Pathways For Formation Of Products Research Articles

Directing CO2 electroreduction pathways for selective C2 product formation using single-site doped copper catalysts

Directing CO2 electroreduction pathways for selective C2 product formation using single-site doped copper catalysts

Effective electronic waste valorization via microwave-assisted pyrolysis: investigation of graphite susceptor and feedstock quantity on pyrolysis using experimental and polynomial regression techniques.

Waste printed circuit board (WPCB) was subjected to microwave-assisted pyrolysis (MAP) to investigate the energy and pyrolysis products. In MAP, pyrolysis experiments were conducted, and the effects of WPCB to graphite mass ratio on three-phase product yields and their compositions were analyzed. In addition, the role of the initial WPCB mass (10, 55, and 100 g) and susceptor loading (2, 22, and 38 g) on the quality of product yield was also evaluated. By using design of experiments, the effects of graphite susceptor addition and WPCB feedstock quantity was investigated. A significant liquid yield of 38.2 wt.% was achieved at 38g of graphite and 100g of WPCB. Several other operating parameters, including average heating rate, pyrolysis time, microwave energy consumption, specific microwave power used, and product yields, were optimized for the MAP of WPCB. Pyrolysis index (PI) was calculated at the blending of fixed quantity WPCB (100g) and various graphite quantities in the following order: 2g (21) > 20g (20.4) > 38g (19.5). The PI improved by increasing the WPCB quantity (10, 55, and 100g) with a fixed quantity of graphite. This work proposes the product formation and new reaction pathways of the condensable compounds. GC-MS of the liquid fraction from the MAP of WPCBs without susceptor resulted in the generation of phenolic with 46.1% relative composition. The addition of graphite susceptor aided in the formation of phenolic and the relative composition of phenolics was found to be 83.6%. The area percent of phenol increased from 42.8% (without susceptor) to 78.6% (with susceptor). Without a susceptor, cyclopentadiene derivative was observed in a very high composition (~ 31 area %).

Unraveling the effects of sodium carbonate on hydrothermal liquefaction through individual biomass model component and machine learning-enabled prediction

Despite sodium carbonate (Na2CO3) being commonly utilized as a catalyst in actual biomass hydrothermal liquefaction (HTL), its impact on individual biomass components hasn't been well-examined. This study thus delves into the role of Na2CO3 in HTL of biomass model components (carbohydrate, lignin, protein, and lipid) at varying conditions. Na2CO3 at 5 wt% amplified carbohydrate degradation into biocrude and aqueous-gaseous products (AG), resonating with previous work on carbohydrate-rich feedstocks. While Na2CO3 has a marginal effect on lignin HTL, it negatively influences lipid HTL. Here, 5 wt% and 13.5 wt% Na2CO3 decrease the biocrude yield from 95.6% to less than 10%, simultaneously increasing the AG yield to approximately 90%. This is presumably due to the interaction of lipid decomposition intermediates (fatty acids) with sodium cations, resulting in water-soluble soap. For protein HTL, a low Na2CO3 concentration (5 wt%) has no significant impact on product formation, but excessive Na2CO3 (27 wt%) converts a considerable portion of biocrude into AG. In addition to these explorations that provided insights for actual biomass HTL, we also developed a machine learning model to adequately predict HTL biocrude yield by taking Na2CO3 effect into consideration. The Adaboost machine learning model displayed the most satisfactory prediction performance (training and testing R2: 0.96, 0.8) among the three investigated machine learning models. The feature importance analysis reveals lipid content and Na2CO3 concentration as pivotal factors over HTL process conditions and other biochemical components. This research provides fundamental insights into the Na2CO3 role in HTL product formation pathway and offers an intelligent and precise prediction model for HTL biocrude yield, thereby advancing the development of more efficient and sustainable bioenergy production processes.

