Unveiling the Mechanism of Plasma-Catalyzed Oxidation of Methane to C2+ Oxygenates over Cu/UiO-66-NH2.

Nonthermal plasma (NTP) offers the potential for converting CH4 with CO2 into liquid products under mild conditions, but controlling liquid selectivity and manipulating intermediate species remain significant challenges. Here, we demonstrate the effectiveness of the Cu/UiO-66-NH2 catalyst in promising the conversion of CH4 and CO2 into oxygenates within a dielectric barrier discharge NTP reactor under ambient conditions. The 10% Cu/UiO-66-NH2 catalyst achieved an impressive 53.4% overall liquid selectivity, with C2+ oxygenates accounting for ∼60.8% of the total liquid products. In situ plasma-coupled Fourier-transform infrared spectroscopy (FTIR) suggests that Cu facilitates the cleavage of surface adsorbed COOH species (*COOH), generating *CO and enabling its migration to the surface of Cu particles. This surface-bound *CO then undergoes C-C coupling and hydrogenation, leading to ethanol production. Further analysis using CO diffuse reflection FTIR and 1H nuclear magnetic resonance spectroscopy indicates that in situ generated surface *CO is more effective than gas-phase CO (g) in promoting C-C coupling and C2+ liquid formation. This work provides valuable mechanistic insights into C-C coupling and C2+ liquid production during plasma-catalytic CO2 oxidation of CH4 under ambient conditions. These findings hold broader implications for the rational design of more efficient catalysts for this reaction, paving the way for advancements in sustainable fuel and chemical production.

Catalytic fast pyrolysis of waste pine sawdust over solid base, acid and base-acid tandem catalysts.

Catalytic pyrolysis is an effective means for high-value utilization of biomass. This study investigated the effect of solid base catalysts (CaO, calcium aluminate catalysts CaAl-1, CaAl-2, CaAl-3), acid zeolite catalysts (ZSM-5, Fe/ZSM-5, Co/ZSM-5, Ni/ZSM-5, Cu/ZSM-5, Zn/ZSM-5) and base-acid tandem catalysts on pine sawdust pyrolysis using Py-GC/MS. Acid zeolite catalysts exhibited robust deoxidation and aromatization capabilities, favoring aromatics, while solid base catalysts yielded more phenols and ketones. Among the solid base catalysts, CaAl-3 (CaO-Ca12Al14O33) showed comparable deoxygenation activity to CaO and optimal aromatic selectivity with structural stability. Zn/ZSM-5 excelled in deoxygenation and aromatic selectivity (70.42%) among metal-modified ZSM-5 catalysts. Base-acid tandem catalysis promoted the formation of aliphatics and BTX (benzene, toluene, xylene) while suppressing polycyclic aromatics. The highest BTX content (44.35%) was achieved with CaO-Ca12Al14O33&Zn/ZSM-5 tandem catalysts in a 1:3 ratio. This work demonstrates base-acid tandem catalysis as a promising approach for converting pine sawdust into valuable chemicals.

Influence of CaO on the thermal kinetics and formation mechanism of high value-added products during waste tire pyrolysis.

There is a lack of detailed research on the production of isoprene and D-limonene by solid base-catalysed thermal depolymerization of waste tires (WTs). This work aimed to investigate the thermal decomposition characteristics, reaction kinetics, high value-added products production and potential mechanisms during WT pyrolysis in the presence of calcium oxide (CaO) via Thermogravimetry-Fourier Transform Infrared spectrometer (TG-FTIR) and Pyrolyzer-Gas Chromatography/Mass spectrometry (Py-GC/MS). The results obtained from TG indicated that CaO accelerated depolymerization in terms of reducing the reaction temperature, which is also reflected in the kinetic parameters. It can be found that the content of D-limonene increased by 13.76% and that of isoprene increased by 37.57%, which were attributed to differences in the depolymerization mechanisms in the presence of CaO. Furthermore, CaO had a profound impact on desulfurization by reducing benzothiazole, sulfoacid, and thiophene. The potential catalytic mechanisms of isoprene and D-limonene production and desulfurization were also proposed. This work deepens the understanding of the catalytic pyrolysis of WT under CaO and unambiguously demonstrates the great potential of CaO in enhancing isoprene and D-limonene production, providing new insight for the cleaner production of high value-added products from WT.

