the Zr content of the catalyst. Therefore, the catalysts constituted of pure ZrO2 (especially Zr-SG) are the most suitable to carry out the process under study although MgZr mixed solids could be also suitable for overall processes with additional reaction steps.

Design and evaluation of a Fischer-Tropsch process for the production of waxes from biogas

A process for the production of Fischer-Tropsch waxes from biogas is proposed. It is shown that the specific composition of biogas allows the production of syngas suitable for Fischer-Tropsch synthesis in one process step. The absence of an additional reverse water-gas shift reaction step simplifies the process concept, which is advantageous for the targeted application. For two reforming concepts, steam reforming and autothermal reforming, the process efficiency is calculated with help of a process model. The results show, that especially the concept based on steam reforming offers a high energetic efficiency of ηen > 0.5. An economic feasibility study reveals advantages in comparison to state-of-the-art biogas CHP. For existing biogas plants the developed process concept offers a promising alternative for profitable operation. The process modeling results also show that the technical realization depends on the availability of advantageous inexpensive novel reactor concepts that are specifically developed for small-scale decentralized applications.

Comparative numerical analysis and optimization in downhole combustion chamber of thermal spallation drilling

Thermal spallation drilling is a non-contact and efficient technology, which is suitable for hard rock formations. It uses downhole combustion to generate high temperature media to heat the bottom rock, which leads to the spallation of the rock. However, no investigation has been carried out in combustion of thermal spallation drilling. In this paper, three combustion models (eddy dissipation model, eddy dissipation concept model and non-premixed model) are applied and compared to simulate the reaction in the combustion chamber. Through modifying Magnussen constants, the eddy dissipation model is optimized and validated. Results show that under high velocity conditions, combustion models based on infinite fast reaction mechanism may not be accurate. An additional reaction step in eddy dissipation model may significantly improve the accuracy. Besides, there is a linear relationship between the average outlet temperature and Magnussen constant in eddy dissipation model. Moreover, through modifying the Magnussen constants, the accuracy of the results can be significantly improved. The optimized eddy dissipation model with two reaction steps not only has the advantages of small computational cost, but also may reflect the actual situation of the combustion reaction. Results in this paper could provide guidance in the design of combustion chamber in thermal spallation drilling.

On the two-step mechanism for synthesis of transition-metal nanoparticles.

The two-step particle synthesis mechanism, also known as the Finke-Watzky (1997) mechanism, has emerged as a significant development in the field of nanoparticle synthesis. It explains a characteristic feature of the synthesis of transition metal nanoparticles, an induction period in precursor concentration followed by its rapid sigmoidal decrease. The classical LaMer theory (1950) of particle formation fails to capture this behavior. The two-step mechanism considers slow continuous nucleation and autocatalytic growth of particles directly from precursor as its two kinetic steps. In the present work, we test the two-step mechanism rigorously using population balance models. We find that it explains precursor consumption very well, but fails to explain particle synthesis. The effect of continued nucleation on particle synthesis is not suppressed sufficiently by the rapid autocatalytic growth of particles. The nucleation continues to increase breadth of size distributions to unexpectedly large values as compared to those observed experimentally. A number of variations of the original mechanism with additional reaction steps are investigated next. The simulations show that continued nucleation from the beginning of the synthesis leads to formation of highly polydisperse particles in all of the tested cases. A short nucleation window, realized with delayed onset of nucleation and its suppression soon after in one of the variations, appears as one way to explain all of the known experimental observations. The present investigations clearly establish the need to revisit the two-step particle synthesis mechanism.

Enzyme-based logic gates switchable between OR, NXOR and NAND Boolean operations realized in a flow system.

The enzyme-based system performing a biocatalytic cascade reaction was realized in a flow device and was used to mimic Boolean logic operations. Chemical inputs applied to the system resulted in the activation of additional reaction steps, allowing the reversible switch of the logic operations between OR, NXOR and NAND gates for processing of two other biomolecular inputs.

Laccase–cellobiose dehydrogenase-catalyzed detoxification of phenolic-rich olive processing residues

The combination of a laccase–hydroxybenzotriazole (HBT) mediator system with/without cellobiose dehydrogenase (CDH) or an additional Fenton reaction step for the elimination and/or detoxification of phenolic compounds in dry olive mill residues (DOR) and liquid olive mill wastewaters (OMW) was evaluated. The laccase–HBT–CDH and laccase–HBT–CDH–Fenton system were the most effective, removing at least 69 and 72 % of phenolic compounds from a total of 698 and 683 mg in OMW and DOR, respectively, in 12 h. The efficient removal of phenolic compounds was also accompanied by >80 % reduction in biochemical oxygen demand and chemical oxygen demand in both DOR and OMW. Microbial community analysis using single-strand conformation polymorphism (SSCP) gels showed that biogas reactors supplemented with untreated and laccase–HBT–CDH–Fenton-treated DOR and OMW strongly inhibited growth of microorganisms. In contrast, the laccase–HBT- and laccase–HBT–CDH-pretreated OMW and DOR were detoxified as evidenced by SSCP analysis, which also indicated a distinct sensitivity of the individual members of the anaerobic population toward the toxicants. Further, although the laccase–HBT–CDH–Fenton system was effective in bleaching and removing phenolic compounds in both OMW and DOR, it was not able to support methane production. However, laccase–HBT and laccase–HBT–CDH indeed supported biogas production. This study therefore shows that the laccase–HBT–CDH system has a potential for the detoxification of olive mill residues, which can be potentially used as substrates for downstream processes.

Preparing Silica Aerogel Monoliths via a Rapid Supercritical Extraction Method

A procedure for the fabrication of monolithic silica aerogels in eight hours or less via a rapid supercritical extraction process is described. The procedure requires 15-20 min of preparation time, during which a liquid precursor mixture is prepared and poured into wells of a metal mold that is placed between the platens of a hydraulic hot press, followed by several hours of processing within the hot press. The precursor solution consists of a 1.0:12.0:3.6:3.5 x 10-3 molar ratio of tetramethylorthosilicate (TMOS):methanol:water:ammonia. In each well of the mold, a porous silica sol-gel matrix forms. As the temperature of the mold and its contents is increased, the pressure within the mold rises. After the temperature/pressure conditions surpass the supercritical point for the solvent within the pores of the matrix (in this case, a methanol/water mixture), the supercritical fluid is released, and monolithic aerogel remains within the wells of the mold. With the mold used in this procedure, cylindrical monoliths of 2.2 cm diameter and 1.9 cm height are produced. Aerogels formed by this rapid method have comparable properties (low bulk and skeletal density, high surface area, mesoporous morphology) to those prepared by other methods that involve either additional reaction steps or solvent extractions (lengthier processes that generate more chemical waste).The rapid supercritical extraction method can also be applied to the fabrication of aerogels based on other precursor recipes.