Pyrolysis mechanism of β-d-glucopyranose as a model compound of cellulose: A joint experimental and theoretical investigation

This study aims to reveal the pyrolysis reaction mechanism and product formation pathway of cellulose by combining experimental and theoretical calculation results. First, pyrolysis experiments of glucose, cellobiose, and cellulose were conducted by combined thermogravimetry-Fourier infrared spectroscopy-gas chromatography-mass spectrometry (TG-FTIR-GC-MS). The results show that glucose and cellobiose have two obvious mass loss peaks in their pyrolysis processes and cellulose has only a distinct mass loss peak. In the severe weight loss stage, cellulose forms more H2O, CO2, alkanes, and carbonyl compounds than glucose and cellobiose. Then, β-d-glucopyranose was selected as a model compound of cellulose to carry out density functional theory (DFT) calculations. The formation mechanism of furan derivatives and carbohydrate derivatives was systematically studied. And their competitive relationship was revealed. A reaction network from β-d-glucopyranose to main products was constructed. Based on the concerted reaction mechanism, β-d-glucopyranose is easier to generate furfural, followed by furan, 1,4:3,6-dianhydro-α-d-glucopyranose, and levoglucosenone, and finally 2(5H)-furanone. Based on the H radical attack mechanism, β-d-glucopyranose is easier to form 1-(2-furanyl)-ethanone, followed by 5-methyl-2-furancarboxaldehyde, and finally 2-methyl-furan. Finally, the relationship between the functional groups and the pyrolysis behavior of β-d-glucopyranose was clarified by combining the product distribution detected in experiments and DFT calculations.

Volatility of Secondary Organic Aerosol from β-Caryophyllene Ozonolysis over a Wide Tropospheric Temperature Range.

We investigated secondary organic aerosol (SOA) from β-caryophyllene oxidation generated over a wide tropospheric temperature range (213-313 K) from ozonolysis. Positive matrix factorization (PMF) was used to deconvolute the desorption data (thermograms) of SOA products detected by a chemical ionization mass spectrometer (FIGAERO-CIMS). A nonmonotonic dependence of particle volatility (saturation concentration at 298 K, C298K*) on formation temperature (213-313 K) was observed, primarily due to temperature-dependent formation pathways of β-caryophyllene oxidation products. The PMF analysis grouped detected ions into 11 compound groups (factors) with characteristic volatility. These compound groups act as indicators for the underlying SOA formation mechanisms. Their different temperature responses revealed that the relevant chemical pathways (e.g., autoxidation, oligomer formation, and isomer formation) had distinct optimal temperatures between 213 and 313 K, significantly beyond the effect of temperature-dependent partitioning. Furthermore, PMF-resolved volatility groups were compared with volatility basis set (VBS) distributions based on different vapor pressure estimation methods. The variation of the volatilities predicted by different methods is affected by highly oxygenated molecules, isomers, and thermal decomposition of oligomers with long carbon chains. This work distinguishes multiple isomers and identifies compound groups of varying volatilities, providing new insights into the temperature-dependent formation mechanisms of β-caryophyllene-derived SOA particles.

Lithium-Induced Optimization Mechanism for an Ultrathin-Strut Biodegradable Zn-Based Vascular Scaffold.

To reduce incidences of in-stent restenosis and thrombosis, the use of a thinner-strut stent has been clinically proven to be effective. Therefore, the contemporary trend is toward the use of ultrathin-strut (≤70µm) designs for durable stents. However, stents made from biodegradable platforms have failed to achieve intergenerational breakthroughs due to their excessively thick struts. Here, microalloying is used to create an ultrathin-strut (65µm) zinc (Zn) scaffold with modified biodegradation behavior and improved biofunction, by adding lithium (Li). The scaffold backbone consists of an ultrafine-grained Zn matrix (average grain diameter 2.28µm) with uniformly distributed nanoscale Li-containing phases. Grain refinement and precipitation strengthening enable it to achieve twice the radial strength with only 40% of the strut thickness of the pure Zn scaffold. Adding Li alters the thermodynamic formation pathways of products during scaffold biodegradation, creating an alkaline microenvironment. Li2 CO3 may actively stabilize this microenvironment due to its higher solubility and better buffering capability than Zn products. The co-release of ionic zinc and lithium enhances the beneficial differential effects on activities of endothelial cells and smooth muscle cells, resulting in good endothelialization and limited intimal hyperplasia in porcine coronary arteries. The findings here may break the predicament of the next-generation biodegradable scaffolds.