Comparative Study on Pyrolysis Kinetics Behavior and High-Temperature Fast Pyrolysis Product Analysis of Coastal Zone and Land Biomasses.

The pyrolysis characteristics of land biomass (corn stalks (Cs), pine sawdust (Ps)) and coastal zone biomass (Jerusalem artichoke stalks (JAs) and reed (Re)) were investigated based on thermogravimetric analysis (TGA) and products' analysis. The kinetic parameters were obtained by three isoconversional methods (Friedman, KAS, and FWO) and one model-fitting method (DAEM). The simultaneous effect of high temperature (700-900 °C) and high heating rate (1000 °C/s) on the pyrolysis product simulating the typical conditions of a fluidized bed gasifier was studied. TGA showed that high heating rates deepen the thermal cracking process of biomass. Compared with the land biomass, the initial decomposition temperature (T i ) of the coastal biomass is reduced significantly owing to its higher proportion of hemicellulose. These methods agree with the trends shown by the activation energy (E a) distribution calculated, with fluctuations between 160 and 350 kJ/mol. The mean value activation energies of Re and JAs were higher than those of Cs and Ps between 10% and 90% conversion. The DAEM model showed that Cs and JAs have a good linear relationship between ln A and E α during the main pyrolysis stage, while Ps and Re are relatively weaker. The kinetic compensation effect was evident for Cs and JAs during the main thermal cracking stage. Py-GC-MS results confirmed that phenols, hydrocarbons, PAHs, and oxygen heterocycle compounds were strongly present in the released volatile products. High-temperature fast pyrolysis of JAs produced a larger amount of PAH compounds than from Cs, Ps, and Re. A larger amount of hydrocarbons and phenols was generated from high-temperature fast pyrolysis of Ps. Some oxygen-containing volatiles are easily converted into aromatic products with higher stability under high temperature.

Study on the Staged and Direct Fast Pyrolysis Behavior of Waste Pine Sawdust Using High Heating Rate TG-FTIR and Py-GC/MS.

To understand the fast pyrolysis kinetics and product evolution of waste pine sawdust, high heating rate thermogravimetry-Fourier transform infrared (TG-FTIR) was used to obtain the kinetic parameters and the chemical groups formed during the pyrolysis process, while pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) was used to investigate the detailed compositions of products under the staged (seven stages from 300 to 600 °C) and direct fast pyrolysis process. Spectral bands were identified for acids, alcohols, aldehydes, aromatics, esters, ethers, hydrocarbons, ketones, phenols, and sugars. Research found that the apparent activation energy for fast pyrolysis is much higher than that of slow pyrolysis. The evolution of CO2 is the major deoxygenation route. Cracking mainly occurred at the 450 °C stage with phenols, ketones, aldehydes, and sugars as the main products. The product distributions for different stages are significantly different; the selectivity of aldehydes decreased, while phenols showed an upward trend with an increase in pyrolysis temperature. Ketones and sugars reached their peak values at 450 °C. The changes in the molecular composition of each stage helped to understand the pyrolysis process. Compared with the staged pyrolysis, the direct pyrolysis process had higher selectivity of acids, aldehydes, esters, and sugars and lower selectivity of phenols, ketones, and alcohols.

Parametric effect of biomass partial hydropyrolysis process in a downer reactor to co-produce high-quality tar and syngas.

