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In this study, the deoxidizer Na2S was modified by different transition bimetals (Fe–Co, Mn–Co, Cu–Co, and Zn–Co) and Fe–Co ratios as auxiliary. The obtained deoxidizers were characterized by X-ray diffraction, N2adsorption/desorption, X-ray photoelectron spectroscopy, and H2-TPR; their deoxidizing activity for the removal of O2from low-concentration coalbed gas (CBM) were studied. Results showed that reactive oxygen species (O£–) content in Na2S deoxidizer, as well as unit effective deoxidization capacity (QO2) and conversion rate of (CNa2S), increased after modification with Fe–Co, Mn–Co, and Cu–Co. The higher the O£–content in deoxidizers, the higher the activity of the deoxidizers for the removal of O2from CBM was. Fe/Co–Na2S/activated carbon (AC) had the highest amount of O£–content, larger pore volume, and less impurity species with small crystal size, and this made it the largest QO2(63.74 mL/g) and CNa2S(87.24%) at 200 °C and 1 atm. Although the deoxidizer Zn/Co–Na2S/AC modified with Zn–Co had larger O£–content, QO2and CNa2Sof this deoxidizer is the lowest due to the presence of more impurities CoS2, CoO, and NaOH with larger crystal size on its surface. These impurities blocked the pores of the deoxidizer Zn/Co–Na2S/AC and inhibited both mass transfer and reaction of reactants through the material, resulting in declined activity. The deoxidizer Fe/Co (0.33/1)–Na2S/AC showed higher deoxidizing activity when the Fe–Co ratio was 0.33/1.

Deoxidizer Na2S/AC was modified with transition metal ions (Co2+, Ni2+, Fe3+, and Cu2+) by co-impregnation and step-by-step impregnation methods. Those deoxidizers were characterized and tested for the removal of O2from low-concentration coal bed methane. Results showed that the effective deoxidizing amount of deoxidizers (QO2) and conversion rate of Na2S (CNa2S) of the deoxidizers are in the following order: Co-Na2S/AC > Ni-Na2S/AC > Fe-Na2S/AC > Na2S/AC > Cu-Na2S/AC. As compared to that of the deoxidizer Na2S/AC, the content of reactive oxygen species (O£–) of the modified deoxidizers was enhanced with the doping of transition metal ions (Co2+, Ni2+, Fe3+, and Cu2+). The more content of O£–on the deoxidizer was, the higher deoxidizing activity there was when the dispersion of Na2S and metal ions of deoxidizers was higher. The deoxidizer Co-Na2S/AC had the largest content of O£–and higher dispersion of Na2S and Co2+, and this made it the largest QO2(54.88 mL/g) and CNa2S(75.50%) at 200 °C. However, although the content of O£–of the deoxidizer Cu-Na2S/AC was higher than that of the deoxidizer Na2S/AC, the deoxidizer Cu-Na2S/AC had the smallest QO2and CNa2Sdue to the more severe agglomeration of S6and the larger crystal of Cu(OH)2on this deoxidizer. The deoxidizer Co-Na2S/AC prepared by a step-by-step impregnation method had higher content of O£–, higher dispersion of active component Na2S and assistant Co2+; this made it the higher deoxidizing activity compared with the deoxidizer Co-Na2S/AC(c) prepared by a co-impregnation method.

A series of activated carbons were prepared by H3PO4-mechanical force activation and characterized by N2adsorption/desorption isotherms, SEM, FTIR, CO/CO2-TPD, and XPS. Adsorption isotherms of CH4and N2were measured in the range of 25–760 mmHg at 20 °C and fitted by Langmuir model to calculate separation coefficient of CH4against N2(αCH4/N2). Results showed that H3PO4-mechanical force activation had significantly enhanced the micropore volume of activated carbons (ACs), in which the highest micropore volume (0.8 cm3/g) and BET specific area (1966 m2/g) were obtained under the optimum condition of phosphoric acid impregnation ratio of 1:1, activation temperature of 400 °C, and activation time of 60 min. The micropore volume and surface properties of ACs affected its selectivity adsorption ability toward CH4. The ACs with higher micropore volume had a larger adsorption amount of CH4. And the larger the O/C ratio of the ACs was, the larger the oxygen-containing groups on the ACs would be, which can improve the surface polarity of ACs and enhance the adsorption ability of N2with certain polarity, and thus make the ACs having the smaller separation factor of αCH4/N2. Among all of the samples, AC-1-400 with the largest micropore volume and O/C ratio had the highest CH4adsorption amount but the smallest αCH4/N2.