Investigation of gauze and medical bottle co-pyrolysis on the product formation, reactivity, and reaction pathway of char, liquid oil, and gas.

Effective in-site treatment of medical waste has become a weak link in hospitals. Pyrolysis technology is a treatment method for medical waste that can enable rapid disposal in hospital settings and relieve environmental pressure, while also producing high-value products and reducing disposal costs. In this work, the effects of feedstock ratio and temperature on product yield and components of gauze (GA) and medical bottles (MB) co-pyrolysis have been investigated. The higher yield of solid products was obtained by co-pyrolysis of GA and MB at 400 ℃. With the addition of MB and an increase in temperature for the co-pyrolysis of GA and MB in a similar ratio, the pyrolysis oil and gas yields gradually increased. According to GC–MS analysis, co-feeding 75% MB to GA improved the alcohol content from 33.21% to a maximum yield of 59.8% at a pyrolysis temperature of 700 ℃. The content of aliphatic hydrocarbon reached 38.68% when the pyrolysis temperature and MB addition ratio were 700 °C and 75%, respectively. The GC data shows that the main gas components of co-pyrolysis of GA/MB were CH4 and H2, while the pyrolysis of pure GA or MB resulted in CO or CO2. Additionally, the solid carbon products obtained have an excellent pore structure. This strategy can benefit medical waste control and resource utilization for the low-cost disposal of medical waste and the acquisition of high-value resource products.

Co-pyrolysis of chitin with nitrogen carriers: Kinetics, product characterization and bio-oil analysis

Considering the depletion of fossil fuels and the cumbersome traditional synthesis process of chemical compounds containing nitrogen, there is increased interest in direct production of nitrogenous compounds (bio-oil) from nitrogen-rich pyrolysis of biomass. In this study, a new strategy for the preparation of both nitrogen-rich bio-oil and biochar by co-pyrolysis of chitin and nitrogen carriers was proposed. Four different nitrogen carriers (urea, ammonium acetate, glutamate, and polyurethane) were selected and the thermal behavior of the mixtures as well as the synergistic competitive effects between the pyrolytic volatiles were characterized. Simultaneously, the properties of the co-pyrolysis products and the distribution of the main components in bio-oil were analyzed. The results showed that co-pyrolysis of chitin and nitrogen carriers had a synergistic effect. Glutamate had the most significant inhibitory effect on volatile gases, while only polyurethane promoted the release of volatile gases. Compared to the pyrolysis of chitin alone, the addition of urea, ammonium acetate and polyurethane effectively reduced the activation energy of the reaction. The addition of nitrogen carriers promoted the production of amines. Co-pyrolysis of urea and glutamate (40%) increased the content of nitrogenous compounds by 14.84% and 3.41%, respectively. However, the addition of ammonium acetate and polyurethane hindered the conversion of oxygenated compounds to nitrogen-containing compounds. In addition, the formation pathways of chitin pyrolysis and co-pyrolysis products were summarized. This work expanded the boundaries of high-value utilization of chitin.

Controlling Selectivity in Plasmonic Catalysis: Switching Reaction Pathway from Hydrogenation to Homocoupling Under Visible-Light Irradiation.

Plasmonic catalysis enables the use of light to accelerate molecular transformations. Its application to the control reaction selectivity is highly attractive but remains challenging. Here, we have found that the plasmonic properties in AgPd nanoparticles allowed different reaction pathways for tunable product formation under visible-light irradiation. By employing the hydrogenation of phenylacetylene as a model transformation, we demonstrate that visible-light irradiation can be employed to steer the reaction pathway from hydrogenation to homocoupling. Our data showed that the decrease in the concentration of H species at the surface due to plasmon-enhanced H2 desorption led to the control in selectivity. These results provide important insights into the understanding of reaction selectivity with light, paving the way for the application of plasmonic catalysis to the synthesis of 1,3-diynes, and bringing the vision of light-driven transformations with target selectivity one step closer to reality.