Fast partial hydropyrolysis of biomass was carried out at the level with hydrogen concentration of 0% to 30% and temperatures ranging from 700 to 900 °C by using a downer pyrolyzer. A theoretical parametric effect on yields and properties of the hydropyrolysis products were clarified. It was found that the volatile matter evolved during pyrolysis was substantially increased in the presence of hydrogen. The yields of CH4, C2H6 and light tar increased with increasing elevated H2 ratio, CH4 showed an especially large yield increase. The produced methane mainly comes from the reactions of hydropyrolysis of biomass and secondary hydrogenation of tar. Moreover, the presence of alkali and alkaline earth metals matters was significant catalyzes on both reactions. The CH4 yield increased with elevating the operating temperature and optimal sweeping-gas flow rate is 150 mL/min. These results will be strengthening regulation of feedstocks-operating-products in the practical Biomass Fast Partial Hydropyrolysis technology.

Preparation, characterization, and efficient chromium (VI) adsorption of phosphoric acid activated carbon from furfural residue: an industrial waste.

Furfural residue (FR) is an inevitable by-product of industrial furfural production. If FR is not managed properly, it will result in environmental problems. In this study, FR was used as a novel precursor for activated carbon (AC) production by H3PO4 activation under different conditions. Under optimum conditions, the prepared FRAC had high BET surface area (1,316.7 m2/g) and micro-mesoporous structures. The prepared FRAC was then used for the adsorption of Cr(VI). The effect of solution pH, contact time, initial Cr(VI) concentration, and temperature was systematically studied. Characterization of the adsorption process indicated that the experimental data were well-fitted by the Langmuir isotherm model and pseudo-second-order kinetics model. The maximum adsorption capacity of 454.6 mg/g was achieved at pH 2.0, which was highly comparable to the other ACs reported in the literatures. The preparation of FRAC using H3PO4 activation can make use of FR's characteristic acidity, which could make it preferable in practical industrial production.

High-capacity adsorption of Cr(VI) by lignin-based composite: Characterization, performance and mechanism.

An environmentally friendly lignin-based composite (Lignin-PEI) was facilely prepared via cross-linking enzymatic hydrolysis lignin matrix and branched poly (ethylene imine). The specific physicochemical and structural properties of lignin-PEI were characterized by elemental analysis, N2 physisorption, GPC, TG, SEM, FT-IR and XPS. The nitrogen content of lignin-PEI was 9.02%, and the BET surface area was 20.32 m2/g. The synthetic composite showed high capacity and selectivity of Cr(VI) adsorption. The influence of solution pH, contact time, initial Cr(VI) concentration, and coexisting ions on Cr(VI) adsorption on lignin-PEI was systemically studied. The Cr(VI) adsorption on lignin-PEI was well described by the Langmuir model. According to the Langmuir model, the Cr(VI) adsorption capacity on lignin-PEI was as high as 898.2 mg/g at 318 K and pH 2.0. The calculated thermodynamic parameters, such as ΔG, ΔH, and ΔS, indicated the spontaneous and endothermic adsorption of Cr(VI) on lignin-PEI. The adsorption of Cr(VI) by lignin-PEI was following the pseudo-second-order kinetic model, indicating that it was a chemisorption process. The uptake mechanism was demonstrated to be electrostatic attraction, ion exchange, complexation and partial reduction. This work provided a promising candidate for Cr(VI) uptake with lignin-based biosorbents.

Novel betaine-amino acid based natural deep eutectic solvents for enhancing the enzymatic hydrolysis of corncob.

A novel natural deep eutectic solvent (NDES) with water content ranging from 65 to 93 wt%, in which betaine (Bet) acts as the cation and amino acids (AAs) as the anions, was prepared by a simple and green chemical route. [Bet][AA] NDES showed excellent xylan and lignin solubility, however, scare cellulose solubility. A mild and facile pretreatment process with [Bet][AA] NDES was carried out at 60 °C for 5 h. The enzymatic hydrolysis efficiency of cellulose and corncob was significantly improved. Detailed characterization showed that the enhancement of cellulose digestibility derived mainly from xylan and lignin removal. Xylan and lignin removal for [Bet][Lys]-W87 was 47.68 and 49.06%, while it was 42.20% and 57.01% for [Bet][Arg]-W82, respectively. FT-IR, SEM, XRD, and HSQC NMR studies confirmed the effectiveness and mechanism of [Bet][Lys]-W87 and [Bet][Arg]-W82 on biomass pretreatment.

