Pathways For Formation Of Products Research Articles

Intrinsic Metal Component-Assisted Microwave Pyrolysis and Kinetic Study of Waste Printed Circuit Boards

Waste printed circuit boards (WPCBs) hold great recycling value, but improper recycling can lead to environmental issues. This study combines pyrolysis and microwave technologies, leveraging the unique phenomenon where metal materials tend to “spark” in a microwave field, to develop a microwave pyrolysis process for WPCBs that incorporates metal fillers. The research analyzes the effects of microwave power, metal filler addition, and pyrolysis time on the efficiency of microwave pyrolysis. It explores the mechanisms of microwave pyrolysis and the pathways of pyrolysis product formation, and the kinetics of the pyrolysis reaction of WPCBs. The results indicate that microwave-assisted pyrolysis greatly improves efficiency. Within the experimental range, the optimal conditions are found to be a microwave power of 1600–1800 W, a metal filler addition of 10%, and a pyrolysis time of 10 min. Under these conditions, the yield of pyrolysis liquid was 12.8%, with approximately 5–12 different components, while the yield of pyrolysis gas was 12.7–13.4%, with about 9–11 different components. Compared to conventional pyrolysis products, the liquid products from microwave pyrolysis are simpler and more advantageous for resource utilization. Theoretical calculations show that the average activation energy for the microwave pyrolysis process is 81.05 kJ/mol, with an average reaction order of 0.93, which is greatly better than the 147.75 kJ/mol of the conventional pyrolysis process.

Efficient ethylbenzene production from CO2 and benzene in a single-bed reactor

The selective synthesis of specific value-added aromatic hydrocarbons through CO2 hydrogenation holds significant strategic importance in mitigating energy and climate issues. However, the process of forming ethylated side chains on benzene rings is challenging, and the methods reported are often limited by multi-bed systems. Here, we show the first CO2 hydrogenation in tandem coupling with benzene alkylation to synthesize ethylbenzene over a single-bed system containing ZnFeOx and nano ZSM-5 catalysts. The results indicated that the bifunctional catalyst composed of ZnFeOx with a Zn/Fe ratio of 0.5 and nano-HZSM-5 exhibits excellent catalytic performance under optimized conditions. The benzene conversion reaches 28.0 %, ethylbenzene selectivity is 61.3 % and the conversion of CO2 is remarkably high, achieving 45.0 %. This single-bed system significantly promotes the in-situ utilization of ethylation intermediates. The introduction of zinc promoted the formation of ZnFe2O4 spinel, which increased the number of active sites due to its superior dispersibility and reducibility. Nano-HZSM-5 demonstrated outstanding ethylbenzene selectivity and catalytic stability owing to its unique shape selectivity, moderate acidity, and superior diffusion properties. This study further explores the reaction network and mechanism through GC–MS analysis and various model reactions, elucidating the formation pathways of primary products in detail. This research provides a new strategy for the controllable synthesis of ethylbenzene using CO2 as a C1 source in a single-bed system.

Exploring the catalytic conversion of aromatic model compounds of coal pyrolysis over Ca(OH)2

The distribution of pyrolysis products from aromatic model compounds in coal catalyzed by Ca(OH)2 was investigated at the molecular level. The composition and relative abundance of the pyrolysis products from coal were analyzed using Py-GC/MS. The rapid pyrolysis products of coal at 600 °C consisted of phenols (15.94 %), non-phenolic oxygenated compounds (25.31 %), aliphatics (49.03 %), aromatic compounds (21.74 %), and other compounds (0.03 %). Six representative aromatic model compounds (2-methoxy-4-methylphenol, p-cresol, 2,4-dimethylphenol, o-cresol, guaiacol, and catechol) were selected. The pyrolysis process of model compounds was primarily the cleavage of C-O and C-C bonds, which resulted in the formation of methoxy and methyl radicals. The results revealed that Ca(OH)2 undergoes acid-base reactions with -OH, thereby increasing the stability of the model compounds. Notably, the impact of Ca(OH)2 on the composition and distribution of pyrolysis products was significantly more pronounced in aromatic compounds containing both -OCH3 and -OH compared to those containing solely -OH. The formation pathways of pyrolysis products involving guaiacol and Ca(OH)2 were elucidated through density functional theory (DFT) calculations, demonstrating that Ca(OH)2 could facilitate more free radicals release and the conversion of model compounds. This study contributes to the understanding of the transformation of aromatic compounds during coal pyrolysis at the molecular level.

Multiphase nitrosation based on N2O3 intermediate and process intensification in a microflow reactor

Nitrosation of alcohols with nitrous acid is widely used to prepare alkyl nitrites, but the reaction mechanism and formation pathways of gaseous side products remain unclear. Here, we propose a nitrosation mechanism based on a highly reactive intermediate, dinitrogen trioxide (N2O3). The N2O3-based mechanism shows a lower energy barrier than the previously reported acid-catalyzed and nitrosyl cation mechanism. Furthermore, a microfluidic platform was established to investigate the gas–liquid-liquid reaction system and characterize the gas holdup of the multiphase reaction system. The results suggest that the reaction rate and selectivity primarily depend on the interfacial mass transfer of N2O3 between the aqueous-organic and gaseous-organic phases. A tubular microreactor was employed to intensify the nitrosation process of isopropanol. In contrast to the batch process operated by adding reactants dropwise in several hours, the product yield of 95 % can be achieved in a residence time of only 10 s in the microflow reactor.

Effects of cellulose addition on sodium lignosulfonate pyrolysis: Product distribution and formation pathway

Effects of cellulose addition on sodium lignosulfonate pyrolysis: Product distribution and formation pathway

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.