Controlling Selectivity in Plasmonic Catalysis: Switching Reaction Pathway from Hydrogenation to Homocoupling Under Visible‐Light Irradiation

AbstractPlasmonic catalysis enables the use of light to accelerate molecular transformations. Its application to the control reaction selectivity is highly attractive but remains challenging. Here, we have found that the plasmonic properties in AgPd nanoparticles allowed different reaction pathways for tunable product formation under visible‐light irradiation. By employing the hydrogenation of phenylacetylene as a model transformation, we demonstrate that visible‐light irradiation can be employed to steer the reaction pathway from hydrogenation to homocoupling. Our data showed that the decrease in the concentration of H species at the surface due to plasmon‐enhanced H2 desorption led to the control in selectivity. These results provide important insights into the understanding of reaction selectivity with light, paving the way for the application of plasmonic catalysis to the synthesis of 1,3‐diynes, and bringing the vision of light‐driven transformations with target selectivity one step closer to reality.

Exploring fuel molecular structure effects on the pyrolysis chemistry of branched hexenes

3,3-Dimethyl-1-butene (NEC6D3) and 2,3-dimethyl-2-butene (XC6D2) are representative branched alkene components in gasoline. This work experimentally investigated the pyrolysis of NEC6D3 and XC6D2 in a flow reactor (T = 950–1350 K, P = 0.04 atm) and a jet-stirred reactor (T = 730–1000 K, P = 1 atm) using synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS) and gas chromatography (GC). A pyrolysis model of branched hexenes was proposed and validated against the new experimental data. The combined experimental observations and modeling analyses provide insights into the predominant fuel decomposition pathways and specific formation pathways of products under pyrolysis conditions. NEC6D3 exhibits a much higher reactivity than XC6D2 due to the existence of allylic CC bonds. Unimolecular decomposition reactions play the most crucial role in NEC6D3 decomposition, while in XC6D2 pyrolysis, fuel consumption is dominated by H-abstraction reactions and the H-assisted isomerization reaction. Fuel-specific pathways can remarkably influence the formation of pyrolysis products, especially the key C1C2 products, isomer pairs and dialkenes. Furthermore, the reactions involving propargyl radical dominate the formation of fulvene and aromatic products in the pyrolysis of both fuels, leading to more abundant production of C6 and larger cyclic products in XC6D2 pyrolysis.

A New Saddle-Shaped Aza Analog of Tetraphenylene: Atroposelective Synthesis and Application as a Chiral Acylating Reagent

A New Saddle-Shaped Aza Analog of Tetraphenylene: Atroposelective Synthesis and Application as a Chiral Acylating Reagent

Experiment and theory elucidate the pathways for H3+formation in the ultrafast double ionization in methanol

Experiment and theory elucidate the pathways for H₃⁺formation in the ultrafast double ionization in methanol

Exploration on Thermal Decomposition of Cyclopentanone: A Flow Reactor Pyrolysis and Kinetic Modeling Study

Pyrolysis of cyclopentanone was investigated in a flow reactor at temperatures of 875–1428 K and pressures of 0.04 and 1 atm. Dozens of pyrolysis products including isomers, radicals, and aromatics were detected using synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS). Among them, two groups of keto–enol tautomers were observed; one is cyclopentanone and 1-cyclopentenol, and the other one is 1,4-cyclopentadien-1-ol, 2-cyclopeten-1-one and 3-cyclopeten-1-one. A detailed kinetic model of cyclopentanone was also developed with the consideration of the theoretical progress of key reactions in this work and in the literature. Based on the experimental and simulated results, the main consumption pathways of cyclopentanone and main formation pathways of critical products were explored. Special attention has been paid to the mole fraction ratios of CO-to-fuel and ethylene-to-CO, as CO and ethylene are two of the most abundant primary decomposition products. In addition, the successive decomposition of the diradical produced from the Cβ–Cγ bond dissociation reaction of cyclopentanone was found to be crucial to the formation of C3 species. The recombination of these unsaturated small species also accounts for the abundant formation of 1,3-cyclopentadiene and aromatic species in cyclopentanone pyrolysis.