Catalytic conversion of gaseous tars using land, coastal and marine biomass-derived char catalysts in a bench-scale downstream combined fixed bed system.

The catalytic activity of biochar for tar removal was evaluated in a bench-scale combined fixed bed reactor by comparison of gaseous tar catalytic cracking behaviors over land (Corn stalks, Cs), coastal (Reed, Re) and marine (Sargassum horneri, Sh) char catalyst. The experiments demonstrated that the tar yield after addition of the biochar was reduced significantly; the tar conversion efficiency reached to 94.6% for catalytic at 850 °C with 50 mm char bed length using Re char. And the yield and composition of gas also changed markedly. The percentage of H2 and CO in the product gas were obviously increased. Sh has a higher H2 content (49.3% of the total gas content), whereas, CO dominated in the gas products for Cs (45.4%) and Re (48.1%). The results from GC-MS analysis illustrated that the increase in temperature promoted the tar cracking and also promotes the polymerization of some tar components.

Controlling Deoxygenation Pathways in Catalytic Fast Pyrolysis of Biomass and Its Components by Using Metal-Oxide Nanocomposites.

Selectively breaking the C-O bonds within biomass during catalytic fast pyrolysis (CFP) is desired, but extremely challenging. Herein, we develop a series of metal-oxide nanocomposites composed of W, Mo, Zr, Ti, or Al. It is demonstrated that the nanocomposites of WO3-TiO2-Al2O3 exhibit the highest deoxygenation ability during CFP of lignin, which can compete with the commercial HZSM-5 catalyst. The nanocomposites can selectively cleave the C-O bonds within lignin-derived phenols to form aromatics by direct demethoxylation and subsequent dehydration. Moreover, the nanocomposites can also achieve the selective breaking of the C-O bonds within xylan and cellulose to form furans by dehydration. The Brønsted and Lewis acid sites on the nanocomposites can be responsible for the deoxygenation of lignin and polysaccharides, respectively. This study provides new insights for the rational design of multifunctional catalysts that are capable of simultaneously breaking the C-O bonds within lignin and polysaccharides.

Facile preparation of lignosulfonate/N-methylaniline composite and its application in efficient removal of Cr(VI) from aqueous solutions.

A lignin-based biosorbent (LSMA) was prepared by cross-linking lignosulfonate and N-methylaniline with the aid of ammonium persulfate for efficient removal of Cr(VI) from aqueous solution. Since LSMA possessed both amino groups and oxygen-containing functional groups, such as phenolic, carboxyl, and sulfonic groups, the maximum adsorption capacity of 1264.8 mg/g was achieved at 318 K according to the Langmuir isotherm. LSMA also showed excellent performance at low Cr(VI) concentration solution. The hazardous Cr(VI) solution of 50 mg/L can be fully removed within 10 min. The adsorption process of LSMA fitted the pseudo-second-order kinetic model, suggesting the chemical adsorption characteristics. Moreover, the adsorption process was spontaneous and endothermic. LSMA worked very well even with high content of competing anions. The removal mechanism was demonstrated to be the adsorption of Cr(VI) anions on LSMA with abundant functional groups, and reduction of Cr(VI) to less toxic Cr(III) by the adjacent electron donor groups. The generated Cr(III) was immobilized on LSMA by surface complexation and precipitation. LSMA composite has a great potential for the treatment of Cr(VI)-contaminated water.

Steam gasification of land, coastal zone and marine biomass by thermal gravimetric analyzer and a free-fall tubular gasifier: Biochars reactivity and hydrogen-rich syngas production.

