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.

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.

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.

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.

Preparation of methyl alginate and its application in acidified milk drinks.

A series of methyl alginate with different degree of esterification (DE) were prepared with low cost, and its application in acidified milk drinks (AMDs) was investigated. The gel strength, molecular weight, solution apparent viscosity and optical rotation value of methyl alginate all decreased with the increase of DE. Methyl alginate with DE equal or larger than 60.7% was more effective in stabilizing AMDs than high-methoxyl pectin (HMP) under the same conditions, and the higher the DE, the better its stabilizing ability. The methyl alginate had better synergistic action for stabilizing AMDs with propylene glycol alginate (PGA) than HMP. The reason for this could be attributed to that methyl alginate and PGA had the same main chain structure, and the same levorotatory optical activity. The results indicated that the methyl alginate had a potential industry application prospect for stabilizing AMDs as an alternative to HMP.

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.