NOx Reduction Pathways during LNT Operation over Ceria Containing Catalysts: Effect of Copper Presence and Barium Content

Ceria-based catalysts, with Cu in substitution of noble metals, were studied in a vertical microreactor system under isothermal conditions, where NOx was previously stored, followed by the reduction step conducted under H2. The possible remaining ad-NOx species after the reduction stage, were investigated by Temperature Programmed Desorption in He. In situ DRIFTS was used as a complementary technique for the analysis of the surface species formation/transformation on the catalysts’ surface. Catalysts containing both Ba and Cu were found to be selective in the NOx reduction, producing N2 and minor amounts of NH3 during the reduction step, as well as NO. The different ceria-based formulations (containing copper and/or barium) were prepared and tested at two different temperatures in the NOx reduction (NSR) processes. Their catalytic activities were analyzed in terms of their compositions and have been useful in the elucidation of the possible origin and relevant pathways for NOx reduction product formation, which seems to involve the oxygen vacancies of the ceria-based materials (whose generation seems to be promoted by copper) during the rich step. The scope of this work involves an interdisciplinary study of the impact that catalysts’ formulations (noble metal-free) have on their LNT performance under simulated conditions, thus covering aspects of Materials Science and Chemical Engineering in a highly applied context, related to the development of control strategies for hybrid powertrains and/or the reduction of the impact of cold-start emissions.

Intermolecular Photoredox Coupling: Alternative to Norrish Type II Reaction and Yang Cyclization in Ketones with γ‐C−H Bonds

AbstractA new reaction pathway for the photoconversion of butyrophenone in acetonitrile was investigated. In addition to the classic intramolecular photoreactivity of ketones with γ‐C−H bonds (Norrish type II fragmentation and Yang cyclization), intermolecular generated species were isolated and characterized: 1,2‐Dibenzoylethane, 2‐phenacylacetonitrile (oxidized species) and pinacols (reduced species). They account for approx. 20 % of the converted starting material, similar to the Yang product. The acetophenone enol intermediate, formed in situ via the Norrish type II reaction, has been identified as an H‐atom donor for the main intermolecular reaction steps, and has been distinguished from other conceivable mechanistic possibilities. Experimental results with analogue compounds suggest that the intermolecular product formation pathway may be of general relevance.

Experimental and kinetic modeling studies of di-n-propyl ether pyrolysis at low and atmospheric pressures

The pyrolysis of di-n-propyl ether (DPE), a potential biofuel candidate, was studied under a temperature range of 850–1350 K in a flow reactor at low and atmospheric pressures. Synchrotron vacuum ultraviolet photoionization mass spectrometry was used for isomeric identification and mole fraction measurements of the pyrolysis products, especially the free radicals. Specific products were observed and measured for the unimolecular decomposition reactions of DPE. A detailed kinetic model of DPE pyrolysis was developed based on the n-propanol combustion model. Modeling analyses including the rate of production (ROP) and sensitivity analyses were performed to reveal the consumption pathways of DPE, as well as the formation and consumption pathways of intermediates and products. ROP and sensitivity analyses indicated that the consumption reaction of DPE was mainly controlled by the unimolecular decomposition reactions and H-abstractions at both low and atmospheric pressures. The pericyclic reaction, leading to n-propanol + propylene, was the most important unimolecular decomposition reactions, especially at low pressure. The H-abstraction reactions of DPE played crucial roles in its consumption. Further β-C–C and β-C–O scission reactions of the three primary radicals can produce some oxygenated and hydrocarbon products. Relatively high mole fractions of C1–C3 aldehydes and C1–C3 alkane, alkene, and alkyl radicals were observed, which demonstrated the structural feature of DPE. Comparison of the product distribution between DPE and n-propanol were also analyzed.

How Small Molecules Affect the Thermo-Oxidative Aging Mechanism of Polypropylene: A Reactive Molecular Dynamics Study.