The steam gasification properties and kinetics, products distribution and syngas composition derived from land, coastal zone and marine biomass have been studied by TGA and free-fall tubular gasifier. Volume model, shrinking core model and random pore model were applied to describe the reaction kinetics. The influence of temperature and fuel types on steam gasification in a free-fall tubular gasifier were clarified simultaneously. Results showed that gasification reactivity of reed (Re) and Sargassum horneri (Sh) chars were better than that of corn stalks (Cs) char, which mostly determined by its carbonaceous structure and the varying inorganic contents. RPM model was applied successfully to corresponding to the experimental data. Bench scale reactor test found that the steam gasification of Re gave the largest amount of gaseous product than Sh and Cs, while no liquidus formation in Sh. An increase in the temperature during gasification process boosted produced sharply total gas production yield, more yield of H2 and CO2 and less CO and CH4 from different biomass.

Fast pyrolysis characteristics of two typical coastal zone biomass fuels by thermal gravimetric analyzer and down tube reactor.

This study aimed at investigating fast pyrolysis behavior and products distribution of two typical coastal zone biomass fuels (Jerusalem artichoke stalk (JAS) and reeds (Re) by TGA and a homemade down tube reactor. The kinetic analysis with different ramping rates was conducted by FWO and DAEM models. The liquid, gaseous and solid products are characterized to study the influence of temperature. Results indicate that high heating rates may be overcome some resistances to mass or heat transfer inside the particles of biomass, and lead to a higher conversion rates and Re species is preferable to JAs in terms of thermochemical conversion because of the lower apparent activation energy for total conversion. Moreover, the pyrolysis conditions - temperature under fast pyrolysis in a down tube pyrolysis unit will make the covalent bonds in the biomass degradation more rapidly, gave significant influence on the yields and properties of liquid, gaseous and solid products.

Thermal decomposition of castor oil, corn starch, soy protein, lignin, xylan, and cellulose during fast pyrolysis.

The aim of this work was to study the pyrolysis behavior of castor oil, corn starch, soy protein, lignin, xylan, and cellulose. The pyrolysis behavior, gaseous product evolution, kinetics and thermodynamics of these model compounds were investigated via TG-FTIR under high heating rates. The TG/DTG curves showed that castor oil had the widest pyrolysis temperature zone and lignin had the highest residual rate. The apparent activation energy of these model compounds was calculated by Kissinger-Akahira-Sunose method. The kinetic results revealed that the average bond energy of chemical compositions was in the order of lipid > lignin > starch > cellulose > protein > hemicellulose. The pre-exponential factor analysis showed that there were a large number of surface reactions for soy protein and xylan during pyrolysis, however other model compounds were not surface controlled. The thermodynamic parameters including G, ΔS, ΔH for six model compounds were also calculated.

The steam gasification reactivity and kinetics of municipal solid waste chars derived from rapid pyrolysis.

Municipal solid waste treatment has been and will continue to be a major issue facing countries worldwide, and gasification has recently gained more attention as an efficient and clean technology. The steam gasification characteristics and kinetics of five different municipal solid waste chars had been investigated by the method of isothermal thermogravimetric analysis. The results showed that the gasification reactivity increased with gasification temperature. Effect of H/C and O/C ratios, ash composition and particle pore structure of chars on gasification reactivity were studied, which illustrated that the H/C and O/C ratios and ash composition had great influence on gasification reactivity and the pore structure cannot explain well in this study. A homogeneous model, unreacted shrinking core model and random pore model were employed to describe the kinetic behavior of different chars, and the kinetic parameters were also obtained. Finally, through the evaluation of the three kinetic models by comparing the experimental data with the fitted results, the random pore model was determined to perform best. This study should, therefore, be of some value to solid waste gasification industrialization.

Pyrolytic Characteristics and Kinetics of Phragmites australis.

The pyrolytic kinetics of Phragmites australis was investigated using thermogravimetric analysis (TGA) method with linear temperature programming process under an inert atmosphere. Kinetic expressions for the degradation rate in devolatilization and combustion steps have been obtained for P. australis with Dollimore method. The values of apparent activation energy, the most probable mechanism functions, and the corresponding preexponential factor were determined. The results show that the model agrees well with the experimental data and provide useful information for the design of pyrolytic processing system using P. australis as feedstock to produce biofuel.