Understanding the aging mechanism of polypropylene (PP) is fundamental for the fabrication and application of PP-based materials. In this paper, we present our study in which we first used reactive molecular dynamics (RMD) simulations to explore the thermo-oxidative aging of PP in the presence of acetic acid or acetone. We studied the effects of temperature and oxygen on the aging process and discussed the formation pathways of typical small molecule products (H2, CO, CO2, CH4, C2H4, and C2H6). The effect of two infection agents, acetic acid and acetone, on the aging reaction was analyzed emphatically. The simulation results showed that acetone has a weak impact on accelerating the aging process, while acetic acid has a significant effect, consistent with previous experimental studies. By tracking the simulation trajectories, both acetic acid and acetone produced small active free radicals to further react with other fragment products, thus accelerating the aging process. The first reaction step of acetic acid is often the shedding of the H atom on the hydroxyl group, while the reaction of acetone is often the shedding of the H atom or the methyl. The latter requires higher energy at lower temperatures. This is why the acceleration effect of acetone for the thermo-oxidative aging of PP was not so significant compared to acetic acid in the experimental temperature (383.15 K).

Effect of unsaturated fatty acids on glycation product formation pathways

Glycation and lipid oxidation in high-nutrient foods are closely related and exhibit complex interactions. To evaluate the effect of unsaturated fatty acids (UFAs) on glycation pathways, glycation products in glucose-lysine-UFA models were detected by ultra performance liquid chromatography-tandem mass spectrometry and electron spin resonance spectroscopy, together with multivariate data analysis. Results indicated that UFAs inhibited glucose oxidation by decreasing the contents of carbonyl compounds about 73.85–86.19%. UFAs promoted the formation of glycation products mainly via production of active radical. In three models, linoleic acid (LA) exhibits stronger glycation activity than oleic acid and eicosapentaenoic acid. LA significantly promoted radical formation, as well as the formation and degradation of fructosyllysine (FL), the signal intensity of active radical increased 647.45% and FL increased 78.73%. The comparison of E(k3), E(k7) and variable importance in projection values of orthogonal projections to latent structures discriminant analysis in three models also proved these conclusions. By studying the characteristics of LA on glycation in three UFA, we hypothesized that unsaturation is not the key factor in evaluating their effects on glycation, the radical activity, UFA solubility, spatial structure and interaction should be considered as potentially important factors.

Atmospheric and high pressures pyrolysis study of n-decane in a flow reactor with online GC-MS/FID analysis: Experiments and modeling

The atmospheric and high-pressure pyrolysis of n-decane was studied in a flow tube reactor combined with online GC–MS/FID at 723−1123 K, 0.1–3.0 MPa (highly diluted in helium). Compared with 0.1 MPa, the conversion of n-decane and mole fraction of alkenes clearly increased at 3.0 MPa at the fixed temperature, and more aromatics were observed including toluene, styrene, ethylbenzene, indene and naphthalene, suggesting that the secondary reactions are more intense under high pressure. To account for these differences, a detailed kinetic model with 191 species and 1117 reactions was constructed by incorporating the aromatics subset to a n-decane model developed in previous low-pressure work, and further validated against literature data covering a wide pressure range (0.004–7.2 MPa) with reasonable reproducibility. The current model was compared against three literature kinetic models (LLNL, JetSurf 2.0 and Rev1stGen) and showed a better accordant with the conversion of n-decane and the selectivity of major products. Based on the rate of production and sensitivity analysis using the current model, the results show that although the total consumption of n-decane is weakly pressure-dependent at fixed temperature and residence time under the investigated conditions, the formation and consumption pathways of primary products change significantly attributed to the enhanced bimolecular abstraction and combination reactions at higher pressures. For the formation of benzene, the combination of 1,3-butadien-2-yl with ethylene is the main pathway at both 0.1 and 3.0 MPa, while the additional combination reactions: propargyl with allyl and cyclopentadienyl (c-C5H5) with CH3 become dominant at 0.1 MPa and 3.0 MPa, respectively. For the formation of larger aromatic naphthalene, the self-recombination of c-C5H5 is the most important channel at all investigated pressures.